Rate-sensitive inhibition of ACTH release in depression

Hypothalamic-Pituitary--Adrenal Axis-Feedback Control

The hypothalamo-pituitary-adrenal axis (HPA) is responsible for stimulation of adrenal corticosteroids in response to stress. Negative feedback control by corticosteroids limits pituitary secretion of corticotropin, ACTH, and hypothalamic secretion of corticotropin-releasing hormone, CRH, and vasopressin, AVP, resulting in regulation of both basal and stress-induced ACTH secretion. The negative feedback effect of corticosteroids occurs by action of corticosteroids at mineralocorticoid receptors (MR) and/or glucocorticoid receptors (GRs) located in multiple sites in the brain and in the pituitary. The mechanisms of negative feedback vary according to the receptor type and location within the brain-hypothalmo-pituitary axis. A very rapid nongenomic action has been demonstrated for GR action on CRH neurons in the hypothalamus, and somewhat slower nongenomic effects are observed in the pituitary or other brain sites mediated by GR and/or MR. Corticosteroids also have genomic actions, including repression of the pro-opiomelanocortin (POMC) gene in the pituitary and CRH and AVP genes in the hypothalamus. The rapid effect inhibits stimulated secretion, but requires a rapidly rising corticosteroid concentration. The more delayed inhibitory effect on stimulated secretion is dependent on the intensity of the stimulus and the magnitude of the corticosteroid feedback signal, but also the neuroanatomical pathways responsible for activating the HPA. The pathways for activation of some stressors may partially bypass hypothalamic feedback sites at the CRH neuron, whereas others may not involve forebrain sites; therefore, some physiological stressors may override or bypass negative feedback, and other psychological stressors may facilitate responses to subsequent stress.

Cushing’s disease and melancholia

Striking similarities exist in the endocrinology of Cushing's disease and melancholic depression.Laboratory abnormalities, which have been found in both, include raised urinary,plasma and salivary cortisol, non-suppression of cortisol in the dexamethasone suppression test and adrenocorticotrophin (ACTH) hypersecretion. The hypercortisolism can be so severe in melancholic depression that it is difficult to distinguish from Cushing's disease and has been described as a "pseudo-Cushing's" state. Cerebrospinal fluid corticotrophin-releasing hormone (CRH) levels have been found to be lower in patients with Cushing's disease than in depressed subjects. Dynamic endocrine tests may help to distinguish between the two disorders.An exaggerated response to synacthen has been found in both but a reduced ACTH response to CRH occurs in depression, unlike those with Cushing's disease who show ACTH hyper-responsiveness. Other tests, which may help to distinguish between the two disorders,include the dexamethasone-CRH test, the naloxone test, the insulin-induced hypoglycemia test and the desmopressin stimulation test. Similarities in psychiatric symptoms have been recognised for many years. More recently, the physical complications of melancholic depression have been noted. These include osteoporosis, an increased risk of death from cardiovascular disease, hypertension, a redistribution of fat to intra abdominal sites and insulin resistance. Cushing's disease shares these physical complications and we propose that the common underlying factor is excessive plasma glucocorticoids. The increasing recognition of the physical complications and the increased morbidity and mortality in those who suffer from depression underscores the necessity for early detection and treatment of this illness and screening for undetected physical complications.

Hypothalamic-pituitary-adrenal axis early-feedback responses are preserved in melancholic depression: a study of sertraline treatment

Major depression with melancholia is associated with hypercortisolaemia. Loss of the early-phase of negative feedback - acute suppression of ACTH in response to rising cortisol levels - is the subject of conflicting reports in patients with major depression. Using a within-subjects design, six patients with DSM-IIIR melancholic depression received a 60 min infusion of hydrocortisone at 0900 with measurement of ACTH and cortisol before and after 4 weeks of antidepressant treatment. All patients responded clinically. ACTH responses (early feedback) did not differ between test conditions. Baseline cortisol fell significantly following treatment response. This provides further evidence for the preservation of the acute phase of negative feedback, even in the presence of hypercortisolism. Copyright 2000 John Wiley & Sons, Ltd.

Differential effects of hydrocortisone and dexamethasone on cortisol suppression in a child psychiatric population

The suppressive effect of hydrocortisone and dexamethasone on salivary cortisol was investigated in a 2-year study of pituitary-adrenal function in a variety of child psychiatric patients and healthy controls. Symptomatology was assessed using the Child Behavioral Checklist (CBCL). Cortisol day profiles were assessed at 2-h intervals from 0800 to 2000 h on three occasions. Dexamethasone and hydrocortisone were administered orally twice at 2000 h, the doses being adjusted for bodyweight according to the standard dexamethasone suppression test. Fifty-one patients, including patients with dysthymia, oppositional defiant disorder, pervasive developmental disorder, and attention deficit hyperactivity disorder, and ten age and sex matched controls participated. Basal cortisol levels in patients were generally lower than in controls. Both dexamethasone and hydrocortisone were effective in suppressing salivary cortisol, although dexamethasone was somewhat more potent and its effect lasted longer. Hyporesponsiveness to hydrocortisone, but not to dexamethasone, distinguished patients with dysthymia and oppositional defiant disorder from controls. Responsiveness to hydrocortisone was correlated with the symptom clusters social problems and anxious/depressed. The data support the idea that there exist syndrome aspecific disturbances in feedback activity beyond the level of the pituitary, i.e. at the hypothalamic level, at an early age. From this perspective, hydrocortisone suppression is a useful tool for studying pituitary-adrenal function in children. Behavioral correlates of these disturbances of pituitary-adrenal function should be determined.

Intermediate glucocorticoid feedback of corticotropin secretion in patients with major depression

The effects of a 2-h infusion of a low dose of cortisol on concentrations of adrenocorticotropic hormone (ACTH) and cortisol were studied in six inpatients with recurrent major depression and six healthy volunteers. Each subject was studied twice and received, in random order, from 11:00 to 13:00 h a 25 ml/h infusion of either 3 mg/h of cortisol or saline. Blood samples for ACTH and cortisol determination were drawn between 10:45 and 13:00 h every 15 min. ACTH and cortisol measurements in patients did not differ significantly from those in volunteers at any of the time points tested. The finding of an intact intermediate feedback in depression, where nonsuppression on the dexamethasone suppression test is frequently observed, may be explained by the binding of cortisol at limbic and hypothalamic corticosteroid receptors, while dexamethasone acts primarily at the pituitary. Findings of this pilot investigation should be confirmed in larger groups of patients for whom data from the dexamethasone suppression test are also available.

Involvement of corticosteroids in the processing of stressful life-events. A possible implication for the development of depression

In a sub-population of endogenously depressed patients, disturbances of the hypothalamic-pituitary-adrenal axis can be observed. Increased cortisol and CRH levels combined with normal ACTH concentrations have often been reported. Corticosteroids appear to play a role in the mood changes, in depressed subjects. However, their mechanism of action is unknown. In animal experiments, the involvement of corticosteroids in stressor-induced learning was investigated. Three paradigms were used. In the Porsolt swimtest an animal had to learn to adapt to an inescapable situation. In the lithium chloride conditioned taste aversion an animal learned to avoid sugar water. In the amphetamine sensitization a second injection of amphetamine caused a potentiated response, because of conditioning. All three conditions appeared to be stressful because they induced a corticosterone release. When adrenalectomized (ADX) mice were compared to control animals it appeared that, in all three paradigms, their memory function was disturbed. The data indicated that this was a specific glucocorticoid-mediated effect since corticosterone and dexamethasone injections were able to reverse the ADX-induced deficit. The ADX-induced disturbances were only observable at moderate stress levels. More severe stressors (lower water temperature in the Porsolt swimtest, higher lithium chloride and amphetamine doses) also made ADX mice remember their previous experiences. The results suggest that corticosteroids are involved in the consolidation of stressful events and the corresponding coping responses. They play, however, only a role in the case of moderate stressors. In ADX animals no stressor-induced corticosterone increase can occur and therefore these animals only remember severe stressors. In a depressed patient basal steroid levels are increased and consequently very mild stressors, which induce only a small extra steroid release, will be remembered. The remembering of all these negative experiences might be of importance for the development and maintenance of the depression.

Inhibition of the pituitary-adrenal axis with dexamethasone and cortisol in depressed patients and healthy subjects: a dose-response study

Different doses dexamethasone (0.25, 0.5, and 1 mg) or cortisol (30, 60, and 120 mg) were administered PO at 2230h to 39 depressed patients and 20 healthy subjects on nonsuccessive days. The inhibiting capacity of the two steroids on hypothalamo-pituitary axis (HPA) function was evaluated by measuring the plasma levels of cortisol, ACTH, and beta-endorphin at 0900h and 1530h each day following treatment. Baseline levels of the hormones were measured before starting treatment. A dose-dependent suppressive effect of both steroids on the plasma levels of cortisol, ACTH, and beta-endorphin was found both in patients and controls, except for the 0900h levels of cortisol after cortisol treatment. The effects were most profound in the morning. Differences between patients and controls were observed after cortisol treatment, but not dexamethasone, with respect to cortisol, ACTH, and beta-endorphin plasma levels in the morning. Cortisol treatment discriminated dexamethasone nonsuppressors from suppressors (patients and controls) and patients categorized as dexamethasone suppressors from controls in a way that dexamethasone treatment could not. The data favour the idea of impaired corticosteroid feedback beyond the pituitary level as part of HPA dysfunction.

Steroids and depression

Patients with endogenous depression (major affective disorder) frequently have high cortisol levels, but the diurnal rhythm is usually maintained and they do not develop the physical signs of Cushing's syndrome. On the other hand, depression is a frequent feature of Cushing's syndrome regardless of etiology, and it is often relieved when the cortisol levels are reduced, by whatever means. The mechanisms of the hypercortisolemia and resistance to dexamethasone suppression commonly found in endogenous depression are poorly understood; contrary to expectations, ACTH levels are not clearly elevated. There is a striking difference in the psychiatric features seen in endogenous hypercorticism compared to those seen after exogenous administration of glucocorticoids or ACTH. This suggests that either there are other stimulating or modifying factors besides ACTH or that the steroids stimulated by ACTH or other peptides differ from those in control subjects, i.e. there may be an alteration in the metabolism of steroids in depression. Little is known about the metabolic changes or the many steroids besides glucocorticoids produced by the hyperactive steroid-producing tissue. Preliminary studies suggest that major depression may be improved by steroid suppression. It is hypothesized that steroids themselves may be important in causing and perpetuating depression.

Fast feedback regulation of ACTH by cortisol

1. Fast feedback regulation of ACTH by cortisol has not been well studied in humans. The authors studied the existence and characteristics of fast feedback regulation in normal humans. 2. Hydrocortisone hemisuccinate was infused at two different rates: 6 mg/hour and 12 mg/hour for two hours. 3. The studies did not demonstrate the existence of fast feedback regulation of basal ACTH concentration by cortisol in man. Further, the response was variable and the rate sensitive character was difficult to demonstrate.

Psychoneuroendocrine research in depression. I. Hormone levels of different neuroendocrine axes and the dexamethasone suppression test

Psychoneuroendocrinology is of major importance in the biological research of depression. Most studies have focussed on the regulation of the hypothalamic-pituitary-adrenal (HPA) axis but other endocrine systems such as the hypothalamic-pituitary-thyroid (HPT), hypothalamic-pituitary-somatotropic (HPS), and the hypothalamic-pituitary-gonadal (HPG) axis have also been shown to be involved in the psychobiology of depression. There are close interrelations between various endocrine axes which possibly are affected during depressive illness. A variety of neuroendocrine abnormalities has been detected in depressive disorder but the pathophysiology of these derangements remains still unclear. Although the currently used neuroendocrine tests are not of diagnostic validity they may help to clarify the pathophysiological significance of the complex regulatory mechanisms of different neuroendocrine axes in affective disorders. Neuroendocrine regulation is determined both by peripheral and central mechanisms which both have to be adequately considered as well as potent interactions between various endocrine systems in further neuroendocrine depression research.

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.

Paradoxical effect of corticosteroids on pituitary ACTH/beta-endorphin release in stressed animals

We have previously demonstrated a number of changes in the anterior lobe proopiomelanocortin (POMC) system in chronically stressed rats. The purpose of the present experiments was to investigate whether chronically stressed rats demonstrate changes in pituitary sensitivity to glucocorticoid negative feedback. To study this question we compared the effects of glucocorticoids on ovine corticotropin releasing factor (oCRF)-stimulated ACTH and beta-endorphin release from cell suspensions prepared from naive unhandled rats versus chronically stressed rats. After dexamethasone, there was a 50% decrease in oCRF-stimulated hormone release in control rats but no inhibition of oCRF-stimulated hormone release in anterior lobe suspension from chronically stressed rats. Rather, the chronically stressed group exhibited a 50% hormone increase above the oCRF-stimulated baseline. The same pattern was observed after the addition of corticosterone to the medium. These findings suggest that there may be a positive feedback effect of glucocorticoids at the pituitary level under some conditions of chronic stress.

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.

ACTH, cortisol, and corticosterone output after ovine corticotropin-releasing factor challenge during depression and after recovery

Synthetic ovine corticotropin releasing factor (o-CRF) was administered as an intravenous bolus (100 micrograms) to eight patients suffering from a major depressive disorder, endogenous subtype. All patients showed inadequately suppressed cortisol levels after 1 mg dexamethasone. After clinical remission and normalized dexamethasone responses, these patients were reinvestigated with o-CRF stimulation. The mean adrenocorticotropic hormone (ACTH) release from the pituitary corticotroph cells was indiscriminate at both test sessions. Cortisol and corticosterone output after o-CRF tended to be higher during depression than after recovery. The o-CRF-induced increments observed with corticosterone were more marked in comparison with cortisol. Within the limitations of the current protocol, our preliminary data lend support to the view that an increased pituitary ACTH reserve or adrenocortical steroid reserve is not likely to be responsible for the defective pituitary-adrenal regulation in some dexamethasone-resistant depressives.