The human growth hormone response to clonidine: relationship to clinical and neuroendocrine profile in depression

Harmful effects of functional hypercortisolism: a working hypothesis

Functional hypercortisolism (FH) is caused by conditions able to chronically activate hypothalamic-pituitary-adrenal axis and usually occurs in cases of major depression, anorexia nervosa, bulimia nervosa, alcoholism, diabetes mellitus, simple obesity, polycystic ovary syndrome, obstructive sleep apnea syndrome, panic disorder, generalized anxiety disorder, shift work, and end-stage renal disease. Most of these states belong to pseudo-Cushing disease, a condition which is difficult to distinguish from Cushing's syndrome and characterized not only by biochemical findings but also by objective ones that can be attributed to hypercortisolism (e.g., striae rubrae, central obesity, skin atrophy, easy bruising, etc.). This hormonal imbalance, although reversible and generally mild, could mediate some systemic complications, mainly but not only of a metabolic/cardiovascular nature, which are present in these states and are largely the same as those present in Cushing's syndrome. In this review we aim to discuss the evidence suggesting the emerging negative role for FH.

Growth hormone and physiological responses to clonidine in depression

Clonidine (1.3 micrograms/kg) was administered to 62 control and 55 depressed patients free of psychoactive drugs for at least 7 days and fasted overnight. Growth hormone (GH), pulse, blood pressure and sedation were measured every 15 min for 1 h before and 2 h after clonidine infusion. GH response did not differ significantly between control and depressed subjects overall or when divided by sex. The systolic hypotensive and sedative responses were blunted in depressed subjects compared with controls; these effects appeared to be secondary to residual antidepressant drugs since the differences were only significant for those depressed subjects with short drug-free intervals. No differences between depressed subjects and controls were seen in diastolic hypotensive or bradycardic responses and no differences in GH, cardiovascular or sedative responses were found between endogenous and non-endogenous depressed subjects.

Cardiovascular, neuroendocrine, and sedative responses to four graded doses of clonidine in a placebo-controlled study

Effects of four doses of the alpha 2-receptor agonist clonidine (CLO) (0.25, 0.5, 1, and 2 micrograms/kg IV) and placebo were studied in seven healthy men who volunteered in a double-blind randomized design in order to delineate possible presynaptic and postsynaptic components in the mechanism of action of CLO. Blood pressure, heart rate, plasma noradrenaline (NOR), plasma 3-methoxy-4-hydroxyphenylglycol (MHPG), plasma growth hormone (GH), and subjective sedation were monitored for a period of 1 hr following infusion of CLO. NOR and MHPG were also analyzed in urine, collected at 1 and 4 hr after the infusions. Dose-dependent decrements were observed in systolic and diastolic blood pressure and plasma NOR levels, and dose-dependent increases in subjective sedation and plasma GH. CLO did not influence plasma MHPG levels, whereas only urinary MHPG excretion was reduced 4 hr after infusion of 2 micrograms/kg CLO. Because no obvious differences between dose-response relations of plasma NOR (believed to be a presynaptic and peripheral effect), blood pressure (believed to be mainly a central presynaptic and postsynaptic effect), and subjective sedation (believed to be a central and probably postsynaptic effect) were observed, our results do not provide simple parameters to discern the multiple mechanisms of action of CLO. However, at a dose of 0.5 micrograms/kg CLO (a dose lower than that generally used) clear effects on plasma NOR, blood pressure, and sedation, but not on plasma GH (a central postsynaptic effect) or urinary MHPG (a presynaptic effect), were observed. When using CLO as a challenge test in psychiatric disorders, a design with 0.5 micrograms/kg CLO, in addition to the traditional 2 micrograms/kg CLO, may provide more information to characterize discrete abnormalities in the noradrenergic system at the level of the brainstem, the pituitary, or the peripheral sympathetic nervous system.

Neuroendocrine evidence for decreased function of alpha 2-adrenergic receptor after electroconvulsive therapy

Growth hormone (GH) and hypotensive responses to clonidine (150 micrograms, i.v.) were investigated before and after electroconvulsive therapy (ECT) in 16 depressed patients. Because of high baseline serum GH concentrations, results from only 10 patients could be evaluated. The level of GH secretion induced by clonidine was significantly reduced after ECT, but the hypotensive responses to clonidine remained unchanged. The results indicate downward regulation of the sensitivity of alpha 2-adrenergic receptors in the hypothalamus after ECT.

Growth hormone and other hormonal responses to clonidine in melancholic and nonmelancholic depressed subjects and controls

To study putative differences in central neurotransmitter function in depressive subtypes, growth hormone, adrenocorticotropic hormone (ACTH), cortisol, and prolactin responses to the alpha 2-noradrenergic receptor agonist clonidine (1.3 micrograms/kg i.v.) were examined in 26 subjects with major depression, 13 of whom had melancholia. The responses of 10 of these endogenous/melancholic subjects were compared with those of 10 controls who were matched to the patients on age, sex, and menopausal status. In 15 of the depressed subjects, prolactin and cortisol responses to the putative serotonergic agonist fenfluramine were also examined to test for associations between these challenges. There were no significant differences in any of the responses between melancholic and nonmelancholic depressive subgroups after controlling for age and sex. With the exception of a greater reduction in ACTH in the endogenous/melancholic subjects, there were also no significant differences in hormonal responses between these patients and controls. There was, however, a significantly greater reduction in systolic blood pressure in the control subjects. There were no significant correlations between the responses to clonidine and fenfluramine. The findings suggest that clonidine at a dosage of 1.3 micrograms/kg is neither able to differentiate reliably between depressive subtypes nor to differentiate reliably between depressed and control subjects.

Hormonal responses to fenfluramine in depressive subtypes

In order to study putative differences in central neurotransmitter function in depressive subtypes, serum cortisol and prolactin responses to the putative serotonin agonist fenfluramine were examined in 30 subjects with major depression. Patients with endogenous depression (melancholia) as defined by each of ICD-9, DSM-III, RDC and Newcastle scale demonstrated a reduced prolactin response to 60 mg oral fenfluramine when compared with non-endogenous subjects. This was independent of either prolactin or cortisol baseline levels, and indicates that there are differences in brain neurotransmitter function in the endogenous and non-endogenous subtypes of depression. Basal prolactin levels were reduced in bipolar compared with unipolar subjects, and delusional compared with non-delusional patients, although there were no differences in the prolactin responses to fenfluramine between these subgroups. Basal cortisol levels and cortisol response to fenfluramine did not distinguish between any of the subtypes.

Responses of growth hormone to desipramine in endogenous and non-endogenous depression

Desipramine, a monoamine reuptake inhibitor, was used to stimulate release of growth hormone (GH) in 29 DSM-III major depressives and in 10 healthy controls. Eighteen of the depressives showed a blunted response. The GH-stimulation test was unable to distinguish endogenous from non-endogenous patients. The 13 dexamethasone non-suppressors were more likely to have a blunted GH response than the 14 suppressors. The results indicate that at least a subset of non-endogenous depressives have significant neuroendocrine abnormality.

Growth hormone response to clonidine in untreated depressed patients

Growth hormone (GH) responses to i.v. clonidine administration (150 micrograms) were compared in untreated depressed patients and controls. There were 8 controls (6 males, 2 females), 16 patients with a major depressive episode (8 males, 8 females), and 16 matched patients with a minor depressive episode according to Research Diagnostic Criteria. Differences in the GH response to clonidine only occurred between male patients and controls. These results suggest that endocrinological variables are important in the interpretation of this neuroendocrine test. Findings in the subgroup of unmedicated male patients with a nonendogenous major depressive episode support the hypothesis of decreased noradrenergic receptor sensitivity.

Multiple hormone responses to clonidine administration in depressed patients and healthy volunteers

Abnormalities in several hypothalamic-pituitary-target organ axes in depression may reflect alterations in central neurotransmitter receptor function. As the alpha 2-adrenergic receptor has been implicated in a variety of neuroendocrine abnormalities in depression, we assessed the role of alpha 2-adrenoceptor dysfunction in mediating response abnormalities of growth hormone, cortisol, and prolactin after intravenous clonidine administration (an alpha 2-adrenergic receptor agonist) in 18 patients with major depression (12 with melancholic features, 6 without melancholic symptoms) and 9 healthy volunteers. In particular, we examined the hypothesis that these abnormalities might be more evident in patients with DSM-III melancholic depression. After clonidine, the mean growth hormone response was significantly lower in melancholic depressives compared to controls (p = 0.02), and the shape of the growth hormone response profile was also significantly different in melancholic patients (p = 0.04). There was an overall decrease in the mean cortisol concentration after clonidine in melancholic patients and control subjects (p = 0.02), as well as a larger cumulative prolactin response in melancholic patients compared to those without melancholic features (p = 0.02). The present results confirm prior observations of a blunted growth hormone response after clonidine and suggest that alterations in alpha 2-adrenergic receptor activity might also contribute to several neuroendocrine abnormalities in patients with melancholic depression.

Tricyclic wash-out and growth hormone response to clonidine

We have observed a significantly higher growth hormone (GH) response to clonidine administration (150 micrograms i.v.) in 14 patients with a major depressive disorder who had never received antidepressant therapy than in 14 matched depressive patients who had not received tricyclic drugs for at least 15 days. Compared with a control group of eight subjects, untreated depressed patients, as a group, had a normal response, while matched patients had markedly blunted response. Results for the group of untreated depressed patients showed that some patients had a blunted response while others had a response in the normal range. The results suggest that studies on the GH response to clonidine in psychiatric patients need to take into account the confounding and long-lasting effects of tricyclics.

Morning and evening adrenocortical responses to ACTH stimulation in endogenously depressed patients: a preliminary report

Adrenocortical stimulation with ACTH both in the morning (M-test) and in the evening (E-test) and the dexamethasone suppression test were carried out in patients suffering from endogenous depression (DEP) and normal controls (NOR). A greater cortisol release in DEP was recognized than in NOR in the M-test, an earlier peak response of DEP was shown in the M-test than in the E-test, and a lack of association between hypersecretion of cortisol during depression and cortisol output after ACTH administration was noted. These findings, together with the results of DST, suggest that excessive activity of the hypothalamic-pituitary-adrenal (HPA) axis in depression may result, partly, from adrenocortical hyperresponsiveness.

Blunted response of growth hormone to clonidine and apomorphine in endogenous depression

We measured the growth hormone (GH) response to clonidine (an alpha-2-adrenergic agonist) and to apomorphine (a dopaminergic agonist) in 15 major endogenous and 15 minor depressive in-patients matched for gender and age. Results showed a significantly smaller GH response in the major depressives to both clonidine (P less than 0.01) and apomorphine (P less than 0.001). No significant difference existed between the two groups with regard to changes in blood pressure and pulse rate during either test. While major depressives showed a trend toward smaller sedative side-effects than minor depressives after clonidine, they showed significantly smaller sedative and gastro-intestinal side-effects after apomorphine. No significant correlation was present either in the major depressive or in the minor depressive group between the GH responses following clonidine and apomorphine challenges. These results support the hypothesis of both noradrenergic and dopaminergic neurotransmitter disturbances in major depression, with individual variability with regard to those biochemical anomalies.

Clonidine challenge testing of alpha-2-adrenoceptor function in man: the effects of mental illness and psychotropic medication

The clonidine challenge test is a means of assessing alpha-2-adrenoceptor sen sitivity in man. We review studies which have used this test to investigate central alpha-2- adrenoceptor changes in psychiatric illness, and to determine receptor changes after adminis tration and withdrawal of psychotropic treatments. Patients with severe depression show evidence of reduced alpha-2-adrenoceptor sensitivity, especially a reduced growth hormone response to clonidine. This may delineate a subgroup of patients with severe depressive illness from those with milder depression, and may even provide a trait marker for some depressed patients. Patients with panic disorder show evidence of subsensitivity to some and supersensitivity to other clonidine-induced responses. Other disorders, although less well investigated, may have abnormal test responses which may provide additional information about their cause and treatment. Changes in response after drug treatment have provided important information on the mode of action of antidepressants, and have suggested that noradrenergic function is altered by a variety of different antidepressants.