Dietary regulation of hepatic enzymes in taurine biosynthesis in rats

Abstract

The effect of various dietary fibers, cholesterol, and bile acid on tissue taurine levels and the activity of hepatic enzymes in the taurine synthetic pathway was compared in rats. Compared with water-insoluble dietary fibers (10% in the diet, cellulose, and chitin), water-soluble dietary fibers (10% in the diet, pectin, and konjak mannan) decreased taurine levels in the liver and serum. A diet containing cholesterol (1%), sodium cholate (0.25%), and both of these steroids also reduced taurine levels in the liver and serum accompanying the decrease in urinary excretion of this compound. Cysteine dioxygenase activity was significantly lower in rats fed water-soluble fibers than in those fed water-insoluble fibers. Compared to water-insoluble dietary fibers, water-soluble fibers increased cysteinesulfinic acid decarboxylase activity. Compared with the steroid-free control diet, diets containing cholesterol, bile acid, and both of these steroids reduced cysteine dioxygenase activity. Dietary bile acid also reduced cysteinesulfinic acid decarboxylase activity, in contrast with cholesterol which increased it. Decarboxylase activity in rats fed a diet containing both of these steroids was comparable to that in animals fed a control diet. Aspartate aminotransferase activity was also modified by these dietary factors in some cases, but to a lesser extent. Fiber and steroids thus are dietary factors that demonstrably alter hepatic taurine synthesis in the rat.