Rapid Effects of Aldosterone and Spironolactone in the Isolated Working Rat Heart

Chronic administration of aldosterone promotes myocardial fibrosis in rats. The Randomized Aldactone Evaluation Study reported that the aldosterone antagonist spironolactone improved outcome in patients with congestive heart failure, suggesting a deleterious effect of aldosterone in the heart. Aldosterone has been shown to have rapid nongenomic effects in different tissues including the heart. However, the hemodynamic actions of aldosterone and spironolactone are not well characterized. In this study, we examined the hemodynamic effects of aldosterone and its receptor antagonist, spironolactone, in the isolated rat heart by use of the Langendorff-Neely technique. Perfusion with 10 nmol/L aldosterone increased contractility by 45% within 2 to 4 minutes (P<0.01). Similar to the aldosterone effect, 10 nmol/L spironolactone increased contractility by 41% (P<0.01). Furthermore, 100-fold molar excess of spironolactone did not block the aldosterone effect. Perfusion of aldosterone plus spironolactone resulted in the highest increase in contractility 106% (P<0.01). The threshold response for aldosterone occurred within physiological concentrations (0.5 to 1 nmol/L), and maximal contractility was achieved with 10 nmol/L aldosterone. For spironolactone, the threshold and maximal contractile responses occurred at concentrations readily achieved with clinical dosing, 0.1 to 0.5 nmol/L and 1.0 nmol/L, respectively. These data demonstrate that aldosterone and spironolactone have rapid, positive inotropic actions on the myocardium. Moreover, addition of spironolactone to aldosterone increased contractility beyond the maximal responses elicited by each agent when perfused alone, thus suggesting different pathways of action. Furthermore, the intrinsic inotropic effects of spironolactone might be relevant to the apparent beneficial effect this compound has in patients with congestive heart failure.