MECHANISM OF ACTION OF SPIRONOLACTONE ON ADRENOCORTICAL FUNCTION IN GUINEA-PIGS

Abstract

Spironolactone administration (50 mg/kg per day for 3 days) to male guinea pigs decreased cortisol production by adrenal slices in vitro. Adrenal microsomal and mitochondrial cytochrome P-450 levels were also decreased after treatment with spironolactone. The decline in adrenal cytochrome P-450 content was accompanied by decreases in microsomal 21-hydroxylase and mitochondrial cholesterol side-chain cleavage and 11.beta.-hydroxylase activities. Activities of other adrenal enzymes, such as .DELTA.4-hydrogenase and NADPH-cytochrome c reductase, were unaffected by spironolactone treatment. Cortisone administration to guinea pigs failed to mimic the effects of spironolactone on adrenal function, which indicates specificity of spironolactone action and excludes inhibition of ACTH secretion as a mode of action. Addition of spironolactone to isolated adrenal mitochondria or microsomes produced type I spectral changes with spectral dissociation constants similar to those for endogenous steroid substrates. Spironolactone, in vitro, inhibited 11.beta.- but not 21-hydroxylase activity. Spironolactone administration diminishes the activity of adrenal mitochondrial and microsomal cytochrome P-450-containing enzymes, resulting in a fall in corticosteroid output.