Metabolism of [3H]arachidonic acid- and [14C]linoleic acid-labelled chylomicrons in essential fatty acid-deficient rats

Mesenteric duct chylomicrons labelled with [3H]arachidonic (20:4) and [14C]linoleic (18:2) acid were injected intravenously into essential fatty acid-deficient (EFAD) and control rats. The rats were killed after 5, 10, 20 and 240 min, and serum and different organs were analysed for radioactivity of different lipid classes. 3H and 14C in the triacylglycerol (TG) and phosphatidylethanolamine (PE) fractions were cleared from blood faster in the EFAD than in the control rats. The incorporation of [14C]18:2 into liver and heart phospholipids was increased compared to control rats at all time intervals, the increase in the incorporation of [3H]20:4 being less pronounced. Furthermore, the total incorporation of [14C]18:2 was increased in the heart of the EFAD group. The increased incorporation into phosphatidylcholine (PC) and particularly into PE was observed already at 5-20 min, whereas a marked increase in the 14C radioactivity of cardiolipin occurred between 20 and 240 min. The 3H and 14C radioactivity per g white adipose tissue was lower in the EFAD group than in the controls. After 5-20 min there were no differences between the groups in the lipid radioactivity of the stomach and the small and the large intestine. In the upper small intestine, the 3H radioactivity in both groups and the 14C radioactivity in the EFAD group increased markedly between 20 and 240 min. The study demonstrates an increased plasma clearance and an efficient hepatic uptake and initial incorporation into PC and PE of chylomicron [14C]18:2 and [3H]20:4 in EFAD rats. In these rats a marked selective transfer of [14C]18:2 to cardiolipin from other tissue lipids occurred with time. In addition, the study demonstrates a preferential transfer of injected [3H]20:4, and in EFAD rats also of [14C]18:2, into lipids of the upper small intestine, possibly by secretion of [3H]20:4 and [14C]18:2 in bile phospholipids.