The uncoupling of biliary lipid from bile acid secretion by organic anions in the rat

A number of organic anions has been shown to inhibit biliary phospholipid and cholesterol secretion without affecting bile acid secretion. However, the mechanism of this uncoupling phenomenon is still unclear. This study shows a comparison of the effects of ampicillin (18 mumol/100g body wt), sulfated taurolithocholic acid (0.2 and 1.0 mumol/100 g body wt), and indocyanine green (0.6 mumol/100 g body wt) in control and Groningen Yellow-Wistar rats with chronic (8 days) biliary drainage. Groningen Yellow rats have a hereditary defect in hepatobiliary transport of various organic anions. Bile secretion, but not hepatic uptake, of the three organic anions was strongly impaired in Groningen Yellow rats compared with controls. Ampicillin and sulfated taurolithocholic acid caused a strong uncoupling in control rats but had no effect or a much smaller effect on lipid secretion in Groningen Yellow rats. Indocyanine green did not affect lipid secretion, in either control or in Groningen Yellow rats. Gel-filtration chromatography of bile showed a specific coelution of ampicillin and sulfated taurolithocholic acid with the bile acid fraction, whereas indocyanine green coeluted with the phospholipid/cholesterol fraction. This study concludes that the uncoupling by ampicillin and sulfated taurolithocholic acid occurs after their secretion into bile and is caused by interaction of these compounds with bile acids. It is hypothesized that this interaction inhibits the capacity of bile acids to induce secretion of phospholipids and cholesterol into the bile.