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

Endogenous cholinergic modulation of growth-hormone secretion in normal and acromegalic humans

Endogenous cholinergic stimulation, produced by the intravenous injection of edrophonium (10 mg), an acetylcholinesterase inhibitor, into 8 normal human subjects, resulted in an increase in the mean (+/- SE) serum growth hormone (GH) concentration from 0.6 +/- 0.1 ng/ml to 5.6 +/- 1.4 ng/ml (p < 0.01) at 40 min with no changes in serum prolactin. In 2 subjects sampled for 140 min. maximum serum GH levels of 19.4 and 10.2 ng/ml (from baseline values of 0.4 and 0.6 ng/ml) occurred at 65 min after edrophonium injection. Thus, enhancement of endogenous cholinergic activity stimulates GH secretion, providing further evidence for a role of cholinergic mechanisms in the physiologic regulation of GH secretion in man. The theoretical possibility that excessive endogenous cholinergic activity might be involved in the pathophysiologic regulation of GH secretion in man. The theoretical possibility that excessive endogenous cholinergic activity might be involved in the pathophysiologic regulation of GH secretion in acromegaly was not, however, supported, since methscopolamine (0.5 mg s.c.), a cholinergic antagonist, did not reduce mean serum GH levels in 3 acromegalic patients.

The inhibiting effect of atropine on growth hormone release during exercise

The effects of atropine upon changes in the circulating levels of growth hormone (GH), cortisol, lactate, glucose, and free fatty acids (FFA) were studied during exercise using both constant and progressively increasing work loads. At low work loads, atropine had no effect upon the changes in either cortisol or lactate levels, but the normal exercise-induced rise in GH was abolished or markedly reduced. At higher work loads, especially when prolonged, the usual rises in cortisol and lactate were enhanced by atropine, but the rise in GH was diminished and delayed. In no circumstances were the changes in FFA or glucose significantly affected by atropine. We regard the effect of atropine upon changes in cortisol and lactate responses as secondary to its cardiovascular effect, but suggest that the inhibition of Gh release may be evidence of a cholinergic mechanism in the control of Gh release during exercise.

Scopolamine-induced muscarinic supersensitivity in normal man: changes in sleep

Scopolamine (6 microgram/kg) was administered on 3 consecutive mornings to normal human subjects. Sleep recordings obtained at night (when the central anticholinergic effect of the morning scopolamine was no longer present) indicated a significant reduction in latency to REM-sleep onset on the nights following the second and third injections. This effect is opposite to the direct pharmacological action of nighttime administration of scopolamine (i.e., prolongation of REM latency). In addition, total sleep time and sleep efficiency were reduced, and sleep latency was increased. Furthermore, scopolamine pretreatment on 2 consecutive mornings also potentiated the REM-inducing effect of arecoline, a central muscarinic agonist. These data are consistent with the development of cholinergic supersensitivity following cholinergic blockade.