Effect of Partial Ileal Bypass on Cholesterol and Bile Acid Metabolism in Rats

In order to clarify the effect of ileal bypass on cholesterol and bile acid metabolism, partial (20 cm) ileal bypass rats were fed a 2% cholesterol supplemented diet for a week after 4 weeks of the operation. The serum and liver cholesterol and phospholipid levels, biliary cholesterol, phospholipid and bile acid secretions, and fecal cholesterol, coprostanol and bile acid excretions were examined. The serum cholesterol level in ileal bypass rats was lower than in normal rats and no hypercholesterolemia was brought about in ileal bypass rats by feeding them the cholesterol diet. The liver cholesterol level increased by feeding the cholesterol diet even in ileal bypass rats but the increase was far less than that in normal rats (22% versus 57%). Biliary bile acid secretion decreased and fecal bile acid excretion increased markedly in ileal bypass rats. Deoxycholic acid increased remarkably in both bile and feces and resulted in an increase in the ratio of the sum of bile acids derived from cholic acid over the sum of bile acids derived from chenodeoxycholic acid (CA/CDCA ratio) in the feces. These results suggest that the absorption of bile acids is impaired, the pool size of bile acids decreases and the hepatic synthesis of bile acids, especially that of cholic acid, increases in ileal bypass rats. As a result, cholesterol feeding to ileal bypass rats produces neither hypercholesterolemia nor a further increase in bile acid synthesis.