Antagonism of the inotropic action of ouabain by aldosterone

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Abstract
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.

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