Dietary fat dependence of intestinal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity in rats

The effects of dietary fats on intestinal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity were studied in rats. Animals were fed experimental diets ad libitum for 7-13 d then killed in the morning for the determination of the reductase activity in an epithelial cell homogenate. When corn oil was the source of dietary fat, the specific activity of jejunal reductase depicted a biphasic pattern in response to dietary fat level with a peak activity when the diet contained 10% fat (by weight) whereas the specific activity of ileal reductase was independent of the fat level. Reductase activities were apparently independent of the degree of saturation of dietary fat (safflower oil, olive oil, lard and tallow) when each was fed as 10% of the diet. Both jejunal and ileal reductase activities were higher when trilaurin was fed than when other saturated fats (tricaprylin, trimyristin, tripalmitin and tristearin) were fed. The jejunum synthesized more cholesterol than the ileum. There was no significant correlation among the reductase activity, cholesterol content of the epithelial cells and the rate of fat absorption, suggesting a complex regulatory mechanism.