Blockade of hp-GRF-40-induced GH release in normal men by a cholinergic muscarinic antagonist.

In five healthy young men, pretreatment with the cholinergic muscarinic antagonist pirenzepine (0.6 mg/kg iv) almost completely abolished the rise in plasma growth hormone (GH) elicited by an iv bolus injection of 1 microgram/kg human pancreatic GH-releasing factor 1-40 (hp-GRF-40). These data demonstrate that cholinergic receptor sites involved in GH-releasing mechanisms do not interact with GRF-secreting structures in the central nervous system. A mechanism mediated via hypothalamic release of somatostatin or, alternatively, a direct pituitary site of action, can be postulated for the blocking effect of pirenzepine.