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.