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

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 mu mol of [1-C-14]-labeled FA: C-2, C-8, C-10, C-12, C-16; and C-18:1. One to 1.36 mu mol of medium-chain fatty acids (MCFA, C-8, C-10, and C-12) and 6.6 mu mol of long-chain FA (LCFA) were incorporated into liver lipids, 40% of the latter into phosphatidylcholine (PC). C-14-acetate (13 nmol) was incorporated into biliary cholesterol; C-14-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 C-2 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 C-14-C-12; while C-14-C-10 was not detected. Biliary PC, in contrast, contained 18% of unchanged C-14-C-12 and 3% C-14-C-10. These results suggest that after prolonged infusion of medium-chain triacylglycerols/long-chain triacylglycerols to patients, biliary PC may become enriched with MCFA, In addition, the oxidation of these FA may provide C-2 units which increase cholesterol synthesis.