Disproportional changes in the rates of biliary bile acid, phospholipid and cholesterol secretion in the SHR/N-corpulent rat.

Lean and obese male rats of the SHR/N-cp strain were fed a plain chow diet ad libitum and studied at 11-13 weeks of age. Compared to their lean littermates the obese animals manifested 2-4-fold higher plasma levels of cholesterol, triacylglycerol and glucose. In the obese rats, the mass of the liver was increased more than 70% and there was a significant increase in the total hepatic content of free cholesterol (42%), cholesteryl ester (2.9-fold) and triacylglycerol (7.4-fold). Despite the difference in liver mass, the rate of bile secretion was the same in the lean and obese groups. Bile acid pool size was 2.5-fold greater in the obese rats and this was reflected in an enhanced rate of biliary bile acid secretion. In contrast, there was little or no increase in biliary cholesterol and phospholipid secretion, so the relative content (molar percentage) of these lipids decreased significantly in the obese animals. In both the lean and obese groups, biliary cholesterol and phospholipid output could be enhanced by the intravenous administration of taurocholate, but the proportion of both lipids in the bile of the obese rats remained significantly lower than in their lean controls. Thus the difference in biliary lipid composition between the two groups is not due to a limited availability of cholesterol and phospholipid for transport into bile, but more likely reflects a difference in the reaction whereby the secretion of cholesterol and phospholipid is coupled to the transport of bile acids across the canalicular membrane.