The incorporation of fatty acids of different chain length into liver and biliary lipids in the perfused rat liver.

Abstract

In an attempt to correlate the incorporation of fatty acids (FA) of different chain length into liver and biliary lipids, isolated rat livers were perfused for 2 h with Krebs-Ringer bicarbonate containing 1% albumin and 10 mumol of [1-14C]-labeled FA: C2, C8, C10, C12, C16, and C18:1. One to 1.36 mumol of medium-chain fatty acids (MCFA, C8, C10, and C12) and 6.6 mumol of long-chain FA (LCFA) were incorporated into liver lipids, 40% of the latter into phosphatidylcholine (PC). 14C-acetate (13 nmol) was incorporated into biliary cholesterol; 14C-MCFA contributed only 3.2-5 nmol; LCFA did not lead to newly synthesized cholesterol. Newly synthesized liver PC (2.75 to 3.25%) and newly synthesized liver cholesterol (6.5 to 10%) were secreted into bile. The specific radioactivity of biliary PC after infusion of all-saturated FA was 3.8-6.8 times higher than that of liver PC; for C18:1 it was only 1.7-fold. The specific radioactivity of biliary cholesterol, as compared to liver cholesterol, was 12 times higher for C2 and five times higher for MCFA. This indicates that a considerable proportion of the newly synthesized lipids was secreted into bile prior to significant mixing with preexisting liver PC and cholesterol pools. Liver PC contained 8% of unchanged 14C-C12; while 14C-C10 was not detected. Biliary PC, in contrast, contained 18% of unchanged 14C-C12 and 3% 14C-C10. These results suggest that after prolonged infusion of medium-chain triacylglycerols/long-chain triacylglycerols to patients, biliary PC may become enriched with MCTA. In addition, the oxidation of these FA may provide C-2 units which increase cholesterol synthesis.