Adrenal Cortex and Medulla Physiology During Pregnancy, Labor, and Puerperium

Chapter 8

Adrenal Cortex and Medulla Physiology During Pregnancy, Labor, and Puerperium Matthieu St-Jean, Isabelle Bourdeau and Andr
e Lacroix Division of Endocrinology, Department of Medicine and Research Center, Centre hospitalier de l’Universit
e de Montr
eal (CHUM), Montr
eal, QC, Canada

Key Clinical Changes l

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Hypothalamo-pituitary-adrenal (HPA) axis is upregulated in pregnancy, with elevation in total and free cortisol, increased sensitivity of the adrenals to ACTH, and refractoriness to negative feedback by glucocorticoids. The placenta plays a major role in the regulation of the HPA axis by its production of CRH and ACTH throughout pregnancy, and by acting as a protective barrier for the fetus against the hypercortisolism of pregnancy. The HPA axis maintains its circadian variation during pregnancy, but the diurnal variation may be partially blunted. Pregnancy is associated with an upregulation of almost all the components of the Renin-Angiotensin-Aldosterone System (RAAS) to counteract the mineralocorticoid antagonists and kaliuretic effects of progesterone and to preserve the hemodynamic stability in pregnancy. Total testosterone, free testosterone, and SHBG increase during pregnancy, but DHEAS, a substrate for placental estrogen synthesis, decreases by 50%. Catecholamine levels are unchanged throughout pregnancy, and the placenta possesses MAO and COMT, which inactivate catecholamines and protect the fetus against excess catecholamine.

The adrenal glands are composed of two embryologically distinct parts: the outer adrenal cortex and the inner adrenal medulla. The adrenal cortex is composed of three zones of cells that synthesize, through multiple enzymatic steps, the different steroid hormones from cholesterol.1 Each layer expresses specific steroidogenic enzymes that differentiate their function. The outer zona glomerulosa (ZG) specifically contains CYP11B2, or aldosterone synthase, which is responsible for aldosterone synthesis.1 ZG is devoid of 17-a-hydroxylase, which is necessary for cortisol and androgen synthesis. Aldosterone synthesis is regulated by three principal secretagogues: angiotensin II, potassium, and to a lesser extent adrenocorticotropic hormone (ACTH).1 The zona fasciculata (ZF) is the most prominent part of the adrenal cortex, producing mainly cortisol, but also androgens (mostly dehydroepiandrosterone sulfate (DHEAS) and androstenedione).1 The inner zona reticularis (ZR) produces mostly androgens (i.e., DHEAS and androstenedione) due to its higher 17.20 lyase activity, but it makes cortisol as well. The synthesis of cortisol and androgens is regulated by ACTH, which is produced by the corticotroph cells of the anterior pituitary gland under the pulsatile control of hypothalamic corticotropin-releasing hormone (CRH) and of vasopressin.1 The adrenal medulla produces and releases catecholamines (mostly norepinephrine and epinephrine). During pregnancy, maternal adrenal glands undergo minimal changes in weight and size, but the ZF enlarges.2,3 This chapter will review the physiological changes occurring in the adrenal glands during pregnancy. We will mostly focus on the changes in glucocorticoid and mineralocorticoid physiology. We also present a brief overview of the alterations occurring in the adrenal androgens and catecholamines during pregnancy.

8.1 8.1.1

GLUCOCORTICOID PHYSIOLOGY IN PREGNANCY, LABOR, AND PUERPERIUM Plasma CRH and CRH-bp: Origin and Roles During Pregnancy

CRH is a 41-amino-acid peptide synthesized and released by the paraventricular nucleus neurons of the hypothalamus. Its principal functions is to regulate the anterior pituitary corticotrope synthesis of POMC and release of ACTH and Maternal-Fetal and Neonatal Endocrinology. https://doi.org/10.1016/B978-0-12-814823-5.00008-8 Copyright © 2020 Elsevier Inc. All rights reserved.

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102 SECTION 1 The Mother

b-endorphin into the bloodstream.4 Maternal plasma CRH levels increase exponentially from the eighth week of pregnancy and onward to levels which are up to 1000 times those found in nonpregnant women.5–8 After 35 weeks of gestation, there is a sharp increase in the plasma levels of CRH with a mean peak, ranging from 1462 to 4346 pg/mL between 38 and 40 weeks of pregnancy.9–11 Most of plasma CRH is not of hypothalamic origin as it is rapidly degraded by enzymes in the pituitary gland.12 CRH was isolated from the placenta in 1988.13 Placental CRH was shown to be identical to the hypothalamic CRH in structure, immunoreactivity, and bioactivity.4,6 CRH messenger ribonucleic acid (mRNA) was demonstrated in human placental extracts between 7 and 40 weeks of gestation.14,15 A 20-fold increase of CRH mRNA is found in placental extracts 5 weeks prior to parturition, which parallels the marked elevation of plasma CRH.15 CRH synthesis was demonstrated in vitro by superfusion studies of human placenta fragments.16 Thus, the placenta is the major source of circulating CRH during pregnancy.4 Compared to the massive rise in CRH, ACTH, and cortisol levels increase modestly during pregnancy,4 despite a demonstration that placental CRH is a secretagogue for pituitary and placental ACTH.17,18 Two explanations for this discrepancy were proposed. The human CRH-binding protein (CRH-bp), a 322-amino-acid glycoprotein, attenuates the bioactivity of CRH by binding free CRH.4,6,12,19 CRH-bp binds human CRH (hCRH), but not ovine CRH (oCRH).20 CRH-bp levels are similar to nonpregnant women during the first two trimesters, but they fall by 50% between weeks 38 and 40 of pregnancy.21 As CRH-bp does not increase in early pregnancy, its biosynthesis is not upregulated by estrogen.6,21 In vitro, CRH-bp inhibits the ACTH-releasing-activity of the placenta but not of pituitary corticotropes of rat, supporting its inhibitory role on the bioactivity of the placental CRH, but it allows maternal stress response in late pregnancy.22 Second, there is a possible partial desensitization of maternal corticotrophs after chronic stimulation by placental CRH,4 as shown in vivo in rats23 and in vitro in ovine pituitary cells.24 The regulation of placental CRH production is incompletely understood. Opposite to their effects on corticotropes, glucocorticoids stimulate the expression of the CRH gene and CRH production in the placenta.12,25,26 This increase in CRH can stimulate pituitary ACTH release and result in increased cortisol secretion, which in turn can stimulate placental CRH release, resulting in a feed-forward mechanism.26 Estrogens, progesterone, and nitric oxide have an inhibitory action on CRH release by the placenta.26 In human placental culture cells, norepinephrine, acetylcholine, angiotensin II, Interleukine-1, oxytocin, and arginine vasopressin (AVP) stimulate the production of CRH27; the contribution of these factors on placental CRH production in vivo is unknown. During pregnancy, in addition to playing an important regulator role of the hypothalamic-pituitary axis (HPA), CRH may play other functions.4,5 CRH stimulates estrogen biosynthesis in cultured human placental cells.12 CRH produced by the embryo and endometrium facilitates decidualization and implantation by modulating the antirejection process and regulating endometrial invasion.5 CRH acts as a clock that determines pregnancy duration, and it is usually higher in women with spontaneous labor compared with those requiring induction.4,28 In women with impending premature delivery, higher levels of CRH indicate that labor will begin within a day.4 CRH is probably involved in the transition of the upper myometrium from a initial relaxed state to one sensitive to contractile signals from oxytocin and prostaglandins at term.4 CRH stimulates prostaglandin E2 production, which favors cervical ripening and myometrial contractions.4 CRH also regulates the expression of glucose transporters (GLUT), which facilitates placental glucose transport.4 Of the 14 GLUT family proteins,29 GLUT1 and GLUT3 are essential for glucose transport from the maternal circulation to the fetus through the placenta.4 Placental GLUT1 expression is increased by locally produced CRH acting via CRH-R1,29 while binding CRH-R2 downregulates GLUT1 in the placenta.4,29 Higher CRH levels in later stages of pregnancy may bind mainly to CRH-R1 in order to increase GLUT1 expression and glucose transport to the growing fetus, but this remains to be demonstrated.4

8.1.2

CRH Receptors

There are two isoforms of the CRH receptor (CRH-R): CRH-R1 and CRH-R2.4–6,12 Both belong to the seven transmembrane, G-protein-coupled superfamily and are positively coupled to adenylate cyclase.12 Both isoforms of CRH-R share 70% sequence homology, but they have different pharmacologic profiles.6,12,14 CRH-receptors (CRH-Rs) are expressed in numerous peripheral tissues, including the placenta, endometrium, central nervous system, heart, muscle, skin, and lymphatic organs.6,14 CRH has 10 times higher affinity for CRH-R1 than CRH-R2.12 CRH binds to CRH-R1 of the corticotroph cells,5,12 where the ACTH response is modulated by the number of CRH-Rs. Factors such as immobilization, stress, adrenalectomy, administration of CRH, AVP, and glucocorticoids reduce the number of CRH-Rs in corticotrophs.5,12 CRH and AVP have an additive effect on the levels of CRH-Rs on corticotrophs.5 During pregnancy and labor, CRH-R1 and CRH-R2 expression in the myometrium enables CRH and CRH-like peptides to modulate myometrial contractility.30 The CRH-R1 subtype mediates the inhibition of CRH on myometrial contractility, causing relaxation of myometrial cells.4 In contrast, CRH-R2 promotes smooth muscle contraction.12

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8.1.3

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Urocortin in Pregnancy: Their Origin and Possible Role

The urocortins (UCN) UCN1 and UCN2 are 40-amino-acid peptides of members of the CRH peptide family, and they share 34%–45% sequence homology with CRH.6,31,32 UCN3 has also been described, but its role during pregnancy is unknown. UCN levels during pregnancy are constant until onset of labor, when they increase.6,33 UCN circulates in plasma bound to CRH-bp.31 Free UCN exerts its action through its binding with CRH-R1 and CRH-R2. UCN binds with six times greater affinity to CRH-R1 and 40 times greater affinity to CRH-R2 than CRH.31 UCN1 can bind to both CRH-R1 and CRH-R2, but UCN2 can only bind to CRH-R2.34 UCN1 is expressed in anterior pituitary, cerebellum, heart, gastrointestinal tract, fetal membranes, placenta, decidua, chorion, and amnion.34,35 UCN1 was demonstrated in vitro to increase uterine contractility induced by endometrial prostaglandins.6,31 UCN1 also increases the secretion of prostaglandin E2 by the trophoblasts, and it decreases the expression of 15-hydroxyprostaglandin dehydrogenase (PGDH), an enzyme that usually metabolizes the prostaglandins.31,36 All these effects are inhibited by astressin, a CRH-R2 inhibitor. Therefore, the prostaglandins increase induced by UCN1 is explained by a CRH-R2-mediated effect.36 Also, UCN1 can increase ACTH and cortisol secretion in healthy humans35 and ACTH release by human placental cells in culture.37 UCN2 is expressed in multiple organs, including the brain, colon, small intestine, stomach, thyroid, adrenal, heart, skeletal muscles, and vascular endothelial cells.32 During pregnancy, UCN2 is also found in the maternal decidua, trophoblast, fetal membranes, and myometrium.32,37 UCN2 was demonstrated to stimulate estradiol release by trophoblast cell cultures in the presence of DHEAS, androstenedione, or testosterone.32 At term, the expression of UCN2 gene is significantly higher in human laboring gestational tissues compared to nonlaboring gestational tissues (placenta, fetal membranes, and myometrium).32 Like UCN1, UCN2 also decreases PDGH expression, which probably contributes to increased concentrations of prostaglandins.36 UCN2 also accelerates the procontractile effect of prostaglandin F2a (PGF2a), likely by upregulating the expression of the PGF2a receptor and the myometrial expression of proinflammatory cytokines.32 The upregulation of proinflammatory cytokines within the laboring myometrium stimulates uterine contractions and potentiates the prostaglandin-induced uterine contractions.32 However, UCN2 does not have a direct effect on line contraction in myometrial cells. Therefore, UCN2 plays an indirect role on the enhancement of myometrial cell contraction through the production of proinflammatory cytokines and the accentuation of the contractile response to prostaglandins.32 UCN2 is also proposed to be a regulator of the placental vascular tone, given that it is expressed in endothelial cells in the placental villi.37 Unlike UCN1, UCN2 does not induce ACTH secretion in either rat pituitary cells.38 or cultured human placental cells.37 Because UCN2 binds to CRH-R2 only and UCN1 and CRH bind to CRH-R1 and CRH-R1, the ACTH release action was attributed to activation of CRH-R1.37

8.1.4

Plasma ACTH: Origin and Roles During Pregnancy

ACTH is a 39-amino-acid peptide that is secreted by the pituitary corticotropes following posttranslational proteolytic cleavage of its precursor peptide proopiomelanocortin (POMC).6,39 The cleavage of POMC can give rise to related peptides, including b-endorphin, b-lipotropin, and a-MSH.6,39 In men and nonpregnant women, b-endorphin, b-lipotropin, and ACTH follow a similar diurnal rhythm, and their phasic secretion is under a common central control.40 The principal action of ACTH is through its binding with melanocortin 2 receptor (MC2R) to stimulate the synthesis and release of glucocorticoids from the adrenal ZF.41 ACTH is unable to cross the placenta, so its effects are limited to the mother.6 ACTH levels increase twofold by the end of the second half of pregnancy compared to the first trimester.8,33,39,42–45 Some studies reported that the basal levels of ACTH during pregnancy were higher39,46 compared to nongravid women, and others reported that they were lower.45,47 In the second half of pregnancy, the ACTH rises in spite of the elevated level of free cortisol, suggesting that there is another source of ACTH besides the pituitary that is not subject to negative feedback by cortisol.6,45 Term placenta extracts contain ACTH and immunoreactive b-endorphin and b-lipoprotein.43,48,49 These peptides arise from POMC in the placenta.6,48,49 CRH stimulates the secretion of peptides containing the ACTH sequence in primary culture of human placental cells, and this effect is reversed by a CRH antagonist.18 Glucocorticoids that usually suppress the secretion of pituitary ACTH have no influence on the release of ACTH by the placenta.18 In vitro, human placental ACTH is bioactive to the same extent in early and late gestation.50

8.1.5 Cortisol-Binding Globulin: Changes in Levels and Isoforms During Pregnancy and its Possible Role in Pregnancy Cortisol-binding globulin (CBG), or transcortin, is a 50–60-kDA transport glycoprotein that binds cortisol and progesterone with high affinity.51 CBG synthesis occurs mainly in the liver,52,53 but also in the endometrium, corpus luteum, and

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placenta, where CBG mRNA is expressed.54–57 Approximatively 90% of circulating cortisol is bound to CBG, 5% to albumin and 5% is free.51,58 During pregnancy, CBG levels increases progressively two- to threefold following stimulation by the circulating estrogen,59 similarly to women taking oral contraceptives.60–62 CBG levels during the second half of pregnancy are threefold higher than in nonpregnant patients.60,63 The primary role of CBG is to protect steroid hormones from catabolism and to deliver them to target cells.64 CBG contains six sites for N-glycosylation, and there is an average of five sites occupied by biantennary or triantennary oligosaccharides with variable additional terminal sialic acid residues, leading to different glycoforms.65 A pregnancy-associated glycoform of CBG is produced by an altered posttranslational modulation of CBG protein66 under the influence of estradiol51; this glycoform has only triantennary oligosaccharides and represents 10% of total CBG during pregnancy.65,66 This specific type of CBG is usually present at 6 months of pregnancy and has a 60-fold increased binding affinity for syncytiotrophoblast cell membranes compared to normal CBG.66 It might facilitate the specific delivery of steroids to the developing fetus because 25% of the fetal cortisol in late pregnancy is of maternal origin,67 and it may also possibly play a role in the regulation of glucocorticoid-induced placental CRH release.51,64–66 In the postpartum period, there are inconsistent data for the kinetics of CBG. Some studies demonstrate normalization of CBG levels at 3–6 weeks postpartum,61,63,68 whereas other reported elevated levels until 3–6 months postpartum.60,69 This persistence of CBG in the postpartum period might be explained by an increase in its half-life51,66 or a continued secretion of the pregnancy-associated variant by the maternal organism.66

8.1.6

Total and Free Cortisol Levels During Pregnancy

Pregnancy is a state characterized by an elevation of plasma total cortisol, plasma free cortisol, urine free cortisol, and salivary cortisol.6 Plasma total cortisol, which comprises the level of bound cortisol (to CBG and albumin) and unbound cortisol (also termed free cortisol), increases progressively during pregnancy6,45,60,61,63,70–75 in parallel to the CBG increase.63 This increase was shown to start as early as the 11th to 12th week of gestation and is maintained throughout pregnancy.63,71 During the third trimester of pregnancy, total cortisol levels are increased two- to threefold compared to nonpregnant women (Tables 8.1–8.6).60,71,73,78–80

TABLE 8.1 Variation of the different components of the hypothalamo-pituitary adrenal axis and feto-placental unit during pregnancy and pregnancy Change during pregnancy (T3 vs T1)

Changes in pregnancy compared to normal nonpregnant women

Time for normalization in postpartum

Placental CRH

Progressive increase with a sharp increase after 35 weeks

Increase by 1000-fold


24 h

CRH-bp

Unchanged until 38 weeks of pregnancy, where it falls to 50% of those levels

Same than nongravid women until 38 weeks of gestation where it falls to 50% of those levels

NA

ACTH (pituitary + placental)

Increased by 2-fold

Inconsistent (up or down depending on the study)


24 h

Plasma total cortisol

Increases progressively by 1.5- to 2-fold

Increased by 2- to 3-fold

<1 week to
3 months

Plasma free cortisol

Increased progressively by 1.3-to 3-fold

Increased by 1.5- to 3-fold

<1 week

24-h urinary free cortisol excretion

Increased progressively by 1.5- to 2-fold

Increased by 2- to 3-fold


2–3 months

Late-night free salivary cortisol

Increased

Equivocal results (mostly increased)

NA

CBG

Increased by 2- to 3-fold during pregnancy

Increased by 3-fold in late pregnancy

Variable (3–6 weeks until 3–6 months depending on the study)

Parameters

NA, not assessed.

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TABLE 8.2 Normal values for mean morning total cortisol observed during pregnancy and postpartum

References 73

Ambroziak et al. Mean (2.5%– 97.5%)

60

Assays

Trimesters

Values (nmol/L)

Elecsys 2010 (Hitachi, Japan)

T1

586.2 (281.7–954.8)

LC-MSMS

Jung et al. Mean  SD

Suri et al.75 Mean  SD

Chemiluminescence enzyme immunoassay

Abou-Samra et al.71 (not the same patient assessed at each trimester) Mean  SD

Radiocompetition after chromatographic separation

Nonpregnant values (nmol/L)

a

T2

833.1 (456.8–1305.4)

T3

973.5 (406.6–1464.5)a

PP

487.4 (293.8–706.2)

T1

577  30a

T2

878  28

T3

1043  41a

PP (2–3 months)

486  38a

T1

257  61b

T2

400  119

T3

458  116b,c

PP (11–14 weeks)

251  132b

T1

452  88a

T2

675  160

T3

924  201a

484.9 (274.8–721.4)

364  28

a

NA b,c

303  55 a

a

Different than the nonpregnant values. The values of the study in mg/dL were converted to nmol/L by using the conversion factor: 1 mg/dL ¼ 27.59 nmol/L. Different than the postpartum and T1. NA, not assessed. b c

TABLE 8.3 Normal values for mean morning free serum cortisol observed during pregnancy and postpartum References 60

Jung et al. Mean  SD

71

Abou-Samra et al. Mean  SD

a

Assays

Trimesters

Values (nmol/L)

Nonpregnant values (nmol/L)

Equilibrium dialysis

T1

14.5  1.2

12.2  1.6

T2

17.2  1.4

T3

19.6  1.5a

PP (2–3 months)

12.3  2.0

T1

11.9  3.3

T2

18.5  6.1

T3

34.2  7.5a

Equilibrium dialysis

Different than the nonpregnant values.

a

11.0  2.8 a

TABLE 8.4 Normal values for mean morning salivary cortisol observed during pregnancy and postpartuma References

Assays

Trimesters

Values (nmol/L)

Nonpregnant values (nmol/L)

Ambroziak et al.73 Mean (2.5%–97.5%)

Elecsys 2010 (Hitachi, Japan)

T1

18.4 (7.2–34.2)

18.5 (5.27–37.8)

T2

19.6 (6.9–36.4)

T3

21.9 (8.9–39.7)

PP (3 months)

13.8 (4.08–26.01)

T1

5.79  2.76a

T2

9.93  4.69

T3

12.97  4.97a,b

PP

6.06  4.69a

75

Enzyme-linked immunoassay (Salimetrics, State College, PA)

Suri et al. Mean  SD

NA

a,b

The values of the study in mg/dL were converted to nmol/L by using the conversion factor: 1 mg/dL ¼ 27,59 nmol/L. Different than the first trimester and postpartum. NA, not assessed. a

b

TABLE 8.5 Normal values for mean late-night/midnight salivary cortisol observed during pregnancy and postpartum References

Assays

Trimesters

Values (nmol/L)

Nonpregnant values (nmol/L)

Manetti et al.76 Mean  SD

RIA (Immunotech, Marseille, France)

T2 and T3

6.64  3.67a,b

3.78  1.57

Lopes et al.77 Median (min–max)

ELISA—Cortisol (expanded range)

T1

2.20 (0.55–6.90)c

T2

c

2.76 (0.55–7.73)

T3

4.13 (1.93–9.38)a,c

T1

4.4 (1.8–9.1)

T2

4.6 (1.7–9.8)

T3

5.6 (1.3–13.5)

PP (3 months)

3.0 (1.0–5.3)

Ambroziak et al.73 Mean (2.5%– 97.5%)

Elecsys 2010 (Hitachi, Japan)

1.93 (0.83–4.14)

4.6 (1.1–9.0)

a

Different than the nonpregnant values. The values of the study in ng/mL were converted to nmol/L by using the conversion factor: 1 ng/mL ¼ 2759 nmol/L. c The values of the study in mg/dL were converted to nmol/L by using the conversion factor: 1 mg/dL ¼ 27.59 nmol/L. NA, not assessed. b

TABLE 8.6 Normal values for mean 24-h urinary free cortisol excretion observed during pregnancy and postpartum Parameters 60

Jung et al. Mean  SD

60a

Chico et al. Mean  SD

a

Assays LC-MSMS

RIA

Different than the nonpregnant values. Different than the first trimester. NA, not assessed. b

Trimester

Values (nmol/day)

Nonpregnant values (nmol/day)

T1

135  10

78  12

T2

187  13

T3

242  15a

PP (2–3 months)

75  9

T1

262  118

T2

463  256b

T3

424  210b

a a

NA

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Free cortisol increases progressively during pregnancy in parallel to total cortisol. Plasma free cortisol was shown to be increased in pregnancy, especially during the second and third trimesters.60,63,71,81 Plasma free cortisol levels, measured by equilibrium dialysis during the third trimester, increase 1.5- to 3-fold compared to nonpregnant controls.60,71 Progressive elevation in urinary free cortisol (UFC) were also noted during pregnancy, which also parallel the increase in total cortisol.79 During the third trimester, the 24 h UFC values are two to three times higher than in nonpregnant patients.60,79,82 Even if the glomerular filtration rate is increased during pregnancy, it does not seem to explain the elevated UFC excretion.83 Free salivary cortisol showed a strong correlation with total or free plasma cortisol.72,75,84 However, studies on the measure of salivary cortisol levels during pregnancy are inconsistent, showing both increased61,74–77,85 or normal levels.72,73 Manetti et al.76 and Lopes et al.77 showed that late-night salivary cortisol (LNSC) was higher in patients in the third trimester of pregnancy than in nonpregnant patients. However, Ambroziak et al.,73 recently showed that morning salivary cortisol and LNSC were not different in pregnant patients compared to nonpregnant controls, no matter the trimester. However, in this study, LNSC is 20% higher in the third trimester of pregnancy than in the controls, and it is also higher than in the postpartum period, but it was not statistically significant.73 In the study of Lopes et al.77 the LNSC sampling during the third trimester were done at 40 weeks of pregnancy compared to 31 weeks as found by Ambroziak et al.73 Given the fact that free cortisol is higher at the end of the third trimester, it seems appropriate to say that LNSC is probably higher for patients in the third trimester of pregnancy than for nonpregnant patients, but the extent of this increase might depend on the timing of the samples during the third trimester.

8.1.7

Diurnal Variation of the HPA Axis and the Feto-Placental Unit During Pregnancy

The secretion of placental CRH does not exhibit a circadian rhythm.5,6,69 There is no relation between the diurnal variation of CRH and the diurnal variation of ACTH or cortisol.69,85 The circadian rhythm of ACTH is maintained during pregnancy,39,47,69,85 and it parallels the diurnal variation of b-endorphin.39 The highest values of ACTH are in the morning, around 8 a.m., and the lowest are at midnight.39,69 There is a close correlation between the levels of ACTH and cortisol during the third trimester, and ACTH precedes cortisol secretion by 30 min.69 Total and free cortisol also preserved a daynight variation during pregnancy, but it may be partly blunted.45,61,63,69,82,85–88 Also, in the morning, the peak in cortisol was demonstrated to be an hour later in pregnant patients (8 a.m. instead of 7 a.m.) than nongravid women.74 Some explanations were suggested to explain the lack of correlation between the diurnal variation of CRH and ACTH or cortisol. It was suggested that a nonpulsatile CRH stimulation could still produce a pulsatile pattern of ACTH and cortisol secretion.69 This hypothesis is supported by the fact that during a continuous infusion of ovine CRH in normal humans, the secretion of ACTH and cortisol remained pulsatile.69 Another explanation is that vasopressin, which is secreted in pulsatile fashion with a circadian rhythm, might regulate the circadian and pulsatile ACTH release by the pituitary during pregnancy and be potentiated by the chronically high level of circulating CRH.69,89 Goland et al.89 have demonstrated that in pregnant baboons, the secretion of ACTH and cortisol in response to vasopressin is higher in late pregnancy, when the level of CRH is higher, than in early pregnancy. Therefore, even if the secretion of CRH is nonpulsatile, it appears to be a major regulator of ACTH and cortisol during pregnancy.6,69

8.1.8 Physiologic Hypercortisolism of Pregnancy: Particular Regulation of the HPA Axis During Pregnancy The higher level of free cortisol during pregnancy results in a greater exposure of maternal tissues to glucocorticoids.60,82,85,86,88 This progressive elevation in free and total cortisol and its metabolite levels that is seen in pregnancy can result from an upregulation of the HPA axis in addition to the estrogen-stimulated CBG elevation.6,60 The upregulation of the HPA axis maybe secondary to a resistance of the HPA axis to cortisol.6,88 It was found that during pregnancy, the HPA axis is resistant to suppression by dexamethasone.43,79,88 Progesterone, which increases progressively by threefold between the first and third trimester of pregnancy,71 might be implicated in that process, given that progesterone levels in late pregnancy correlate with salivary cortisol.85 Progesterone competes with cortisol for the binding with CBG.63,85 However, the effect of progesterone on the glucocorticoid receptor in vitro is unclear, with some studies reporting an agonist action90,91 and other and antagonist action.71,92,93 Therefore, high levels of progesterone can contribute to the increase in free cortisol by its reduction of the cortisol-CBG binding.71,85 Other mechanisms have been proposed to explain the rise in free cortisol during pregnancy.60 As described previously, during the second half of pregnancy, there is an increase in plasma CRH and ACTH,44,45 which are autonomous6,45,60 and possibly of placental origin.13,18 This increase in CRH and ACTH might also upregulate the HPA axis. Also, the adrenal glands have increased responsiveness to ACTH during pregnancy, as demonstrated by the higher cortisol response to

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synthetic ACTH compared to nonpregnant women.6,88,94,95 Brown et al.95 found that the mean maximum cortisol response to continued ACTH infusion in a normal three-trimester pregnancy was 963 nmol/L compared to 507 nmol/L in the nonpregnant controls. One study was done to evaluate the response of the adrenal in pregnancy to an intravenous bolus of 1 mg of cortrosyn96; 6 pregnant women who were at a mean of 31.4  2.3 weeks of pregnancy reached a peak cortisol value of 1215 nmol/L (99% IC 917–1535 nmol/L) at a mean of 27.4  1.6 min.96 However, no nonpregnant control groups have been studied. Suri et al.75 examined the response of serum cortisol and salivary cortisol to a 250-mg cortrosyn intravenous bolus in pregnant women through pregnancy and at 3 months postpartum. They demonstrated that the response of salivary cortisol to the intravenous bolus of cortrosyn increases progressively during pregnancy when compared to the postpartum period. However, the response of the total serum cortisol was only higher in the second trimester compared to the postpartum state.75 All these data confirmed that pregnancy represents a state where the adrenal glands have a higher sensitivity to ACTH compared to nonpregnant women and the postpartum period.

8.1.9 Specific Role of Glucocorticoids During Pregnancy and the Impact of Excessive Fetal Glucocorticoid Exposure Glucocorticoids are important during the various phases of pregnancy. In early pregnancy, glucocorticoids have been shown to promote the establishment of gestation.97 They inhibit immune rejection responses during the peri-implantation windows, and they also play a beneficial role in the induction of decidualization in early pregnancy.97 Also, glucocorticoids play an important role in late fetal development, such as lung maturation.6 However, prolonged exposure to excessive levels of glucocorticoids is detrimental to placental and fetal development.98 Fetal exposure to excessive amounts of glucocorticoids during pregnancy leads to intrauterine growth retardation and may lead to the development of chronic disease, such as hypertension and diabetes, later in life.99

8.1.10

Fetus Protection Against the High Maternal Glucocorticoids Levels During Pregnancy

The fetus is protected during gestation from the effects of maternal hypercortisolism by the 11-bhydroxysteroid dehydrogenase 2 (11-bHSD 2) enzyme located in the syncytial trophoblastic cells.6 Here, 11-bHSD 2 catalyzes the conversion of cortisol to its inactive metabolite cortisone.100 Also, 11-bHSD 2 expression is already observable in the placenta at 3 weeks postconception, but its activity at that time was not assessed.101 Its expression increases exponentially to more than 56-fold between weeks 4–6 and weeks 35–40 of gestation.102 Cortisol and CRH upregulates the expression of 11-bHSD 2 in villous trophoblastic cells, which may represent a mechanism of self-defense to counteract maternal hypercortisolism.97,103 The capacity of 11-bHSD 2 is high enough to ensure that the fetal cortisol levels are much lower than maternal levels during gestation.6 However, despite the efficacy of 11-bHSD 2, 25% of the fetal cortisol is of maternal origin at term.104 Mutations or epigenetic modifications of the gene encoding 11-bHSD 2, which diminish the function of the enzyme, is associated with a significant reduction in birth weight.99 Dexamethasone and betamethasone, which are synthetic glucocorticoids, are poor substrates for 11-bHSD 2, and they can cross the placental barrier without being inactivated following maternal administration.99

8.1.11

Change in the HPA Axis and Cortisol Levels During Parturition and in the Postpartum

Peak CRH levels occurs within 48 h prior to delivery, and it decreases during labor.28 In contrast to the decreasing level of CRH during labor, ACTH increases markedly by 10- to 15-fold during labor and delivery, demonstrating that the HPA axis is not completely suppressed.6,28,39,45 The increase in ACTH levels is higher in women who had oxytocin-induced labor than those who underwent spontaneous labor or elective caesarean, which suggests that oxytocin can possibly potentiate the CRH-stimulated ACTH release from corticotropes.28,105 Also, ACTH levels immediately after vaginal delivery are higher than those found in elective caesarean delivery.39 The level of ACTH in the elective caesarean reached their peak 30 min after delivery, reflecting the stress associated with the surgery.39 During labor, levels of total and free cortisol sharply increase to values that are almost double those that are seen in the third trimester.45,80,106,107 The increase in cortisol is higher in vaginal delivery when compared to elective caesarean delivery, which reflects the stress induced by the onset of labor.106 In the postpartum period, CRH and ACTH fall rapidly toward the nonpregnant range within 24 h.10,44 After delivery, total and free cortisol levels slowly decrease to the nonpregnant range over a period of several days in some studies.61,85 However, a recent study showed a delay in the normalization of total cortisol of up to 3 months.60 The time for normalization of UFC in the postpartum period is not well defined. However, it is known that at 2–3 months after delivery, UFC is

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normalized.60 The possible explanations for the normalization delay of total cortisol might be the longer half-life or the continued biosynthesis of pregnancy-associated CBG in the postpartum period, given that the free cortisol was normalized at that time.60,73 The circadian rhythm of ACTH and cortisol is also maintained in the early postpartum period.39,85 In the postpartum period, the abnormal cortisol suppression after 1 mg of dexamethasone may persist for up to 2–3 weeks.108 This finding is consistent with the fact that total cortisol probably requires 2 weeks to months to normalize in the postpartum period, but the time for normalization varies between individuals, given that some women have normal dexamethasone test 5 days after delivery.109

8.2

MINERALOCORTICOID PHYSIOLOGY IN PREGNANCY, LABOR, AND PUERPERIUM

Normal pregnancy is characterized by a decrease in blood pressure despite a 45% expansion of the intravascular volume and an increase in cardiac output of 25%–50%, explained by a decrease in peripheral vascular resistance.6,110 Mineralocorticoids and the renin-angiotensin system (RAS) play an important role in these adaptations.110 Here, we will describe briefly changes in the RAS and aldosterone physiology during pregnancy (see Chapter 10 for more detail). The RAS is a hormone-signaling cascade implicated in the regulation of blood pressure and systemic electrolyte balance.111 In the context of diminished circulating blood volume, the juxtaglomerular apparatus, in the afferent arteriole of the kidney, senses the diminished renal perfusion and increases renin secretion. Renin, an enzyme, cleaves the angiotensinogen, a protein synthesized by the liver, to produce angiotensin I (ANG-I). ANG-I, a biologically inactive peptide, is then cleaved by the angiotensin-converting enzyme (ACE), expressed by endothelium particularly in the lungs, to the biologically active angiotensin II (ANG-II).111 ANG-II exerts its action through binding with two major angiotensin receptors, AT1R and AT2R, which are seven-transmembrane, G-protein-coupled receptors that have 34% sequence homology and similar affinity for ANG-II. The AT1R is the predominant ANG-II receptor in adults and is responsible for the majority of the ANG-II effects.111 AT1R is localized in several tissues, such as blood vessels, kidneys, adrenals, heart, and the central and peripheral autonomic nervous systems.112 ANG-II, by its binding with AT1R, induced vasoconstriction, increased sympathetic activity, aldosterone production, and release by the ZG.6,111 Progesterone and estradiol concentrations increase progressively in the maternal blood during pregnancy, mostly as a result of placental production.6,113 Progesterone acts as a mineralocorticoid receptor antagonist. It reduces sodium reabsorption in the distal tubule, and it also causes smooth muscle relaxation, which contribute to reduce systemic vascular resistance.6,114 Progesterone is also associated with an antikaliuretic effect.115

8.2.1

RAS Modifications During Pregnancy

Pregnancy is associated with an upregulation of all components of the RAS, partly to counteract the effects of progesterone.111,116 Plasma renin activity (PRA) increases early in the first trimester until the 20th week of pregnancy and reaches values threefold to sevenfold greater than the normal range, after which it remains stable until delivery.6,113,117 Approximatively 50% of the increase in plasma renin activity during pregnancy is explained by the increase in synthesis of the renin substrate, angiotensinogen, and the other 50% represents the real increase in renin concentration.113 The concentration of plasma renin is higher in pregnant women at 28–38 weeks of pregnancy compared to nonpregnant women.118 Extrarenal production of renin by the ovaries and the maternal decidua probably contributes to the early increase in renin.119 Other factors that might explain the increase in renin are the hemodynamic changes of the pregnancy, which include the prostaglandin-induced peripheral vasodilatation and the arteriovenous shunt effect of the uteroplacental unit. These changes lead to decreased blood pressure, and the RAS could be activated to maintain organ perfusion and blood pressure.113 Progesterone elevation might also contribute to the renin elevation by its previously described effects.6,120 The ovary also secretes prorenin during pregnancy.6,121 Prorenin is the precursor of renin in renin-producing cells.119 The maternal plasma levels of prorenin reach their maximum at 8–12 weeks of gestation, which reaches 10 times the nonpregnant levels.121 To become active, prorenin requires being in an open conformation.122 Some authors suggested that binding of prorenin to the prorenin soluble receptor is activated and participates in the generation of ANG-I from angiotensinogen.121 However, a recent study reported that in physiological conditions (pH of 7.4 and temperature of 37°C), only a small percentage ( 1%) of prorenin is in the open conformation.122 Thus, prorenin contribution to the increased activity of the RAS in pregnancy remains to be determined. Angiotensinogen in pregnancy paralleled the renin increase; there is an increase in the first trimester until the 20th week, where it reaches a plateau until delivery.6,113,123 Angiotensinogen synthesis by the liver is stimulated by estradiol during pregnancy, which is supported by the demonstration of estradiol-induced, hepatic angiotensinogen synthesis in animal

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models, and a polymorphism in the estradiol response element of the angiotensinogen gene is negatively associated with angiotensinogen levels during pregnancy.111,113,116,124,125 The placenta might also contribute, as angiotensinogen mRNA and protein are found in human placental tissues.6,119 There is a high-molecular-weight angiotensinogen that circulates specifically in the plasma of pregnant women. The levels of this high-molecular-weight angiotensinogen increases throughout pregnancy and constitutes about 16% of the total angiotensinogen.121 However, the role of this specific form of angiotensinogen remains unknown.6 ACE activity remains constant during pregnancy, but the levels are lower than in nonpregnant women.121 This is the only component of the RAS that is decreased during pregnancy.111 ANG-II plasma levels correlate with the plasma levels of ANG-I, which is consistent with the fact that angiotensin-converting enzymes have no limiting role in the synthesis of ANG-II.117 ANG-II levels increase throughout pregnancy, reaching maximal values in the third trimester.117 ANG-II concentrations in the third trimester are 50% above the nonpregnant values.121 Several studies have revealed immunoreactivity for ANG-II in the placenta.119 As demonstrated by the higher levels of ANG-II in the second half of pregnancy, activation of renin-angiotensin-aldosterone system (RAAS) is higher in the second and third trimesters of pregnancy, despite the early increase in PRA and its substrate angiotensinogen.117 However, blood pressure in pregnancy remains normal despite this increase in ANG-II levels because ANG-II efficacy is reduced through changes in AT1R sensitivity, elevated progesterone levels, and elevated prostacyclin levels, which cause vasodilatation.126 The placental RAS plays key roles in the implantation, placentation, and development of the uteroplacental and umbilicoplacental circulation, as well as regulation of uteroplacental vascular resistance, but they also contribute to the activity of the circulating maternal RAS.119,121

8.2.2

Aldosterone Levels During Pregnancy

In normal pregnancy, plasma and urinary aldosterone increase progressively, in parallel with progesterone, with levels being five- to sevenfold more during the first trimester and 10- to 20-fold more at the end of the third trimester.6,80,113,117,123 Plasma aldosterone circulates mostly unbound to plasma protein.6 Plasma aldosterone correlates with the levels of urinary aldosterone, but the proportional increase in urinary aldosterone during the second and third trimesters is twice the increase in plasma aldosterone.113 The relationship between PRA and plasma aldosterone is dissociated during the second and third trimesters of pregnancy.127 This particular findings suggest that either the adrenals are more sensitive to ANG-II or that other factors known to regulate aldosterone secretion in normal patients, such as norepinephrine, ACTH, and digitalis-like factor, contribute to the elevation in aldosterone.127 ACTH which increases during pregnancy may contribute to the increased aldosterone secretion.127 In twin pregnancies, the plasma aldosterone and PRA were reported in one study to be higher in the second trimester, but they decrease during the third trimester to lower levels than normal singleton pregnancy.128 However, there are no explanations for these findings. Potassium levels remain normal in pregnancy despite the elevation in aldosterone levels, probably because of the mineralocorticoids’ antagonist action of progesterone.114 Urinary excretion of sodium and potassium remains constant throughout pregnancy.123 The plasmatic aldosterone concentration (PAC) and PRA ratio increase in the third trimester of pregnancy, as aldosterone increases more than PRA during the second half of pregnancy.128 Aldosterone is an important factor for fetus development, as demonstrated with a blockade of the mineralocorticoid receptor in animal models that resulted in inhibition of organogenesis.129

8.2.3

Regulation of RAAS During Pregnancy

The physiological regulation of RAAS is intact during pregnancy, as the response of plasma renin to posture or intravenous or oral saline loading is similar to that of nonpregnant women.118,127,130 Aldosterone also maintains a normal response to diuretics, volume depletion, and administration of mineralocorticoids.6

8.2.4

Other Mineralocorticoids

During pregnancy, the levels of corticosterone, deoxycortisol, and cortisone increase by two- to threefold, in parallel with cortisol.80 The plasma levels of 11-deoxycorticosterone (DOC), a potent mineralocorticoid, increases progressively during pregnancy to reach a peak (60–100 ng/100 mL) in the third trimester.6,114 DOC elevation might contribute to the sodium retention of pregnancy.114 During pregnancy, it appears that most of DOC is produced from the 21-hydroxylation of progesterone in an extraadrenal source.123 The fetoplacental unit probably contributes to the circulating maternal DOC levels because concentrations of DOC have been shown to be elevated in mixed cord blood.131

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RAAS in the Postpartum Period

In the postpartum period, the levels of all the component of the RAAS decrease rapidly within 3 days128 and return to nonpregnant values 6 weeks later.117

8.2.6

RAAS in Pregnancy-Associated Hypertension

RAAS modifications are observed during pregnancy-associated hypertension or preeclampsia. The level of plasma renin, ANG-I, ANG-II, and aldosterone are reduced compared to healthy pregnant patients.117,126,128 The reduced ANG-II levels are not explained by diminished activity of ACE in preeclampsia compared to normal pregnancy.111 Reduced RAAS might explain the reduced circulating volume that is found in preeclampsia.128 However, in gestational hypertension, the sensitivity to ANG-II on the adrenal glands or vessels is increased through AT1R heterodimers.111,126 Based on animal studies, the implication of autoantibodies directed against the AT1R is also suggested in the pathophysiology of preeclampsia.126 Preeclampsia is a state of dysregulated RAAS, but the triggering factors that lead to these modifications remain to be defined.111

8.3

ADRENAL SEX STEROIDS DURING PREGNANCY

Total testosterone levels increase progressively from the first trimester to term.132–134 In the normal state, testosterone mostly circulates in plasma bound to proteins; 38% is bound to albumin and 60% is bound to sex hormone-binding globulin (SHBG).135 During the third trimester of pregnancy, testosterone is bound 95.4% with SHBG, 0.82% with CBG, and 3.55% with albumin.136 Only free testosterone, a small fraction of the total testosterone, can cross the placenta membrane and interact with the androgen receptor.133 The increase in total testosterone can be partially explained by an early increase in estrogen-induced SHBG synthesis by the liver.133 SHBG increases through all pregnancy, reaching its peak, which is almost six times the nonpregnant value, in the third trimester.132,133,135,136 Also, the binding capacity of SHBG increases in pregnancy.135 Free testosterone and bioavailable testosterone also increase significantly throughout pregnancy, but levels of bioavailable testosterone stay in the normal nonpregnant range in most (but not all) pregnant women.133,136 Androstenedione levels are more variable between studies.132 Some reported a significant increase during the end of the third trimester compared to nonpregnant women,133 while others reported an early significant increase in the first trimester without further changes during pregnancy,137 and some have reported a nonsignificant increase in the third trimester.135,136 Androstenedione concentrations during pregnancy display a high interindividual variation,134,135 which may explain the differences between the studies. DHEAS decreases by 50% compared to nonpregnant levels during the first half of pregnancy and remains stable thereafter.133,135,137 DHEAS metabolic clearance rate increases by fivefold starting at midpregnancy, probably because it is a substrate for the increasing placental estradiol synthesis throughout pregnancy.133 However, even if the maternal level of DHEAS are lower in the second half of pregnancy than nonpregnant patients, it was demonstrated that the production rate of DHEAS by the maternal adrenal glands almost doubled during pregnancy.3,133 Therefore, higher metabolic clearance rather than decreased production explains the decreased level of DHEAS during pregnancy. Androgens are probably implicated in parturition.133 In vivo and in vitro studies have demonstrated that androgens promote cervical remodeling, and they also have an inhibitory action on myometrial contraction.133 It is suggested that the ovaries are the major contributors to the circulating level of testosterone and androstenedione in pregnancy, given that the level of these androgens during pregnancy are lower in women with premature ovarian failure and assisted-reproduction pregnancy compared to normal pregnant women.133 In contrast, DHEAS is produced only by the maternal adrenal glands, similar to nonpregnant women.133 In animal models, fetectomy, which removes the fetal precursor (DHEAS) of the placental estradiol synthesis without modifying the metabolic clearance rate of DHEAS, have resulted in an increase in maternal DHEAS plasma levels, and the administration of estradiol in these animals decreases the maternal DHEAS levels. This suggests that the placental production of estradiol probably downregulates the adrenal production of androgens by the mother.133 The placenta also has the capacity to produce androgens de novo; syncitiotrophoblasts express the enzyme CYP17, which converts C21 steroids to C19 steroids such as testosterone. The activity of this latter enzyme was confirmed in vitro.133 The fetus is protected against the virilizing effects of maternal androgens in pregnancy by the physiological increase in SHBG, which binds and inactivates androgens; the elevation of the progesterone levels, which compete for the androgen receptor binding and inhibits the 5a-reductase conversion of testosterone to its more potent dihydrotestosterone; and by the presence of aromatase complex in the placenta, which converts testosterone and androstenedione to estradiol or estrone.133

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The importance of the placenta aromatase in these protective mechanisms against maternal androgen has been confirmed by the finding that aromatase deficiency in the placenta results in virilized fetuses.133 In the postpartum period, the total testosterone decreases, but the time for normalization is unknown.132,136 Bioavailable testosterone levels were normalized 4 days postpartum.136 SHBG decreases progressively in the postpartum period to levels that are 25% lower by the fourth day postpartum compared to level at the end of the third trimester.136 Androstenedione also decreases in the postpartum period compared to values in the third trimester.136,138 DHEAS increases to values similar to nonpregnant women 1 month postpartum.139

8.4

CATECHOLAMINE PHYSIOLOGY DURING PREGNANCY

Secretion of catecholamines is not increased during pregnancy, as demonstrated by plasma and urinary catecholamine levels, which are not increased at all, or only slightly, during pregnancy.140 Even in the context of hypertension or preeclampsia, plasma catecholamines are only slightly elevated 140 or not at all,141 and urinary catecholamines are normal.142 Maternal catecholamines do not cross the placental barrier easily. Even in the context of high circulating concentrations of catecholamines in the maternal plasma such as a pheochromocytoma, the umbilical cord blood contains <10% of the maternal concentration.143 The placental cells have noradrenaline transporters that enable intracellular uptake of catecholamines, and they also contain catecholamine-metabolizing enzymes such as monoamine oxidase (MAO) and catechol-Omethyltransferase (COMT), which inactivate catecholamines.144 However, excess catecholamines during pregnancy, as in patients with pheochromocytoma, might induce vasoconstriction in the placental vascular bed and may be responsible for placental abruption and intrauterine hypoxia.140

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51. Mihrshahi R, Lewis JG, Ali SO. Hormonal effects on the secretion and glycoform profile of corticosteroid-binding globulin. J Steroid Biochem Mol Biol 2006;101(4–5):275–85. 52. Khan MS, Adent D, Rosner W. Humancorticosteroid binding globulin is secreted by a hepatoma-derived cell line. J Steroid Biochem 1984; 20(2):677–8. 53. Hammond G, Smith C, Goping I, Underhill D, Harley M, Reventos J, et al. Primary structure of human corticosteroid binding globulin, deduced from hepatic and pulmonary cDNAs, exhibits homology with serine protease inhibitors. Proc Natl Acad Sci U S A 1987;84(15):5153–7. 54. Misao R, Iwagaki S, Sun WS, Fujimoto J, Saio M, Takami T, et al. Evidence for the synthesis of corticosteroid-binding globulin in human placenta. Horm Res 1999;51(4):162–7. 55. Miska W, Pen˜a P, Villegas J, Sanchez R. Detection of a CBG-like protein in human Fallopian tube tissue. Andrologia 2004;36(1):41–6. 56. Misao R, Hori M, Ichigo S, Fujimoto J, Tamaya T. Corticosteroid-binding globulin mRNA levels in human uterine endometrium. Steroids 1994; 59(10):603–7. 57. Misao R, Nakanishi Y, Fujimoto J, Iwagaki S, Tamaya T. Levels of sex hormone-binding globulin and corticosteroid-binding globulin mRNAs in corpus luteum of human subjects: correlation with serum steroid hormone levels. Gynecol Endocrinol 1999;13(2):82–8. 58. Nenke MA, Zeng A, Meyer EJ, Lewis JG, Rankin W, Johnston J, et al. Differential effects of estrogen on corticosteroid-binding globulin forms suggests reduced cleavage in pregnancy. J Endocr Soc 2017;1:202–10 (March 2017). 59. Rosenthal HE, Slaunwhite Jr WR, Sandberg AA. Transcortin: a corticosteroid-binding protein of plasma. X. Cortisol and progesterone interplay and unbound levels of these steroids in pregnancy. J Clin Endocrinol Metab 1969;29:352–67. 60. Jung C, Ho JT, Torpy DJ, Rogers A, Doogue M, Lewis JG, et al. A longitudinal study of plasma and urinary cortisol in pregnancy and postpartum. J Clin Endocrinol Metab 2011;96(5):1533–40. 60a. Chico A, Manzanares JM, Halperin I, Martinez de Osaba MJ, Adelantado J, Webb SM. Cushing’s disease and pregnancy: Report of six cases. Eur J Obstet Gynecol Reprod Biol 1996;64:143–6. 61. Scott EM, McGarrigle HH, Lachelin G. The increase in plasma and saliva cortisol levels in pregnancy is not due to the increase in corticosteroidbinding globulin levels. J Clin Endocrinol Metab 1990;71:639–44. 62. Potter JM, Mueller UW, Hickman PE. Corticosteroid binding globulin in normotensive and hypertensive human pregnancy. Clin Sci 1987;72:725–35. 63. Demey-Ponsart E, Foidart JM, Sulon J, Sodoyez JC. Serum CBG, free and total cortisol and circadian patterns of adrenal function in normal pregnancy. J Steroid Biochem 1982;16:165–9. 64. Benassayag C, Souski I, Mignot T-M, Robert B, Hassid J, Duc-Goiran P, et al. Corticosteroid-binding globulin status at the fetomaternal interface during human term pregnancy1. Biol Reprod 2001;64(3):812–21. 65. Mitchell E, Torpy DJ, Bagley CJ. Pregnancy-associated corticosteroid-binding globulin: high resolution separation of glycan isoforms. Horm Metab Res 2004;36(6):357–9. 66. Strel’chyonok OA, Avvakumov GV. Specific steroid-binding glycoproteins of human blood plasma: novel data on their structure and function. J steroid Biochem 1990;35(5):519–34. 67. Murphy BEP. Human fetal serum cortisol levels related to gestational age: evidence of a midgestational fall and a steep late gestational rise independent of sex or mode of delivery. Am J Obstet Gynecol 1982;144:276–82. 68. Sandberg AA, Slaunwhite R, Carter AC. Transcortin: a corticosteroid-binding protein of plasma. III. The effects of various steroids. J Clin Invest 1960;39:1914–26. 69. Magiakou MA, Mastorakos G, Rabin D, Margioris AN, Dubbert B, Calogero AE, et al. The maternal hypothalamic-pituitary-adrenal axis in the third trimester of human pregnancy. Clin Endocrinol 1996;44(4):419–28. 70. Phocas I, Sarandakou A, Rizos D. Maternal serum total cortisol levels in normal and pathologic pregnancies. Int J Gynaecol Obstet 1990;31(1):3–8. 71. Abou-Samra AB, Pugeat M, Dechaud H, Nachury L, Bouchareb B, Fevre-Montange M, et al. Increased plasma concentration of N-terminal betalipotrophin and unbound cortisol during pregnancy. Clin Endocrinol 1984;20(2):221–8. 72. Abrao ALP, Leal SC, Falcao DP. Salivary and serum cortisol levels, salivary alpha-amylase and unstimulated whole saliva flow rate in pregnant and non-pregnant. Rev Bras Ginecol Obstet 2014;36(2):72–8. 73. Ambroziak U, Kondracka A, Bartoszewicz Z, Krasnodębska-Kilja
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