Adrenal mitochondrial metabolism of spironolactone. Absence of metabolic activation.

Previous investigations have established that spironolactone (SL) administration to guinea pigs decreases adrenal mitochondrial and microsomal cytochrome P-450 content, and that the latter requires microsomal activation of the drug. Studies were carried out to determine if adrenal mitochondrial metabolism (activation) of SL was similarly involved in the effects of the drug on mitochondrial cytochrome P-450 destruction. Incubation of guinea pig adrenal mitochondria with SL in the absence of NADPH resulted in the formation of 7 alpha-thio-SL as the only metabolite. In the presence of an NADPH-generating system, an unknown polar metabolite was also produced. The mass spectrum of the unknown compound suggested that it was a hydroxylated derivative of SL. Incubation of mitochondrial preparations with 7 alpha-thio-SL also resulted in the formation of a polar metabolite, but the latter had a different HPLC retention time than that of the SL metabolite. Formation of the polar SL metabolite was prevented by metyrapone, an 11 beta-hydroxylase inhibitor, and was greatest in mitochondria from the adrenal zone having the highest 11 beta-hydroxylase activity. Steroid substrates for 11 beta-hydroxylation inhibited the production of the SL metabolite. Mitochondrial incubations with SL or with 7 alpha-thio-SL in the presence or absence of an NADPH-generating system did not affect cytochrome P-450 concentrations. The results indicate that, unlike the microsomal effects of SL, local activation of SL is not responsible for the destruction of adrenal mitochondrial cytochromes P-450. The major adrenal mitochondrial metabolites of SL appear to be 11 beta-hydroxy-SL and 7 alpha-thio-SL.

Effects of cadmium in vitro on microsomal steroid metabolism in the inner and outer zones of the guinea pig adrenal cortex.

Studies were carried out to evaluate the effects of cadmium in vitro on microsomal steroid metabolism in the inner (zona reticularis) and outer (zona fasciculata and zona glomerulosa) zones of the guinea pig adrenal cortex. Microsomes from the inner zone have greater 21-hydroxylase than 17 alpha-hydroxylase activity, resulting in the conversion of progesterone primarily to 11-deoxycorticosterone and of 17 alpha-hydroxyprogesterone principally to its 21-hydroxylated metabolite, 11-deoxycortisol. Microsomes from the outer zones, by contrast, have far greater 17 alpha-hydroxylase and C17,20-lyase activities than 21-hydroxylase activity. As a result, progesterone is converted primarily to its 17-hydroxylated metabolite, 17 alpha-hydroxyprogesterone; and 17 alpha-hydroxyprogesterone is converted principally to delta 4-androstenedione, with only small amounts of 21-hydroxylated metabolites being produced. Addition of cadmium to incubations with inner zone microsomes causes concentration-dependent decreases in 21-hydroxylation and increases in 17 alpha-hydroxylase and C17,20-lyase activities, resulting in a pattern of steroid metabolism similar to that in normal outer zone microsomes. Cadmium similarly decreases 21-hydroxylation by outer zone microsomes but has no effect on the formation of 17-hydroxylated metabolites or on androgen (delta 4-androstenedione) production. In neither inner nor outer zone microsomes did cadmium affect cytochrome P-450 concentrations, steroid interactions with cytochrome(s) P-450, or NADPH-cytochrome P-450 reductase activities. The results indicate that cadmium produces both quantitative and qualitative changes in adrenal microsomal steroid metabolism and that the nature of the changes differs in the inner and outer adrenocortical zones. In inner zone microsomes, there appears to be a reciprocal relationship between 21-hydroxylase and 17 alpha-hydroxylase/C17,20-lyase activities which may influence the physiological function(s) of that zone.

Metabolism of spironolactone by adrenocortical and hepatic microsomes: relationship to cytochrome P-450 destruction.

Previous investigations have established that spironolactone (SL) is converted to a reactive metabolite by adrenocortical NADPH-dependent enzymes, resulting in the destruction of microsomal cytochrome(s) P-450 and decreases in steroid hydroxylase activities. Hepatic microsomes, by contrast, do not activate SL. Studies were done to characterize the activation pathway by comparing adrenal with hepatic metabolism of SL in guinea pigs. In the absence of NADPH, both adrenal and hepatic microsomal preparations converted SL to its deacetylated metabolite, 7 alpha-thio-SL. NADPH had no effect on hepatic SL metabolism but stimulated adrenal metabolism of SL. In the presence of NADPH, very little 7 alpha-thio-SL was recovered from the adrenal incubations, suggesting that the 7 alpha-thio-SL was further metabolized by NADPH-dependent enzymes. The latter hypothesis was confirmed by incubating microsomal preparations with 7 alpha-thio-SL as the substrate. In the presence of NADPH, 7 alpha-thio-SL was rapidly metabolized by adrenal microsomes but was not metabolized by hepatic preparations. Under the same incubation conditions, 7 alpha-thio-SL promoted the destruction of adrenal cytochrome(s) P-450 but had no effect on hepatic monooxygenases. 7 alpha-Thio-SL was far more potent than SL in promoting the destruction of cytochrome(s) P-450, suggesting that the metabolite might be an intermediate in the actions of the parent compound. Indeed, inhibition of SL conversion to 7 alpha-thio-SL by the esterase inhibitor, diethyl p-nitrophenyl phosphate blocked the effects of SL on adrenal cytochrome(s) P-450. Diethyl p-nitrophenyl phosphate did not affect the actions of 7 alpha-thio-SL on cytochrome(s) P-450.(ABSTRACT TRUNCATED AT 250 WORDS)