Antagonism of the inotropic action of ouabain by aldosterone

¹ Department of Physiology, Western Reserve University School of Medicine, Cleveland, Ohio

Aldosterone (3.3 x 10^–8 to 10^–7 m) exerted a small positive inotropic effect on cat Langendorff heart preparations depressed by pentobarbital and on cat papillary muscles depressed by low calcium. Equimolar concentrations of ouabain exerted a much greater inotropic effect in both preparations compared to aldosterone. Aldosterone (3.3 x 10^–8 to 10^–7 m) antagonized both the positive inotropic effect of cardiotonic concentrations and the bradycardia and cardiac arrest of toxic concentrations of ouabain. Cortisol (10^–7 to 10^–5 m) did not antagonize the effects of ouabain. Addition of aldosterone 20 min prior to the ouabain exerted maximal inhibition. Simultaneous aldosterone and ouabain addition resulted in a lesser degree of inhibition. Addition of aldosterone at the peak of the ouabain effect did not influence the subsequent course of the ouabain-induced inotropic effect.

Key Words: cardiac glycosides • corticosteroids • cardiac arrest • physiological antagonism • papillary muscle • Langendorff preparation • isolated heart • cardiotonic action • toxic effect

Submitted on July 16, 1964