Quantitative role of plasma free fatty acids in the supply of arachidonic acid to extrahepatic tissues in rats.

Local desaturation-elongation of linoleic acid, uptake of 2-arachidonyl-lysophosphatidylcholine, and uptake plasma unesterified arachidonic acid (AA) are assumed to be the most important sources of AA for extrahepatic tissues. In this study, we investigated the clearance rate as well as the retention rate of plasma unesterified (14)C-AA in different tissues in fed rats. The initial half-life of (14)C-AA in rat plasma was 3.8 s, and the average pool size of rat plasma unesterified AA was 76 nmol. We calculated that 604 nmol of unesterified AA was cleared from the rat plasma per minute. The retention rate of AA per gram of tissue in the heart (13 nmol/min per g), lungs (12 nmol/min per g), kidney (8 nmol/min per g) and bone marrow (6 nmol/min per g) was higher than that in other tissues but was lower than that in liver (23 nmol/min per g). The total uptake was highest in skeletal muscle (249 +/- 27 nmol/min), in liver (226 +/- 15 nmol/min) and in bone marrow (39 +/- 3 nmol/min). More than 80% of retained (14)C-AA was found in phospholipids in most tissues. The conclusion is that despite the low concentration plasma unesterified, AA is a major source of phospholipid AA in several extrahepatic tissues in rats, due to its rapid turnover and selective acylation into phospholipids.