Effect of cytosol fractions from lutropin-stimulated rat testes on pregnenolone production by mitochondria from normal rat testes.

The rate limiting step in the production of steroids in the testis is the mitochondrial conversion of cholesterol to pregnenolone. This conversion can be stimulated by lutropin, but the precise interaction between lutropin-induced cytoplasmic factors and the mitochondrial activity in steroid production is as yet unknown. The results described in the present paper concern the steroid production of isolated mitochondrial fractions in recombination experiments with isolated supernatant fractions from total testes homogenates. Cyanoketone as well as SU-10603, an inhibitor of steroid 17 alpha-hydroxylase activity are required to block pregnenolone metabolism. The results show that the cytoplasm contains lutropin-induced factor(s) which can exert its effect in vitro on the cholesterol side-chain cleavage activity in intact mitochondria isolated from control testes.