Effect of dietary taurine on cholesterol 7 alpha-hydroxylase activity in the liver of mice fed a lithogenic diet.

The effect of dietary taurine on hepatic cholesterol 7 alpha-hydroxylase activity was investigated in mice. At first, male ICR strain mice were fed a commercial non-purified diet for 4 weeks and killed at 01:00 h (midnight) or 13:00 h (daytime) and the cholesterol 7 alpha-hydroxylase activity in the hepatic microsomal fraction was measured. The enzyme activity was 5.9-fold higher at midnight than in the daytime. Next, to investigate the effect of dietary taurine on the activity of this enzyme, male ICR strain mice were fed semi-purified diets for 5 weeks: a cholesterol-free diet (standard), a lithogenic diet containing 0.5% cholesterol and 0.25% sodium cholate (C-CA), and a lithogenic diet supplemented with 5% taurine (C-CA + 5% taurine). All mice were killed at midnight and cholesterol 7 alpha-hydroxylase activity was measured. The enzyme activity of the mice fed the lithogenic diet was about 20% that of mice fed the standard diet. Dietary taurine increased the activity by 1.9-fold. Therefore, it was concluded that the inhibitory effect of dietary taurine on cholesterol gallstone formation was related to increased bile acid synthesis as reflected by stimulation of cholesterol 7 alpha-hydroxylase activity.