Cholic acid synthesis from 26-hydroxycholesterol and 3-hydroxy-5-cholestenoic acid in the rabbit.

Intravenous administration of 26-hydroxycholesterol to the rabbit with a bile fistula yielded cholic acid in proportions (84 and 86%) not significantly different from that derived from cholesterol. By contrast, the naturally occurring C27 bile acid 3 beta-hydroxy-5-cholestenoic acid yielded not more than 8% cholic acid. Thus initial 26-hydroxylation of cholesterol followed by 7-alpha-hydroxylation can provide sufficient amounts of cholic acid to be considered a quantitatively significant pathway for bile acid synthesis, and in addition it is the only pathway that can be the source of the circulating levels of C24 and C27 monohydroxy bile acids.