Regurgitation of bile acids in rat liver under bile drainage: quantitative analysis by taurine or ursodeoxycholate loading test.

In rats with an interrupted enterohepatic circulation of bile acids, levels of serum taurine-conjugated bile acids were increased significantly 3 h after intravenous administration of taurine. Similarly, serum taurine- or glycine-conjugated ursodeoxycholic acid (UDCA) was increased significantly 2 h after UDCA administration. These findings suggested that the administered taurine or UDCA was taken up into hepatocytes and utilized to form conjugated bile acids, which were thereafter regurgitated into the systemic circulation from the liver. The proportion of regurgitated taurine-conjugated bile acids relative to total serum bile acids measured by taurine loading (30%) almost coincided with that of regurgitated taurine- or glycine-conjugated UDCA relative to total serum bile acids measured by UDCA loading (31.6%). Thus, the present study showed conclusively that at least 30% of serum bile acids are derived from newly conjugated bile acids that are regurgitated from the liver in rats with bile fistula.