Suppression of sleep-related prolactin secretion and enhancement of sleep-related growth hormone secretion

Looking back at a life in sleep research-and some thoughts for the future

In reviewing my studies, some of which are nearing the half century mark, I've described work on sleep-related growth hormone, the effects of hypnotics on the perception of sleep, REM sleep induction in humans by cholinergic drugs, the benzodiazepine receptor, the anatomic sites of action of hypnotics, the endocannabinoid system and sleep, and the relation of anesthesia to sleep. Special mention along the way goes to cases in which drugs produced totally unexpected effects, including methysergide producing opposite effects on growth hormone secretion in sleep and a waking provocative test, the converse actions on sleep of the B-10 benzodiazepine enantiomers, and the promotion of wakefulness by microinjection of the hypnotic triazolam into the dorsal raphe nuclei. This work is placed in the context of what was known at the time, as well as what has been observed in subsequent years. Many of these studies indicate that the medial preoptic area may be a common site for the sleep-promoting action of a wide range of agents including traditional hypnotics, ethanol, propofol and melatonin. In the future it may be worthwhile looking at the beta-carbolines, and also the endocannabinoid system, when exploring drugs with new mechanisms of action for treating sleep/wake disorders. An Addendum to this paper describes memories of working with Frederick Snyder, J. Christian Gillin, Richard Jed Wyatt, and Floyd E. Bloom.

Hyperprolactinemia as a Marker of Neurotransmitter Imbalance in Uremic Population

Serum prolactin (PRL) levels are elevated in patients with chronic renal failure (CRF) but the mechanisms responsible for these abnormalities are not fully understood. PRL secretion is undoubtedly influenced by many substances, which can be variously altered in uremia: monoamines, endogenous opiates and PTH. Our data suggest that in early renal failure PRL levels are already significantly high and the 24-h pattern of PRL secretion is significantly different from that in controls.

PRL derangements could be due in mild renal failure, to unknown factors (GABA?); in severe CRF, to a major change in dopaminergic activity; in hemodialysis (HD), to a low turnover of monoamines, and in peritoneal dialysis (PD) to increased activity of sero-toninergic and dopaminergic systems.

The effect of IV L-tryptophan on prolactin, growth hormone, and mood in healthy subjects

In order to assess the effects of increased CNS serotonergic function in humans on prolactin (PRL), growth hormone (GH), and mood, IV L-tryptophan (TRP) was administered to ten healthy subjects. The TRP infusion induced robust increases in PRL in all ten subjects. A significant increase in GH concentration was also observed, although the response was more variable. The subjects reported feeling significantly more 'high', 'mellow', and 'drowsy' following the TRP infusion in comparison to placebo. These findings indicate an important role for serotonin in PRL and GH secretion, as well as in mood regulation. The IV TRP challenge may be of use in the study of serotonergic function in a variety of neurologic and psychiatric diseases.

The effect of intravenous L-tryptophan on prolactin and growth hormone and mood in healthy subjects

In order to assess the effects of increased central nervous system serotonergic function in humans on prolactin (PRL), growth hormone (GH) and mood, intravenous L-tryptophan (TRP) was administered to ten healthy subjects. The TRP infusion induced robust increases in PRL in all ten subjects. A significant increase in GH concentration was also observed, although the response was more variable. The subjects reported feeling significantly more high, mellow, and drowsy following the TRP infusion in comparison to placebo. These findings indicate an important role for serotonin in PRL and GH secretion, as well as in mood regulation. The intravenous TRP challenge may be of use in the study of serotonergic function in a variety of neurologic and psychiatric diseases.

Psychoneuroendocrinology of schizophrenia

The study of psychoneuroendocrinology of schizophrenia has yielded an extensive but inconclusive body of data. Investigations to date have been limited by several factors, including the confounding effects of neuroleptic drugs, methodological limitations, and lack of appreciation for the heterogeneity of the illness. Previously, the focus of research has been on the measurement of anterior pituitary hormones, guided by the assumptions that these hormones are regulated by the central nervous system (CNS) to a significant degree and that the unique anatomic relationship of the pituitary gland to the hypothalamus and the CNS is potentially relevant. Patients with schizophrenia do appear to have distinct endocrinologic profiles. However, although the hormonal differences between patients with schizophrenia and the general population appear to be subtle in magnitude. Nonetheless, investigation, and the exploration of the possible effect of gonadal and posterior pituitary hormones merits particular attention.

Growth hormone secretion during sleep in male depressed patients

1. Growth hormone (GH) secretion during sleep was studied in ten male patients with major depression according to DSM III and eight normal controls. 2. Samples were collected through a continuous blood withdrawal pump while sleep was recorded in the laboratory. 3. The results showed a marked decrease in the GH secretion mainly during the first three hours of sleep in depressed patients as compared to normal controls. DST and TRH tests were also administered to the same patients but no correlation was observed between a positive test and a blunted GH secretion, suggesting that the various neuroendocrinological disturbances do not coexist in all depressed patients. 4. This disturbance in GH secretion during sleep, along with reduced slow wave sleep (SWS), gives support to the theory that GHRH is the common stimulus of SWS and GH release and that the ratio of GHRH and its counterpart CRH plays a major role in the pathophysiology of disturbed endocrine activity during sleep in depression.

Influence of partial sleep deprivation on the secretion of thyrotropin, thyroid hormones, growth hormone, prolactin, luteinizing hormone, follicle stimulating hormone, and estradiol in healthy young women

The influence of partial sleep deprivation during the second half of the night on the secretion of thyroid stimulating hormone (TSH), thyroxin (T4), free T4 (fT4), triiodothyronine (T3), prolactin (PRL), growth hormone (GH), luteinizing hormone (LH), follicle stimulating hormone (FSH), and estradiol (E2) was investigated in 10 healthy young women. Blood samples were drawn at hourly intervals over a 64-hour period (i.e., 3 consecutive days and nights). During night 2, all subjects were awakened at 1:30 a.m. During partial sleep deprivation, TSH concentrations increased significantly and remained elevated throughout the following day. Levels of T4, fT4, and T3 were enhanced during the partial sleep deprivation hours only, and changes in these hormones seemed to be independent of TSH. PRL levels decreased, LH and E2 concentrations increased, and GH and FSH secretion remained unchanged during partial sleep deprivation. This pattern of change of different endocrine axes during partial sleep deprivation resembles those seen after total sleep deprivation, suggesting that similar neurochemical changes are induced by both forms of antidepressant therapy. The late evening GH peak occurred almost exclusively before the onset of sleep. Partial sleep deprivation did not influence the chronobiological profiles of any of the hormones investigated. The chemical changes underlying these alterations are speculated to involve enhancement of central norepinephrine and dopamine activity with a concomitant increase in the activity of the sympathetic nervous system.

Circadian patterns of cortisol, prolactin, and growth hormonal secretion during bingeing and vomiting in normal weight bulimic patients

Women who are of normal weight and have bulimia nervosa exhibit multiple neuroendocrine disturbances. We hypothesized that bingeing and vomiting behavior could be contributory because food consumption in healthy volunteers increases plasma cortisol and prolactin secretion and suppresses growth hormone secretion. Thus, we investigated the effects of bingeing and vomiting on the circadian pattern (measurements every 20 min for 24 hr) of these hormones in comparison to healthy control women eating normally. Bingeing and vomiting were associated with modest increases in cortisol and prolactin and reductions in growth hormone secretion. However, this bingeing or purging did not alter mean 24-hr pattern of cortisol and growth hormone secretion as values for bulimics were similar to controls. While mean daytime patterns of prolactin secretion were similar in bulimics and controls, bulimic patients had a significant reduction of nocturnal prolactin levels. In summary, bingeing and vomiting does not appear to have a substantial influence on hormonal secretion. However, bulimic women have blunted nocturnal prolactin patterns.

Effect of ritanserin, specific 5HT-2 antagonist, on PRL secretion in normal subjects and in different hyperprolactinaemic conditions

The availability of a new specific anti 5HT-2 compound, ritanserin (RTS), led us to further investigate the role of serotonin in controlling PRL secretion. The drug was administered to normoprolactinaemic subjects and to patients with differing hyperprolactinaemic conditions. While RTS failed to modify PRL levels in normoprolactinaemic subjects and in patients with PRL-secreting pituitary adenomas, a marked decrease in the hormone was obtained in patients with functional and puerperal hyperprolactinaemia. The lack of effect of RTS in PRL-secreting pituitary adenomas suggests that the reported suppression of PRL by other antiserotoninergic drugs, such as metergoline, is probably due to their concomitant dopaminergic activity.

Neuroendocrine rhythms and sleep in aging men

To delineate the physiological effects of aging on basal levels and temporal patterns of neuroendocrine secretions, the 24-h profiles of cortisol, thyroid-stimulating hormone (TSH), melatonin, prolactin, and growth hormone (GH) levels were simultaneously obtained at frequent intervals in eight healthy, active elderly men, age 67-84 yr and in eight young male adults, age 20-27 yr. The study was preceded by an extended period of habituation to laboratory conditions, and sleep was polygraphically recorded. Mean cortisol levels in the elderly were normal, but the amplitude of the circadian rhythm was reduced. Circulating levels of daytime and nighttime levels of both TSH and GH were greatly diminished in old age. In contrast, prolactin and melatonin concentrations were decreased during the nighttime only. The circadian rises of cortisol, TSH, and melatonin occurred 1-1.5 h earlier in elderly subjects, and the distribution of rapid-eye-movement stages during sleep was similarly advanced, suggesting that circadian timekeeping is modified during normal senescence. Despite perturbations of sleep, sleep-related release of GH and prolactin occurred in all elderly men. Age-related decreases in hormonal levels were associated with a decrease in the amplitude, but not the frequency, of secretory pulses. These findings demonstrate that the normal process of aging involves alterations in the central mechanisms controlling the temporal organization of endocrine release in addition to a reduction of secretory outputs.

A dose-response study examining the effects of ritanserin on human slow wave sleep

This study investigated the effects of placebo, 1 mg, 3 mg, 10 mg and 30 mg ritanserin and 10 mg diazepam on human sleep. Twelve normal volunteers participated in this randomized, double-blind, placebo-controlled cross-over sleep study. A clear dose-response relationship was found for ritanserin with higher doses evoking increased duration of slow wave sleep.

Acute effect of intravenous clomipramine upon sleep-related hormone secretion in depressed outpatients and healthy control subjects

Tricyclic antidepressants have been used frequently as pharmacological probes in neuroendocrine studies even though they appear to lack neurochemical specificity. Despite this, the hormonal responses to these drugs have been used to provide evidence that depressed patients have alterations in both noradrenergic and serotonergic tone within the central nervous system. Most studies have been conducted in the morning, which is not a time of high physiological neuroendocrine secretory activity. The present study has used the relatively specific serotonergic probe intravenous clomipramine given to depressed patients and healthy subjects immediately before sleep onset, which is a time of increased neuroendocrine activity. Under these conditions, 12.5 mg clomipramine stimulates the secretion of both cortisol and prolactin, but unlike studies conducted in the morning, clomipramine suppresses the secretion of growth hormone in both groups. These data suggest that serotonergic mechanisms are involved in the regulation of the secretion of these three hormones at the time of sleep onset.

Neuroendocrinological investigations during sleep deprivation in depression. II. Longitudinal measurement of thyrotropin, TH, cortisol, prolactin, GH, and LH during sleep and sleep deprivation

Thyrotropin (TSH), thyroxin (T4), triiodothyronine (T3), free T3 (fT3), cortisol, prolactin, and human growth hormone (HGH) were measured every 2 hr during a night of sleep, the following day, and a night of sleep deprivation (SD) in 14 patients with major depressive disorder. In subgroups fT4 (n = 5), reverse T3 (rT3), and luteinizing hormone (LH) (n = 6) were also investigated. Significant increases in TSH, T4, fT4, T3, fT3, rT3, and cortisol and decreases in prolactin levels occurred during the night of SD, compared to the pattern during the night of sleep. The pre-SD T4 and T3 levels of the responders to SD were already higher than in the nonresponders, and increased less during SD. The cortisol and HGH concentrations of the responders rose higher during SD than those of the nonresponders. Changes in TSH and prolactin were not correlated to clinical response. Analysis of possible neurochemical mechanisms underlying this "pattern" of changes in different endocrine profiles suggests that enhanced noradrenergic activity might play a role in the changes in TSH, cortisol, thyroid hormones, and possibly HGH secretion during SD, and increased dopaminergic tone probably induced the decline in prolactin levels. Additional effects of the serotonergic system cannot be excluded at present. In conclusion, the data suggest that enhanced noradrenergic activity of the locus coeruleus stimulates alpha and/or beta adrenergic receptors in depressed patients during SD. This mechanism could well be involved in the antidepressant effect of this therapy.

Evidence that the reversible MAO-A inhibitor moclobemide increases prolactin secretion by a serotonergic mechanism in healthy male volunteers

The serotonin receptor antagonist methysergide was used to investigate the mechanism mediating stimulation of prolactin release after single doses of the reversible MAO-A inhibitor moclobemide. Eight healthy male volunteers participated in a placebo-controlled cross-over study, where pretreatment with methysergide almost totally prevented the moclobemide-induced increase in plasma prolactin levels. MAO-A inhibition, as evidenced by up to 80% decreases in the plasma concentration of 3,4-dihydroxyphenylglycol, a deaminated metabolite of norepinephrine, was similar after both pretreatments. This result suggests that moclobemide stimulates prolactin release through activation of serotonergic receptors, and provides evidence that the drug is capable of augmenting central serotonergic neurotransmission in humans.

Effect of moderate weight loss on prolactin secretion in normal female volunteers

Sleep-related prolactin secretion and prolactin responses to the infusion of low doses of the dopamine antagonist, metoclopramide, and thyrotropin-releasing hormone were measured in 11 female volunteers before and after undertaking a diet in which they lost a mean of 3.1 kg in weight in 3 weeks. No effect of weight loss on these measures was found, but there was a significant, although modest, reduction in fasting plasma tryptophan concentration without any change in the concentration of competing amino acids.

Wake and sleep cardiovascular reflex tests and GH profiles in diabetic patients

Fourteen diabetic patients (13 males, 1 female, 7 IDDM and 7 NIDDM) were tested during wakefulness with a battery of tests examining parasympathetic and sympathetic control of the cardiovascular system. Subsequently sleep recordings including EEG, EOG, submental, left and right anterior tibialis EMGs, ECG, nasal airflow, thoracic and abdominal respirograms, nocturnal penile tumescence, were performed in each subject. The assessment of cardiovascular functions during sleep was based on the following parameters: Rbm, R-wake, apnea index, adequate penile tumescence during phase REM. Parasympathetic and sympathetic control of cardiovascular system were both impaired during wakefulness in only one patient, who also showed a low Rbm index indicative of ascertained autonomic neuropathy. Indices Rbm sufficiently low to be considered an evidence of probable autonomic neuropathy were found in 5 patients (3 IDDM and 2 NIDDM); all but one with normal cardiovascular tests during wakefulness. Five patients showed gross deficiency upon nocturnal penile tumescence monitoring. In comparison with a control group the patients showed a significantly lower overall Rbm index (p less than 0.001). IDDM patients showed an increased plasma GH response to insulin-induced hypoglycemia compared to NIDDM and normal subjects. Increased GH secretion was furthermore confirmed by GH values obtained in blood samples drawn during the first REM stage of the night in IDDM patients. The evaluation of the variables taken into consideration during sleep appears to be crucial for the assessment and prevention of autonomic neuropathies and neuroendocrine dysregulation in diabetic patients.

Functional role of 5-HT2 receptors in the regulation of sleep and wakefulness in the rat

Recently developed agents specifically acting on different 5-hydroxytryptamine (5-HT) receptor populations were used to analyze the functional role of 5-HT2 receptor subtypes in the sleep-wakefulness cycle of the rat. The 5-HT2 receptor antagonist ritanserin injected intraperitoneally (IP) (0.04-2.5 mg/kg) induced an increase in deep slow wave sleep (SWS2) duration at the expense of wakefulness (W), light slow wave sleep (SWS1) and paradoxical sleep (PS). The stimulation of 5-HT2 receptors by 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) produced a dose-related increase in W and a dose-dependent decrease in both SWS2 and PS. Pretreatment with ritanserin (0.16-2.5 mg/kg) or with cinanserin (2.5-5 mg/kg), another 5-HT2 receptor antagonist, dose-dependently reversed the W enhancement and the SWS2 deficit produced by DOM, but not the PS deficit. Sleep-wakefulness alterations (increase in W and SWS1 combined with a suppression of SWS2 and PS) observed after IP injection of two putative 5-HT1 receptor agonists, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (2.5 mg/kg) and 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969) (0.63 mg/kg), were not modified by ritanserin pretreatment (0.16-2.5 mg/kg). These results further support the hypothesis that the serotonergic system plays an active role in the regulation of the sleep-wakefulness cycle in the rat and that 5-HT2 receptors are involved in this action. In addition, it is suggested that 5-HT1 receptor subtypes are unlikely to interact with 5-HT2 receptors in the sleep-wakefulness modulation mediated through 5-HT2 receptors.

Growth hormone response to desmethylimipramine in depressed and suicidal adolescents

Desipramine 75 mg i.m. was given in the morning to 20 adolescents with major depressive disorder and 23 normal controls. Depressed adolescents secreted significantly less growth hormone (GH) over the next 2 h than did normal adolescents, although a substantial proportion of the differences were accounted for by the depressed adolescents who had a specific suicidal plan or attempt during the episode. Severity of depression or the presence of other depressive symptoms did not predict GH secretion within the depressed group. Age, sex and maturational factors in the control of GH are discussed. It is concluded that these differences in GH secretion probably reflect differences in CNS beta-adrenergic and/or serotonergic function. Suicidality and depression may have different psychobiological correlates in adolescents.

The circadian rhythms of thyrotrophin and prolactin secretion

As with other anterior pituitary hormones, the secretion of both thyrotrophin (TSH) and prolactin (PRL) displays a circadian variation with different patterns for each hormone. In recent years there has been a substantial increase in the understanding of the neuroregulation of TSH and PRL. However the primary events involved in the generation of their circadian rhythms remains unclear. Regulatory pathways comprise two major groups: central factors, where the control is exerted by the central nervous system via the hypothalamus and peripheral factors, which include all extra CNS mechanisms. The first group is represented mainly by neuropeptides and neurotransmitters controlling TSH and PRL release, whereas the second one comprises both physical phenomena such as variations in plasma volume or postural changes and hormonal influences arising from target glands such as the adrenal, the thyroid and the gonads.

Subnormal prolactin responsiveness to thyrotropin-releasing hormone (TRH) in women with primary empty sella syndrome

Basal prolactin (PRL) levels and PRL responsiveness to thyrotropin-releasing hormone (TRH) were studied in 10 women with primary empty sella (PES) syndrome (mean age 38.2 yr). Hyperprolactinemia (34 to 72 ng/ml) was found in 5 patients (hyperprolactinemic PES, H-PES), whereas 5 patients showed normal (9.5 to 19 ng/ml) PRL levels (normoprolactinemic PES, N-PES). The results were compared with those obtained in 10 healthy women (mean age 32.8 yr, PRL = 7 to 15 ng/ml) and in 8 women with a PRL-secreting pituitary microadenoma (MA) (mean age 37.5 yr, PRL = 39 to 85 ng/ml). The mean basal levels of PRL were significantly higher in patients with H-PES (50.8 +/- 13.2 ng/ml) or MA (64.0 +/- 18.3 ng/ml) than in the control group (10.9 +/- 2.6 ng/ml, p less than 0.02) and in the patients with N-PES (13.9 +/- 3.7 ng/ml, p less than 0.02). In contrast, the relative maximum response (RMR) of PRL to TRH (peak PRL/basal PRL) was significantly lower in the patients with PES (both H-PES and N-PES) or MA (1.4 +/- 0.4, 2.3 +/- 0.7 and 1.2 +/- 0.2, respectively) than in the control subjects (3.6 +/- 1.1; p less than 0.02, less than 0.05 and less than 0.02, respectively). Our results show that the pituitary responsiveness to the acute stimulation with TRH is significantly decreased both in patients with a PRL-secreting pituitary MA and in those with PES. Therefore, the clinical value of the TRH test in distinguishing the PES syndromes from prolactinomas seems to be questionable.

Hormonal probes of central serotonergic activity: do they really exist?

The response of a hormone allegedly under 5-hydroxytryptaminergic (5-HT-ergic) control to a compound stimulating or inhibiting serotonergic activity has been used as a measure of the functional state of central serotonergic systems. The relevant literature is reviewed, and based on that, it is concluded that, as yet, no reliable hormonal 5-HT probe exists. The main problems are nonselectivity of the challengers and noncomparability of individual studies because of variations in dose and route of administration. An acceptable hormonal 5-HT probe should at least have passed the following three tests. The influence of the challenger on catecholaminergic (CA) systems must be rendered unlikely in humans to avoid the pitfalls of, say, the 5-HT precursors whose CA-ergic influences have been overlooked. Dose-response relationships must be established to avoid the confusion caused by different investigators using the challenger in different doses. It must be demonstrated that the effect of the challenger is counteracted by its functional opponent.

The effects of chronic ritanserin treatment on sleep and the neuroendocrine response to L-tryptophan

A previous study has shown that acute administration of the 5-HT2 receptor antagonist ritanserin doubles Slow Wave Sleep (SWS) and increases the prolactin (PRL) response to L-tryptophan (LTP). The present study investigated the effect of repeated ritanserin treatment on sleep, neuroendocrine response to LTP and 5-HT2 platelet receptor binding. After 2 weeks, ritanserin administration SWS was persistently increased but the PRL response to LTP was unchanged. Platelet 5-HT receptor binding was undetectable at the end of ritanserin treatment but recovered 2 weeks after drug withdrawal. The results suggest that ritanserin causes a sustained effect on the 5-HT mechanisms mediating SWS and on platelet 5-HT2 receptors. However, adaptation occurs to its effect on 5-HT-mediated neuroendocrine responses.

Growth hormone neurosecretory dysfunction

The basis for understanding clinical disorders in the neuroregulation of GH secretion is derived from the complexity of the CNS-hypothalamic-pituitary axis. Studies in animals and humans demonstrate an anatomic, physiological and pharmacological evidence for neurosecretory control over GH secretion including neurohormones (GRH, somatostatin), neurotransmitters (dopaminergic, adrenergic, cholinergic, serotonergic, histaminergic, GABAergic), and neuropeptides (gut hormones, opioids, CRH, TRH, etc). The observation of a defect in the neuroregulatory control of GH secretion in CNS-irradiated humans and animals led to the hypothesis of a disorder in neurosecretion, GHND, as a cause for short stature. We speculate that in this heterogeneous group of children a disruption in the neurotransmitter-neurohormonal functional pathway could modify secretion ultimately expressed as poor growth velocity and short stature.

5-Hydroxytryptamine-2 antagonist increases human slow wave sleep

Ritanserin, a specific 5-HT2 antagonist, was given to volunteers in a double-blind placebo controlled sleep study. Slow wave sleep doubled in duration at the expense of stage 2. The finding that a serotonin antagonist changed the architecture of sleep without producing insomnia is of fundamental importance and calls for a re-examination of traditional theories of sleep control which assign a facilitatory role to serotonin.

Cholinergic but not serotonergic mediation of exercise-induced growth hormone secretion

In order to clarify the roles of cholinergic and serotonergic neurotransmission in the mediation of exercise-induced growth hormone (GH) release, normal young volunteers of both sexes were studied. Exercise was for 20 minutes at 800 kpm for the men and 500 kpm for the women. Pretreatment with 0.4 mg atropine 1 hour prior to exercise, or with methysergide 2 mg po q 6 h for 48 hours prior to exercise, were used to evaluate the influence of cholinergic and serotonergic blockade, respectively. Five of the ten men studied failed to raise GH values with exercise, perhaps because the exercise was not vigorous enough for their high degree of fitness. Of three non-responders restudied, at the same workload, one responded on the second occasion. The mean peak GH with exercise 13.4 +/- 3.27 ng/ml, was reduced to 2.4 +/- 1.28 ng/ml (p less than 0.01) after atropine, but was unaffected by methysergide (15.2 +/- 6.58 ng/ml, p greater than 0.5). Prolactin did not rise with exercise, and was not affected by atropine, but lowered by methysergide as expected. Cholinergic neurotransmission therefore represents a key link in exercise-induced GH secretion, but serotonergic influences are probably not involved.

Hypothalamic control of GH secretion: pathophysiology and clinical implications

GH is secreted episodically. Its pattern is regulated by the interplay of a releasing and a release-inhibiting hormone of hypothalamic origin. Modulation occurs by metabolic factors (glucose, free fatty acids, ketone bodies, amino acids). Altered GH secretion has been observed in states of metabolic derangement such as diabetes mellitus, malnutrition and obesity. Further modulation occurs by extrahypothalamic CNS structures. In man--but not in animals, including subhuman primates--sleep has an important effect on GH secretion. A defective GH secretory pattern has been found to occur in several states of sleep disturbance, such as sleep deprivation, narcolepsy, severe psychosocial derangement, the apallic syndrome. Other CNS influences on GH secretion are related to stress, emotional changes and psychiatric disturbances. The exact mechanisms by which most of these influences are relayed to the GH secretory apparatus of the hypothalamus remain yet to be investigated.

Clinical strategies for evaluating ECT mechanisms--pharmacological, biochemical and psychophysiological approaches

Although ECT is a highly effective treatment for severe depression and other psychiatric syndromes, its mode of action is not known. Recent studies have suggested that effects of ECT on central neurotransmitter receptors may underlie its therapeutic action. The effects of chronically administered electroconvulsive shock on receptors for dopamine, serotonin, noradrenaline, acetylcholine and endorphins in rodent brain, are reviewed. Strategies for evaluating the relevance of these animal findings to mechanisms of action of ECT in humans are discussed.

Role of midbrain raphe nuclei in stress-, pentobarbital-, beta-endorphin-, or TRH-induced changes in plasma PRL levels of adult male rats

Radiofrequency lesions of either the dorsal (LD) or the median (LM) raphe nuclei of male rat mesencephalon did not modify baseline levels of plasma prolactin (PRL). However, the PRL releasing effect of 30 min of immobilization stress was suppressed in LM rats and enhanced in LD rats. The PRL releasing effect of pentobarbital (PB, 50 mg/kg, IP) or of beta-endorphin (END, 15 micrograms/rat, intracerebroventricularly, ICV) also was enhanced in LD rats. TRH (10 micrograms/rat, ICV) administered concomitantly with either PB or END, antagonized the releasing effect of the former and enhanced the releasing effect of the latter in sham operated rats. Lesions of the raphe nuclei blocked the antagonizing effect of TRH, while the enhancing effect was heightened in LD rats. These results indicate that neurons originating in the raphe nuclei are not involved in the control of baseline plasma PRL levels. They indicate, furthermore, the existence of an inhibitory pathway originating in the dorsal raphe nucleus the suppression or activation of which is, at least partly, the mechanism of PB, END or TRH effects on PRL release. The PRL releasing effect of immobilization stress seems to be under a dual, mutually antagonistic control: activating through the median and inhibitory through the dorsal nucleus.

Characterization of ergot and non-ergot serotonin antagonists by prolactin and growth hormone profiles during wakefulness and sleep

In order to further clarify the involvement of serotonin in the control of secretion of pituitary lactogens, diurnal and sleep prolactin (PRL) and growth hormone (GH) profiles were investigated in healthy subjects treated with ergot and non-ergot serotonin antagonists. A group of 10 subjects received a single oral dose of 2 mg each of pizotifen, methysergide, and the dopaminergic drug bromocriptine as reference substance, in comparison with placebo. Blood was collected at hourly intervals for 6 h. Another group of 10 individuals received either a placebo, 2.5 mg bromocriptine (n = 6) twice daily for 4 days or pizotifen (n = 10) 0.5 mg 3 times daily for 12 days before undergoing EEG recording and blood sampling during night sleep. The diurnal plasma profiles of PRL and GH were not modified by pizotifen, a non-ergot drug. Methysergide and bromocriptine, two ergot derivatives, significantly (P < 0.01 and P < 0.001 respectively) suppressed the basal secretion of PRL throughout the trial and increased plasma GH significantly (P < 0.01). The sleep profile of PRL was not modified by pizotifen but there was a moderate reduction in GH reaching the level of significance (P < 0.02) between hours 1 and 2 of sleep. Bromocriptine suppressed completely PRL secretion throughout the entire sleep period and significantly (P < 0.05) prolonged the secretory profile of GH. The results indicate the presence in the ergot molecule of a dopaminergic moiety responsible for PRL inhibition and GH stimulation. This effect is independent of the serotonin active component of the drug.

Neuroendocrine tests of monoamine function in man: a review of basic theory and its application to the study of depressive illness

Neuroendocrine tests are now available for studying monoamine function in the brains of patients with mental illness. Great care is required in the selection of drugs which act upon specific monoamine receptors to produce specific hormonal responses. Equal care is required in the control of biological variables which may influence hormonal release. Recently reported neuroendocrine studies of depressive illness are assessed in these terms. The results of these studies support the hypothesis that there is defective noradrenergic function in the brains of some patients with depressive illness.

Neuroendocrine effects of apomorphine: characterization of response patterns and application to schizophrenia research

Apomorphine, a direct-acting dopamine agonist, stimulates release of growth hormone (hGH) and suppresses release of prolactin (PRL) from the anterior pituitary. Previous studies comparing the magnitude of these responses in schizophrenics and controls suggest that many acute (and some chronic) schizophrenics have exaggerated hGH responses; many chronic schizophrenics (and patients with tardive dyskinesia) have blunted hGH responses to apomorphine, and possibly blunted PRL responses. The present studies extend and confirm these findings in chronic schizophrenics; in addition, several studies were undertaken to further characterize these apomorphine-induced endocrine responses. Studies in which apomorphine was given on 2 or 3 separate occasions to each of five subjects indicate that the hGH response is a highly reproducible individual index, but PRL suppression is a less satisfactory measure. hGH responses to apomorphine were consistently antagonized by pretreatment with haloperidol, supporting the concept that the hGH-releasing effect of apomorphine is mediated by its action on dopamine receptors. Cyproheptadine pretreatment was associated with erratic increases or decreases in the hGH response to apomorphine, but did not alter PRL levels or apomorphine-induced PRL suppression. The relationship of these findings to biological hypotheses of schizophrenia and to neuroleptic-induced receptor changes is discussed.

The effect of lisuride hydrogen maleate in the hyperprolactinaemia-amenorrhoea syndrome: clinical and hormonal responses

Eleven women with secondary amenorrhoea and hyperprolactinaemia were treated with lisuride, a new semisynthetic ergot derivative. Acute administration of lisuride (100 microgram orally) significantly suppressed serum prolactin (PRL) levels in nine out of eleven subjects. In these nine patients, prolonged treatment with lisuride (50--200 microgram daily) lowered PRL levels into the normal range, menstrual cycles were resumed and eight patients ovulated. Two patients, in whom lisuride failed to lower PRL levels into the normal range, did not resume normal menstruation. These data demonstrate that lisuride may be used clinically to lower PRL levels and to restore cyclic gonadotrophin secretion and ovulation in amenorrhoeic patients with hyperprolactinaemia.

Inhibition of prolactin release by serotonin antagonists in hyperprolactinemic subjects

Metergoline (4 mg) and methysergide (3 mg), two serotonin antagonists known to inhibit prolactin secretion in normal subjects, and the dopaminergic agonist, bromocriptine (2.5 mg) were orally administered in hyperprolactinemic patients. Mean serum prolactin concentration was significantly decreased between 120 and 240 min following the ingestion of all three drugs in comparison with a placebo; a consistent reduction to below 50% of basal values occurred in 10 of 14 patients after metergoline, in 5 of 10 after methysergide, and in 11 of 14 after bromocriptine administration. These data indicate that serotonin antagonists may acutely lower serum prolactin levels in hyperprolactinemic patients similarly to bromocriptine, though their mechanism of action is most likely different.

Antiserotonin treatment of hyperprolactinemic amenorrhea: long-term follow-up with metergoline, methysergide, and cyproheptadine

Twenty patients affected by hyperprolactinemic amenorrhea-galactorrhea have been treated with one or more of the following serotonin antagonists: metergoline, methysergide, and cyproheptadine. Among the 11 patients without evidence of pituitary tumor resumption of menses was observed in five, two of whom had ovulatory cycles; one patient became pregnant; ovulations occurred only during treatment with metergoline. In the group of nine patients with enlarged sellae, three experienced isolated episodes of bleeding, while two had three and four menses each, respectively; all cycles were anovulatory. Plasma prolactin levels and galactorrhea were favorably affected by treatment only in a minority of amenorrhea-galactorrhea patients with and without tumors.

Methoscopolamine inhibition of sleep-related growth hormone secretion. Evidence for a cholinergic secretory mechanism

We have examined the effects of cholinergic blockade with 0.5 mg methscopolamine bromide, intramuscularly, on sleep-related and insulin-induced growth hormone (GH) secretion. 17 normal young men were studied; 8 had sleep studies, and 12 (including 3 who also had sleep studies) had insulin tolerance tests (ITT) with 0.1 U/kg of regular insulin. After an adjustment night in the sleep laboratory, saline control night and methscopolamine night studies were done in random sequence; study procedures included electroencephalographic, electromyographic, and electrooculographic recordings, and blood sampling every 20 min for hormone radioimmunoassays. Prolactin levels were also measured during sleep. For methscopolamine night studies, the mean overall control GH level of 2.89+/-0.44 ng/ml and the mean peak control GH level of 11.09+/-3.11 ng/ml were dramatically reduced to 0.75+/-0.01 and 1.04+/-0.25 ng/ml, respectively (P<0.0001 and <0.001). Despite virtual absence of GH secretion during the night in every study subject, no measured sleep characteristic was affected by methscopolamine, including total slow-wave sleep (12.1+/-2.6% control vs. 10.3+/-2.5% drug, P>0.2). Sleep prolactin levels were not changed by methscopolamine. In contrast to the abolition of sleep-related GH secretion, administration of methscopolamine had only a marginal effect on the GH response to insulin hypoglycemia. None of nine time points differed significantly, as was also the case with peak levels, mean increments, and areas under the curves (P>0.2). Analysis of variance did, however, indicate that the lower GH concentrations achieved during ITT after methscopolamine (average 31.7% below control) were significantly different than control concentrations. We conclude that the burst of GH secretion which normally occurs after sleep onset is primed by a cholinergic mechanism which does not influence slow-wave sleep. Cholinergic mechanisms do not appear to play an important role in sleep-related prolactin secretion. The contrast between the complete suppression of sleep-related GH release and the relatively small inhibitory effect on ITT-induced GH secretion suggests that the neurotransmitter mechanisms, and presumably the pathways, which subserve sleep-related GH secretion in man may be different from those which mediate the GH response to pharmacologic stimuli such as insulin.