Effect of adriamycin on myocardial contractility and on the action of antibiotic ionophores.

In the isolated guinea pig atria adriamycin exerted a negative inotropic effect; calcium ionophores A23187 and X537A increased the force of contraction. In the presence of adriamycin only the positive inotropic effect of ionophore A23187 was significantly reduced. It may be deduced that adriamycin shows its negative inotropic effect by inhibiting the entry of extracellular Ca++ into the myocardial cells and the release of Ca++ from intracellular stores.