Interaction of metyrapone with adrenal microsomal cytochrome P450 in the guinea pig

Studies were carried out to compare the actions of metyrapone on adrenal mitochondrial and microsomal cytochrome P450-containing enzymes in the guinea pig and rat. As expected. addition of metyrapone to adrenal mitochondria inhibited 11β-hydroxylation in both species. the shape of the type II difference spectrum produced by metyrapone in mitochondria differed somewhat in rat (gDO.D._425?405nm) and guinea pig (gDO.D._425?390nm) and the magnitude of the speetrum was far greater in rat adrenal mitochondria, paralleling species differences in cytochrome P450 concentration (rat > guinea pig). In rat adrenal microsomes, metyrapone produced a small “reverse type I” spectral change (ΔO.D._420-385nm) but did not affect either 21-hydroxylation or the interaction of progesterone with eytochrome P450(as determined spectrally). In guinea pig adrenal microsomes, in contrast, metyrapone produced a large type II spectral change (ΔO.D._423-408nm) and inhibited both 21-hydroxylation and ethylmorphine demethylation, cytochrome P450-dependent reactions. The magnitudes of type I spectra produced by 17α-hydroxyprogesterone and ethylmorphine in guinea pig adrenal microsomes were significantly diminished by prior addition of metyrapone. The results indicate that metyrapone interacts with both microsomal and mitochondrial cytochrome P450 in the guinea pig and that its adrenal sites of action, therefore, are species dependent.