[Positive inotropic action of acetylcholine on the heart ventricles of the chick embryo].

Acetylcholine increased twitch tension in the whole ventricle or in ventricular strips from 2-10-day chick embryos. The effect of acetylcholine was mediated by muscarinic receptors, since it was prevented by atropine, but not by tubocurarine or propranolol. Prostigmine significantly increased the sensitivity to acetylcholine in the strips from 7-day embryos, being almost ineffective in the strips from 3-day embryos. The decrease in acetylcholine sensitivity in the developing chick embryo is presumably associated with the increase in cholinesterase activity of the myocardial tissue.