Changes in cholesterol accumulation and steroid excretion in response to cellulose, alfalfa or oats in cholesterol-fed rats

Abstract

Experiments were conducted to investigate the mechanisms by which some sources of dietary fiber reduce accumulation of liver cholesterol in rats fed a cholesterol-containing diet. Male Wistar rats were fed a semipurified diet containing no fiber (sucrose replacing dietary fiber) or 15% cellulose, alfalfa or whole ground oats as a source of dietary fiber with a without 0.25% cholesterol added. Serum and liver cholesterol level, liver HMG CoA reductase activity, and fecal bile acid and neutral steroid excretion were measured after 21 days. Serum cholesterol levels were not different in any of the diet groups. In cholesterol-fed rats, alfalfa resulted in a reduction in the level of liver cholesterol accumulation in comparison to cellulose or the fiber-free diet but oats did not. Daily bile acid and neutral steroid excretion were increased in response to cholesterol feeding but little difference was observed among the groups fed the various dietary fiber sources except that alfalfa resulted in lower excretion rates compared to other fiber-containing diets. HMG CoA reductase activity was reduced by cholesterol feeding and was significantly increased in response to alfalfa in the absence of dietary cholesterol. The relative amounts of bile acids excreted was altered both by cholesterol feeding and by the source of dietary fiber. Cholesterol feeding resulted in an increase in the amount of chenodeoxycholic acid derivatives excreted, especially in the 6β-hydroxylated, muricholic acids. Dietary fiber appeared to increase the contribution of chenodeoxycholic and lithocholic acids to the resultant increase in response to dietary cholesterol. These changes in the relative amounts of bile acids excreted in response to this cholesterol challenge are suggested as a partial explanation of the reduction in accumulation of liver cholesterol in rats in response to dietary cholesterol.