Dose-dependent actions of spironolactone on the inner and outer zones of the guinea pig adrenal cortex.

The results of prior in vitro studies indicated that spironolactone (SL) caused far greater degradation of cytochromes P-450 in the outer (zona glomerulosa plus zona fasciculata) than inner (zona reticularis) zone of the guinea pig adrenal cortex and selectively decreased microsomal 17 alpha-hydroxylase activity. Studies were done to determine if the effects of SL in vivo were similarly zone and/or enzyme selective. Administration of high doses of SL (100 mg/kg) to guinea pigs altered the gross appearance of the adrenal glands and caused declines in 17 alpha- and 21-hydroxylase activities in both inner and outer zone microsomal preparations. The losses in enzyme activities were accompanied by decreases in microsomal cytochrome P-450, cytochrome b5 and heme concentrations, and in mitochondrial P-450 levels in both zones. Microsomal P-450(17 alpha) apoprotein levels were also decreased in both zones. A lower dose (25 mg/kg) of SL did not affect adrenal morphology, but decreased microsomal P-450 levels in both zones. Neither mitochondrial P-450 nor microsomal b5 concentrations were affected in either zone. 17 alpha-Hydroxylase activities and P-450(17 alpha) apoprotein concentrations in both zones were decreased by the lower dose of SL, but 21-hydroxylase activity declined in the inner zone only. The results indicate that very high doses of SL have a variety of nonspecific effects on the adrenals which may be the consequence of drug toxicity. Nontoxic doses exert more selective effects on microsomal cytochromes P-450 in both adrenal zones, more closely mimicking the in vitro actions of the drug.