ANTAGONISM BY SOME BETA-ADRENOCEPTOR-BLOCKING AGENTS TO CHOLINERGIC STIMULATION OF SKELETAL-MUSCLE INVITRO

Antiacetylcholine activity of some β-adrenoceptor-blocking drugs was investigated using isolated guinea pig cremaster muscle and frog rectus abdominis muscle. On the cremaster muscle, the antagonism to acetylcholine was noncompetitive in Kö 1313, (±)-INPEA and (–)-INPEA, competitive in (+)-INPEA and functional in practolol. All three INPEA isomers, practolol and propranolol behaved as noncompetitive antagonists of acetylcholine on frog rectus muscle. Caffeine-induced contractions of this muscle were partially inhibited by propranolol but not by the other drugs. It is suggested that the β-adrenoceptor-blocking drugs produce their antiacetylcholine action by interacting with sites on the muscle which are different from the cholinoceptor, and which vary between compounds and species. © 1979 S. Karger AG, Basel.