Cortisol and corticosterone response after syn-corticotropin in relationship to dexamethasone suppressibility of cortisol

How to measure glucocorticoid receptor's sensitivity in patients with stress-related psychiatric disorders

Stress is a state of derailed homeostasis and a main environmental risk factor for psychiatric diseases. Chronic or uncontrollable stress may lead to a dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, which is a common feature of stress-related psychiatric disorders. One of the key mechanisms underlying a disturbed HPA axis is an impaired function of the glucocorticoid receptor (GR) with an enhanced or reduced feedback sensitivity for glucocorticoids and subsequently altered concentrations of peripheral cortisol. GR function is regulated by a multiprotein complex including the different expression of the hsp90 co-chaperone FK 506 binding protein 51 (FKBP5) that may be genetically determined or acquired in response to stressful stimuli. Specific patterns of a dysregulation of the HPA axis and GR function are found in different stress-related psychiatric entities e.g. major depression, job-related exhaustion or posttraumatic stress disorder. GR challenge tests like the dexamethasone-suppression test (DST), the dexamethasone-corticotropin-releasing hormone (dex-CRH) test or most recently the analysis of the dexamethasone-induced gene expression are employed to sensitively measure HPA axis activity in these disorders. They provide information for a stratification of phenotypic similar but neurobiological diverse psychiatric disorders. In this review we present a synopsis of GR challenge tests with a focus on the application of the DST, the CRH test and the dex-CRH test as well as the dexamethasone-induced gene expression in stress-related psychiatric entities.

Behavioral and neurobiological consequences of prolonged glucocorticoid exposure in rats: relevance to depression

Stress is a critical environmental trigger for the development of clinical depression, yet little is known about the specific neurobiological mechanisms by which stress influences the development of depressive symptomatology. Animal models provide an efficient way to study the etiology of human disorders such as depression, and a number of preclinical models have been developed to assess the link between stress, glucocorticoids, and depressive behavior. These mode ls typically make use of repeated exposure to physical or psychological stressors in rodents or other small laboratory animals. This review focuses primarily on a recently developed preclinical model of depression that uses exogenous administration of the stress hormone corticosterone (CORT) in rodents instead of exposure to physical or psychological stressors. Repeated CORT administration in rats or mice produces reliable behavioral and neurobiological alterations that parallel many of the core symptoms and neurobiological changes associated with human depression. This provides an opportunity to study behavior and neurobiology in the same animal, so that the neurobiological factors that underlie specific symptoms can be identified. Taken together, these findings suggest that exogenous CORT administration is a useful method for studying the relationship between stress, glucocorticoids, and depression. Further study with this model may provide important new data regarding the neurobiological bases of depression.

The combined dexamethasone/CRH Test (DEX/CRH test) and prediction of acute treatment response in major depression

Background

In this study the predictive value of the combined dexamethasone/CRH test (DEX/CRH test) for acute antidepressant response was investigated.

Methodology/Principal Findings

In 114 depressed inpatients suffering from unipolar or bipolar depression (sample 1) the DEX/CRH test was performed at admission and shortly before discharge. During their stay in the hospital patients received different antidepressant treatment regimens. At admission, the rate of nonsuppression (basal cortisol levels >75.3 nmol/l) was 24.6% and was not related to the later therapeutic response. Moreover, 45 out of 114 (39.5%) patients showed an enhancement of HPA axis function at discharge in spite of clinical improvement. In a second sample, 40 depressed patients were treated either with reboxetine or mirtazapine for 5 weeks. The DEX/CRH test was performed before, after 1 week, and after 5 weeks of pharmacotherapy. Attenuation of HPA axis activity after 1 week was associated with a more pronounced alleviation of depressive symptoms after 5-week mirtazapine treatment, whereas downregulation of HPA system activity after 5 weeks was related to clinical response to reboxetine. However, early improvement of HPA axis dysregulation was not necessarily followed by a beneficial treatment outcome.

Conclusions/Significance

Taken together, performance of a single DEX/CRH test does not predict the therapeutic response. The best predictor for response seems to be an early attenuation of HPA axis activity within 1 or 2 weeks. However, early improvement of HPA system dysfunction is not a sufficient condition for a favourable response. Since a substantial part of depressive patients display a persistence of HPA axis hyperactivity at discharge, downregulation of HPA system function is not a necessary condition for acute clinical improvement either. Our data underline the importance of HPA axis dysregulation for treatment outcome in major depression, although restoration of HPA system dysfunction seems to be neither a necessary nor a sufficient determinant for acute treatment response.

The cardiovascular toll of stress

Psychological stress elicits measurable changes in sympathetic-parasympathetic balance and the tone of the hypothalamic-pituitary-adrenal axis, which might negatively affect the cardiovascular system both acutely-by precipitating myocardial infarction, left-ventricular dysfunction, or dysrhythmia; and chronically-by accelerating the atherosclerotic process. We provide an overview of the association between stress and cardiovascular morbidity, discuss the mechanisms for this association, and address possible therapeutic implications.

Neuroendocrinological mechanisms of actions of antidepressant drugs

Noradrenaline or serotonin (5-HT) reuptake-inhibiting antidepressants such as reboxetine or citalopram acutely stimulate cortisol and adrenocorticotrophic hormone (ACTH) secretion in healthy volunteers, whereas mirtazapine acutely inhibits the ACTH and cortisol release, probably due to its antagonism at central 5-HT(2) and/or H(1) receptors. These differential effects of antidepressants on cortisol and ACTH secretion in healthy subjects after single administration are also reflected by their different time course in the down-regulation of hypothalamic-pituitary-adrenocortical (HPA) axis hyperactivity in depressed patients as assessed by serial dexamethasone (DEX)/corticotrophin-releasing hormone (CRH) tests: Reuptake-inhibiting antidepressants such as reboxetine gradually normalise HPA axis hyperactivity in depressed patients during several weeks of treatment via up-regulation of mineralocorticoid and glucocorticoid receptor function and by step-by-step restoration of the disturbed feedback control. By contrast, mirtazapine markedly reduces HPA axis activity in depressed patients within 1 week, but there is a partial re-enhancement of HPA hormone secretion after several weeks of therapy. In all studies performed to date, the short-term effects of daily treatment with antidepressants on the DEX/CRH test results are comparable in responders and nonresponders. Moreover, a reduction in HPA axis activity is not necessarily followed by a favourable clinical response and some depressed patients keep on showing nonsuppression in the DEX/CRH test despite clinical improvement. Therefore, the importance of HPA axis dysregulation for the short-term efficacy of antidepressants continues to be a matter of debate. However, there are convincing data suggesting that persisting nonsuppression in the DEX/CRH test despite clinical remission predicts an enhanced risk for relapse of depressive symptomatology with respect to the medium- and long-term outcome.

Adrenal cortical responses to low- and high-dose ACTH(1-24) administration in major depressives vs. matched controls

Increased hypothalamo-pituitary-adrenocortical (HPA) axis activity occurs in 30-50% of patients with major depression. This includes normal-to-increased adrenal cortical hormone (cortisol) secretion in spite of reduced corticotropin (ACTH) stimulation. A possible explanation is increased adrenal responsiveness to ACTH. Supporting this possibility is the finding of increased adrenal volume, which reverts to normal with successful treatment. Eight female and six male patients with major depression, and eight female and six male individually matched controls, underwent two test sessions 5-7 days apart. On the first day, a low ACTH(1-24) dose (0.014 microg/kg i.v.), equivalent to 1 microg in a 70-kg individual, was given. On the second day, a supramaximal stimulating dose (250 microg i.v.) was given. Serial blood samples were analyzed for immunoreactive (IR-)ACTH, ACTH(1-39), and cortisol. There were no significant sex or patient-control differences in IR-ACTH areas under the curve (AUCs) following low-dose ACTH(1-24), and the correlation between patient and matched control AUCs was +0.71, indicating good correspondence in the amount of circulating ACTH(1-24) available for adrenal stimulation. There were no significant sex or patient-control differences in cortisol response and no significant interaction between dose and subject group, indicating that patients did not differ from controls in their cortisol responses to either low- or high-dose ACTH(1-24). These findings do not indicate increased adrenal cortical responsiveness in patients with major depression. Neurochemical/neurohormonal and neural stimulatory factors other than ACTH might be responsible for the increased adrenal gland size and cortisol secretion, in spite of reduced pituitary ACTH secretion, that has been reported in this illness.

Neuroendocrine aspects of hypercortisolism in major depression

A consistent finding in biological psychiatry is that hypothalamic-pituitary-adrenal (HPA) axis physiology is altered in humans with major depression. These findings include hypersecretion of cortisol at baseline and on the dexamethasone suppression test. In this review, we present a process-oriented model for HPA axis regulation in major depression. Specifically, we suggest that acute depressions are characterized by hypersecretion of hypothalamic corticotropin-releasing factor, pituitary adrenocorticotropic hormone (ACTH), and adrenal cortisol. In chronic depressions, however, enhanced adrenal responsiveness to ACTH and glucocorticoid negative feedback work in complementary fashion so that cortisol levels remain elevated while ACTH levels are reduced. In considering the evidence for hypercortisolism in humans, studies of nonhuman primates are presented and their utility and limitations as comparative models of human depression are discussed.

Decreased pituitary volume in patients with bipolar disorder

BACKGROUND

Neuroendocrinologic investigations in bipolar disorder have suggested abnormalities in pituitary function. However, few imaging studies have evaluated possible anatomical differences in this brain structure in mood disorder patients. Our aim was to examine potential abnormalities in pituitary volume in patients with bipolar and in a comparison group of patients with unipolar disorder.

METHODS

We measured the volumes of the pituitary gland in 23 patients with bipolar disorder (mean +/- s.d. = 34.3 +/- 9.9 years) and 13 patients with unipolar disorder (41.2 +/- 9.6 years), and 34 healthy control subjects (36.6 +/- 9.6 years) using 1.5 mm thick T1-weighted coronal 1.5 T MRI images. All measurements were done blindly by a trained rater.

RESULTS

Patients with bipolar disorder had significantly smaller pituitary volumes than healthy control subjects (mean volume +/- s.d. = 0.55 +/- 0.15 ml and 0.68 +/- 0.20 ml, respectively; ANCOVA, F = 8.66, p = 0.005), and than patients with unipolar disorder (0.70 +/- 0.12 ml, F = 5.98, p = 0.02). No differences were found between patients with unipolar disorder and healthy control subjects (F = 0.01, p = 0.91).

CONCLUSIONS

To our knowledge, this is the first study that reports smaller pituitary volumes in bipolar disorder. Our findings suggest that detectable abnormalities in pituitary size are present in patients with bipolar disorder, which may reflect a dysfunctional HPA axis.

Effects of antidepressant treatment on corticotropin-induced cortisol responses in patients with melancholic depression

To date, there appears to be no consensus of opinion as to whether the adrenal glands are hyperresponsive during depression and, if so, whether this a state-dependent phenomenon. We aimed to determine the effects of antidepressant treatment on ACTH-induced cortisol responses in patients with melancholic depression. Seven female patients with DSM-III-R major depressive disorder, non-psychotic, melancholic subtype, were evaluated using the following rating scales: the Hamilton Depression Rating Scale, the Montgomery-Asberg Depression Rating Scale and the Newcastle Endogenicity Scale. All subjects were then given an intravenous bolus dose (250 micrograms) of tetracosactrin, a potent stimulus of adrenocortical hormone secretion. Plasma levels of cortisol were measured at times 0, + 30, + 60, + 90, + 120 and + 180 min. Patients were then randomised to receive either 50 mg of sertraline or 20 mg of paroxetine (both of which are selective serotonin re-uptake inhibitors) and were re-tested while medication-free. Treatment resulted in a significant decrease in delta (the difference between the baseline values and the maximum increase post-ACTH administration) cortisol values of 1633.3 +/- 378.5 nmol/l vs. 595.1 +/- 207.7 nmol/l. Successful pharmacological treatment of major depressive disorder appears to be associated with a reduction in ACTH-induced cortisol release in drug-free patients.

Corticotropin-releasing hormone challenge in prepubertal major depression

This study investigates cortisol and ACTH (corticotropin) responses to an infusion of human CRH (corticotropin-releasing hormone) in prepubertal children with major depressive disorder (MDD). Following a period of 24 hours of adaptation to the laboratory environment with an intravenous catheter in place, 34 children with MDD and 22 healthy controls received 1 microgram/kg of human CRH at 5:00 PM. Blood samples for cortisol and ACTH were measured at baseline and post-CRH. Overall, there were no significant differences between the MDD and the normal controls in baseline or post CRH stimulation values of either cortisol or ACTH. Melancholic (n = 4) patients had significantly higher baseline cortisol levels than nonmelancholic (n = 24) patients. Compared with the outpatients and the nonmelancholics, the inpatients (n = 10) and the melancholics showed significantly lower total ACTH secretion (effect size: 0.9 and 1.4, respectively) after CRH infusion. These results are consistent with a broad literature suggesting that the HPA axis abnormalities occur less frequently in early-onset depression than reported in adult studies. The pattern of results in the subgroups of inpatients and in melancholic children, however, raise questions about possible continuities with adult studies.

Multiple steroid hormone levels in depressed patients and normal controls before and after exogenous ACTH

Forty depressed patients and 36 age- and sex-matched controls were given 250 micrograms ACTH1-24 by IV bolus. Plasma steroid hormone levels were measured prior to and 60 min after ACTH administration. The depressed patients had significantly greater cortisol (F), 11-deoxycortisol (S), androstenedione (AD), and 17 alpha-hydroxyprogesterone (17 alpha-OHP) responses (delta; p less than 0.05) and a marginally greater 11 beta-hydroxyandrostenedione (11 beta-OHAD) response (delta; p = 0.091) than the controls. There was no significant difference in the corticosterone (B) response between the two groups. With the exception of 11 beta-OHAD, all the steroid hormones were significantly negatively correlated with age in the controls, but only S and AD marginally demonstrated this relationship in the depressed patients. F, S, AD, 17 alpha-OHP, and B, but not 11 beta-OHAD, were significantly positively correlated with each other in the controls, but only F was significantly correlated with AD in the depressed patients. These data suggest that the hypercortisolemia found in some depressed patients involves increased precursor and metabolite levels both at baseline and in response to exogenous ACTH, compared to controls. Furthermore, variability in these precursors is greater in depressed patients, and their relationship to age is lost. These findings are consistent with the hypothesis that adrenal products other than cortisol also could be related to affective symptoms.

Hypercortisolism and its possible neural bases

As is clear from the pages of this journal, biological psychiatrists remain fascinated by the phenomenon of dexamethasone (DEX) resistance and the hypercortisolism of various neuropsychiatric disorders. The mere existence of the endocrine abnormalities attests to the biological reality of these disorders. Furthermore, progress continues in using the occurrence of these endocrine defects as both diagnostic and prognostic markers of disease subtypes. Progress has also been made in understanding the mechanisms underlying the endocrine defects. The adrenocortical axis is vastly complex, involving multiple hypothalamic-releasing factors under CNS control, shifting pituitary and adrenal sensitivies to hormonal signals, and feedback regulation at all three levels. What defects within this system produce DEX resistance and hypercortisolism? In this paper, we review data suggesting that the endocrine problems is, at least in part, neural in nature. Drawing upon a rodent literature, we will also suggest some models by which this can occur. The hypercortisolism found in cases of affective disorders, anorexia nervosa, Alzheimer's disease, among the very aged or the chronically stressed, is not a uniform phenomenon. Basal cortisol concentrations can be elevated in all or part of the circadian cycle. Resistance to glucocorticoid (GC) feedback inhibition (as typically demonstrated by DEX resistance) can occur; the resistance can be complete, or occur as early escape from DEX suppression. Finally, elevated basal cortisol concentrations and DEX resistance can occur independently of each other. Until the end of this review, we will conveniently refer to these variants of adrenocortical hyperactivity as "hypercortisolism." In addition, rather than using the term "hypercortisolism" for the rat, we will use "hyperadrenocorticism" (as they secrete corticosterone, rather than cortisol).

Diurnal variation of plasma corticosterone in depression

Hypersecretion of cortisol is associated with depression. Because corticosterone may show greater responsiveness than cortisol to exogenous ACTH in depression and it has behavioural effects in rodents, we determined whether depression is also associated with hypersecretion of corticosterone. Both cortisol and corticosterone were significantly elevated in depression, with greatest differences from control subjects during the afternoon and evening. The ratio of corticosterone/cortisol was constant and similar throughout the day in both depressed patients and controls. We conclude that there is no disproportionate endogenous hypersecretion of corticosterone in depression.

Consistent reduction of ACTH responses to stimulation with CRH, vasopressin and hypoglycaemia in patients with major depression

Eleven patients with major depression and 12 control subjects were administered corticotropin-releasing hormone (CRH), aqueous arginine vasopressin (AVP), and insulin hypoglycaemia (IH) to test for differences in hypothalamic-pituitary-adrenal (HPA) axis function. Patients with major depression demonstrated lower ACTH responses to CRH when compared with controls, and a trend toward such after administration of AVP. Despite lower ACTH responses in patients with depression, there were no differences in cortisol responses to these stimuli. In the CRH and AVP tests, there was no correlation between the basal cortisol and ACTH responses in either controls or patients, but in the IH test there was a negative correlation between these responses for both groups. The ACTH responses to CRH and AVP were positively correlated in controls and patients. Cortisol responses to all three provocative stimuli were positively correlated in both subject groups. These findings are consistent with the hypothesis that hypothalamic or supra-hypothalamic overactivity may be involved in the development of HPA-axis abnormalities in patients with depression.

Psychiatric implications of altered limbic-hypothalamic-pituitary-adrenocortical activity

Hormones of the limbic-hypothalamic-pituitary-adrenocortical (LHPA) system are much involved in central nervous system regulation. The major LHPA neuropeptides, corticotropin-releasing hormone (CRH), vasopressin (AVP) and corticotropin (ACTH) do not only coordinate the neuroendocrine response to stress, but also induce behavioral adaptation. Transcription and post-translational processing of these neuropeptides is regulated by corticosteroids secreted from the adrenal cortex after stimulation by ACTH and other proopiomelanocortin derived peptides. These steroids play a key role as regulators of cell development, homeostatic maintenance and adaptation to environmental challenges. They execute vitally important actions through genomic effects resulting in altered gene expression and nongenomic effects leading to altered neuronal excitability. Since excessive secretory activity of this particular neuroendocrine system is part of an acute stress response or depressive symptom pattern, there is good reason to suspect that central actions of these steroids and peptides are involved in pathophysiology determining the clinical phenotype, drug response and relapse liability. This overview summarizes the clinical neuroendocrine investigations of the author and his collaborators, while they worked at the Department of Psychiatry in Mainz. The major conclusions from this work were: (1) aberrant hormonal responses to challenges with dexamethasone, ACTH or CRH are reflecting altered brain physiology in affective illness and related disorders; (2) hormones of the LHPA axis influence also nonendocrine behavioral systems such as sleep EEG; (3) physiologically significant interactions exist between LHPA hormones, the thyroid, growth hormone, gonadal and other neuroendocrine systems; (4) hormones of the LHPA axis constitute a bidirectional link between immunoregulation and brain activity; and (5) future psychiatric research topics such as molecular genetics of affective disorders, familial risk studies, drug response analysis and neurobiology of aging will benefit from extended knowledge of neural corticosteroid effects at a clinical, cellular, and molecular level.

The assessment of abnormalities in hormonal responsiveness at multiple levels of the hypothalamic-pituitary-adrenocortical axis in depressive illness

A substantial body of data suggests that excessive cortisol secretion in depression may result from dysregulation at several sites within the hypothalamic-pituitary-adrenocortical (HPA) axis. The alterations in regulatory mechanisms are thought to result from a limbic system-hypothalamic "overdrive" of corticotropin-releasing hormone (CRH). We also have demonstrated that excessive secretion of cortisol may result from an abnormal adrenocortical responsiveness to adrenocorticotropic hormone (ACTH), and we have postulated that corticotropic cells within the pituitary mediate between excessive secretion of CRH from the hypothalamus and hypercortisolemia secondary to adrenocortical hyperplasia and enhanced sensitivity to ACTH at the adrenal cortex. The present report describes a series of clinical experiments utilizing several neuroendocrine probes, as well as computer-assisted tomography, to examine the complexities of the HPA axis dysregulation in depression. These studies support the hypothesis that a limbic system-hypothalamic disturbance results in excessive CRH secretion as well as enhanced adrenocortical activity, and that these factors contribute to excessive cortisol secretion in patients with depression. These data further support the hypothesis that endogenous affective disorders are best characterized in the framework of a generalized biological disturbance of HPA axis function which involves both central and peripheral endocrine sites.

Electrodermal activity in relation to cortisol dysregulation in depressive patients

Electrodermal activity (EDA), basal morning plasma cortisol, outcome of the dexamethasone suppression test (DST), and nocturnal urinary cortisol excretion were studied in a somewhat confined number of originally 59 depressive patients and 59 matched healthy subjects. The patients showed nocturnal hypercortisolism. According to the DST, EDA and cortisol dysregulation were unrelated. In the total patient group, the correlations between EDA and cortisol in plasma and in urine were small and insignificant. However, in suicide attempters, in nonsuicidal patients, and in the healthy subjects, complex patterns of correlations were found between tonic electrodermal activity, electrodermal responsivity, basal morning plasma cortisol, and nocturnal urinary cortisol. Some inconsistencies in the patterns may be explained by differences in the sampling of data. Future research should try to delineate possible relationships between EDA and hormones on all levels of the hypothalamic-pituitary-adrenocortical axis.

Corticotropin and cortisol response to human CRH as a probe for HPA system integrity in major depressive disorder

To explore the integrity of the hypothalamic-pituitary-adrenal (HPA) system in major depressive disorder, 12 patients and normal controls matched for sex, age, and body weight received 100 micrograms synthetic human corticotropin-releasing hormone (hCRH) as an i.v. bolus dose. Compared to controls, depressed patients showed an elevation in baseline cortisol and a significant attenuation of net adrenocorticotropin (ACTH) responses, while cortisol secretion in response to hCRH was normal. These abnormalities in HPA axis function and apparent discordances in the interrelationships of ACTH and cortisol baseline and net stimulation responses between depressed patients and normal controls indicate, at least in part, a derangement of the glucocorticoid-dependent negative feedback circuitry and support the hypothesis that HPA hyperactivity in depression involves neurotransmitter-mediated hypothalamic hypersecretion of CRH.

Cortisol response to ACTH infusion in depressed patients: comparison with age-, sex-, and weight-matched normal subjects

Adrenal responsiveness to Cosyntropin (synthetic ACTH) was investigated in five patients with major depression and five individually matched normal subjects. Three hours following suppression of endogenous ACTH secretion with dexamethasone (1 mg orally), the adrenal response to a 10-min infusion of Cosyntropin (0.05 micrograms/kg body weight) was monitored for 2 1/2 hr by plasma cortisol measured at 15-min intervals. The depressed patients had significantly higher baseline plasma cortisol, but not higher baseline ACTH, than the controls. During the 3-hr post-dexamethasone (and prior to Cosyntropin infusion), the depressed patients maintained significantly higher cortisol secretion, but not higher ACTH secretion, than the controls. After Cosyntropin infusion, there were no differences in ACTH and cortisol increases between the two groups. These findings stand in contrast to previous reports of enhanced adrenal responsiveness to the administration of much larger amounts of Cosyntropin in major depression.

Stable adrenocorticotropin-stimulated 11-beta-hydroxylase activity but loss of age-related changes in patients with hypercortisolemia

Eleven-beta-hydroxylase activity was measured before and after acute adrenocorticotrophic hormone (ACTH) stimulation in 28 controls, 25 depressed Dexamethasone Suppression Test (DST) suppressors, 13 DST nonsuppressor patients, and 8 patients with Cushing's syndrome to investigate changes in states of cortisol hypersecretion. Eleven-beta-hydroxylase activity was equivalent among groups both before and after stimulation. Such 11-beta-hydroxylase stability, however, resulted in higher cortisol and 11-deoxycortisol poststimulation levels in both depressed DST nonsuppressors and Cushing's patients than in controls. Basal 11-beta-hydroxylase activity is positively correlated and 11-deoxycortisol is negatively correlated with age in controls and DST suppressors, but not in the patients tested with evidence of cortisol hypersecretion. These findings suggest that in vivo basal 11-beta-hydroxylase activity rises gradually with age, but does not rise after acute administration of exogenous ACTH. The age relationship is lost in states of cortisol hypersecretion, but the lack of response to acute exogenous ACTH is not affected.

Human corticotropin-releasing hormone in depression--correlation with thyrotropin secretion following thyrotropin-releasing hormone

Twenty-two subjects (11 patients with major endogenous depression and 11 controls) received an intravenous test dose of 100 micrograms human corticotropin-releasing hormone (h-CRH). Corticotropin (ACTH), but not cortisol, responses were blunted in depressives. Basal cortisol secretion was higher in depressives than in controls and was negatively correlated to the corticotropin response following h-CRH. This finding indicates the integrity of the glucocorticoid-dependent negative feedback regulation in depression and supports the view that hypercortisolism in depression is primarily due to a suprapituitary disturbance. Comparison of ACTH responses after h-CRH with thyrotropin (TSH) output following thyrotropin-releasing hormone (TRH) revealed a positive correlation (r = 0.65, p less than 0.001). The concordance between ACTH and TSH responses after specific challenges suggests that regulation of both systems is at least in part under a common control.