Leptin and the Regulation of the Hypothalamic–Pituitary–Adrenal Axis

C H A P T E R

T W O

Leptin and the Regulation of the Hypothalamic–Pituitary–Adrenal Axis Ludwik K. Malendowicz,* Marcin Rucinski,* Anna S. Belloni,† Agnieszka Ziolkowska,* and Gastone G. Nussdorfer† Contents 64 65 65 68

1. Introduction 2. Biology of Leptin and Its Receptors 2.1. Leptin 2.2. Leptin receptors 3. Expression of Leptin and Its Receptors in the Hypothalamic–Pituitary–Adrenal Axis 3.1. Hypothalamus 3.2. Anterior pituitary 3.3. Adrenal gland 4. Effects of Leptin on the Central Branch of the Hypothalamic–Pituitary–Adrenal Axis 4.1. Hypothalamus and CRH secretion 4.2. Anterior pituitary and ACTH secretion 5. Effects of Leptin on the Peripheral Branch of the Hypothalamic–Pituitary–Adrenal Axis 5.1. Adrenal cortex 5.2. Other steroid-secreting cells 5.3. Adrenal medulla 6. Involvement of Leptin in the Pathophysiology of the Hypothalamic–Pituitary–Adrenal Axis 6.1. Response to stresses 6.2. Pituitary adenomas 6.3. Adrenocortical tumors and pheochromocytomas 6.4. Macronodular adrenal hyperplasia 6.5. Hyperreninemic hypoaldosteronism

69 69 70 73 76 76 77 78 78 83 84 85 85 86 86 87 87

*Department of Histology and Embryology, School of Medicine, Karol Marcinkowski University of Medical Sciences, PL-60781 Poznan, Poland Department of Human Anatomy and Physiology, Section of Anatomy, School of Medicine, University of Padua, I-35121 Padua, Italy

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International Review of Cytology, Volume 263 ISSN 0074-7696, DOI: 10.1016/S0074-7696(07)63002-2

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2007 Elsevier Inc. All rights reserved.

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7. Concluding Remarks Acknowledgments References

88 89 89

Abstract Leptin, the product of the obesity gene (ob) predominantly secreted from adipocytes, plays a major role in the negative control of feeding and acts via a specific receptor (Ob-R), six isoforms of which are known at present. Evidence has been accumulated that leptin, like other peptides involved in the central regulation of food intake, controls the function of the hypothalamic–pituitary– adrenal (HPA) axis, acting on both its central and peripheral branches. Leptin, along with Ob-R, is expressed in the hypothalamus and pituitary gland, where it modulates corticotropin-releasing hormone and ACTH secretion, probably acting in an autocrine–paracrine manner. Only Ob-R is expressed in the adrenal gland, thereby making it likely that leptin affects it by acting as a circulating hormone. Although in vitro and in vivo findings could suggest a glucocorticoid secretagogue action in the rat, the bulk of evidence indicates that leptin inhibits steroid-hormone secretion from the adrenal cortex. In keeping with this, leptin was found to dampen the HPA axis response to many kinds of stress. In contrast, leptin enhances catecolamine release from the adrenal medulla. This observation suggests that leptin activates the sympathoadrenal axis and does not appear to agree with its above-mentioned antistress action. Leptin and/or Ob-R are also expressed in pituitary and adrenal tumors, but little is known about the role of this cytokine in the pathophysiology. Key Words: Leptin, Leptin receptor (Ob-R), Hypothalamus, Anterior pituitary, Adrenal gland, Corticotropin-releasing hormone (CRH), ACTH, Steroid hormone, Catecholamine. ß 2007 Elsevier Inc.

1. Introduction Leptin (from the Greek lEpto´B, thin) is a 147-amino acid residue peptide, first described by Zhang et al. (1994). It is the product of the obesity gene (ob) and is predominantly secreted by adipocytes and stomach (Myers, 2004; Zhang et al., 1994, 2005). Leptin plays a role in the control of feeding, acting to decrease caloric intake and to increase energy expenditure (Ahima and Flier, 2000; Mantzoros and Moschos, 1998; Myers, 2004; Remesar et al., 1997; Unger, 2000; Zhang et al., 2005). Compelling evidence indicates that peptides involved in the regulation of food intake (e.g., beacon, cholecystokinin, galanin, neuropeptide-W, neuropeptide-Y, and orexins) (Baker et al., 2003; Bedecs et al., 1995; Cerda-Reverter and Larhammar, 2000; Collier et al., 2000; Crawley and

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Corwin, 1994; Wolf, 1998) control the function of the hypothalamic– pituitary–adrenal (HPA) axis, acting on both its central and peripheral branch (Andreis et al., 2005, 2007; Hocho´l et al., 2007; Krysiak et al., 1999; Malendowicz et al., 1994, 2003b; Mazzocchi et al., 1998, 2005; Nussdorfer et al., 2005; Rucinski et al., 2005a,b; Spinazzi et al., 2005, 2006). Accordingly, leptin also regulates neuroendocrine axes, including the HPA one (Ahima et al., 2000; Bates and Myers, 2003; Casanueva and Dieguez, 1999; Sahu, 2003; Wauters et al., 2000). The interactions of peptides regulating food intake, and especially leptin, with the HPA axis are of great relevance, inasmuch as glucocorticoid hormones are known to be involved in the control of energy homeostasis and adipogenesis (Jeong et al., 2004; Mastorakos and Zapanti, 2004). At low concentrations, glucocorticoids exert anabolic effects and stimulate feeding, adipocyte differentiation, and normal fat deposition (Campfield et al., 1996; Dallman et al., 1993; Freedman et al., 1986; Hauner et al., 1987). The permissive role of glucocorticoids in the development of obesity is suggested by experiments showing that adrenalectomy prevents the progression of obesity in genetically obese Zucker rats (Freedman et al., 1986) and high doses of glucocorticoids cause excessive fat storage (Davenport et al., 1989). On the other hand, glucocorticoids have been reported to enhance leptin expression in and secretion from adipocytes (Slieker et al., 1996; Zakrzewska et al., 1997), an effect that could dampen their anabolic action. Despite the large number of investigations carried out in the past 12 years and the physiological relevance of the matter, only two short survey articles have been published on the role of leptin in the regulation of the HPA axis (Glasow and Bornstein, 2000; Wauters et al., 2000). Thus, after a brief account of the biology of the leptin system, we will review findings indicating that leptin and/or its receptors (R) are expressed in the anatomical components of the HPA axis and that leptin plays a role in the functional regulation of the HPA axis under both physiological and pathological conditions.

2. Biology of Leptin and Its Receptors 2.1. Leptin 2.1.1. Biosynthesis and secretion The human ob gene is located on chromosome 7q31.3, has more that 15,000 base pairs, and consists of three exons and two introns. It encodes for the leptin precursor, peptides of 167 amino acids including the 21 residues of the signal peptide (Fig. 2.1). The tertiary structure of the leptin molecule resembles that of the members of the growth hormone (GH) four-helical cytokine subfamily (Zhang et al., 2005). There is considerable homology in

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1 H2N-

22 26 SP

39

56

93

105 116 130 138 150

167 COOH

Figure 2.1 Scheme illustrating the human leptin precursor. Signal peptide (SP) and leptin fragments used in experimental works (see Section 5) are shown in gray and/or dashed-gray.

the leptin sequence among the various mammalian species and astonishingly also among mammals, birds, and fish (Table 2.1). Leptin synthesized in the rat adipose tissue is secreted into the bloodstream probably via a constitutive mechanism (Barr et al., 1997; Hardie et al., 1996). However, in humans leptin secretion is pulsatile, with
32 pulses every 24 h and a pulse duration of
33 min (Licino et al., 1997). The biological half-life of circulating leptin has been reported to be 25–70 min in humans (Hill et al., 1998; Klein et al., 1996), about 100 min in monkeys, 6–7 min in rats, and about 50 min in mice (Ahren et al., 2000; Vila et al., 1998). 2.1.2. Structure–function relationships There is a remarkable disagreement on this matter. According to Imagawa et al. (1998), the N-terminal region of the human leptin molecule (94amino acid residues), but not the C-terminal loop region (51-amino acid residues), is essential for both R-binding and biological activities. Also the region between the N-terminal and C-terminal regions does not possess biological activity because synthetic leptin(109–133)S-S(159–166) was shown to be ineffective. In contrast, Grasso et al. (1997) localized the active domain of the murine leptin molecule in the 106–140 amino acid sequence and Rozhavskaya-Arena et al. (2000) localized it in the 116–122 sequence. In vivo experiments identified the 85–119 sequence, which includes the end of a-helix C and the intervening C/D loop with helix E and is outside the region where leptin contacts its R (i.e., the interface of a-helices A and C), as critical for appetite suppression and weight loss in obese mice (Grasso et al., 1997, 1999). These investigators also showed that the leptin fragment between amino acids in the 21 and 105 positions is deprived of functional epitopes connected with feeding regulation and that the administration of leptin fragments 106–120, 116–130, and 126–140 causes body weight loss in female obese mice. Of interest, Tena-Sempere et al. (2000) reported that in the rat pituitary gland and ovary leptin fragment 116–130 exerts actions both similar to and distinct from those of the native molecule. The implications of this observation in explaining the role of leptin in adrenal gland regulation will be discussed in Section 5.1.1.

Table 2.1 Leptin sequences among various organismsa Homo sapiens

a

Rattus norvegicus

Mus musculus

Species

% identity

% positives

% identity

% positives

% identity

% positives

Homo sapiens (M) Rattus norvegicus (M) Mus musculus (M) Pongo pygmaeus orangutan (M) Pan troglodytes (M) Gorilla gorilla (M) Bubalus bubalis (M) Bos taurus (M) Ursus thibetanus japonicus (M) Sus scrofa (M) Capra hircus (M) Ovis aries (M) Canis familiaris (M) Felis catus (M) Halichoerus grypus (M) Anas platyrhynchos (A) Gallus gallus domesticus (A) Ctenopharyngodon idella (P) Cyprinus carpio (P) Megalobrama amblycephala (P) Silurus asotus (P) Channa argus (P) Aristichthys nobilis (P)

– 83.7 85.0 97.3 99.3 98.6 87.1 87.1 83.7 87.1 87.1 87.1 82.3 86.4 66.0 84.4 81.6 85.0 84.4 83.7 83.7 83.0 82.3

– 90.5 92.5 98.6 100 99.3 93.9 93.9 92.5 93.9 93.2 93.2 89.8 92.5 78.2 91.8 89.1 92.5 91.8 91.8 91.2 90.5 90.5

83.7 – 95.9 81.0 83.0 82.3 85.7 85.7 81.6 83.7 85.0 85.0 79.6 82.3 63.3 95.9 92.5 95.9 95.2 94.6 93.9 93.9 93.2

90.5 – 98.0 89.1 90.5 89.8 91.2 91.2 89.1 90.5 90.5 90.5 86.4 87.8 73.5 98.0 94.6 98.0 97.3 97.3 96.6 95.9 95.9

85.0 95.9 – 82.3 84.4 83.7 85.0 85.0 81.0 83.0 84.4 84.4 78.9 81.6 62.6 99.3 95.9 100 99.3 98.6 98.0 98.0 97.3

92.5 98.0 – 91.2 92.5 91.8 91.2 91.2 89.1 90.5 90.5 90.5 86.4 87.8 74.1 99.3 96.6 100 99.3 99.3 98.6 98.0 98.0

Leptin sequence homology of different species of mammals (M), aves (A), and pisces (P) in relation to leptin molecule of Homo sapiens, Rattus norvegicus, and Mus musculus. The alignment was performed in AlignX software.

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2.2. Leptin receptors Leptin exerts its biological effects through the activation of a specific R, the Ob-R, the product of the db gene (Tartaglia et al., 1995). The human Ob-R gene contains 18 exons and 17 introns and encodes for six R isoforms (see following), the longest of which is composed of 1162 amino acid residues. The Ob-R structurally belongs to the Class-I cytokine R family. The extracellular part of the human Ob-R contains at least seven structural domains (Fong et al., 1998): domains 1 (62–178 residue) and 2 (235–327 residue) possess a fibronectin type III fold and together form the cytokine R homology module 1; domain 3 (328–427 residue) has an Ig-like fold; domains 4 (428–535 residue) and 5 (536–635 residue) again display a fibronectin type III fold and together form the cytokine R homology module 2; and domains 6 and 7 also adopt a fibronectin type III fold. Multiple splice variants of the Ob-R mRNA encode for at least six isoforms (from Ob-Ra to Ob-Rf ), which all share a common extracellular ligand-binding domain. Ob-Re does not contain transmembrane and intracellular domains and circulates as soluble R (Friedman and Halaas, 1998). The other isoforms possess intracellular domains, but only the longest one, Ob-Rb (also called Ob-Rl), contains all domains required to activate the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway (Ahima et al., 2000; Tartaglia, 1997). The short isoforms may serve as leptin-binding poteins, and play a role in leptin transport across the blood–brain barrier and clearance from circulation. Ob-Rb is primarily expressed in the hypothalamus (see Section 3.1.2), but, along with other isoforms, also in peripheral tissues, including lungs, kidneys, liver, pancreas, thyroid gland, adrenal glands (see Section 3.3.2), and gonads (see Section 5.2) (Ahima et al., 2000; Baldelli et al., 2002; Bendinelli et al., 2000; Lloyd et al., 2001; Malendowicz et al., 2004a; Mantzoros, 1999; Nowak et al., 1998, 2002a; Seufert, 2004; Tena-Sempere and Barreiro, 2002; Zhang et al., 2005). Ob-Rb not only activates the JAK/STAT cascade, but, along with Ob-Ra, also mitogen-activated protein kinase (MAPK) p42/p44 and p38 signaling pathways, as well as stress-activated protein kinase (PK) c-Jun N-terminal kinase (JNK). Ob-Rb has also been reported to signal via phosphoinositide-3-kinase (PI3K)/phosphodiesterase-3B/cyclic-adenosine 30 ,50 -monophosphate (cAMP) and 50 -AMP-activated PK cascades. PI3K products may in turn stimulate PKB (Akt) and PKC isoforms and endothelial nitric oxide (NO) synthase (NOS). The extremely complex and not yet settled signaling mechanism of Ob-Rb may also involve its cross talk with other R, for example, insulin and insulin-like growth factor (IGF) R (Ahima and Osei, 2004; Bjorbaek et al., 1997; Fru¨hbeck, 2006; Hegyi et al., 2004; Murakami et al., 1997; Peelman et al., 2006; Yamashita et al., 1998).

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3. Expression of Leptin and Its Receptors in the Hypothalamic–Pituitary–Adrenal Axis 3.1. Hypothalamus 3.1.1. Leptin Available data on ob gene expression in the hypothalamus are few and rather conflicting. Reverse transcription (RT)-polymerase chain reaction (PCR) and immunocytochemistry (ICC), but not Western blotting, detected leptin mRNA and protein in the rat hypothalamus (Morash et al., 1999). In subsequent studies, semiquantitative PCR analysis did not evidence agerelated changes in leptin mRNA expression in the female rat hypothalamus from day 2 to day 28 of postnatal life (Morash et al., 2001). Double-label fluorescent ICC showed that in the rat paraventricular and supraoptic nuclei (PVN and SON, respectively) most oxytocin- and vasopressinimmunoreactive neurons also contained leptin immunoreactivity (ir) (Ur et al., 2002). Leptin expression was not detected in the hypothalamus of calves (Chelikani et al., 2003) and sheep (Dyer et al., 1997). In the female pig, leptin gene expression in the medial basal hypothalamus was found to be higher in the mid- than in the late-luteal phase and at days 30–32 than days 14–16 of pregnancy (Kaminski et al., 2006). 3.1.2. Leptin receptors After the pioneeristic demonstration of the presence of high-affinity leptinbinding sites in the rat hypothalamus (Stephens et al., 1995), PCR, Northern blotting, in situ hybridization, Western blotting, and ICC studies consistently showed the expression of the Ob-R, and especially of the long isoform Ob-Rb, in the hypothalamus of humans (Burguera et al., 2000; Couce et al., 1997), monkeys (Finn et al., 1998; Hotta et al., 1998), cows (Chelikani et al., 2003; Ren et al., 2002), sheep (Iqbal et al., 2001; Muhlhausler et al., 2004; Williams et al., 1999), pigs (Czaja et al., 2002; Kaminski et al., 2006; Lin et al., 2000; Smolinska et al., 2004; Zhou et al., 2004), rats (Hakansson and Meister, 1998; Schwartz et al., 1996a,b; Zamorano et al., 1997), mice (Fei et al., 1997; Mercer et al., 1996; Raber et al., 1997), and fowls (Taouis et al., 2001). There is general consensus that Ob-R is primarily in the PVN, and colocalization of Ob-Rb with corticotropin-releasing hormone (CRH) or proopiomelanocortin (POMC) in many hypothalamic neurons has been demonstrated in the sheep (Iqbal et al., 2001) and rat (Hakansson and Meister, 1998). Evidence has also been provided that the level of Ob-R expression does vary according to the age, sex, and strain of animals. In the pig hypothalamus, Ob-Rb mRNA was higher in the Large White than in the Erhualian

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strain. The expression in the former strain was very low after birth, increased gradually until weaning, and then decreased with age. In the Erhualian pigs, Ob-Rb expression displayed a net rise from day 120 to day 180 of postnatal life (Zhou et al., 2004). Elevated Ob-R expression was detected in the gilt hypothalamus at days 14–16 and 30–32 of pregnancy (Kaminski et al., 2006; Smolinska et al., 2004). In the rat hypothalamus, Ob-Rb mRNA was undetectable at day 4 of postnatal life, then rose significantly from day 4 to days 14–22. However, ICC detected Ob-Rbir also at day 4 (Morash et al., 2003). Ob-Rb mRNA was elevated at day 7 of pregnancy, but returned to the prepregnancy level by midgestation and then remained stable during lactation (Seeber et al., 2002). In contrast, it has been recently reported that hypothalamic Ob-R mRNA expression decreased in rats during pregnancy and then rose after delivery (Szczepankiewicz et al., 2006). Leptin expression has been firmly demonstrated only in the pig and rat hypothalamus. In contrast, abundant evidence showed the expression of Ob-R (especially the Ob-Rb isoform) in the hypothalamus of all mammalian species so far examined. Ob-R expression occurs in the PVN, and the localization of the Ob-Rb in many hypothalamic CRH- and POMC-positive neurons has been reported.

3.2. Anterior pituitary 3.2.1. Leptin Leptin expression, as mRNA and protein, has been detected in the anterior pituitary of humans (Isono et al., 2003; Jin et al., 1999; Korbonits et al., 2001a,b; Lloyd et al., 2001; Vidal et al., 2000), cows (Yonekura et al., 2003), pigs (Kaminski et al., 2006; Smolinska et al., 2004), rats ( Jin et al., 2000; Morash et al., 1999, 2001, 2003; Yonekura et al., 2003), and mice ( Jin et al., 2000). Probably due to the different primers used, Chelikani et al. (2003) failed to demonstrate by PCR leptin mRNA in bovine (Holstein strain) anterior pituitary. In the rat, pituitary leptin mRNA levels were maximal during postnatal days 7–14 and then decreased gradually to adulthood (Morash et al., 2001, 2003). Marked interspecies differences were observed in leptin-ir localization in the various anterior-pituitary cell types. ICC showed leptin-ir in 25–50% of cells of the human anterior pituitary, mostly in hormone-secreting ones (Isono et al., 2003; Jin et al., 1999; Lloyd et al., 2001; Vidal et al., 2000). Leptinpositive cells were corticotrophs, 70–80%; somatotrophs, 10–21%; thyreotrophs, 20–32%; gonadotrophs, 25–33%; lactotrophs, 3%; and folliculostellate cells, 64%. Immunoelectron microscopy showed the colocalization of leptin with the respective hormone in the secretory granules, suggesting its intracellular storage. Of interest, confocal ICC analysis of a murine ACTH-secreting

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AtT20 cell line expressing an epitope-tagget human leptin (FLAG-leptin) demonstrated that leptin-ir was colocalized with endogenus ACTH at the tips of the cytoplasmic processes, where regulated secretory granules accumulate (Chavez and Moore, 1997). In contrast with humans, ICC revealed the presence of leptin-ir only in a small fraction of rodent anterior-pituitary cells (about 5% and 7% in rats and mice, respectively) and showed that less than 1% of rat corticotrophs expressed leptin ( Jin et al., 2000). These observations may suggest different regulatory functions of leptin in the human and rodent pituitary during its evolutionary development. 3.2.2. Leptin receptors Ob-R expression, as mRNA and protein, has been demonstrated in the anterior pituitary of humans (Dieterich and Lehnert, 1998; Jin et al., 1999; Korbonits et al., 2001a,b; Shimon et al., 1998), monkeys (Finn et al., 1998), cows (Chelikani et al., 2003; Yonekura et al., 2003), sheep (Dyer et al., 1997; French et al., 2006; Iqbal et al., 2000), pigs (Kaminski et al., 2006; Lin et al., 2000, 2001, 2003; Siawrys et al., 2005), rats ( Jin et al., 2000; Morash et al., 1999, 2003; Sone et al., 2001; Szczepankiewicz et al., 2006; Yonekura et al., 2003; Zamorano et al., 1997), and mice (Cai and Hyde, 1998; Raber et al., 1997). Interesting findings have been reported on the splice variant of the Ob-R expressed, which can be summarized as follows. Ob-Ra and Ob-Rb have been detected in the anterior pituitary of humans (Dieterich and Lehnert, 1998), cows (Chelikani et al., 2003), and rats ( Jin et al., 2000; Morash et al., 1999); however, according to Shimon et al. (1998), both isoforms were expressed only in the adult human pituitary, the fetal gland expressing only Ob-Rb. Only Ob-Ra expression was found in cultured bovine and rat anterior-pituitary cells (Yonekura et al., 2003), and no Ob-Rb mRNA was detected in the ovine pituitary by in situ hybridization (Williams et al., 1999). Pituitary Ob-Ra mRNA levels were high in neonatal rats (day 4) and then declined, paralleling the fall in leptin expression, whereas Ob-Rb mRNA was stable from day 4 to day 22 of postnatal life (Morash et al., 2003). Ob-Rb expression in the gilt and rat pituitary has been reported to decrease in the late phases of pregnancy (Kaminski et al., 2006; Szczepankiewicz et al., 2006). ICC revealed that Ob-R was present in about 97% of rat somatotrophs and less than 1% of lactotrophs, thyreotrophs, gonadotrophs, and corticotrophs (Sone et al., 2001). In contrast, Iqbal et al. (2000) by double-label immunofluorescence observed Ob-R in about 27% of corticotrophs of the sheep pituitary. The concomitant expression of leptin and Ob-R in the anterior pituitary may suggest that autocrine–paracrine loops are operative, mediating leptin effects on the secretion of pituitary hormones. In contrast with other

72 Size marker

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500

ZG

ZF/R

AM Ob

200 50 500

Ob-Ra 235 bp

200 50 500

Ob-Rb

200 171 bp 50 500

Ob-Rc

200

161 bp

50 500

Ob-Re

200

184 bp

50 500 200

Ob-Rf 151 bp

50

Figure 2.2 Ethidium bromide-stained 2% agarose gel showing cDNA amplified with rat leptin (Ob) and Ob-R-isoform-specific primers from ZG, ZF/R, and adrenal medulla (AM) of adult rat adrenals. Primer sequences were leptin sense (190^209), 50 GACATTTCACACACGCAGTC-30 and leptin antisense (366^384), 50 -GAGGAGGTCTCGCAGGTT-30 (195 bp; accession number NM 013076); Ob-Ra sense (110^131), 50 -CACTGTTAATTTCACACCAGAG-30 and Ob-Ra antisense (323^344), 50 -GTCATTCAAACCATAGTTTAGG-30 (235 bp; accession number AF 304191); Ob-Rb sense (2635^2653), 50 -TGCTCGGAACACTGTTAAT-30 and Ob-Rb antisense (2785^2805), 50 GAAGAAGAGGACCAAATATCA-30 (171 bp; accession number U52966); Ob-Rc sense (35^53), 50 -TGCTCGGAACACTGTTAAT-30 and Ob-Rc antisense (172^195), 50 -ATAGAGTATCTAAACTGCAACCTT-30 (161 bp; accession number AF 007818); Ob-Re sense (595^614), 50 -TCCTGGACACTGTCACCTAA-30 and Ob-Re antisense (759^778), 50 -ATCAGGATTGCCAATTTACA-30 (184 bp; accession number AF 007819); and Ob-Rf sense (2676^2696), 50 -GCTGCTCGGAACACTGTTAAT-30 and Ob-Rf antisense

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mammalian species so far examined, only a very low percent of corticotrophs of rodents express leptin and Ob-R, which could cast doubt on the relevance of the leptin system in the regulation of ACTH secretion in this order of animals.

3.3. Adrenal gland 3.3.1. Leptin RT-PCR did not detect leptin mRNA either in the cortex or the medulla of human (Glasow et al., 1998), calf (Chelikani et al., 2003), and rat adrenals (see Figs. 2.2 and 2.3), as well as in the human carcinoma-derived NCIH295 cell line and primary human adrenal cultures containing both cortical and medullary cells (Glasow and Bornstein, 2000). Personal ICC data confirmed the absence of leptin-ir in the cortex but evidenced the presence of leptin-positive cells in the medulla (Fig. 2.4). The location of these cells near the blood vessels and their positivity to tryptase (not shown) could suggest that they are mast cells. It must be noted that colocalization of leptin with tryptase has been recently demonstrated in mast cells of human myometrium (Ribatti et al., 2007). 3.3.2. Leptin receptors Adrenal cortex RT-PCR demonstrated Ob-Rb mRNA expression in the adrenal cortex of humans (Glasow and Bornstein, 2000; Glasow et al., 1998, 1999; Pralong et al., 1998), cows (Chelikani et al., 2003), pigs (Lin et al., 2000), rats (Malendowicz et al., 2003a, 2004b; Pralong et al., 1998; TenaSempere et al., 2000), and mice (Hoggard et al., 1997), as well as in NCIH295 cells (Biason-Lauber et al., 2000; Glasow and Bornstein, 2000). Noteworthy, Northern blot analysis only partially confirmed the presence of Ob-R mRNA in human and rat adrenal cortex (Pralong et al., 1998; Zamorano et al., 1997). Ob-Ra mRNA expression, in addition to Ob-Rb expression, was found in cow and rat adrenal cortex (Chelikani et al., 2003; Malendowicz et al., 2003a, 2004b; Tena-Sempere et al., 2000). Semiquantitative PCR showed the predominant expression of the Ob-Ra and Ob-Rb isoforms over that of the Ob-Rc and Ob-Rf isoforms in the rat adrenal cortex, Ob-Re expression being negligible (Tena-Sempere et al., 2000). Personal unpublished real-time PCR findings demonstrated the expression of Ob-Ra, Ob-Rb, Ob-Rc, Ob-Re, and Ob-Rf in dispersed (2806^2826), 50 -ACGGCATCCACTCTATATCCT-30 (151 bp; accession number D84125). The PCR program was denaturation step (95 C for 10 min), followed by 35 cycles of three step amplification (denaturation, 95 C for 10 sec; annealing, 58 C for 5 sec; and extension,72 C for 10 sec). Lane1was loaded with Roche MarkerVIII (200 ng).

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Relative mRNA expression (target gene/GAPDH ratio ⫻[ ])

4

Leptin (⫻ 10−12)

4

Ob-Ra (⫻ 10−6)

16

3

3

12

2

2

8

1

1

4

0 8

ZG ZF

AM

Ob-Rc (⫻ 10−6)

0 16

ZG ZF

AM

Ob-Re (⫻ 10−8)

0 16

6

12

12

4

8

8

2

4

4

0

ZG ZF

AM

0

ZG ZF

AM

0

Ob-Rb (⫻ 10−8)

ZG ZF

AM

Ob-Rf (⫻ 10−4)

ZG ZF

AM

Figure 2.3 Real-time PCR semiquantitative analysis of rat leptin and Ob-R gene expression in the ZG, ZF, and adrenal medulla (AM) of adult rat adrenals. Primer sequences for Ob-Rwere those indicated in the legend to Fig. 2.2, and that for GAPDH was sense (18^27), 50 -TTCTAGAGACAGCCGCATCT-30 and antisense (104^123), 50 TGGTAACCAGGTGTCCGATA-30 (106 bp; accession number X02231). The program, as described in the legend to Fig. 2.2, was a total of 45 cycles, followed by a melting curve (60^90 C with a heating rate of 0.1C/sec). All samples were amplified in duplicate and the GAPDH gene was used as reference to normalize data.

rat zona glomerulosa (ZG) and zona fasciculata-reticularis (ZF/R) cells, the level of expression being Ob-Rf > Ob-Ra ¼ Ob-Rc > Ob-Rb > Ob-Re. Except for Ob-Re, the level of expression of other Ob-R isoforms was lower in the cortex than in the medulla (see Figs. 2.2 and 2.3). ICC showed intense Ob-Rb immunostaining in the human adrenal cortex (Glasow and Bornstein, 2000; Glasow et al., 1998). In contrast, earlier studies did not detect Ob-R protein in the rat adrenal cortex (Cao et al., 1997).

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Figure 2.4 ICC demostration of leptin-ir in exemplary cryosections of human adrenal gland. Leptin-ir is absent in the capsule (c), subcapsular ZG, and ZF (A), while in adrenal medulla few leptin-positive cells (arrowheads), either isolated (B) or grouped in small clusters (C) near blood vessels (*), can be observed. Negative controls (D) were obtained by incubating cryosections with primary antibodies preabsorbed with leptin. Sections were incubated with the primary rabbit antibody to human leptin (Phoenix Pharmaceuticals, Belmont, CA) (1:500 dilution) at 37 for 60 min and then with the secondary peroxidase-conjugated antirabbit IgG goat antibodies (Santa Cruz Biotechnology, Santa Cruz, CA) (1:50 dilution) at 37 for 40 min. After rinsing, the reaction was developed for 5 min with Sigma Fast 30,30 -diaminobenzidine 0.7-mg tablets (Sigma-Aldrich Corp., St. Louis, MO). Magnification 750.

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Adrenal medulla The expression of Ob-Rb mRNA has been demonstrated in the adrenal medulla of humans (Glasow and Bornstein, 2000; Glasow et al., 1998), pigs (Takekoshi et al., 1999), and mice (Hoggard et al., 1997). In cultured bovine adrenomedullary cells only the expression of Ob-Ra was found (Yanagihara et al., 2000). Personal unpublished real-time PCR data showed that Ob-R expression was markedly higher in the medulla than in the cortex of rat adrenals, the level of expression of the various Ob-R isoforms being that described in the cortex (Fig. 2.3). ICC revealed the presence of Ob-R protein in the adrenal medulla of humans, where Ob-Rb immunostaining was weaker than in the cortex (Glasow and Bornstein, 2000; Glasow et al., 1998), and rats (Cao et al., 1997). Consistent evidence indicates that at variance with the hypothalamus and anterior pituitary, leptin is not expressed in the adrenal gland. In contrast, Ob-R is expressed in both adrenal cortex and medulla, leading to the view that leptin can modulate the secretion of both corticosteroid hormones and catecholamines, acting as a circulating hormone.

4. Effects of Leptin on the Central Branch of the Hypothalamic–Pituitary–Adrenal Axis 4.1. Hypothalamus and CRH secretion 4.1.1. CRH expression and biosynthesis Earlier studies showed that the intracerebroventricular (icv) injection of leptin raised by about 40% CRH mRNA in the PVN of normal rats, but not leptin-resistant Zucker animals (Schwartz et al., 1996a), as well as induced c-fos protein in the parvocellular division of PVN (Elmquist et al., 1998; Masaki et al., 2003; Van Dijk et al., 1996). There is also an indication that icv leptin administration specifically activated CRH sympathetic neurons giving rise to descending autonomic transmission (Elmquist et al., 1997; Okamoto et al., 2000). Leptin, either icv or systemically administered, was found to increase within 2–6 h the hypothalamic CRH concentration (Uehara et al., 1998) and CRH mRNA in the rat PVN, as revealed by in situ hybridization (Nishiyama et al., 1999). However, subcutaneous (sc) leptin infusion for 5 days did not change CRH expression (Nishiyama et al., 1999). The leptin-induced increase in CRH mRNA in rat PVN was prevented by pretreatment with a V1a-R antagonist, suggesting that the effect was at least partly mediated by arginin-vasopressin (AVP) (Morimoto et al., 2000). Daily leptin administration for 5 days did not alter CRH mRNA expression in PVN of obese ob/ob mice (Schwartz et al., 1996a), but leptin prolonged infusion (for 7 days) prevented the starvation-induced CRH biosynthesis and c-fos protein induction in PVN of ob/ob male animals (Huang et al., 1998).

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Accordingly, leptin was found to downregulate CRH expression in mouse PVN and to prevent the bilateral adrenalectomy-induced increase in CRH mRNA (Arvaniti et al., 2001). To conclude, we wish to mention that continuous infusion with leptin for 6 h failed to alter CRH mRNA expression in the fowl hypothalamus (Dridi et al., 2005). 4.1.2. CRH release Evidence has been provided that leptin, but not the heat-inactivated peptide, enhanced (from 1010 to 107M) CRH release from male rat hypothalamic explants, the maximal effective concentration being 108M (Costa et al., 1997). Similar findings have been obtained in mice (Raber et al., 1997). Although leptin has been reported to inhibit hypoglycemia-induced CRH release from perfused male rat hypothalamic explants (Heiman et al., 1997), more recent studies confirmed the stimulating action of leptin (Jethwa et al., 2006). In contrast to CRH, AVP release was not affected by leptin in mice (Raber et al., 1997); however, it was increased in rabbits and rats (Matsumura et al., 2000; Yamamoto et al., 1999). Some data suggest that the effect of leptin on CRH secretion may depend on the presence of glucocorticoid hormones ( Jang et al., 2000). Leptin icv administration did not change within 1–3 h either CRH concentration in the PVN of lean and obese mice or CRH release from hypothalamic explants of animals with intact adrenal glands. Conversely, it raised by about 50% CRH secretion from hypothalamic preparations of adrenalectomized animals. Taken together, these findings indicate that leptin acutely stimulates hypothalamic CRH biosynthesis in rats, while its prolonged administration exerts an inhibitory effect in mice. It remains unsettled whether these apparently conflicting observations depend on the different modalities of treatment (acute versus chronic) or interspecies differencies (rat versus mouse). In contrast, there is large consensus that leptin enhances hypothalamic CRH release in rodents, the secretagogue action being perhaps restrained by the presence of endogenous glucocorticoids.

4.2. Anterior pituitary and ACTH secretion 4.2.1. ACTH expression and biosynthesis Northern blot analysis revealed that acute leptin icv administration raised POMC mRNA expression in the rat anterior pituitary. The effect was partially reversed by pretreatment with an antagonist of the V1a-R, thereby suggesting the involvement of AVP (Morimoto et al., 2000). The prolonged (from 2 to 16 days) systemic administration of leptin increased pituitary ACTH concentration in both adrenalectomized female rats (Malendowicz et al., 2001) and intact animals (Nowak et al., 2002b). In contrast, leptin has been reported to decrease POMC and PC2 (a POMC processing enzyme)

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mRNAs in the anterior pituitary of obese mice (where the expression was elevated), but not in primary cultures of anterior pituitary cells from young female C57BL/6J mice (Renz et al., 2000). 4.2.2. ACTH release Leptin did not affect either basal or CRH-stimulated ACTH release from primary cultures of rat pituitary cells (Heiman et al., 1997; Pralong and Gaillard, 2001). In contrast, it enhanced ACTH release from superfused mouse pituitary slices, and the effect was specific because it was blocked by antileptin antibodies (Raber et al., 1997). In light of the rather scanty investigations herein surveyed, it seems legitimate to conclude that leptin exerts opposite effects on the anterior pituitary of rats and mice. Leptin appears to enhance ACTH biosynthesis in rats, and to inhibit (or not to affect) it in mice, and to raise ACTH release in mice, without affecting it in rats.

5. Effects of Leptin on the Peripheral Branch of the Hypothalamic–Pituitary–Adrenal Axis 5.1. Adrenal cortex 5.1.1. Steroid-hormone secretion In vitro studies Humans Pralong et al. (1998) reported that the 24- (but not 6-) h exposure to leptin inhibited ACTH-stimulated, but not basal, cortisol secretion from primary cultures of human adrenocortical cells, and subsequent studies confirmed this observation (Glasow and Bornstein, 2000; Glasow et al., 1998). It was shown that leptin lowered ACTH-stimulated aldosterone secretion by about 30% and lowered cortisol and dehydroepiandrosterone (DHEA) yield by about 15% and that the drop in cortisol secretion was associated with a 50% decrease in cytochrome P450 (CYP) 17a mRNA expression. Completely different results were obtained using the human adrenocortical carcinoma-derived NCI-H295 cell line, which is commonly used as a reliable model of normal human steroid synthesis (Rainey et al., 2004). Earlier studies did not show any effect of leptin on basal and forskolinstimulated cortisol secretion (Lado-Abeal et al., 1999). However, further investigations evidenced a twofold effect of leptin on CYP17, which combines 17a-hydroxylase and 17,20-lyase activities, in NCI-H295 cells expressing Ob-R (Biason-Lauber et al., 2000). Leptin (3  108M) exposure for 24 h stimulated 17,20-lyase activity and DHEA production, without markedly changing 17a-hydroxylase activity. Conversely, shorter incubations raised 17a-hydroxylase activity and 17-hydroxyprogesterone

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synthesis, the effect becoming manifest within 30 min and disappearing within 4 h. Cows Bornstein et al. (1997) reported that within 24 h recombinant murine leptin inhibited basal and ACTH-stimulated cortisol release (about 20–50% decrease) from cultured bovine adrenocortical cells, as well as reduced CYP17 mRNA expression. Further investigations also showed the inhibition of the expression of CYP11A and CYP21A, which possess cholesterol side-chain cleaving and 21C-hydroxylase activity, respectively (Kruse et al., 1998). Rats Investigations on the direct effect of leptin on adrenocortical steroidogenesis in the rat gave intriguing and controversial results. The first studies showed that within 60 min recombinant murine leptin enhanced basal, but not ACTH-stimulated, aldosterone (108 and 107M, but not lower and higher concentrations) and corticosterone output (from 109 to 106M) from dispersed ZG and ZF/R cells, respectively (Malendowicz et al., 1997). Subsequent investigations, carried out using adrenocortical cells cultured for 48 h in normal growth medium and then for 24 h in fetal calf serum-free medium, demonstrated that the 24 h exposure to 107M leptin lowered ACTH-stimulated, but not basal, corticosterone yield (Pralong et al., 1998). An acute inhibitory effect of leptin on ACTH-stimulated aldosterone and corticosterone production has also been shown in freshly dispersed adrenocortical cells of newborn rats (Salzmann et al., 2004) and on basal and ACTH-stimulated corticosterone secretion in adult rat adrenocortical slices (Tena-Sempere et al., 2000). Cherradi et al. (2001), although unable to observe any effect of leptin on basal and ACTH-stimulated pregnenolone production from primary cultures of rat adrenocortical cells, observed that leptin pretreatment significantly lowered the acute pregnenolone response to ACTH. These investigators suggested that the target for the inhibitory action of leptin resides upstream of pregnenolone synthesis and requires a chronic exposure to leptin. Accordingly, neither cAMP production nor CYP11A expression was affected by leptin, which, however, downregulated the steroidogenic acute regulatory protein (StAR) expression induced by an exogenous ACTH challenge (Cherradi et al., 2001; Salzmann et al., 2004). The biological effects of leptin on target tissues are mediated by several ObR isoforms (see Section 2.2), which could variously interact with native leptin and its fragments (see Fig. 2.1). This consideration prompted us to investigate the effects of leptin and several leptin fragments (108 and 106M) on corticosteroid-hormone secretion from dispersed or cultured rat adrenocortical cells (Malendowicz et al., 2003a, 2004b). In freshly dispersed cells, native murine leptin, its fragment 116–130, and human leptin fragments 138–167, 150–167, and [Tyr]26–39 acutely raised basal aldosterone and corticosterone secretion. Human leptin fragment 93–105 was ineffective, while fragment

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22–56 lowered corticosterone (but not aldosterone) output. In cultured ZF/R cells, the 96-h exposure to native leptin and leptin fragments 150–167 and 26– 39 enhanced corticosterone secretion, fragment 116–130 was ineffective, and fragments 138–167 and 22–56 exerted an inhibitory effect. Fragment 93–105 displayed a dose-dependent biphasic effect: stimulating and inhibitory actions at low and high concentrations, respectively. Collectively, these findings led to the conclusion that in rat adrenocortical cells leptin and its fragments may interact differently with Ob-R or interact with different isoforms. They also suggested that the direct adrenocortical secretagogue action of leptin depends on the C-terminal sequence 116–166 and that the N-terminal sequence is not needed for leptin to activate Ob-R positively coupled to steroidogenesis, but is possibly responsible for a direct inhibitory action on glucocorticoid secretion. Mice As expected, leptin was ineffective on steroid secretion of cultured adrenocortical cells obtained from db/db mice (Pralong et al., 1998) because this strain bears a spontaneous mutation of Ob-Rb, rendering it totally devoid of signal-transduction capability (Vaisse et al., 1996). Of interest, leptin was found to concentration-dependently raise 11b-hydroxysteroid dehydrogenase (11b-HSD) type I activity in primary cultures of ob/ob (but not db/db) mouse hepatocytes (Liu et al., 2003). Since 11b-HSD-I regenerates glucocorticoids from inactive 11-keto forms (Stewart and Krosowski, 1999), leptin could be an important metabolic signal activating intrahepatic corticosterone production. It is to be stressed that in vivo experiments should take into account this extra-HPA axis action of leptin. In vivo studies Humans The fluctuations of the 24-h pattern of circulating leptin were found to be inverse to those of ACTH and cortisol in human healthy volunteers (Licino et al., 1997), or leptin maxima followed cortisol maxima (Wagner et al., 2000). Dexamethasone or cortisol administration evoked an acute substained increase in blood leptin concentration (Miell et al., 1996; Newcomber et al., 1998), but rises in the plasma cortisol in the physiological range did not influence the level of circulating leptin (Nye et al., 2000).

Monkeys The infusion of recombinant human leptin (for 4 or 48 h) did not change basal and ACTH-stimulated cortisol blood levels in fed or fasted Rhesus monkeys (Lado-Abeal et al., 1999, 2000). However, the prolonged infusion with leptin blunted the CRH-induced increase in ACTH and cortisol plasma concentrations and lowered the morning (but not evening) surge in ACTH in ovariectomized animals (Wilson et al., 2005).

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Sheep Late fetal life is characterized in the sheep by an increased HPAaxis activity that prepares the fetus for extrauterine life and initiates the endocrine cascade leading to parturition (Challis and Brooks, 1989). The icv infusion for 5 days of leptin to the fetus in late gestation was found to inhibit a prepartum surge of ACTH and cortisol in the mother (Howe et al., 2002). The intravenous (iv) infusion of recombinant ovine leptin for 4 days of pregnant sheep at day 136 of gestation did not change the levels of ACTH and cortisol in the fetal blood, while the infusion at day 144 (i.e., near term; 145  2 days) suppressed cortisol without affecting ACTH (Yuen et al., 2004). Rats Earlier studies described an inhibitory action of leptin on the HPA axis and its involvement in the regulation of a diurnal pattern of corticosterone secretion (Ahima et al., 1996; Heiman et al., 1997). More recent findings confirmed this contention, showing that icv or ip administration of leptin lowered the blood level of corticosterone (Akirav et al., 2004; Clark et al., 2006). A negative feedback loop has been proposed between leptin and the HPA axis, where the increase in ACTH blood level raises leptin, which in turn inhibits corticosterone secretion (Spinedi and Gaillard, 1998). Accordingly, evidence has been provided that experimental conditions able to increase plasma leptin (as the monosodium L-glutamateinduced destruction of the hypothalamic arcuate nucleus) downregulated Ob-Rb mRNA expression in adrenals and enhanced their in vivo and in vitro corticosterone response to ACTH (Perello´ et al., 2003, 2004). Other studies obtained opposite findings. The icv injection of leptin was found to increase plasma corticosterone levels, the effect lasting 4 h and being especially intense at the onset of the dark phase (Van Dijk et al., 1996, 1997). Analogous observations have been described by Morimoto et al. (2000) and Jethwa et al. (2006), who reported a rise in both ACTH and corticosterone within 15–20 min after the leptin icv or ip injection. The bolus sc administration of recombinant murine leptin was found to raise the blood level of corticosterone within 60 min and the levels of both corticosterone and ACTH within 120 min (Hocho´l et al., 2000; Malendowicz et al., 1998). Further studies showed that the systemic administration not only of leptin, but also of leptin fragments 150–167, 138–167, 93–105, 22–56, and 26–39 was able to evoke a clearcut corticosterone response, suggesting that the in vivo stimulating action of leptin on glucocorticoid secretion is not connected, as occurred in vitro (see previously), to specific sequences of its molecule (Malendowicz et al., 2004a). The bolus sc injection of leptin also evoked within 120 min a net increase in the aldosterone plasma concentration (Malendowicz et al., 1998). In this connection, it is to be recalled that leptin icv injection increased the level of circulating AVP (see Section 4.1.2), which not only activates hypothalamic CRH neurons to

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drive ACTH secretion (Aguilera and Rabadan-Diehl, 2000; Engelmann et al., 2004), but also directly stimulates aldosterone production from ZG cells (Nussdorfer, 1996). Before concluding, it is necessary to mention the intriguing findings showing that leptin, although lowering corticosterone blood levels in normal rats (see previously), increased blood levels in streptozotocin-induced diabetic animals (Akirav et al., 2004). Mice The prolonged systemic administration of leptin (for up to 30 days) decreased corticosterone blood levels in ob/ob C57BL/6J, but not lean mice (Huang et al., 1998; Stephens et al., 1995). Accordingly, leptin partially blunted the fast-induced rise in the concentration of circulating corticosterone in C57BL/6J mice (Ziotopoulou et al., 2000). In summary, consistent findings show that leptin exerts a direct in vitro inhibitory effect on human and cow adrenocortical cells, connected with the downregulation of StAR and CYP17 expression. Contrasting results have been described in the rat, where leptin was found to either inhibit or stimulate steroid-hormone secretion. It is likely that the experimental model used (dispersed versus cultured cells) and the duration of exposure (short versus long term) may profoundly influence the in vitro leptin effects. In vivo studies indicate that leptin tends to inhibit the HPA axis in humans, monkeys, sheep, and mice. In the rat, contrasting findings have been again reported: Leptin appears to inhibit the HPA axis when centrally administered, but to stimulate it when given systemically. Probably, in this species, the in vivo effects of leptin are dependent on its route of administration and are the result of its combined action on the central and peripheral branches of the HPA axis. 5.1.2. Adrenocortical growth Adult and newborn adrenals The prolonged sc administration of leptin (six daily injections of 20 nmol/kg) resulted in a marked atrophy of adult rat adrenal cortex (Malendowicz et al., 2000b; Ziolkowska et al., 2001). The adrenal weight and the volume of ZF and its parenchymal cells were decreased. The proliferating cell nuclear antigen (PCNA) index was lowered in the ZG, and the apoptotic index (in situ TUNEL assay) was increased in the ZF and to a lesser extent in the ZR. Neither leptin nor leptin 116–130 altered the ZG mitotic index, as evaluated by the stachmokinetic method in adult rats, indicating that this technique is less sensible than the PCNA index assay (Malendowicz et al., 1999). In contrast, leptin fragment 116–130, but not native leptin, induced a 40% rise in the ZG mitotic index of immature (20-day–old) rats. Regenerating adrenals Adrenal regeneration after enucleation and contralateral adrenalectomy is a well-established model of adrenal growth, resembling that occurring during embryonal development and mainly involving cell proliferation (Dalmann, 1984–1985). The sc injection of

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leptin fragments 116–130, 138–167, and 150–167 (10 nmol/kg, 28, 16, and 4 h before the sacrifice) decreased the mitotic index of regenerating subcapsular tissue, while fragments 22–56 and [Tyr]26–39 and 93–105 were ineffective (Malendowicz et al., 2000a; Markowska et al., 2004). Adrenocortical cells cultured in vitro No effect of leptin on the proliferative activity of human adrenocortical cells in primary culture and cultured NCIH295 cells has been observed (Glasow and Bornstein, 2000; Glasow et al., 1999). In contrast, the 96-h exposure to leptin(1–147) lowered and fragment 26–39 enhanced proliferation of cultured rat adrenocortical cells, while fragments 22–56 and 138–167 were ineffective. Fragments 93–105 and 150– 167 exerted proliferogenic and antiproliferogenic effects at the concentrations of 108 and 106M, respectively (Malendowicz et al., 2004b). In summary, collectively, these reviewed findings indicate that in the rat, leptin suppresses the growth of the adrenal cortex. It is likely that the growth-promoting action of some leptin fragments (but not native leptin) on immature rat adrenals and adrenocortical cells cultured in vitro may be connected to their ability to bind and activate specific Ob-R isoforms specifically coupled to proliferogenic signaling pathways.

5.2. Other steroid-secreting cells Leptin plays a role in the functional regulation of steroid-secreting cells other than adrenocortical ones, namely those of endocrine gonads, and we will review this topic. 5.2.1. Testis Ob-Ra and Ob-Rb expression has been demonstrated in Leydig cells of the rat testis and Ob-Rb expression in a murine Leydig cell tumor line (Caprio et al., 1999). Leptin inhibited human chorionic gonadotropin (hCG)-stimulated testosterone secretion from rat Leydig cells (Caprio et al., 1999; Tena-Sempere et al., 2000), and the effect was associated with the downregulation of StAR and CYP11A (but not CYP17) expression (Tena-Sempere et al., 2001). As shown in adrenocortical cells, monosodioL-glutamate-induced hyperleptinemia lowered Ob-Rb mRNA in rat Leydig cells and counteracted the leptin-induced inhibition of their testosterone production (Giovanbattista et al., 2003). 5.2.2. Ovary Ob-Rb expression has been detected in human granulosa and cumulus cells (Cioffi et al., 1997) and in granulosa and corpus luteum cells of the rabbit ovary (Zerani et al., 2004). Leptin was reported to inhibit hCG-stimulated (but not basal) progesterone secretion from cultured human granulosa lutein cells in the presence of insulin (Brannian et al., 1999) and from a granulosa

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cell line (Barkan et al., 1999), as well as follicle-stimulating hormone (FSH)and IGF-I-stimulated progesterone yield from bovine granulosa lutein cells (Spicer et al., 2000), basal progesterone production from rabbit granulosa and corpus luteum cells (Zerani et al., 2004), and FSH-stimulated progesterone secretion from rat granulosa cells, this last effect being associated with downregulation of CYP11A expression (Barkan et al., 1999). A dosedependent biphasic effect of leptin has been observed in cultured porcine granulosa cells: At nanomole and micromole concentrations the cytokine increased and decreased progesterone synthesis and StAR mRNA expression, respectively (Ruiz-Corte´s et al., 2003). Earlier findings suggested a leptin-induced increase in estradiol (but not progesterone) production from human granulosa lutein cells, coupled to a rise in CYP aromatase expression (Kitawaki et al., 1999). However, subsequent investigations showed that leptin lowered basal (but not hCG- or IGF-I/II-stimulated) estradiol yield, although without inducing significant changes in StAR, CYP17, and CYP aromatase expression (Ghizzoni et al., 2001). Moreover, leptin was shown to inhibit FSH-stimulated estradiol secretion from rat granulosa cells (Barkan et al., 1999). Before concluding, we wish to recall that leptin, although inhibiting ovulation, was not found to alter in vivo progesterone and estradiol secretion from perfused rat ovary (Duggal et al., 2000). Taken together, the findings summarized herein provide firm evidence that leptin inhibits sex hormone secretion from endocrine gonads, its target point of action being the early step of steroid synthesis.

5.3. Adrenal medulla 5.3.1. In vitro studies Leptin was not found to affect catecholamine secretion from cultured human adrenomedullary cells (Glasow and Bornstein, 2000; Glasow et al., 1998). In contrast, leptin (3  109 and 3 108 M) enhanced catecholamine synthesis in cultured bovine adrenomedullary cells (Yanagihara et al., 2000). This last effect occurred via the activation of tyrosine hydroxylase (TH) through two mechanisms, one dependent on TH phosphorylation via the MAPK cascade and one independent of TH phosphorylation (Utsunomiya et al., 2001). In interest, according to Yanagihara et al. (2000), the leptininduced rise in catecholamine synthesis was not associated with the increase in their release. However, other findings indicate that leptin raises both catecholamine synthesis in and release from the adrenal medulla. Leptin (5 108 and 107M) enhanced catecholamine release via a mechanism mainly involving the activation of the voltage-gated Ca2þ L- and N-type channels (Takekoshi et al., 1999, 2001a) and the new synthesis of TH through the activation of the JAK/STAT, MAPK, and PKC-dependent Raf pathways (Takekoshi et al., 2001a,b).

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5.3.2. In vivo studies The icv injection of leptin was found to elicit a marked rise in the plasma catecholamine concentration in rabbits (Matsumura et al., 2000). Furthermore, evidence has been provided that leptin may increase catecholamine secretion from the adrenal medulla by stimulating the central sympathetic nervous system outflow (Satoh et al., 1999). Although rather scarce, these findings indicate that leptin stimulates catecholamine secretion from the adrenal medulla, at least of cows and pigs. Hence, leptin seems to exert opposite effects on the functions of the HPA and the hypothalamic sympathoadrenal axes.

6. Involvement of Leptin in the Pathophysiology of the Hypothalamic–Pituitary–Adrenal Axis 6.1. Response to stresses Leptin has been reported to dampen the HPA axis response (ACTH and/or glucocorticoid secretion) to an unpredictable situation in monkeys (Wilson et al., 2005) and starvation in mice (Ahima et al., 1996; Ziotopoulou et al., 2000). HPA axis activation by metabolic stress (glucose deprivation by means of 2-deoxyglucose administration), insulin-induced hypoglycemia, and restraint stress were also blunted by leptin in the rat (Giovanbattista et al., 2000; Heiman et al., 1997; Nagatani et al., 2001). However, in the rat only the corticosterone response was hampered; the plasma level of ACTH remained unchanged (Heiman et al., 1997). The sc bolus injection of leptin (5 nmol/kg) was found to induce a moderate magnification of ACTH response to ether stress at 2 h, followed by a net depression at 4 h. The corticosterone response was not affected (Hocho´l et al., 2000). It has been reported that newborn rodents exhibit adrenal hyporesponsiveness to stress during the first 2 weeks of life, probably induced by maternal leptin (Salzmann et al., 2004; Trottier et al., 1998). However, in 10-day–old rat pups daily leptin pretreatment from day 2 to day 9, although not inducing appreciable changes in basal HPA axis activity, was shown to lower the stress-evoked rise in CRH mRNA expression in PVN and to markedly shorten the duration of the ACTH response (Oates et al., 2000). In contrast, the sc bolus administration of leptin has been reported to enhance the ACTH response to cold stress, without altering the corticosterone response (Hocho´l et al., 2000). In conclusion, leptin prevents or attenuates the HPA response to various stresses, with the exception of cold stress. How leptin differentially regulates the activity of the HPA axis during stressful conditions is unclear (Nagatani et al., 2001). It is likely that the central mechanisms involved in the response

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to cold stress are different from those underlying the response to ether and other stresses.

6.2. Pituitary adenomas Leptin mRNA expression has been detected in three of four ACTHsecreting, one of four GH-secreting, one of four gonadotropin-secreting, and two of four nonsecreting pituitary adenomas ( Jin et al., 1999). Although, Knerr et al. (2001) found very low quantities of leptin mRNA in various pituitary tumors, leptin expression was demonstrated in two of three (Korbonits et al., 2001a,b) and four of five ACTH-secreting tumors (Isono et al., 2003). Electron microscopy showed leptin immunogold labeling only in ACTH-secreting adenomas (Vidal et al., 2000). Of interest, confocal microscopy ICC colocalized leptin-ir and ACTH-ir in the murine pituitary adenoma-derived cell line AtT20 (Chavez and Moore, 1997). Ob-R, almost exclusively of the b subtype, has been demonstrated in pituitary tumors (Dieterich and Lehnert, 1998; Jin et al., 1999, Knerr et al., 2001; Shimon et al., 1998). According to Korbonits et al. (2001a,b), Ob-Rb expression was present in five of nine ACTH-secreting, two of four GH-secreting, one of two prolactin-secreting, two of two gonadotropinsecreting, and 12 of 17 nonsecreting pituitary tumors. Both Ob-Ra and Ob-Rb isoforms are expressed in adult human pituitary, but only Ob-Rb is expressed in the fetal gland (see Section 3.2.2): hence, Shimon et al. (1998) suggested that human pituitary adenomas revert to a fetal type of Ob-R activity. The simultaneous expression of leptin and Ob-R makes it likely that the leptin system may be involved in the autocrine–paracrine regulation of secretion and differentiation of pituitary adenomas, and especially of the ACTH-secreting tumors. However, as pointed out by Garofalo and Surmacz (2006), its possible role in tumorigenesis is doubtful.

6.3. Adrenocortical tumors and pheochromocytomas Ob-Rb, but not leptin, mRNA, and protein expression, has been found in adrenocortical adenomas and carcinomas, but not pheochromocytomas (Glasow and Bornstein, 2000; Glasow et al., 1998, 1999). A 2-h exposure to leptin was reported to lower in vitro basal and ACTH-stimulated secretion from cortisol-secreting adenomas, without altering aldosterone production from aldosteronomas (Szucs et al., 2001). No studies have been carried out on the effects of leptin on catecholamine secretion from pheochromocytomas. High levels of circulating leptin have been measured in patients bearing cortisol-secreting adenomas causing Cushing’s syndrome (LealCerro et al., 1996; Masuzaki et al., 1997), but not in aldosteronoma patients

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(Haluzik et al., 2002; Torpy et al., 1999). Despite the reported inhibitory action of catecholamines on leptin secretion from human adipocytes (Scriba et al., 2000), no apparent changes in the leptin blood concentration were observed in patients bearing pheochromocytomas (Bo¨ttner et al., 1999). The surgical removal of cortisol-secreting adenomas or ACTH-secreting pituitary tumors causing Cushing’s disease, although normalizing the blood levels of ACTH and cortisol, did not alter the concentration of circulating leptin (Licino et al., 1997; Weise et al., 1999). Conversely, aldosteronoma removal caused a significant rise in the levels of circulating leptin (Haluzik et al., 2002; Torpy et al., 1999). Taken together, the findings now reviewed cast doubt on the possibility that leptin, acting as a circulating hormone, may be involved in adrenal tumorigenesis and/or may blunt the excessive hormone production from adrenal tumors.

6.4. Macronodular adrenal hyperplasia Macronodular adrenal hyperplasia (MAH) causes Cushing’s syndrome, which may be ACTH independent due to the presence in the hyperplastic tissue of ‘‘aberrant’’ secretagogue R for AVP, luteinizing hormone, angiotensin-II, and/or 5-hydroxytryptamine. In some instances, ACTHindependent MAH may be food dependent: Patients display marked cortisol surges after meals, which ensue from the presence in the MAH of ‘‘aberrant’’ R for gastric inhibitory polypeptide (GIP) (Antonini et al., 2006; Bertherat et al., 2005; Bourdeau et al., 2004; Lacroix et al., 1992, 2001). Of great interest, rather old studies showed that food-dependent, but not foodindependent, MAH displayed a clearcut in vitro cortisol secretory response to leptin (Pralong et al., 1999), whose molecular basis remains to be ascertained in light of the interrelationships among leptin, insulinotrophic GIP, and diabetes.

6.5. Hyperreninemic hypoaldosteronism Leptin via its sympathoexcitatory action (see Section 5.3.2.) induces a sizeable increase in blood pressure, which may account for the hypertension frequently associated with human obesity (Haynes et al., 1997; Shek et al., 1998). Evidence has been provided that leptin administration caused a moderate increase in plasma renin activity (PRA) and a significant decrease in aldosterone blood concentration in rats (Bornstein and Torpy, 1998; Shek et al., 1998). The rise in PRA could ensue from leptin-induced sympathetic activation and the lowering of plasma aldosterone from the direct inhibitory action of leptin on ZG cells (see Section 5.1). Critically ill patients (e.g., acute sepsis) frequently display hyperleptinemia (Bornstein et al., 1998), and these surveyed findings suggest that this may contribute to

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the hyperreninemic hypoaldosteronism observed in a substantial percentage of these patients (Zipser et al., 1981).

7. Concluding Remarks The preceding sections have shown that leptin plays a relevant role in the regulation of the HPA axis. Leptin and its R are both expressed in the central branch of the HPA axis, where they can modulate CRH and ACTH secretion acting in an autocrine–paracrine manner. In contrast, only leptin R is expressed in the adrenal gland, suggesting that leptin affects the peripheral branch of the HPA axis exclusively, acting as a circulating hormone. The levels of circulating leptin are in the nanomolar range in both lean and obese subjects (Baumgartner et al., 1999; Considine et al., 1996; Mann et al., 2003), which makes this possibility likely. However, despite extensive experimental work, many points remain unsettled, including the following, which are the most relevant. Although the bulk of evidence indicates that leptin exerts an overall inhibitory effect on the HPA axis, there is also proof that this cytokine in rodents may enhance HPA axis activity (see Sections 4 and 5). Hence, leptin could behave as an ‘‘antistress’’ or ‘‘emergency hormone,’’ depending on the species and probably the experimental conditions used. Parenthetically, the stimulating effect of leptin on catecholamine release and sympathetic outflow (see Section 5.3) appears to be in keeping with this latter action of leptin. At least five Ob-R isoforms are expressed in the HPA axis (see Section 3), but nothing is known about their functions. Leptin fragments frequently evoke effects other than those of the native molecule (see Section 5.1.1). Does this depend on their binding capacity to different Ob-R isoforms? This possibility could explain the rather conflicting results obtained in the rat on the effect of leptin on the peripheral branch of the HPA axis, but obviously it would be necessary to admit that in this species a proteasemediated posttranslational processing of leptin occurs, which may give rise to different levels of circulating leptin fragments. The signaling cascade coupled to Ob-R, and especially the long isoform b, has been extensively investigated (see Section 2.2). However, the signaling mechanisms mediating the effects of leptin on the HPA axis have not yet been examined. This is very surprising in view of the huge mass of studies devoted to ascertaining the signaling mechanisms of other regulatory peptides modulating HPA axis function and feeding (e.g., orexins, neuropeptides B and W, and cholecystokinin) (Mazzocchi et al., 2005; Nussdorfer et al., 2005; Spinazzi et al., 2006).

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Although leptin and Ob-R are expressed in pituitary adenomas and Ob-R in adrenal tumors, investigations on the possible involvement of leptin as a growth promoter are lacking. Likewise, the modulating action of leptin on tumor secretion has been poorly studied. For instance, despite findings that indicate that leptin enhances catecholamine release from adrenomedullary cells (see Section 5.3), no investigations are available on the effect of this cytokine on pheochromocytoma secretion. Resolving these and many other basic issues, along with the development of selective agonists and antagonists of Ob-R, will not only increase our knowledge of HPA axis physiology, but also, and more importantly, open novel perspectives for the treatment of diseases coupled with dysregulation of feeding and adrenal gland secretion.

ACKNOWLEDGMENTS We wish to thank Miss Alberta Coi for her secretarial support and invaluable help in the provision of bibliographic items.

REFERENCES Aguilera, G., and Rabadan-Diehl, C. (2000). Vasopressinergic regulation of the hypothalamic-pituitary-adrenal axis: Implication for stress adaptation. Regul. Pept. 96, 23–29. Ahima, R. S., and Flier, J. S. (2000). Leptin. Annu. Rev. Physiol. 62, 413–437. Ahima, R. S., and Osei, S. Y. (2004). Leptin signaling. Physiol. Behav. 81, 223–241. Ahima, R. S., Prabakaran, D., Mantzoros, C., Qu, D., Lowell, B., Maratos-Flier, E., and Flier, J. S. (1996). Role of leptin in the neuroendocrine response to fasting. Nature 382, 250–252. Ahima, R. S., Saper, C. B., Flier, J. S., and Elmquist, J. K. (2000). Leptin regulation of neuroendocrine system. Front. Neuroendocrinol. 21, 263–307. Ahren, B., Baldwin, R. M., and Havel, P. J. (2000). Pharmacokinetics of human leptin in mice and rhesus monkeys. Int. J. Obes. Relat. Metab. Disord. 24, 1579–1585. Akirav, E. M., Chan, O., Inouye, K., Riddell, M. C., Matthews, S. G., and Vranic, M. (2004). Partial leptin restoration increases hypothalamic-pituitary-adrenal activity while diminishing weight loss and hyperphagia in streptozotocin diabetic rats. Metabolism 53, 1558–1564. Andreis, P. G., Rucinski, M., Neri, G., Conconi, M. T., Petrelli, L., Parnigotto, P. P., Malendowicz, L. K., and Nussdorfer, G. G. (2005). Neuropeptides B and W enhance the growth of human adrenocortical carcinoma-derived NCI-H295 cells by exerting MAPK p42/p44-mediated proliferogenic and antiapoptotic effects. Int. J. Mol. Med. 16, 1021–1028. Andreis, P. G., Malendowicz, L. K., Rebuffat, P., Spinazzi, R., Ziolkowska, A., and Nussdorfer, G. G. (2007). Galanin enhances corticosterone secretion from dispersed rat adrenocortical cells through the activation of GAL-R1 and GAL-R2 receptors coupled to the adenylate cyclase-dependent signaling cascade. Int. J. Mol. Med. 19, 149–155. Antonini, S. R., Baldacchino, V., Tremblay, J., Hamet, P., and Lacroix, A. (2006). Expression of ACTH receptor pathway genes in glucose-dependent insulinotrophic peptide (GIP)-dependent Cushing’s syndrome. Clin. Endocrinol. (Oxf.) 64, 29–36.

90

Ludwik K. Malendowicz et al.

Arvaniti, K., Huang, Q., and Richard, D. (2001). Effects of leptin and corticosterone on the expression of corticotrophin-releasing hormone, agouti-related protein, and proopiomelanocortin in the brain of ob/ob mouse. Neuroendocrinology 73, 227–236. Baker, J. R., Cardinal, K., Bober, C., Taylor, M. M., and Samson, W. K. (2003). Neuropeptide W acts in brain to control prolactin, corticosterone, and growth hormone release. Endocrinology 144, 2816–2821. Baldelli, R., Dieguez, C., and Casanueva, F. F. (2002). The role of leptin in reproduction: Experimental and clinical aspects. Ann. Med. 34, 5–18. Barkan, D., Jia, H., Dantes, A., Vardimon, L., Amsterdam, A., and Rubinstein, M. (1999). Leptin modulates the glucocorticoid-induced ovarian steroidogenesis. Endocrinology 140, 1731–1738. Barr, V. A., Malide, D., Zarnowski, M. J., Taylor, S. I., and Cushman, S. W. (1997). Insulin stimulates both leptin secretion and production by rat white adipose tissue. Endocrinology 138, 4463–4472. Bates, S. H., and Myers, M. G., Jr. (2003). The role of leptin receptor signaling in feeding and neuroendocrine function. Trends Endocrinol. Metab. 14, 447–452. Baumgartner, R. N., Waters, D. L., Morley, J. E., Patrick, P., Montoya, D., and Garry, P. J. (1999). Age-related changes in sex hormones affects the sex difference in serum leptin independently of changes in body fat. Metabolism 48, 378–384. Bedecs, K., Berthold, H., and Bartfai, T. (1995). Galanin. 10 Years with a neuroendocrine peptide. Int. J. Biochem. Cell Biol. 27, 337–349. Bendinelli, P., Maroni, P., Pecori-Giraldi, F., and Piccoletti, R. (2000). Leptin activates Stat3, Stat1 and AP-1 in mouse adipose tissue. Mol. Cell. Endocrinol. 168, 11–20. Bertherat, J., Contesse, V., Louiset, E., Barande, G., Duparc, C., Groussin, L., Emy, P., Bertagna, X., Kuhn, J. M., Vaudry, H., and Lefebvre, H. (2005). In vivo and in vitro screening for illegitimate receptors in adrenocorticotropin-independent macronodular adrenal hyperplasia causing Cushing’s syndrome: Identification of two cases of gonadotropin/gastric inhibitory polypeptide-dependent hypercortisolism. J. Clin. Endocrinol. Metab. 90, 1302–1310. Biason-Lauber, A., Zachmann, M., and Schoenle, E. J. (2000). Effect of leptin on CYP17 enzymatic activities in human adrenal cells: New insight in the onset of adrenarche. Endocrinology 141, 1446–1454. Bjorbaek, C., Uotani, S., Da Silva, B., and Flier, J. S. (1997). Divergent signaling capacities of the long and short isoforms of the leptin receptor. J. Biol. Chem. 272, 32686–32695. Bornstein, S. R., and Torpy, D. J. (1998). Leptin and the renin-angiotensin-aldosterone system. Hypertension 32, 376–377. Bornstein, S. R., Uhlmann, K., Haidan, A., Ehrhart-Bornstein, M., and Scherbaum, W. A. (1997). Evidence for a novel peripheral action of leptin as a metabolic signal to the adrenal gland: Leptin inhibits cortisol release. Diabetes 46, 1235–1238. Bornstein, S. R., Licino, J., Tauchnitz, R., Engelmann, L., Negrao, A. B., Gold, P., and Chrousos, G. P. (1998). Plasma leptin levels are increased in survivors of acute sepsis: Associated loss of diurnal rhythm in cortisol and leptin secretion. J. Clin. Endocrinol. Metab. 23, 280–283. Bo¨ttner, A., Eisenhofer, G., Torpy, D. J., Ehrhart-Bornstein, M., Keiser, H. R., Chrousos, G. P., and Bornstein, S. R. (1999). Lack of leptin suppression in response to hypersecretion of catecholamines in pheochromocytoma patients. Metabolism 48, 543–545. Bourdeau, I., Antonini, S. R., Lacroix, A., Kirschner, L. S., Matyakhina, L., Lorang, D., Libutti, S. K., and Stratakis, C. A. (2004). Gene array analysis of macronodular adrenal hyperplasia confirms clinical heterogeneity and identifies several candidate genes as molecular mediators. Oncogene 23, 1575–1585.

Leptin and Adrenals

91

Brannian, J. D., Zhao, Y., and McElroy, M. (1999). Leptin inhibits gonadotropin-stimulated granulosa cell progesterone production by antagonizing insulin action. Hum. Reprod. 14, 1445–1448. Burguera, B., Couce, M. E., Long, J., Lamsam, J., Laakso, K., Jensen, M. D., Parisi, J. E., and Lloyd, R. V. (2000). The long form of the leptin receptor (OB-Rb) is widely expressed in the human brain. Neuroendocrinology 71, 187–195. Cai, A., and Hyde, J. F. (1998). Upregulation of leptin receptor gene expression in the anterior pituitary of human growth hormone-releasing hormone transgenic mice. Endocrinology 139, 420–423. Campfield, L. A., Smith, F. J., and Burn, P. (1996). The OB protein (leptin) pathway: A link between adipose tissue mass and central neural networks. Horm. Metab. Res. 28, 619–632. Cao, G. Y., Considine, R. V., and Lynn, R. B. (1997). Leptin receptors in the adrenal medulla of the rat. Am. J. Physiol. 273, E448–E452. Caprio, M., Isidori, A. M., Carta, A. R., Moretti, C., Dufau, M. L., and Fabbri, A. (1999). Expression of functional leptin receptors in rodent Leydig cells. Endocrinology 140, 4939–4947. Casanueva, F. F., and Dieguez, C. (1999). Neuroendocrine regulation and actions of leptin. Front. Neuroendocrinol. 20, 317–363. Cerda-Reverter, J. M., and Larhammar, D. (2000). Neuropeptide Y family of peptides: Structure, anatomical expression, function, and molecular evolution. Biochem. Cell Biol. 78, 371–392. Challis, J. R., and Brooks, A. N. (1989). Maturation and activation of hypothalamicpituitary-adrenal function in fetal sheep. Endocr. Rev. 10, 182–204. Chavez, R. A., and Moore, H. P. (1997). Targeting of leptin to the regulated secretory pathway in pituitary AtT-20 cells. Curr. Biol. 7, 349–352. Chelikani, P. K., Glimm, D. R., and Kennelly, J. J. (2003). Tissue distribution of leptin and leptin receptor mRNA in the bovine. J. Dairy Sci. 86, 2369–2372. Cherradi, N., Capponi, A. M., Gaillard, R. C., and Pralong, F. P. (2001). Decreased expression of steroidogenic acute regulatory protein: A novel mechanism participating in the leptininduced inhibition of glucocorticoid biosynthesis. Endocrinology 142, 3302–3308. Cioffi, J. A., Van Blerkom, J., Antczak, M., Shafer, A., Wittmer, S., and Snodgrass, H. R. (1997). The expression of leptin and its receptors in pre-ovulatory human follicles. Mol. Hum. Reprod. 3, 467–472. Clark, K. A., Mohan-Kumar, S. M., Kasturi, B. S., and Mohan-Kumar, P. S. (2006). Effects of central and systemic administration of leptin on neurotransmitter concentrations in specific areas of the hypothalamus. Am. J. Physiol. 290, R306–R312. Collier, G. R., McMillan, J. S., Windmill, K., Walder, K., Tenne-Brown, J., De Silva, A., Trevaskis, J., Jones, S., Morton, G. J., Lee, S., Augert, G., Civitarese, A., et al. (2000). Beacon: A novel gene involved in the regulation of energy balance. Diabetes 49, 1766–1771. Considine, R. V., Sinha, M. K., Heiman, M. L., Kriauciunas, A., Stephens, T. W., Nyce, M. R., Ohannesian, J. P., Marco, C. C., McKee, I. J., Bauer, T. L., and Caro, J. F. (1996). Serum immunoreactive-leptin concentrations in normal-weight and obese human. N. Engl. J. Med. 334, 292–295. Costa, A., Poma, A., Martignoni, E., Nappi, G., Ur, E., and Grossman, A. (1997). Stimulation of corticotrophin-releasing hormone release by the obese (ob) gene product, leptin, from hypothalamic explants. Neuroreport 8, 1131–1134. Couce, M. E., Burguera, B., Parisi, J. E., Jensen, M. D., and Lloyd, R. V. (1997). Localization of leptin receptor in the human brain. Neuroendocrinology 66, 145–150. Crawley, J. N., and Corwin, R. L. (1994). Biological actions of cholecystokinin. Peptides 15, 731–755.

92

Ludwik K. Malendowicz et al.

Czaja, K., Lakomy, M., Sienkiewicz, W., Kaleczyc, J., Pidsudko, Z., Barb, C. R., Rampacek, G. B., and Kraeling, R. R. (2002). Distribution of neurons containing leptin receptors in the hypothalamus of the pig. Biochem. Biophys. Res. Commun. 298, 333–337. Dalmann, M. F. (1984–1985). Control of adrenocortical growth in vivo. Endocr. Res. 10, 213–242. Dallman, M. F., Strack, A. M., Akana, S. F., Bradbury, M. J., Hanson, E. S., and Smith, M. (1993). Feast and famine: Critical role of glucocorticoids with insulin in daily energy flow. Front. Neuroendocrinol. 14, 303–347. Davenport, L., Knehans, A., Sundstrom, A., and Thomas, T. (1989). Corticosterone’s dual metabolic action. Life Sci. 45, 1389–1396. Dieterich, K. D., and Lehnert, H. (1998). Expression of leptin receptor mRNA and the long form splice variant in human anterior pituitary and pituitary adenoma. Exp. Clin. Endocrinol. Diabetes 106, 522–525. Dridi, S., Swennen, Q., Decuypere, E., and Buyse, J. (2005). Mode of leptin action in chicken hypothalamus. Brain Res. 1047, 214–223. Duggal, P. S., Van der Hoek, K. H., Milner, C. R., Ryan, N. K., Armstrong, D. T., Magoffin, D. A., and Norman, R. J. (2000). The in vivo and in vitro effects of exogenous leptin on ovulation in the rat. Endocrinology 141, 1971–1976. Dyer, C. J., Simmons, J. M., Matteri, R. L., and Keisler, D. H. (1997). Leptin receptor mRNA is expressed in ewe anterior pituitary and adipose tissues and is differentially expressed in hypothalamic regions of well fed and feed-restricted ewes. Domest. Anim. Endocrinol. 14, 119–128. Elmquist, J. K., Ahima, R. S., Maratos-Flier, E., Flier, J., and Saper, C. B. (1997). Leptin activates neurons in ventrobasal hypothalamus and brainstem. Endocrinology 138, 839–842. Elmquist, J. K., Bjorbaek, C., Ahima, R. S., Flier, J. S., and Saper, C. B. (1998). Distribution of leptin receptor mRNA isoforms in the rat brain. J. Comp. Neurol. 395, 535–547. Engelmann, M., Landgraf, R., and Wotjak, C. T. (2004). The hypothalamicneurohypophyseal system regulates the hypothalamic-pituitary-adrenal axis under stress: An old concept revisited. Front. Neuroendocrinol. 25, 132–149. Fei, H., Okano, H. J., Lee, G. H., Zhao, C., Darnell, R., and Friedman, J. M. (1997). Anatomic localization of alternatively spliced leptin receptors (Ob-R) in mouse brain and other tissues. Proc. Natl. Acad. Sci. USA 94, 7001–7005. Finn, P. D., Cunningham, M. J., Pau, K. Y., Spies, H. G., Clifton, D. K., and Steiner, R. A. (1998). The stimulatory effect of leptin on the neuroendocrine reproductive axis of the monkey. Endocrinology 139, 4652–4662. Fong, T. M., Huang, R. R. C., Tota, M. R., Mao, C., Smith, T., Varnerin, J., Karpitskiy, V. V., Krause, J. E., and Van der Ploeg, L. H. T. (1998). Localization of leptin binding domain in the leptin receptor. Mol. Pharmacol. 53, 234–240. Freedman, M. R., Horwitz, B. A., and Stern, J. S. (1986). Effect of adrenalectomy and glucocorticoid replacement on development of obesity. Am. J. Physiol. 250, R595–R607. French, M. C., Littlejohn, R. P., Greer, G. J., Bain, W. E., McEwan, J. C., and Tisdall, D. J. (2006). Growth hormone and ghrelin receptor genes are differentially expressed between genetically lean and fat selection lines of sheep. J. Anim. Sci. 84, 324–331. Friedman, J. M., and Halaas, J. L. (1998). Leptin and the regulation of body weight in mammals. Nature 395, 763–770. Fru¨hbeck, G. (2006). Intracellular signaling pathways activated by leptin. Biochem. J. 393, 7–20. Garofalo, C., and Surmacz, E. (2006). Leptin and cancer. J. Cell Physiol. 207, 12–22. Ghizzoni, L., Barreca, A., Mastorakos, G., Furlini, M., Vottero, A., Ferrari, B., Chrousos, G. P., and Bernasconi, S. (2001). Leptin inhibits steroid biosynthesis by human granulosa-lutein cells. Horm. Metab. Res. 33, 323–328.

Leptin and Adrenals

93

Giovanbattista, A., Chisari, A. N., Gaillard, R. C., and Spinedi, E. (2000). Food intake-induced leptin secretion modulates hypothalamo-pituitary-adrenal axis response and hypothalamic Ob-Rb expression to insulin administration. Neuroendocrinology 72, 341–349. Giovanbattista, A., Suescun, M. O., Nessralla, C. C. D. L., Franc¸a, L. R., Spinedi, E., and Calandra, R. S. (2003). Modulatory effects of leptin on Leydig cell function of normal and hyperleptinemic rats. Neuroendocrinology 78, 270–279. Glasow, A., and Bornstein, S. R. (2000). Leptin and the adrenal gland. Eur. J. Clin. Invest. 30, 39–45. Glasow, A., Haidan, A., Hilbers, U., Breidert, M., Gillespie, J., Scherbaum, W. A., Chrousos, G. P., and Bornstein, S. R. (1998). Expression of Ob receptor in normal human adrenals: Differential regulation of adrenocortical and adrenomedullary function by leptin. J. Clin. Endocrinol. Metab. 83, 4459–4466. Glasow, A., Bornstein, S. R., Chrousos, G. P., Brown, J. W., and Scherbaum, W. A. (1999). Detection of Ob-receptor in human adrenal neoplasms and effect of leptin on adrenal cell proliferation. Horm. Metab. Res. 31, 247–251. Grasso, P., Leinung, M. C., Ingher, S. P., and Lee, D. W. (1997). In vivo effects of leptinrelated synthetic peptides on body weight and food intake in female ob/ob mice: Localization of leptin activity to domains between amino acid residues 106–140. Endocrinology 138, 1413–1418. Grasso, P., Leinung, M. C., and Lee, D. W. (1999). Epitope mapping of secreted mouse leptin utilizing peripherally administered synthetic peptides. Regul. Pept. 85, 93–100. Hakansson, M. L., and Meister, B. (1998). Trancription factor STAT3 in leptin target neurons of the rat hypothalamus. Neuroendocrinology 68, 420–427. Haluzik, M., Sindelka, G., Widimsky, J., Jr., Prazny, M., Zelinka, T., and Skrha, J. (2002). Serum leptin levels in patients with primary hyperaldosteronism before and after treatment: Relationships to insulin sensitivity. J. Hum. Hypertens. 16, 41–45. Hardie, L. J., Guilhot, N., and Trayhurn, P. (1996). Regulation of leptin production in cultured mature white adipocytes. Horm. Metab. Res. 28, 685–689. Hauner, H., Schmid, P., and Pfeiffer, E. F. (1987). Glucocorticoids and insulin promote the differentiation of human adipocyte precursor cells into fat cells. J. Clin. Endocrinol. Metab. 64, 832–835. Haynes, W. G., Sivitz, W. I., Morgan, D. A., Walsh, S. A., and Mark, A. L. (1997). Sympathetic and cardiorenal actions of leptin. Hypertension 30, 619–623. Hegyi, K., Fu¨lo¨p, K., Kova´cs, K., Toth, S., and Falus, A. (2004). Leptin-induced signal transduction pathways. Cell Biol. Int. 28, 159–169. Heiman, M. L., Ahima, R. S., Craft, L. S., Schoner, B., Stephens, T. W., and Flier, J. S. (1997). Leptin inhibition of the hypothalamic-pituitary-adrenal axis in response to stress. Endocrinology 138, 3859–3863. Hill, R. A., Margetic, S., Pegg, G. G., and Gazzola, C. (1998). Leptin: Its pharmacokinetics and tissue distribution. Int. J. Obes. Relat. Metab. Disord. 22, 765–770. Hocho´l, A., Nowak, K. W., Belloni, A. S., Nussdorfer, G. G., and Malendowicz, L. K. (2000). Effects of leptin on the response of rat pituitary-adrenocortical axis to ether and cold stresses. Endocr. Res. 26, 129–140. Hocho´l, A., Tortorella, C., Rucinski, M., Ziolkowska, A., Nussdorfer, G. G., and Malendowicz, L. K. (2007). Effects of neuropeptides B and W on the rat pituitaryadrenocortical axis: In vivo and in vitro studies. Int. J. Mol. Med. 19, 207–211. Hoggard, N., Mercer, J. G., Rayner, D. V., Moar, K., Trayhurn, P., and Williams, L. N. (1997). Localization of leptin receptor splice variants in murine peripheral tissues by RT-PCR and in situ hybridization. Biochem. Biophys. Res. Commun. 232, 383–387. Hotta, K., Gustafson, T. A., Ortmeyer, H. K., Bodkin, N. L., and Hansen, B. C. (1998). Monkey leptin receptor mRNA: Sequence, tissue distribution, and mRNA expression in

94

Ludwik K. Malendowicz et al.

the adipose tissue of normal, hyperinsulinemic, and type 2 diabetic rhesus monkeys. Obes. Res. 6, 353–360. Howe, D. C., Gertler, A., and Challis, J. R. (2002). The late gestation increase in circulating ACTH and cortisol in the fetal sheep is suppressed by intracerebroventricular infusion of recombinant ovine leptin. J. Endocrinol. 174, 259–266. Huang, Q., Rivest, R., and Richard, D. (1998). Effects of leptin on corticotropin-releasing factor (CRF) synthesis and CRF neuro activation in the paraventricular hypothalamic nucleus of obese (ob/ob) mice. Endocrinology 139, 1524–1532. Imagawa, K., Numata, Y., Katsuura, G., Sakaguchi, I., Morita, A., Kikuoka, S., Matumoto, Y., Tsuji, T., Tamaki, M., Sasakura, K., Teraoka, H., Hosoda, K., et al. (1998). Structure-function studies of human leptin. J. Biol. Chem. 273, 35245–35249. Iqbal, J., Pompolo, S., Considine, R. V., and Clarke, I. J. (2000). Localization of leptin receptor-like immunoreactivity in the corticotropes, somatotropes, and gonadotropes in the ovine anterior pituitary. Endocrinology 141, 1515–1520. Iqbal, J., Pompolo, S., Murakami, T., Grouzmann, E., Samurai, T., Meister, B., and Clarke, I. J. (2001). Immunohistochemical characterization of localization of long-form leptin receptor (Ob-Rb) in neurochemically defined cells in the ovine hypothalamus. Brain Res. 920, 55–64. Isono, M., Inoue, R., Kamida, T., Kobayashi, H., and Matsuyama, J. (2003). Significance of leptin expression in invasive potential of pituitary adenomas. Clin. Neurol. Neurosurg. 105, 111–116. Jang, M., Mistry, A., Swick, A. G., and Romsos, D. R. (2000). Leptin rapidly inhibits hypothalamic neuropeptide Y secretion and stimulates corticotrophin-releasing hormone secretion in adrenalectomized mice. J. Nutr. 130, 2813–2820. Jeong, K. H., Sakihara, S., Widmaier, E. P., and Majzoub, J. A. (2004). Impaired leptin expression and abnormal response to fasting in corticotropin-releasing hormonedeficient mice. Endocrinology 145, 3174–3181. Jethwa, P. H., Smith, K. L., Small, C. J., Abbott, C. R., Darch, S. J., Murphy, K. G., Seth, A., Semjonous, N. M., Patel, S. R., Todd, J. F., Ghatei, M. A., and Bloom, S. R. (2006). Neuromedin U partially mediates leptin-induced hypothalamo-pituitary-adrenal (HPA) stimulation and has a physiological role in the regulation of the HPA axis in the rat. Endocrinology 147, 2886–2892. Jin, L., Burguera, B. G., Couce, M. E., Scheithauer, B. W., Lamsan, J., Eberhardt, N. L., Kulig, E., and Lloyd, R. V. (1999). Leptin and leptin receptor expression in normal and neoplastic human pituitary: Evidence of a regulatory role for leptin on pituitary cell proliferation. J. Clin. Endocrinol. Metab. 84, 2903–2911. Jin, L., Zhang, S., Burguera, B. G., Couce, M. E., Osamura, R. Y., Kulig, E., and Lloyd, R. V. (2000). Leptin and leptin receptor expression in rat and mouse pituitary cells. Endocrinology 141, 333–339. Kaminski, T., Smolinska, N., Gajewska, A., Siawrys, G., Okrasa, S., Kochman, K., and Przala, J. (2006). Leptin and long form of leptin receptor genes expression in the hypothalamus and pituitary during the luteal phase and early pregnancy in pigs. J. Physiol. Pharmacol. 57, 95–108. Kitawaki, J., Kusuki, I., Koshiba, H., Tsukamoto, K., and Honjo, H. (1999). Leptin directly stimulates aromatase activity in human luteinized granulosa cells. Mol. Hum. Reprod. 5, 708–713. Klein, S., Coppack, S. W., Mohamed-Ali, V., and Landt, M. (1996). Adipose tissue leptin production and plasma leptin kinetics in humans. Diabetes 45, 984–987. Knerr, I., Schuster, S., Nomikos, P., Buchfelder, M., Dotsch, J., Schoof, E., Fahlbusch, R., and Rascher, W. (2001). Gene expression of adrenomedullin, leptin, their receptors and neuropeptide Y in hormone-secreting and non-functioning pituitary adenomas, meningiomas and malignant intracranial tumours in humans. Neuropathol. Appl. Neurobiol. 27, 215–222.

Leptin and Adrenals

95

Korbonits, M., Chitnis, M. M., Gueorguiev, M., Jordan, S., Norman, D., Kaltsas, G., Burrin, J. M., and Grossman, A. B. (2001a). Leptin in pituitary adenomas: A novel paracrine regulatory system. Pituitary 4, 49–55. Korbonits, M., Chitnis, M. M., Gueorguiev, M., Norman, D., Rosenfelder, N., Suliman, M., Jones, T. H., Noonan, K., Fabbri, A., Besser, G. M., Burrin, J. M., and Grossman, A. B. (2001b). The release of leptin and its effect on hormone release from human pituitary adenomas. Clin. Endocrinol. (Oxf.) 54, 781–789. Kruse, M., Bornstein, S. R., Uhlmann, K., Paeth, G., and Scherbaum, W. A. (1998). Leptin down-regulates the steroid producing system in the adrenal. Endocr. Res. 24, 587–590. Krysiak, R., Obuchowicz, E., and Herman, Z. S. (1999). Interactions between the neuropeptide Y system and the hypothalamic-pituitary-adrenal axis. Eur. J. Endocrinol. 140, 130–136. Lacroix, A., Bolte´, E., Tremblay, J., Dupre´, J., Poitras, P., Fournier, H., Garon, J., Garrel, D., Bayard, F., Taillefer, R., Flanagan, R. J., and Hamet, P. (1992). Gastric inhibitory polypeptide-dependent cortisol hypersecretion. A new cause of Cushing’s syndrome. N. Engl. J. Med. 327, 974–980. Lacroix, A., N’Diaye, N., Tremblay, J., and Hamet, P. (2001). Ectopic and abnormal hormone receptors in adrenal Cushing’s syndrome. Endocr. Rev. 22, 75–110. Lado-Abeal, J., Mrotek, J. J., Stocco, D. M., and Norman, R. L. (1999). Effect of leptin on ACTH-stimulated secretion of cortisol in Rhesus macaques and on human adrenal carcinoma cells. Eur. J. Endocrinol. 141, 534–538. Lado-Abeal, J., Hickox, J. R., Cheung, T. L., Veldhuis, J. D., Hardy, D. M., and Norman, R. L. (2000). Neuroendocrine consequences of fasting in adult male macaques: Effect of recombinant Rhesus macaque leptin infusion. Neuroendocrinology 71, 196–208. Leal-Cerro, A., Considine, R. V., Peino, R., Venegas, E., Astroga, R., Casanueva, F. F., and Dieguez, C. (1996). Serum immunoreactive-leptin levels are increased in patients with Cushing’s syndrome. Horm. Metab. Res. 28, 711–713. Licino, J., Mantzoros, C., Negrao, A. B., Cizza, G., Wong, M. L., Bongiorno, P. B., Chrousos, G. P., Karp, B., Allen, C., Flier, J. S., and Gold, P. W. (1997). Human leptin levels are pulsatile and inversely related to pituitary-adrenal function. Nat. Med. 3, 575–579. Lin, J., Barb, C. R., Matteri, R. L., Kraeling, R. R., Chen, X., Meinersmann, R. J., and Rampacek, G. B. (2000). Long form leptin receptor mRNA expression in the brain, pituitary, and other tissues in the pig. Domest. Anim. Endocrinol. 19, 53–61. Lin, J., Barb, C. R., Kraeling, R. R., and Rampacek, G. B. (2001). Developmental changes in the long form leptin receptor and related neuropeptide gene expression in the pig brain. Biol. Reprod. 64, 1614–1618. Lin, J., Barb, C. R., Kraeling, R. R., and Rampacek, G. B. (2003). Growth hormone releasing factor decreases long form leptin receptor expression in porcine anterior pituitary cells. Domest. Anim. Endocrinol. 24, 95–101. Liu, Y., Nakagawa, Y., Wang, Y., Li, R., Li, X., Ohzeki, T., and Friedman, T. C. (2003). Leptin activation of corticosterone production in hepatocytes may contribute to the reversal of obesity and hyperglycemia in leptin-deficient ob/ob mice. Diabetes 52, 1409–1416. Lloyd, R. V., Jin, L., Tsumanuma, I., Vidal, S., Kovacs, K., Horvath, E., Scheithauer, B. W., Couce, M. E., and Burguera, B. (2001). Leptin and leptin receptor in anterior pituitary function. Pituitary 4, 33–47. Malendowicz, L. K., Nussdorfer, G. G., Nowak, K. W., and Mazzocchi, G. (1994). The possible involvement of galanin in the modulation of the function of rat pituitaryadrenocortical axis under basal and stressful conditions. Endocr. Res. 20, 307–317. Malendowicz, L. K., Nussdorfer, G. G., and Markowska, A. (1997). Effects of recombinant murine leptin on steroid secretion of dispersed rat adrenocortical cells. J. Steroid Biochem. Mol. Biol. 63, 123–125.

96

Ludwik K. Malendowicz et al.

Malendowicz, L. K., Macchi, C., Nussdorfer, G. G., and Nowak, K. W. (1998). Acute effects of recombinant murine leptin on rat pituitary-adrenocortical function. Endocr. Res. 24, 235–246. Malendowicz, L. K., Neri, G., Jedrzejczak, N., Nussdorfer, G. G., and Hocho´l, A. (1999). Leptin(116–130) enhances the proliferative activity of immature rat adrenal cortex. Med. Sci. Res. 27, 675–676. Malendowicz, L. K., Neri, G., Jedrzejczak, N., Hocho´l, A., and Nussdorfer, G. G. (2000a). Effects of recombinant murine leptin(1–147) and leptin fragment 116–130 on steroid secretion and proliferative activity of the regenerating rat adrenal cortex. Endocr. Res. 26, 109–118. Malendowicz, L. K., Tortorella, C., Nowak, K. W., Nussdorfer, G. G., Hocho´l, A., and Majchrzak, M. (2000b). Leptin prolonged administration inhibits growth and glucocorticoid secretion of rat adrenal cortex. Endocr. Res. 26, 141–152. Malendowicz, L. K., Ziolkowska, A., and Trejter, M. (2001). Anterior pituitary corticotropes of adrenalectomized, leptin-administered rats. Pituitary 4, 57–61. Malendowicz, L. K., Neri, G., Markowska, A., Hocho´l, A., Nussdorfer, G. G., and Majchrzak, M. (2003a). Effects of leptin and leptin fragments on steroid secretion of freshly dispersed rat adrenocortical cells. J. Steroid Biochem. Mol. Biol. 87, 265–268. Malendowicz, L. K., Spinazzi, R., Majchrzak, M., Nowak, M., Nussdorfer, G. G., Ziolkowska, A., Macchi, C., and Trejter, M. (2003b). Effects of prolonged cholecystokinin administration on rat pituitary-adrenocortical axis: Role of the CCK receptor subtypes 1 and 2. Int. J. Mol. Med. 12, 903–909. Malendowicz, L. K., Gorska, T., Tortorella, C., Nowak, M., Majchrzak, M., Spinazzi, R., Nussdorfer, G. G., and Nowak, K. W. (2004a). Acute in vivo effects of leptin and leptin fragments on corticosteroid hormone secretion and entero-insular axis in the rat. Int. J. Mol. Med. 13, 829–834. Malendowicz, L. K., Spinazzi, R., Tortorella, C., Nussdorfer, G. G., Ziolkowska, A., and Rucinski, M. (2004b). Effects of leptin and leptin fragments on corticosterone secretion and growth of cultured rat adrenocortical cells. Int. J. Mol. Med. 14, 873–877. Mann, D. R., Johnson, A. O. K., Gimpel, T., and Castracane, V. D. (2003). Changes in circulating leptin, leptin receptor, and gonadal hormones from infancy until advanced age in humans. J. Clin. Endocrinol. Metab. 88, 3339–3345. Mantzoros, C. S. (1999). Leptin and the hypothalamus: Neuroendocrine regulation of food intake. Mol. Psychiat. 4, 6–7. Mantzoros, C. S., and Moschos, S. J. (1998). Leptin: In search of role(s) in human physiology and pathophysiology. Clin. Endocrinol. (Oxf.) 49, 551–567. Markowska, A., Neri, G., Hocho´l, A., Nowak, M., Nussdorfer, G. G., and Malendowicz, L. K. (2004). Effects of leptin and leptin fragments on steroid secretion and proliferative activity of regenerating rat adrenal cortex. Int. J. Mol. Med. 13, 139–141. Masaki, T., Yoshimichi, G., Chiba, S., Yasuda, T., Noguchi, H., Kakuma, T., Sakata, T., and Yoshimatsu, H. (2003). Corticotropin-releasing hormone-mediated pathway of leptin to regulate feeding, adiposity, and uncoupling protein expression in mice. Endocrinology 144, 3547–3554. Mastorakos, G., and Zapanti, E. (2004). The hypothalamic-pituitary-adrenal axis in the neuroendocrine regulation of food intake and obesity: The role of corticotropin releasing hormone. Nutr. Neurosci. 7, 271–280. Masuzaki, H., Ogawa, Y., Hosoda, K., Miyawaki, T., Hanaoka, I., Hiraoka, J., Yasuno, A., Nishimura, H., Yoshimasa, Y., Nishi, S., and Nakao, K. (1997). Glucocorticoid regulation of leptin synthesis and secretion in humans: Elevated plasma leptin levels in Cushing’s syndrome. J. Clin. Endocrinol. Metab. 82, 2542–2547. Matsumura, K., Abe, I., Tsuchihashi, T., and Fujishima, M. (2000). Central effects of leptin on cardiovascular and neurohormonal responses in conscious rabbits. Am.J. Physiol. 278, R1314–R1320.

Leptin and Adrenals

97

Mazzocchi, G., Rebuffat, P., Gottardo, G., Malendowicz, L. K., and Nussdorfer, G. G. (1998). Galanin stimulates glucocorticoid secretion in rats through a receptor-dependent activation of the adenylate cyclase/protein kinase A-dependent signaling pathway. Peptides 19, 891–895. Mazzocchi, G., Rebuffat, P., Ziolkowska, A., Rossi, G. P., Malendowicz, L. K., and Nussdorfer, G. G. (2005). G protein receptors (GPR) 7 and 8 are expressed in human adrenocortical cells and their endogenous ligands neuropeptides B and W enhance cortisol secretion by activating adenylate cyclase- and phospholipase C-dependent signaling cascades. J. Clin. Endocrinol. Metab. 90, 3466–3471. Mercer, J. G., Hoggard, N., Williams, L. M., Lawrence, C. B., Hannah, L. T., and Trayhurn, P. (1996). Localization of leptin receptor mRNA and the long form splice variant (Ob-Rb) in mouse hypothalamus and adjacent brain regions by in situ hybridization. FEBS Lett. 387, 113–116. Miell, J. P., Englaro, P., and Blum, W. F. (1996). Dexamethasone induces an acute and sustained rise in circulating leptin levels in normal human subjects. Horm. Metab. Res. 28, 704–707. Morash, B., Li, A., Murphy, P. R., Wilkinson, M., and Ur, E. (1999). Leptin gene expression in the brain and pituitary gland. Endocrinology 140, 5995–5998. Morash, B., Wilkinson, D., Murphy, P., Ur, E., and Wilkinson, M. (2001). Developmental regulation of leptin gene expression in rat brain and pituitary. Mol. Cell Endocrinol. 185, 151–159. Morash, B., Imran, A., Wilkinson, D., Ur, E., and Wilkinson, M. (2003). Leptin: Receptors are developmentally regulated in rat pituitary and hypothalamus. Mol. Cell Endocrinol. 210, 1–8. Morimoto, I., Yamamoto, S., Kai, K., Fujihira, T., Morita, E., and Eto, S. (2000). Centrally administered murine leptin stimulates the hypothalamus-pituitary-adrenal axis through arginine-vasopressin. Neuroendocrinology 71, 366–374. Muhlhausler, B. S., McMillen, I. C., Rouzaud, G., Findlay, P. A., Marrocco, E. M., Rhind, S. M., and Adam, C. L. (2004). Appetite regulatory neuropeptides are expressed in the sheep hypothalamus before birth. J. Neuroendocrinol. 16, 502–507. Murakami, T., Yamashita, T., Iida, M., Kuwajima, M., and Shima, K. (1997). A short form of leptin receptor performs signal transduction. Biochem. Biophys. Res. Commun. 231, 26–29. Myers, M. G., Jr. (2004). Leptin receptor signaling and the regulation of mammalian physiology. Recent Prog. Horm. Res. 59, 287–304. Nagatani, S., Thompson, R. C., and Foster, D. L. (2001). Prevention of glucoprivic stimulation of corticosterone secretion by leptin does not restore high frequency luteinizing hormone pulses in rats. J. Neuroendocrinol. 13, 371–377. Newcomber, J. W., Selke, G., Melson, A. K., Gross, J., Vogler, G. P., and Dagogo-Jack, S. (1998). Dose-dependent cortisol-induced increase in plasma leptin concentration in healthy humans. Arch. Gen. Psychiatry 55, 995–1000. Nishiyama, M., Makino, S., Asaba, K., and Hashimoto, K. (1999). Leptin effects on the expression of type-2 CRH receptor mRNA in the ventromedial hypothalamus in the rat. J. Neuroendocrinol. 11, 307–314. Nowak, K. W., Mackowiak, P., Nogowski, L., Szkudelski, T., and Malendowicz, L. K. (1998). Acute leptin action on insulin blood level and liver insulin receptor in the rat. Life Sci. 63, 1347–1352. Nowak, K. W., Kaczmarek, P., Mackowiak, P., Ziolkowska, A., Albertin, G., Ginda, W. J., Trejter, M., Nussdorfer, G. G., and Malendowicz, L. K. (2002a). Rat thyroid gland expresses the long form of leptin receptors, and leptin stimulates the function of the gland in euthyroid non-fasted animals. Int. J. Mol. Med. 9, 31–34. Nowak, K. W., Pierzchala-Koziec, K., Tortorella, C., Nussdorfer, G. G., and Malendowicz, L. K. (2002b). Effects of prolonged leptin infusion on rat pituitaryadrenocortical function. Int. J. Mol. Med. 9, 61–64.

98

Ludwik K. Malendowicz et al.

Nussdorfer, G. G. (1996). Paracrine control of adrenal cortical function by medullary chromaffin cells. Pharmacol. Rev. 48, 495–530. Nussdorfer, G. G., Spinazzi, R., and Mazzocchi, G. (2005). Cholecystokinin (CCK) and adrenal-cortex secretion. Vitam. Horm. 71, 433–453. Nye, E. J., Bornstein, S. R., Grice, J. E., Tauchnitz, R., Hockings, G. I., Strakosch, C. R., Jackson, R. V., and Torpy, D. J. (2000). Interactions between the stimulated hypothalamic-pituitary-adrenal axis and leptin in humans. J. Neuroendocrinol. 12, 141–145. Oates, M., Woodside, B., and Walker, C. D. (2000). Chronic leptin administration in developing rats reduces stress responsiveness partly through changes in maternal behavior. Horm. Behav. 37, 366–376. Okamoto, S., Irie, Y., Ishikawa, I., Kiura, K., and Saito, M. (2000). Central leptin supresses splenic lymphocyte functions through activation of the corticotropin-releasing hormone-sympathetic nervous system. Brain Res. 855, 192–197. Peelman, F., Couturier, C., Dam, J., Zabeau, L., Tavernier, J., and Jockers, R. (2006). Techniques: New pharmacological perspectives for the leptin receptor. Trends Pharmacol. Sci. 27, 218–225. Perello´, M., Gaillard, R. C., Chisari, A., and Spinedi, E. (2003). Adrenal enucleation in MSG-damaged hyperleptinemic male rats transiently restores adrenal sensitivity to leptin. Neuroendocrinology 78, 176–184. Perello´, M., Moreno, G., Camihort, G., Luna, G., Console, G., Gaillard, R. C., and Spinedi, E. (2004). Nature of changes in adrenocortical function in chronic hyperleptinemic female rats. Endocrine 24, 167–175. Pralong, F. P., and Gaillard, R. C. (2001). Neuroendocrine effects of leptin. Pituitary 4, 25–32. Pralong, F. P., Roduit, R., Waeber, G., Castillo, E., Mosimann, F., Thorens, B., and Gaillard, R. C. (1998). Leptin inhibits directly glucocorticoid secretion by normal human and rat adrenal gland. Endocrinology 139, 4264–4268. Pralong, F. P., Gomez, F., Guillon, L., Mosimann, F., Franscella, S., and Gaillard, A. C. (1999). Food-dependent Cushing’s syndrome: Possible involvement of leptin in cortisol hypersecretion. J. Clin. Endocrinol. Metab. 84, 3817–3822. Raber, J., Chen, S., Mucke, L., and Feng, L. (1997). Corticotropin-releasing factor and adrenocorticotrophic hormone as potential central mediators of OB effects. J. Biol. Chem. 272, 15057–15060. Rainey, W. E., Saner, K., and Schimmer, B. P. (2004). Adrenocortical cell lines. Mol. Cell. Endocrinol. 228, 23–38. Remesar, X., Rafecas, I., Fernandez-Lopez, J. A., and Alemany, M. (1997). Leptin. Med. Res. Rev. 17, 225–234. Ren, M. Q., Wegner, J., Bellmann, O., Brockmann, G. A., Schneider, F., Teuscher, F., and Ender, K. (2002). Comparing mRNA levels of genes encoding leptin, leptin receptor, and lipoprotein lipase between dairy and beef cattle. Domest. Anim. Endocrinol. 23, 371–381. Renz, M., Tomlison, E., Hultgren, B., Levin, N., Gu, Q. M., Shimkets, R. A., Lewin, D. A., and Stewart, T. A. (2000). Quantitative expression analysis of genes regulated by both obesity and leptin reveals a regulatory loop between leptin and pituitary-derived ACTH. J. Biol. Chem. 275, 10429–10436. Ribatti, D., Belloni, A. S., Nico, B., Sala`, G., Longo, V., Mangeri, D., Crivellato, E., and Nussdorfer, G. G. (2007). Tryptase- and leptin-positive mast cells correlate with vascular density in uterine leiomyoma. Am. J. Obstet. Gynecol. 190, 470–477. Rozhavskaya-Arena, M., Lee, D. W., Leinung, M. C., and Grasso, P. (2000). Design of a synthetic leptin agonist: Effects on energy balance, glucose homeostasis, and thermoregulation. Endocrinology 141, 2501–2507.

Leptin and Adrenals

99

Rucinski, M., Andreis, P. G., Ziolkowska, A., Nussdorfer, G. G., and Malendowicz, L. K. (2005a). Differential expression and function of beacon in the rat adrenal cortex and medulla. Int. J. Mol. Med. 16, 35–40. Rucinski, M., Spinazzi, R., Ziolkowska, A., Nussdorfer, G. G., and Malendowicz, L. K. (2005b). Effects of beacon on the rat pituitary-adrenocortical axis response to stress. Int. J. Mol. Med. 16, 297–299. Ruiz-Corte´s, Z. T., Martel-Kennes, Y., Ge´vry, N. Y., Downey, B. R., Palin, M. F., and Murphy, B. D. (2003). Biphasic effects of leptin in porcine granulosa cells. Biol. Reprod. 68, 789–796. Sahu, A. (2003). Leptin signaling in the hypothalamus: Emphasis on energy homeostasis and leptin resistance. Front. Neuroendocrinol. 24, 225–253. Salzmann, C., Otis, M., Long, H., Roberge, C., Gallo-Payet, N., and Walker, C. D. (2004). Inhibition of steroidogenic response to adrenocorticotropin by leptin: Implications for the adrenal response to maternal separation in neonatal rats. Endocrinology 145, 1810–1822. Satoh, N., Ogawa, Y., Katsuura, G., Numata, Y., Tsuji, T., Hayase, M., Ebihara, K., Masuzaki, H., Hosoda, K., Yoshimasa, Y., and Nakao, K. (1999). Sympathetic activation of leptin via the ventromedial hypothalamus: Leptin-induced increase in catecholamine secretion. Diabetes 48, 1787–1793. Schwartz, M. W., Seeley, R. J., Campfield, L. A., Burn, P., and Baskin, D. G. (1996a). Identification of targets of leptin action in rat hypothalamus. J. Clin. Endocrinol. Metab. 98, 1101–1106. Schwartz, M. W., Seeley, R. J., Campfield, L. A., Burn, P., and Baskin, D. G. (1996b). Identification of targets of leptin action in rat hypothalamus. J. Clin. Invest. 98, 1101–1106. Scriba, D., Aprath-Husmann, I., Blum, W. F., and Hauner, H. (2000). Catecholamines suppress leptin release from in vitro differentiated subcutaneous human adipocytes in primary culture via b1- and b2-adrenergic receptors. Eur. J. Endocrinol. 143, 439–445. Seeber, R. M., Smith, J. T., and Waddell, B. J. (2002). Plasma leptin-binding activity and hypothalamic leptin receptor expression during pregnancy and lactation in the rat. Biol. Reprod. 66, 1762–1767. Seufert, J. (2004). Leptin effects on pancreatic beta-cell gene expression and function. Diabetes 53(Suppl. 1), S152–S158. Shek, E. W., Brands, M. W., and Hall, J. E. (1998). Chronic leptin infusion increases arterial pressure. Hypertension 31, 409–414. Shimon, I., Yan, X. M., Magoffin, D. A., Friedman, T. C., and Melmed, S. (1998). Intact leptin receptor is selectively expressed in human fetal pituitary and pituitary adenomas and signals human fetal pituitary growth hormone secretion. J. Clin. Endocrinol. Metab. 83, 4059–4064. Siawrys, G., Przala, J., Kaminski, T., Smolinska, N., Gajewska, A., Kochman, K., Skowronski, M., and Staszkiewicz, J. (2005). Long form leptin receptor mRNA expression in the hypothalamus and pituitary during early pregnancy in the pig. Neuroendocrinol. Lett. 26, 305–309. Slieker, L. J., Sloop, K. W., Surface, P. L., Kriauciunas, A., LaQuier, F., Manetta, J., BueValleskey, J., and Stephens, T. W. (1996). Regulation of expression of Ob mRNA and protein by glucocorticoids. J. Biol. Chem. 271, 5301–5304. Smolinska, N., Przala, J., Kaminski, T., Siawrys, G., Gajewska, A., Kochman, K., and Okrasa, S. (2004). Leptin gene expression in the hypothalamus and pituitary of pregnant pigs. Neuroendocrinol. Lett. 25, 191–195. Sone, M., Nagata, H., Takekoshi, S., and Samura, R. Y. (2001). Expression and localization of leptin receptor in the normal rat pituitary gland. Cell Tissue Res. 305, 351–356. Spicer, L. J., Chamberlain, C. S., and Francisco, C. C. (2000). Ovarian action of leptin. Effects of insulin-like growth factor-I-stimulated function of granulosa and thecal cells. Endocrine 12, 53–59.

100

Ludwik K. Malendowicz et al.

Spinazzi, R., Andreis, P. G., and Nussdorfer, G. G. (2005). Neuropeptide-Y and Y-receptors in the autocrine-paracrine regulation of adrenal gland under physiological and pathophysiological conditions. Int. J. Mol. Med. 15, 3–13. Spinazzi, R., Andreis, P. G., and Nussdorfer, G. G. (2006). Orexins in the regulation of the hypothalamic-pituitary-adrenal axis. Pharmacol. Rev. 58, 46–57. Spinedi, E., and Gaillard, R. C. (1998). A regulatory loop between the hypothalamopituitary-adrenal (HPA) axis and circulating leptin: A physiological role of ACTH. Endocrinology 139, 4016–4020. Stephens, T. W., Basinski, M., Bristow, P. K., Bue-Valleskey, J. M., Burgett, S. G., Craft, L., Hale, J., Hoffmann, J., Hsiung, H. M., Kriauciunas, A., MacKellar, W., Rosteck, P. R. J., et al. (1995). The role of neuropeptide Y in the antiobesity action of the obese gene product. Nature 377, 530–532. Stewart, P. M., and Krozowski, Z. S. (1999). 11b-Hydroxysteroid dehydrogenase. Vitam. Horm. 57, 249–324. Szczepankiewicz, D., Wojciechowicz, T., Kaczmarek, P., and Nowak, K. W. (2006). Leptin and its receptors in the course of pregnancy in the rat. Int. J. Mol. Med. 17, 95–99. Szucs, N., Varga, I., Jakab, C., Patocs, A., Glaz, E., Toth, M., Kiss, R., and Racz, K. (2001). Leptin inhibits cortisol and corticosterone secretion in pathologic human adrenocortical cells. Pituitary 4, 71–77. Takekoshi, K., Motooka, M., Isobe, K., Nomura, F., Manmoku, T., Ishii, K., and Nakai, T. (1999). Leptin directly stimulates catecholamine secretion and synthesis in cultured porcine adrenal medullary cells. Biochem. Biophys. Res. Commun. 261, 426–431. Takekoshi, K., Ishii, K., Kawakami, Y., Isobe, K., Nanmoku, T., and Nakai, T. (2001a). Ca2þ mobilization, tyrosine hydroxylase activity, and signaling mechanisms in cultured porcine adrenal medullary chromaffin cells: Effects of leptin. Endocrinology 142, 290–298. Takekoshi, K., Ishii, K., Nanmoku, T., Shibuya, S., Kawakami, Y., Isobe, K., and Nakai, T. (2001b). Leptin stimulates catecholamine synthesis in a PKC-dependent manner in cultured porcine adrenal medullary chromaffin cells. Endocrinology 142, 4861–4871. Taouis, M., Dridi, S., Cassy, S., Benomar, Y., Raver, N., Rideau, N., Picard, M., Williams, J., and Gertler, A. (2001). Chicken leptin: Properties and actions. Domest. Anim. Endocrinol. 21, 319–327. Tartaglia, L. A. (1997). The leptin receptor. J. Biol. Chem. 272, 6093–6096. Tartaglia, L. A., Dembski, M., Weng, X., Deng, N., Culpepper, J., Devos, R., Richards, G. J., Campfield, L. A., Clark, F. T., Deeds, J., Muir, C., Sanker, S., et al. (1995). Identification and expression cloning of a leptin receptor, OB-R. Cell 83, 1263–1271. Tena-Sempere, M., and Barreiro, M. L. (2002). Leptin in male reproduction: The testis paradigm. Mol. Cell Endocrinol. 188, 9–13. Tena-Sempere, M., Pinilla, L., Gonzales, L. C., Navarro, J., Dieguez, C., Casanueva, F. F., and Aguilar, E. (2000). In vitro pituitary and testicular effects of the leptin-related synthetic peptide leptin(116–130) amide involve actions both similar to and distinct from those of the native molecule in the adult rat. Eur. J. Endocrinol. 142, 406–410. Tena-Sempere, M., Manna, P. R., Zhang, F. P., Pinilla, L., Gonzalez, L. C., Dieguez, C., Huhtaniemi, I., and Aguilar, R. (2001). Molecular mechanisms of leptin action in adult rat testis: Potential targets for leptin-induced inhibition of steroidogenesis and pattern of leptin receptor messenger ribonucleic acid expression. J. Endocrinol. 170, 413–423. Torpy, D. J., Bornstein, S. R., Taylor, W., Tauchnitz, R., and Gordon, R. D. (1999). Leptin levels are suppressed in primary aldosteronism. Horm. Metab. Res. 31, 533–536. Trottier, G., Koski, K. G., Brun, T., Toufexis, D. J., Richard, D., and Walker, C. D. (1998). Increased fat intake during lactation modifies hypothalamic-pituitary-adrenal responsiveness in developing rat pups: A possible role for leptin. Endocrinology 139, 3704–3711.

Leptin and Adrenals

101

Uehara, Y., Shimizu, H., Ohtani, K., Sato, N., and Mori, M. (1998). Hypothalamic corticotropin-releasing hormone is a mediator of anorexigenic effect of leptin. Diabetes 47, 890–893. Unger, R. H. (2000). Leptin physiology: A second look. Regul. Pept. 92, 87–95. Ur, E., Wilkinson, D. A., Morash, B. A., and Wilkinson, M. (2002). Leptin immunoreactivity is localized to neurons in rat brain. Neuroendocrinology 75, 264–272. Utsunomiya, K., Yanagihara, N., Tachikawa, E., Cheah, T. B., Kajiwara, K., Toyohira, Y., Ueno, S., and Izumi, F. (2001). Stimulation of catecholamine synthesis in cultured bovine adrenal medullary cells by leptin. J. Neurochem. 76, 926–934. Vaisse, C., Halaas, J. L., Horvath, C. M., Darnell, J. E., Jr, Stoffel, M., and Friedman, J. M. (1996). Leptin activation of Stat3 in the hypothalamus of wild-type and ob/ob mice but not db/db mice. Nat. Genet. 14, 95–97. Van Dijk, G., Thiele, T. E., Donahey, J. C. K., Campfield, L. A., Smith, F. J., Burn, P., Bernstein, I. L., Woods, S. C., and Seeley, R. J. (1996). Central infusion of leptin and GLP-1-(7–36) amide differentially stimulate c-FLI in the rat brain. Am. J. Physiol. 271, R1096–R1100. Van Dijk, G., Donahey, J. C. K., Thiele, T. E., Scheurink, A. J. W., Steffens, A. B., Wilkinson, C. W., Tenenbaum, R., Campfield, L. A., Burn, P., Seeley, R. J., and Woods, S. C. (1997). Central leptin stimulates corticosterone secretion at the onset of the dark phase. Diabetes 46, 1911–1914. Vidal, S., Cohen, S. M., Horvath, E., Kovacs, K., Scheithauer, B. W., Burguera, B. G., and Lloyd, R. V. (2000). Subcellular localization of leptin in non-tumorous and adenomatous human pituitaries: An immuno-ultrastructural study. J. Histochem. Cytochem. 48, 1147–1152. Vila, R., Adan, C., Rafecas, I., Fernandez-Lopez, J. A., Remesar, X., and Alemany, M. (1998). Plasma leptin turnover rates in lean and obese Zucker rats. Endocrinology 139, 4466–4469. Wagner, R., Oberste-Berghaus, C., Herpertz, S., Blum, W. F., Pelz, B., Hebebrand, J., Senf, W., Mann, K., and Albers, N. (2000). Time relationship between circadian variation of serum levels of leptin, insulin and cortisol in healthy subjects. Horm. Res. 54, 174–180. Wauters, M., Considine, R. V., and Van Gaal, L. F. (2000). Human leptin: From an adipocyte hormone to an endocrine mediator. Eur. J. Endocrinol. 143, 293–311. Weise, M., Abad, V., Considine, R. V., Nieman, L., and Rother, K. I. (1999). Leptin secretion in Cushing’s syndrome: Preservation of diurnal rhythm and absent response to corticotrophin-releasing hormone. J. Clin. Endocrinol. Metab. 84, 2075–2079. Williams, L. M., Adam, C. L., Mercer, J. G., Moar, K. M., Slater, D., Hunter, L., Findlay, P. A., and Hoggard, N. (1999). Leptin receptor and neuropeptide Y gene expression in the sheep brain. J. Neuroendocrinol. 11, 165–169. Wilson, M. E., Fisher, J., and Brown, J. (2005). Chronic subcutaneous leptin infusion diminishes the responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis in female rhesus monkeys. Physiol. Behav. 84, 449–458. Wolf, G. (1998). Orexins: A newly discovered family of hypothalamic regulators of food intake. Nutr. Rev. 56, 172–189. Yamamoto, S., Morimoto, I., Kai, K., Arao, T., Fujihira, T., Morita, E., Kannan, H., and Eto, S. (1999). Centrally administered murine leptin stimulates plasma argininevasopressin secretion and increases the level of mRNA expression in the supraoptic nucleus of concious rats. Neuroendocrinology 70, 207–212. Yamashita, T., Murakami, T., Otani, S., Kuwajima, M., and Shima, K. (1998). Leptin receptor signal transduction: OBRa and OBRb of fa type. Biochem. Biophys. Res. Commun. 246, 752–759.

102

Ludwik K. Malendowicz et al.

Yanagihara, N., Utsunomiya, K., Beng-Cheah, T., Hirano, H., Kajiwara, K., Hara, K., Nakamura, E., Toyohira, Y., Uezono, Y., Ueno, S., and Izumi, F. (2000). Characterization and functional role of leptin receptor in bovine adrenal medullary cells. Biochem. Pharmacol. 59, 1141–1145. Yonekura, S., Senoo, T., Kobayashi, Y., Yonezawa, T., Katoh, K., and Obara, Y. (2003). Effects of acetate and butyrate on the expression of leptin and short-form leptin receptor in bovine and rat anterior pituitary cells. Gen. Comp. Endocrinol. 133, 165–172. Yuen, B. S., Owens, P. C., Symonds, M. E., Keisler, D. H., McFarlane, J. R., Kauter, K. G., and McMillen, I. C. (2004). Effects of leptin on fetal plasma adrenocorticotropic hormone and cortisol concentrations and the timing of parturition in the sheep. Biol. Reprod. 70, 1650–1657. Zakrzewska, K. E., Cusin, I., Sainsbury, A., Rohner-Jeanrenaud, F., and Jeanrenaud, B. (1997). Glucocorticoids as counterregulatory hormones of leptin: Toward an understanding of leptin resistance. Diabetes 46, 717–719. Zamorano, P. L., Mahesh, V. B., De Sevilla, L. M., Chorich, L. P., Bhat, G. K., and Brann, D. W. (1997). Expression and localization of the leptin receptor in endocrine and neuroendocrine tissues of the rat. Neuroendocrinology 65, 223–228. Zerani, M., Boiti, C., Zampini, D., Brecchia, G., Dall’Aglio, C., Ceccarelli, P., and Gobbetti, A. (2004). Ob receptor in rabbit ovary and leptin in vitro regulation of corpora lutea. J. Endocrinol. 183, 279–288. Zhang, F., Chen, Y., Heiman, M., and Dimarchi, R. (2005). Leptin: Structure, function and biology. Vitam. Horm. 71, 345–372. Zhang, Y., Proenca, R., Maffei, M., Barone, M., Leopold, L., and Friedman, J. M. (1994). Positional cloning of the mouse obese gene and its human homologue. Nature 372, 425–432. [Erratum in Nature 374, 479, 1995.] Zhou, J., Zhao, R., Wei, X., Xia, D., Xu, Q., and Chen, J. (2004). Developmental patterns of serum leptin levels, leptin gene expression in adipose tissue and Ob-Rb gene expression in hypothalamus of Erhualian and Large White pigs. Sci. China Ser. C 47, 190–196. Ziolkowska, A., Tortorella, C., Nussdorfer, G. G., and Malendowicz, L. K. (2001). Prolonged administration of leptin inhibits proliferation and stimulates apoptosis in the rat adrenal gland. Biomed. Res. 22, 215–218. Ziotopoulou, M., Erani, D. M., Hileman, S. M., Bjorbæk, C., and Mantzoros, C. S. (2000). Unlike leptin, ciliary neurotrophic factor does not reverse the starvation-induced changes of serum corticosterone and hypothalamic neuropeptide levels but induces expression of hypothalamic inhibitors of leptin signaling. Diabetes 49, 1890–1896. Zipser, R. D., Davenport, M. W., Martin, K. L., Tuck, M. L., Warner, N. E., Swinney, R. R., Davis, C. L., and Horton, R. (1981). Hyperreninemic hypoaldosteronism in the critical ill: A new study. J. Clin. Endocrinol. Metab. 53, 867–873.