The formation of ursodeoxycholic acid,the 7P-hydroxy epimer of chenodeoxychoicl acid, was investigated in three subjects with cerebrotendinous xanthomatosis and in four subjects with gallstones. Totalbiliary bile acid composition was analyzed by gas-liquidchromatography before and after 4 months of treatmentwith 0.75 g/day of chenodeoxycholic acid. Individualbile acids were identified by mass spectrometry.

Beforetreatment, bile from cerebrotendinous xanthomatosis(CTX) subjects contained cholic acid, 85%; chenodeoxycholicacid, 7%; deoxycholic acid, 3%; allocholicacid, 3%;andunidentified steroids, 2%; while bile from gallstone subjects contained cholic acid, 45%;chenodeoxycholic acid, 43%; deoxycholic acid, 11%, andlithocholic acid, 1%.Inallsubjects, 4 months of chenodeoxycholic
acid therapy increased the proportion of thisbile acid to approximately 80% and decreased cholic acid3% of the total biliary bile acids, the remaining 17 of bile acids were identified as ursodeoxycholic acid.

After the intravenous injection of [3H]chenodeoxycholicacid, the specific activity of biliary ursodeoxycholic acidexceeded the specific activity of chenodeoxycholic acid,and theresulting specific activity decay curves suggestedprecursor-product relationships. When [2H]7-ketolithocholicacid was administrated to another patient treatedwith chenodeoxycholic acid, radioactivity was detectedin both the ursodeoxycholic acid and chenodeoxycholic acid fractions.