The primary bile acids (cholic acid and chenodeoxycholic acid) are synthesized from choles- terol in the liver. The rate-limiting enzyme in this biosynthetic pathway is cholesterol 70t-hydroxylase, which is feedback-inhibited by cholic acid. These primary bile acids are secreted in bile into the intestinal lumen, where they are dehydroxylated by intestinal bacteria to form the secondary bile acids deoxycholic acid and lithocholic acid. In the intestine, a portion of each primary bile acid is dehydroxylated to form a secondary bile acid, and a portion is left unchanged