Mechanism of Cholic Acid Protection in Lithocholate-Induced Intrahepatic Cholestasis in Rats

Abstract

The mechanism(s) by which the coinfusion of primary bile acids with lithocholate protects against the development of intrahepatic cholestasis was assessed in the present study. Bile ducts of male Wistar rats were cannulated, and bile was collected for 2 hr. The rats were then divided into nine groups (six per group) and each was infused intravenously with one of the following: 7.5% albumin, lithocholic acid (LCA), taurolithocholic acid (T-LCA), cholic acid (CA), dehydrocholic acid (DHCA), CA + LCA, CA + T-LCA, DHCA + LCA, and DHCA + T-LCA at a rate of 0.2 μmol of each bile acid/100 g body wt/min for 60 min. At the end of the infusion the livers were examined by electron-microscopy, and the liver cell plasma membrane fraction rich in bile canalicular membranes was isolated. The morphologic lesion of lithocholate cholestasis was seen in LCA, T-LCA, DHCA + LCA, and DHCA + T-LCA groups. The liver cell plasma membrane fraction rich in bile canalicular membranes obtained from these groups contained high concentrations of cholesterol, but there were no changes in membrane phospholipids. Lithocholic acid was further incorporated in the membranes obtained from LCA and DHCA + LCA groups. In the other groups, the ultrastructure of the livers was normal, and membrane ultrastructure and composition was similar to that of the membranes obtained from control rats, except in the CA infusion where there was a significant increase in the membrane phospholipids. In LCA, T-LCA, DHCA + LCA, and DHCA + T-LCA, bile flow was significantly reduced (30-60 min) after infusion, however, in the other groups bile flow was increased as compared to control infusions. Lithocholate secretion was 0.40-1.32 nmol/g liver/min in LCA and T-LCA infusions alone or during their coinfusion with DHCA. The secretion of lithocholate was increased to 12.03-15.32 nmol/g liver/min in the CA + LCA, and CA + T-LCA, furthermore the LCA secreted was more than 95% in free form in the case of CA + LCA infusions. The increased secretion of lithocholate was associated with a five- to sevenfold increase in biliary cholesterol secretion as well as significant increase in phospholipids secretion. These data suggest that CA protects against lithocholate cholestasis by the formation of a LCA-CA complex that prevents its toxic effect on the bile canalicular membrane.