Initial esterification and conversion of intraportally injected [1- 14C]Linoleic acid in rat liver

Abstract

1. 1. [1- 14C]Linoleic acid bound to serum albumin was injected intraportally into male rats. After 5–300 sec the livers were removed and the lipids were extracted. 2. 2. Phosphatidic acids were rapidly labeled with a maximal isotope amount at 10 sec. The maximum in diacylglycerols was at 30–60 sec, while the amount of isotope in triacylglycerols, phosphatidylcholines and phosphatidylethanolamines rose throughout the experimental period. 3. 3. Among phosphatidic acids the palmitoyl-linoleoyl fraction incorporated most isotope, while synthesis de novo of the stearoyl-linoleoyl fraction was very slow. [1- 14C]-Linoleic acid was located almost exclusively at position 2 in phosphatidic acids, indicating a high positional specificity in phosphatidic acid synthesis. 4. 4. In contrast to synthesis de novo acylation of endogenous 1-acyl- sn-glycero-3-phosphorylcholines and 1-acyl- sn-glycero-3-phosphorylethanolamines by linoleic acid produced phospholipids similar to the preexisting dienoic phospholipids. Consequently, the main part of stearoyl-linoleoyl phospholipids were synthesized by direct acylation reactions, while the palmitoyl-linoleoyl species mainly were produced by synthesis de novo. 5. 5. Trienoic and tetraenoic fatty acids produced from labeled linoleic acid each contained 3–4% of the recovered radioactivity. The proportion of each acyl-CoA which took part in esterification and fatty acid conversion reactions was calculated. Less than 10% of linoleoyl-CoA and arachidonoyl-CoA was directed towards conversion reactions while 60–80% of trienoic acyl-CoA was converted. 6. 6. The incorporation of trienoic fatty acids and particularly arachidonic acid into phospholipids occurred mainly by acyl-CoA:I-acylphospholipid acyltransferase reactions.