Effect of bile salt on phosphatidylcholine composition and secretion of hepatic high-density lipoproteins

Bile salts are necessary for the secretion of phosphatidylcholines (PCs) in bile and result in the selective secretion of highly hydrophilic molecular species of PC that contain a 16:0 acyl group. To determine the effect of bile salt on the secretion of PCs in lipoproteins, isolated rat livers were perfused with and without taurocholate. The PC composition of very-low-density lipoproteins (VLDL), newly synthesized by the liver, precisely mirrored the composition of PCs in the whole liver and was not changed with the administration of taurocholate. In contrast, both the composition of PCs in high-density lipoproteins (HDL) and the absolute amount of newly synthesized HDL were markedly affected by the administration of taurocholate. With taurocholate the PC content of HDL was increased, HDL was enriched, like bile, in 16:0 molecular species of PC, and the amount of HDL that was recovered in the perfusate was 2.5-fold greater than without taurocholate (P less than 0.001). These findings suggest that VLDL and HDL are differently derived from within the liver, that the PCs of HDL and bile originate from the same hepatic pool or by the same mechanism, and that both the secretion of bile and HDL from the liver are susceptible to regulation by bile salt.