Relation of Canrenone to the Actions of Spironolactone on Adrenal Cytochrome P-450-Dependent Enzymes*

Abstract

Studies were carried out to determine the actions of spironolactone (SL) and its metabolite, canrenone, on adrenal mixed function oxidases in the guinea pig. Administration of SL (25 mg/kg day for 3 days) to adult male guinea pigs decreased adrenal mitochondrial and microsomal cytochrome P-450 concentrations. The activities of various cytochrome P-450- dependent enzymes, including mitochondrial 11β-hydroxylase and microsomal 21-hydroxylase, benzo(a)-pyrene (BP) hydroxylase and ethylmorphine (EM) demethylase, were also reduced by SL treatment. Canrenone, when given at the same dose, had no effect on mitochondrial or microsomal cytochrome P-450 levels. Pretreatment with canrenone decreased 11β- and 21- hydroxylase activities but did not affect BP hydroxylation or EM demethylation. Addition of SL or canrenone to isolated adrenal mitochondria or microsomes produced typical type I difference spectra. Both compounds inhibited the binding of steroid substrates to cytochrome P-450 in isolated mitochondria and microsomes, decreasing 11β- and 21-hydroxylase activities. In vitro, canrenone was the more potent inhibitor of 11β- and 21-hydroxylation. SL, in vitro, also inhibited microsomal EM demethylation and BP hydroxylation, whereas canrenone had little or no effect on either reaction. Incubation of adrenal microsomes with SL in the presence of NADPH decreased cytochrome P-450 and heme content. Incubation with canrenone under identical conditions had no effect. The results indicate that the actions of SL on adrenocortical function are not mediated by its metabolite, canrenone, since the two drugs have different effects. In addition, the divergent effects of canrenone and SL on adrenal microsomal metabolism can probably be attributed in part to interactions with different cytochrome P-450 moieties.