Effect of Different Fatty Acids on Glycerolipid Synthesis in Isolated Rat Henatocvtes*

Glycerolipid synthesis from [3H]glycerol and [l*C]dihydroxyacetone operated in enqmically isolated rat hepatocytes at a rate similar to that in the intact organ. Addition of albumin-bound fatty acids with more than 12 carbon atoms to the incubation medium markedly stimulated triacylglycerol synthesis from [3H]glycerol whereas the effects on phospholipid synthesis were smaller and more dependent on fatty acid structure. Capric acid, lauric acid, and erucic acid inhibited both phosphatidylethanolamine and phosphatidylcholine synthesis whereas fatty acids with 16 to 18 carbon atoms were stimulatory or without effect. Since these findings might be explained by the substrate specificities of cholinephosphotransferase, ethanolaminephosphotransferase, and diacylglycerol acyltransferase, the effects of different fatty acids on the formation of molecular species of diacylglycerols and their utilization were investigated. High proportions of labeled diacylglycerols containing 2 molecules of the added fatty acid were formed for all fatty acids. Unsaturated diacylglycerols were well utilized for phospholipid synthesis, while saturated ones were utilized to a lesser degree, especially for phosphatidylethanolamine synthesis. The low utilization of saturated diacylglycerols may represent one mechanism whereby the formation of phospholipid molecules with unsuitably high transition temperatures is avoided.