[The inotropic action of acetylcholine on the heart ventricles during larval development in the frog Rana temporaria].

The effects of acetylcholine and other cholinergic drugs on the isolated electrically driven larval frog ventricles have been studied. The negative inotropic response to acetylcholine appeared as early as stage 33 of the larval development (the stages were determined according to Dabagian and Sleptsova, 1975) and persisted through all the developmental stages including metamorphosis. The response is muscarinic in origin since it was reproduced with a muscarinic agonist methylfurmetide, blocked with atropine but was not modified with tubocurarine. At the stage 41 and following stages, the sensitivity to acetylcholine was decreased while to methylfurmetide was not. The decreased sensitivity to acetylcholine is most likely due to increase of activity of cholinesterases in the myocardial tissues.