Effects of organic anions on biliary lipid secretion in rats. Importance of association with biliary lipid structures.

This study was performed to determine the effects of various organic anions on biliary lipid secretion in rats. We infused bile-salt-pool-depleted rats with sodium taurocholate at a constant rate, with or without various organic anions: Indocyanine Green (ICG), bromosulphophthalein (BSP), BSP-glutathione and Phenol Red (PR). BSP decreased biliary secretion of cholesterol and phospholipids in a dose-dependent manner without affecting bile salt secretion (uncoupling), and this change was fully reversible. In contrast, ICG, BSP-glutathione and PR did not cause such an uncoupling of biliary lipids. In addition, the distribution pattern of each organic anion to various lipid particles was determined by gel-permeation chromatography. BSP was predominantly associated with bile salt micelles, whereas vesicular association was dominant for ICG, and both BSP-glutathione and PR formed only self-aggregations. From these data, we concluded that the uncoupling of biliary lipids from bile salt secretion by BSP resulted from the interaction between BSP and bile salt micelles in the bile canaliculus, and that this interaction inhibited the capacity of bile salts to induce the secretion of phospholipids and cholesterol.