Downregulation of ileal bile acid absorption in bile-duct-ligated rats

Accumulation of toxic bile acids in cholestasis contributes to liver injury and depends on their synthesis, secretion and intestinal absorption. In the present study, we investigated the effect of cholestasis on the active ileal absorption of bile acids in vivo and the adaptation of transporters involved in ileal bile acid absorption.

Male Wistar rats underwent ligation of the common bile duct or biliary diversion. Sham-operated rats served as controls. Active ileal bile acid absorption of taurocholate was measured by an intestinal perfusion technique. Transporter mRNA levels of the Na+/bile acid cotransporting protein (IBAT), ileal lipid binding protein (ILBP) and organic anion transporter subtype 3 (Oatp3) and protein expression of IBAT and ILBP were determined in the distal ileum.

After bile duct ligation the intestinal absorption rates of taurocholate were lower (p<0.05) and after biliary diversion absorption rates were higher compared to sham-operated animals (p<0.05). The absorption rates were inversely correlated to serum bile acid concentrations. Levels of IBAT-, ILBP- and Oatp3- mRNA were not different between the groups. However, in cholestatic rats, the expression of the 99-kDa dimer of IBAT was decreased compared to controls (p<0.05), whereas the 46-kDa monomeric protein of IBAT and the expression of ILBP was unchanged. After biliary diversion a similar pattern of protein expression was observed, despite an increased absorption rate.

Cholestasis leads to a decreased active ileal absorption of taurocholate. The changes in protein expression may not account for the different absorption rates. The intestinal absorption of bile acids seems to be regulated by their systemic concentration.