[Seasonal variability in the cholinergic reaction of the frog heart].

Seasonal changes in sensitivity to acetylcholine were studied on the isolated frog ventricle. The highest sensitivity was observed in autumn and winter (November-January). In spring, from the period of reproduction, the sensitivity to acetylcholine drops to-threefold and remains at a low level until September. Seasonal changes were more obvious in females. The observed seasonal changes are discussed with reference to ecology, state of reproductive system, etc.