We measured intestinal absorption of cholesterol by a plasma isotope ratio method and determined biliary bile acid and lipid composition of fasting gallbladder bile in 5 gallstone patients before therapy and during two randomized treatment periods with chenodeoxycholic or ursodeoxycholic acid (13 mg/kg . day), During chenodeoxycholic acid ingestion, biliary bile acids were composed predominantly (84%) of conjugates of chenodeoxycholic acid, During ursodeoxycholic acid administration, conjugates of ursodeoxycholic acid constituted half the bile acid pool (49%). Fasting gallbladder bile was supersaturated in cholesterol before treatment, but became unsaturated during administration of both chenodeoxycholic and ursodeoxycholic acids, In spite of these marked changes in biliary bile acid and lipid composition, cholesterol absorption was not significantly different before (45.4 ± 4.3%. mean ± SEM) or after chenodeoxycholic (42.7 ± 5,1%) or ursodeoxycholic (46.8 ± 3.7%) acid ingestion. We conclude that chenodeoxycholic and ursodeoxycholie acids unsaturate bile in cholesterol and dissolve gallstones by a mechanism other than the suppression of intestinal absorption of cholesterol.
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