The Effect of Cholesterol Feeding and Alterations in Bile Acid Homeostasis on De Novo Sterologenesis in Diabetic Rats

Previous studies have demonstrated that de novo cholesterol synthesis is increased two- to threefold in the intestines of diabetic animals. This increase is due to a stimulation of cholesterogenesis in both the small and large intestine but, quantitatively, the small intestine is primarily responsible for the observed increase. The present study examined the effect of cholesterol feeding and alterations of bile acid homeostasis on de novo sterol synthesis in intact normal and diabetic animals. Cholesterol feeding in the control animals did not affect sterol synthesis in the small intestine, but in diabetic animals cholesterol feeding markedly inhibited small intestinal sterologenesis. The threefold stimulation of small intestinal sterol synthesis observed in diabetic animals is completely obliterated by cholesterol ingestion. Moreover, this inhibition of sterol synthesis by cholesterol feeding in the small intestine of diabetic animals occurred very rapidly (within 36 h). In the large intestine, cholesterol feeding did not influence sterol synthesis in either the diabetic or control animals. In the liver, cholesterol feeding markedly inhibited sterol synthesis to similar degrees in the diabetics and controls. Colestipol feeding and biliary drainage, procedures that reduce bile acid pool size, stimulated sterol synthesis in the liver and small intestine of both diabetic and control animals. However, reductions in bile acid pool size increased sterologenesis in the large intestine in control animals but had no effect in the diabetics. Bile acid ingestion did not alter either small or large intestinal sterologenesis in the diabetic or control animals. In conclusion, the present study demonstrates the sterol synthesis is enhanced in the small and large intestine of diabetic animals and, moreover, both the cholesterol- and bile acid-mediated regulation of cholesterol synthesis in the intestines of the diabetic animals is altered from normal.