title: Cholinergic mediation of growth hormone secretion elicited by arginine, clonidine, and physical exercise in man.
abstract: The role of acetylcholine in human GH secretion was studied with atropine, which selectively blocks cholinergic muscarinic receptors and crosses the blood-brain barrier. Paired tests were performed in 22 normal subjects divided into 4 groups. The stimuli employed were arginine (30 g/30 min, iv), clonidine (300 micrograms, orally), physical exercise for 20 min, and saline. In the second test, atropine (1 mg, im) was administered before GH stimulation. Arginine elicited a GH secretory peak of 16.6 +/- 5 ng/ml (mean +/- SEM), which was completely blocked when atropine was administered with arginine (0.9 +/- 0.1 ng/ml). Atropine did not, however, modify the PRL secretory response; peak levels after arginine and atropine plus arginine were 16.3 +/- 3.1 and 16.8 +/- 2.5 ng/ml, respectively. Clonidine elicited a GH secretory peak (11.8 +/- 2.7 ng/ml) which also was blocked by pretreatment with atropine (1.2 +/- 0.2 ng/ml). Neither clonidine nor clonidine plus atropine altered PRL secretion. GH levels also were sharply increased after physical exercise, with a peak level of 19.4 +/- 4.9 ng/ml. Atropine completely blocked exercise-induced GH secretion (2 +/- 0.9 ng/ml). Atropine alone did not modify GH or PRL values compared with saline administration. The potency of the atropine-induced suppression of GH secretion by three different stimuli, each with presumably different mechanisms of action, suggests that acetylcholine plays an important role in the regulation of GH secretion.
mesh_terms: D000109:Acetylcholine / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D001120:Arginine / Q000494:pharmacology*; D001285:Atropine / Q000494:pharmacology; D003000:Clonidine / Q000494:pharmacology*; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D006801:Humans; D008297:Male; D005082:Physical Exertion; D011388:Prolactin / Q000097:blood
chemical_list: D001285:Atropine; D011388:Prolactin; D013006:Growth Hormone; D001120:Arginine; D003000:Clonidine; D000109:Acetylcholine