Adrenocortical sensitivity to ACTH in humans

BIOL PSYCHIATRY 1988;24:105-108

Adrenocortical

105

Sensitivity to ACTH in Humans

K. Ranga Rama Krishnan, James C. Ritchie, Ananth N. Manepalli, Charles B. Nemeroff, and Bernard J. Carroll

Introduction Depressed patients show a blunted plasma adrenocorticotrophin (ACTH) response to corticotrophin-releasing factor (CRF) (Gold et al. 1984, 1986; Holsboer et al. 1984). However, the plasma cortisol response following stimulation with CRF in patients with depression remains normal or increased (Gold et al. 1986; Holsboer et al. 1984). The patients with depression have a proportionately higher cortisol response to the ACTH released during stimulation with CRF than do controls. Gold et al. (1986) hypothesized that this may be due to (1) hyperplasia and hyperresponsiveness of the adrenal cortex in patients with depression or (2) may reflect the fact that the higher ACTH responses in the normal controls substantially exceeded the amounts needed for a maximal cortisol response. To assess the relative importance of these two factors, it is important to know what the adrenocortical sensitivity to ACTH really is. At least two studies indicate that threshold adrenocortical responses are obtained in humans with doses of ACTH,_,, as low as 30-50 ng whereas maximal responses occurred with doses of 250400 ng (Landon et al. 1967; Leclerq et al. 1972). The volume of distribution for ACTH has been

From Duke University Medical Center, Durham, NC. Supported by Clinical Associate Physician Award NIH-RR0030 and General Clinical Centers Research Pmgram MH42088, MH40159, and MH40524. Address reprint requests to Dr. K.R.R. Krishnan, Doke University Medical Center, Box 3215, Durham, NC 27710. Received July 1, 1987; revised October 26, 1987.

0 1988 Society of Biological Psychiatry

reported to be approximately 14 liters (Liotta et al. 1978). If we assume such a volume of distribution for ACTH, the doses of ACTH required for maximal adrenal stimulation would have yielded plasma ACTH elevations of only 6-9.7 pmol/liter. These values are similar to, or lower than, what is seen in normal controls after CRF administration. If this hypothesis is correct, then the ACTH values reported by Gold et al (1986) should have been associated with maximal plasma cortisol concentrations in normal controls. To test this hypothesis, we measured adrenocortical responses to ACTHI_24r measuring both ACTH and cortisol simultaneously.

Methods Normal volunteers (aged 20-25 years) were given 4 mg of dexamethasone orally at 1l:OO PM to obviate the confounding influence of spontaneous ACTH and cortisol secretion. ACTHI_ solutions were infused over a 30-min period, beginning at 8:00 AM the next day. The individual infusion rates are given in Figure 1. The ACTHI_ solution was prepared under sterile conditions as follows: 2.5 ml of sterile 1 N HCl was substituted for 2.5 ml of normal saline in a 250-ml saline infusion bag to produce a 0.01 N solution of HCl in saline. Of ACTH1_24(Cortrosyn) 250 p.g was dissolved in 2 ml of sterile acid albumin solution (acid albumin solution-O. 1% solution of recrystallized human serum albumin brought to a pH of 3 with 30% HCl). Of this solution, 0.1 ml was added

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Brief Reports

700,. ACT+_,,

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Figure 1. Plasma cortisol (0) and ACTH (Of concentmtions in four normal subjects who received varying doses of ACTH1_24infusions. Each subject received 4 mg of dexamethasone orally the night before at 1I:00 PM.The ACTH infusion was started at 890 AM the following morning and lasted from 0 to f 30 min.

to the saline bag to produce a 50-ngfmf solution

of ACTHi+,. Bag concentrations were measured before and after each experiment. No loss of ACTH concentration was noted. ACTH was measured by ra~oimmunoassay (MA) method (Krishnan et al. 1986). The antibody used binds to ACTH, 21more easily than

to ACTHI_+ so different standards were used for measuring ACTHI+. The ACTH curves obtained reflect only ACTHL_24.The sensitivity of the assay was 0.22 pmol/liter. The intraassay coefficient of v~ation (CV) was 7%; the interassay coefficient of variation was 12%. Cortisol was measured by a competitive protein

BIOL PSYCHIATRY 1988; 24105-108

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binding method (Ritchie et al. 1985). The intraassay CV was 5.6%; the interassay CV was 8.9%.

Results The measured ACTH infusion rates in the four individuals were 0.4 pmol/min, 1.7 pmoYmin, 3.6 pmol/min, and 4.3 pmol/min. The results are shown in Figure 1. Large changes in plasma cortisol concentrations occurred with minimal changes in plasma ACTHI+, concentrations in all four individuals. The changes in plasma ACTH concentrations were less than 5 pmohliter and were below the detection limit of most commonly used ACTH assays.

Discussion The changes in plasma cortisol concentration were far higher than those observed by Gold et al. (1986) after CRF administration. The ACTH changes were far below those observed by Gold et al. (1986). Our results suggest that the ACTH changes observed by Gold et al. (1986) after CRF should have been associated with maximal plasma cortisol concentrations in both normal controls and depressed patients. However, it must be clearly understood that this study is not fully comparable with that of Gold et al. (1986). We were examining the relationship between ACTH and cortisol following the administration of ACTH in dexamethasone-suppressed subjects and not after the administration of CRF. The administration of dexamethasone might have altered the sensitivity of the adrenocortical response to ACTH, although there is little evidence for this at the doses used (Graybeal et al. 1985). Therefore, the hypothesis that the normal cortisol response associated with a blunted ACTH response to CRF in patients with depression is solely due to hyperresponsiveness of the adrenal cortex to ACTH is not adequate. An alternative hypothesis is that alteration in mechanisms that affect adrenocortical responsivity to ACTH may be responsible for the observation of blunted ACTH, but normal cortisol response following CRF in depressed patients, as reported by Gold

107

et al. ( 1986), becomes more tenable. Evidence for such mechanisms has been described recently (Fehm et al. 1984; Krishnan et al. 1986). Currently, there are three possible candidates: (1) direct sympathetic innervation of the adrenal cortex, (2) indirect sympathetic activation of the adrenal cortex by a paracrine intermediate step involving the adrenal medulla, and (3) humoral factors that modulate adrenal responsiveness to ACTH (Krishnan et al. 1986). Humoral factors that are known to affect adrenocortical sensitivity to ACTH include gamma3 melanocyte-stimulating hormone interfemns, prostaglandins, and other peptides derived from the thymus and thyroid gland (Krishnan et al. 1986). Further studies are needed to identify and characterize the role of these mechanisms in depression and in the normal physiology of the HPA system.

References Fehm HL, Holl R, Kline E (1984): Evidence of extrapituitary mechanisms mediating the morning peak of plasma cortisol in man. J Clin Endocrinol Merab 58:410-414. Gold PW, Chrousos G, Kellner C (1984): Psychiatric implications of basic and clinical studies with cotticotmpin releasing factor. Am J Psychiatry 141:619427. Gold PW, Loriaux L, Roy A, et al. (1986): Responses to corticotropin releasing hormone in the hypercortisolism of depression and Cushing’s Disease. N Engl J Med 3141329-1335. Graybeal ML, Fang VS. Laudau RL (1985): Enhancement of adrenal cortisol secretion after intravenous high dose dexamethasone. Clin Endocrinol Merab 61607-611. Holstmer F, et al (1984): Blunted corticottopin and normal cortisol response to human corticotropin releasing factor in depression. N Engl J Med 311:1127. Krishnan KRR, Nemeroff CB, Manepalli AN, et al. (1986): Physiology of human HPA regulation in depression. In Shagass C, Josiassen RC., Bridger WH, Weiss KJ, Stoff J, Simpson GM (eds), BiologicalPsychiatry. New York: Elsevier, pp 808-810. Landon J, James HT. Wharton MJ, et al. (1%7): Threshold adrenocortical sensitivity in man and its possible application to corticotrophin bioassay. Lancer ii:697-700. LeCleq R, Copinschi G, Bruno OD (1972): Adrenocortical responsiveness to physiological amounts of ACTH1_24. Effect of prior administration of dexamethasone. Horm Merab Res 4:202-206.

Liotta AS, Li CH, Schussler GC, Kmiger DT (1978): Comparative metabolic clearance rate, volume of distribution and plasma half-life of human lipotropin and ACTH. Life Sci 23:2323-2330.

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Ritchie JC, Carroll BJ, Olton R, et al. (1985): Plasma cortisol determination for the Dexamethasone Suppression Test. Arch Gen Psychiatry 42:493-491, Sayers G (1977): Bioassay of ACTH using isolated cortex cells (applications: structure activity relationship for ACTH

and analogues, assay of corticotrophin-releasing factor, and assay of plasma ACTH). In Krieger DT, Ganog WF teds), ACTH and Related Peptides: Structure. Regularions. and Action. New York: New York Academy of Sciences.

Suppression of Plasma Melatonin by a Single Dose of the Benzodiazepine Alprazolam in Humans Iain M. McIntyre,

Graham D. Burrows, and Trevor R. Norman -

Introduction Disturbances in the secretion of the pineal hormone melatonin in affective disorders have now been described by several groups of investigators. Wetterberg et al. (1979) reported lower melatonin in a woman during an unipolar depressive episode compared with levels measured during an euthymic period. Wirz-Justice and Arendt ( 1979) noted lower melatonin levels in patients with unipolar depression at 830 AM compared with healthy control subjects. Subsequent studies have confirmed these differences in nocturnal evaluation of melatonin (Mendlewicz et al. 1979; Beck-Friis et al. 1984; Claustrat et al. 1984; Nair et al. 1984; Brown et al. 1985; McIntyre et al 1986a). Lewy and colleagues (1979) reported higherplasmamelatonin levels in bipolar patients during the manic phase than when in the depressed phase and showed that melatonin concentrations in the manic phase were higher than those measured in normal control subjects. More

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recently, plasma melatonin levels have been reported to be significantly lower in patients with panic disorder compared with normal control subjects (McIntyre et al. 1986b, 1987). Despite efforts by most investigators to employ drug-free periods prior to investigation of patients with affective disorders, the possible influence of medications such as antidepressants and antianxiety compounds on nocturnal melatonin levels cannot be ignored. Most “shortterm” human studies indicate that tricyclic antidepressants increase plasma melatonin levels or leave them unchanged (Cowen et al. 1985: Thompson et al. 1985). The “chronic” effects of several months of treatment in humans have not been reported. In animal studies, however, there is evidence that tricyclics induce pineal beta-adrenergic receptor subsensitivity and lower nocturnal melatonin levels (Heydom et al. 1982). The time required for such effects to disappear after cessation of treatment has not been established. If similar changes occur in humans, the length of drug-free period prior to examination of melatonin levels will be critical. As most patients with depressive illness and panic disorder are treated with benzodiazepines, the possible effects of those compounds on melatonin concentrations also warrant considera-