Effect of bile acid conjugation pattern on bile acid metabolism in normal humans

Six male subjects were fed taurine 0.5 g six times daily for 2 wk to determine the effect of a shift in bile acid conjugation pattern upon bile acid metabolism. Duodenal bile acids were analyzed, and bile acid pool size, daily fecal excretion, and biliary excretion rate were quantified. In addition, daily biliary excretion rate of cholesterol and phospholipid were quantified, and biliary saturation with cholesterol was estimated. The dose of taurine caused reversal of the bile acid glycine-to-taurine conjugation ratio. Total bile acid pool size decreased, as did the pool size of chenodeoxycholic acid. Pool sizes of cholic and deoxycholic acids did not change. Daily fecal bile acid excretion decreased slightly. Biliary secretion rates of cholesterol, phospholipid, and bile acids did not change, nor did biliary cholesterol saturation. Pool size can decrease because of increased bile acid catabolism or decreased synthesis. The fact that bile acid excretion failed to increase, and actually decreased slightly, suggests that the effect is upon bile acid synthesis. In normal humans, the effect is small and probably physiologically unimportant. In special cases, however, such as during ursodeoxycholic acid therapy, the effect of shifting conjugation pattern may become important.