Formation and Metabolism of Cholest-5-ene-3beta,12alpha-diol. Bile Acids and Steroids 205

When labeled cholesterol was incubated with the 20,000 ×g supernatant fluid of rat liver homogenate, cholest-5-ene-3β,12α-diol could be isolated only in very small amounts indicating that cholest-5-ene-3β,7α-diol is the predominant intermediate in the conversion of cholesterol into cholest-5-ene-3β,7α,12α-triol. In the presence of 20,000 ×g supernatant fluid tritium-labeled cholest-5-ene-3β,12α-diol was converted into 7α,12α-dihydroxycholest-4-en-3-one mainly by means of the intermediary formation of cholest-5-ene-3β,7α,12α-triol. In the presence of microsomal fraction fortified with NADP, cholest-5-ene-3β,12α-diol was converted into 12α-hydroxycholest-4-en-3-one. Tritium-labeled 12α-hydroxycholest-4-en-3-one was converted in the presence of 100,000 ×g supernatant fluid into 5β-cholestane-3α,12α-diol by means of the intermediary formation of 12α-hydroxy-5β-cholestan-3-one. When 12α-hydroxycholest-4-en-3-one was incubated with the 20,000 ×g supernatant fluid, small amounts of 5β-cholestane-3α,7α,12α-triol were formed. No 7α-hydroxylated metabolites could be identified when tritium-labeled 12α-hydroxy-5β-cholestan-3-one and 5β-cholestane-3α,12α-diol were incubated with the 20,000 ×g supernatant fluid. After administration of tritium-labeled 12α-hydroxycholest-4-en-3-one to bile fistula rabbits 2–3% of the bile acids formed consisted of cholic acid. After administration of tritium-labeled 12α-hydroxy-5β-cholestan-3-one and 5β-cholestane-3α,12α-diol no significant amounts of cholic acid could be identified. It is concluded that the initial reaction in the conversion of cholesterol into cholic acid is predominantly a 7α-hydroxylation.