Effect of P-450scc inhibitors on corticosterone production by rat adrenal cells.

Suspensions of rat adrenocortical cells produce corticosterone as the major glucocorticoid. Cholesterol side-chain cleavage, the initial and rate-limiting step in the glucocorticoid biosynthetic pathway, is catalyzed by P-450scc. We have examined the effect of a variety of P-450scc inhibitors on corticosterone production by isolated rat adrenocortical cells. These inhibitors include reversible, noncovalently interacting inhibitors as well as mechanism-based inhibitors which irreversibly inactivate P-450scc in vitro. (20S)-22-nor-22-thiacholesterol and (22R)-22-aminocholesterol cause 50% inhibition of corticosterone production at 4 microM and 30 nM, respectively. Inhibition by these compounds was essentially not time-dependent. (20R)-20-(1-hexynyl)-pregn-5-en-3 beta, 20-diol and (20R)-20-(1,5-hexdiynyl)-pregn-5-en-3 beta, 20-diol at 10 microM inhibited corticosterone production in a time-dependent manner, resulting in 30% inhibition of corticosterone production during a 100-min incubation. (20S)-20-(2-trimethylsilyl ethyl)-pregn-5-en-3 beta, 20-diol inhibited in a strongly time-dependent manner. At 10 microM this compound irreversibly inhibited more than 90% of the side-chain cleavage capacity of the cell during a 40-min incubation. Cells treated with this steroid did not regain their capacity for side-chain cleavage after removal of free steroid. None of the inhibitors described above inhibited production of corticosterone by cells supplied with pregnenolone, the product of the P-450scc reaction. We suggest that the only significant effect of these compounds under these conditions is inhibition of the side-chain cleavage enzyme.