Reduction of growth hormone secretion following clomiphene administration

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.

[Circadian rhythms in the endocrine system (author's transl)]

In four sections, the contribution reviews data on 24-hour variations of cortisol, growth hormone, prolactine, testosterone, LH and FSH in the human plasma. 1) Experiments on isolated subjects show that the 24-h variation of cortisol is based on an endogenous circadian rhythm which can be independent from the rhythm of sleep and wakefulness. 2) The various pattern each of which has been described in good correspondence by several groups of authors, suggest a series of hormones with a strong circadian component (e.g. cortisol) to those with a weaker (testosterone) or even without a circadian component (FSH). 3) The sleep-wake-cycle influences the phase of hormone rhythms by various degrees; therefore, a uniform reference to sleep time seems preferable to a reference to local time in order to compare several rhythms. 4) The rhythms of cortisol and growth hormone as described in man agree satisfactorily with those in other vertebrate species.