Inhibition of cholesterol side-chain cleavage by intermediates of an alternative steroid biosynthetic pathway

Mitochondrial preparations from endocrine tissues were incubated with radioactive cholesterol and the effect of hydroxylated metabolites of 23,24-dinor-5-cholen-3 beta-ol (23,24-dinor-5-cholene-3 beta,20-diol and 23,24-dinor-5-cholene-3 beta,21-diol) on the production of pregnenolone was measured. These compounds are intermediates in an alternative, sesterterpene pathway for steroid hormone biosynthesis. It was found that these materials, like the analogous side-chain-hydroxylated derivatives of cholesterol (20 alpha-hydroxycholesterol and 22S-hydroxycholesterol), inhibit cholesterol side-chain cleavage. The possibility that there could be a control mechanism whereby metabolites of 23,24-dinor-5-cholen-3 beta-ol inhibit steroidogenesis occurring by the cholesterol pathway is discussed.