[2 unusual responses of the myocardium in the frog Rana temporaria to acetylcholine].

When studying seasonal variations in acetylcholine sensitivity of isolated frog ventricle, two forms of unusual responses have been observed: 1) tonic response induced by supermaximal concentration of acetylcholine, and 2) double response to the increasing acetylcholine concentrations with two different threshold and maximum doses (KAch values differ by 1-2 orders). The tonic response is blocked by mytolone. Both effects are of a seasonal nature. Similar pattern of these reactions in frogs and molluscs suggests a possibility of restoration of evolutionary more ancient form of cholinergic response, hormonal influences being involved into this process.