Effect of bile salts on hepatic phosphatidylcholine synthesis and transport into rat bile

The effect of transport of micelle-forming and non-micelle-forming conjugated bile salts on phosphatidylcholine synthesis and transport into bile was studied in the ex vivo perfused rat liver. Single additions of sodium taurocholate, a good micelle-forming conjugated bile salt, caused an increase in bile flow associated with increased phosphatidylcholine and taurocholate concentration. The specific activity of phosphatidylcholine with respect to incorporated [1,2-(14)C]choline and [(3)H]methyl of l-[Me-(3)H]methionine was not significantly altered by the increased transport of phosphatidylcholine. The data suggested that bile phosphatidylcholine is synthesized to a great extent, although not exclusively, by phosphorylcholine glyceride transferase. Single additions of the glycine conjugate of dehydrocholate, a poor micelle-forming bile salt, caused an increase in bile flow comparable to that seen with sodium taurocholate administration. However, the concentrations of phosphatidylcholine in bile decreased. Thin-layer and gas-liquid chromatographic analyses of bile secreted before and after glycodehydrocholate administration revealed no significant increase in bile salt secretion other than the administered glycodehydrocholate. Investigations utilizing radiochemically pure [(14)C]glycine dehydrocholate revealed that increased bile flow after [(14)C]-glycine dehydrocholate administration occurs concomitantly with the secretion of 75-95% of the administered [(14)C]glycine dehydrocholate as a single peak into bile. Thus the increased bile flow without increased phosphatidylcholine concentration noted after glycodehydrocholate administration is due to transport of an intact, nonmetabolized, conjugated bile salt with poor micelle-forming properties. The data indicate that the formation of a bile salt-phosphatidylcholine micelle is responsible for phosphatidylcholine transport into bile.