Effect of Spironolactone and Its Metabolites on Contractile Property of Isolated Rat Aorta Rings

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Abstract
Spironolactone and its active metabolites canrenone and potassium canrenoate are normally used as antihypertensive drugs. Although they are classified as antagonists of aldosterone, their mechanism of action cannot be ascribed solely to the regulation of ion transport in the distal tubule of nephrons. Here we have evaluated the effects of spironolactone, canrenone, and potassium canrenoate on contractile properties of isolated rat aorta rings. Spironolactone (1-300 microM), canrenone (1-300 microM), and potassium canrenoate (0.01-10 mM), in a concentration-dependent manner, relaxed rat aorta rings precontracted with phenylephrine (1 microM) or KCl (40 mM). These relaxant effects were not affected by prior treatment with either aldosterone (100 microM), glibenclamide (10 microM), or tetraethylammonium (10 mM), excluding the possibility that these drugs can be involved in either the nongenomic effect of aldosterone or on activation of potassium channels. Spironolactone and canrenone at concentrations of 30 and 100 microM, but not at 10 microM, and potassium canrenoate at concentrations of 0.3 and 1 mM, but not at 0.1 mM, significantly inhibited the phenylephrine (0.001-3 microM) concentration-response curve. Conversely, all tested concentrations of spironolactone (10, 30, and 100 microM), canrenone (10, 30, and 100 microM), and potassium canrenoate (0.1, 0.3, and 1 mM) significantly inhibited the concentration-response curve induced by cumulative concentrations of KCI (10-80 mM). Because both phenylephrine- and KCl-induced contractions imply an intracellular Ca2+ influx, we suggest that these drugs could act through an inhibition of voltage-dependent Ca2+ channels.