The effects of adrenal and gonadal steroids and K+-canrenoate on the metabolism of aldosterone by rat liver microsomes |
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Authors: | S A Latif M J McDermott D J Morris |
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Affiliation: | The Miriam Hospital, Department of Laboratory Medicine and Brown University, Providence, Rhode Island 02906, U.S.A. |
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Abstract: | The synthesis of polar aldosterone metabolites by rat liver microsomes at physiological concentrations of aldosterone (21.5 nM), was markedly inhibited by progesterone, testosterone, corticosterone, K+-canrenoate and estradiol-17 beta. In contrast, corticosterone and estradiol-17 beta significantly increased the synthesis of reduced aldosterone metabolites by 8- and 15-fold respectively, the majority of which were 5 alpha-reduced products of aldosterone. In experiments at higher substrate (aldosterone) concentrations (20-200 microM) the synthesis of ring A-reduced aldosterone metabolites by liver microsomes followed Michaelis-Menten kinetics with a Km[app] for aldosterone of 160 microM and Vmax[app] of 12.2 nmoles/mg protein/5 min. In these experiments progesterone, testosterone and K+-canrenoate all competitively inhibited the synthesis of reduced metabolites with inhibition constants (Ki [app]) of 70, 85 and 55 microM respectively; however, corticosterone did not. In contrast, estradiol-17 beta increased the rate of synthesis of reduced products by 40%, lowering the Km[app] to 83 microM. |
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