Ursodeoxycholic acid (UDCA) decreases biliary secretion of cholesterol and has therefore been used for the dissolution of cholesterol gallstones. It remained unclear whether these changes in biliary cholesterol excretion are associated with changes in cholesterol synthesis and bile acid synthesis. The activities of the rate-limiting enzymes of both, cholesterol and bile acid synthesis, have been studied in normal subjects during 8-14 mg/kg UDCA feeding. Moreover, lipoproteins and bile acids were measured. Before, during, and after 40 days of UDCA ingestion, 7-alpha-hydroxy-4-cholesten-3-one in serum and urinary excretion of mevalonic acid were determined. Ursodeoxycholic acid treatment seems to not affect cholesterol synthesis in the liver, but does increase bile acid synthesis after prolonged treatment. This may attribute to homeostasis of cholesterol in the liver while preventing an excess of cholesterol
