Effect of bile acid on hepatic excretion and storage of bilirubin in ponies.

Endogenous bilirubin uptake from plasma and biliary bilirubin excretion were determined in ponies with chronic biliary T-tube fistulas. Excreted bile was quantitatively recovered. Uptake was calculated from the plasma disappearance of 14C-labeled bilirubin. Biliary bilirubin excretion was determined directly in excreted bile. When bile acid excretion was low (during continuous drainage without bile acid replacment), bilirubin excretion was 37% less than uptake. Uptake and excretion were essentially identical when taurocholic acid was infused to replace bile acids. After depletion of the bile acid pool, replacement of bile acids (by taurocholic acid infusion) greatly increased both bilirubin excretion and its biliary concentration for approximately 1 hour. After this initial increase, bilirubin excretion was maintained at a rate approximately 30% greater than the preinfusion rate. Bile acid excretion was found to be essential for normal, endogenous bilirubin excretion.