[2 Phases of the inotropic action of adrenaline. Calcium dependence].

The biphasic inotropic effect of adrenaline administered for a long time (30 min) was studied on a frog ventricular strip. The fall in the contraction amplitude got more pronounced as the intensity of Ca ions entrance into the myocardial cells was potentiated by the increased frequency of stimulation and calcium or adrenaline concentrations were raised. The mechanisms of the adrenaline-induced decrease in the contraction amplitude are discussed.