Inhibitory effect and interaction of stanozolol with pig testicular cytochrome P-450 (17 alpha-hydroxylase/C17,20-lyase).

The inhibitory effect of an anabolic steroid, stanozolol, on testicular microsomal cytochrome P-450 (17 alpha-hydroxylase/C17,20-lyase) (P-450(17 alpha/lyase] and the nature of the interaction were compared with those of other anabolic steroids, furazabol and mestanolone. Stanozolol markedly inhibited delta 16-C19-steroid synthesizing activity, 17 alpha-hydroxylase and C17,20-lyase activities, which were mediated by oxygenase activities of testicular microsomal cytochrome P-450(17 alpha/lyase). In addition, stanozolol was a competitive inhibitor of 17 alpha-hydroxylase (Ki = 6.31 microM) and C17,20-lyase (Ki = 1.30 microM) activities in the reconstituted enzyme system. The interaction of cytochrome P-450&17 alpha/lyase) with stanozolol induced a type I difference spectrum (peak at 387 nm and trough at 418 nm) with a dissociation constant (Ks) of 1.47 microM.