METABOLIC-FATE OF AN ORAL TRACER DOSE OF [C-13]DOCOSAHEXAENOIC ACID TRIGLYCERIDES IN THE RAT

The appearance of C-13 in rat lipoprotein, blood cells, and brain Lipi ds was followed as a function of time after the ingestion of triglycer ides (TG) containing [C-13]22:6n-3. The time course of C-13 abundance in 22:6n-3 of various lipid pools, measured by gas chromatography comb ustion-isotope mass spectrometry, established precursor-product relati onships within lipids. The [C-13]22:6n-3 was rapidly incorporated into very low density lipoprotein-chylomicron-TG and unesterified fatty ac ids bound to albumin, with a concomitant maximal appearance at 3 h and further decline. Lysophosphatidylcholines (lysoPC) bound to albumin w ere also enriched in [C-13]22:6n-3, and their labeling appeared to be mainly due to hepatic secretion at the earliest time points. From 12 h postingestion, the synthesis of [C-13]22:6n-3-lysoPC was twice as hig h as that of unesterified [C-13] 22:6n-3, making lysoPC a potential so urce of 22:6n-3 supply for tissues. The labeling of platelets, red blo od cells, and brain phospholipids presented different kinetics, presum ably involving the two lipid forms of [C-13]22:6n-3 bound to albumin, to different extents. We conclude that [C-13]22:6n-3 esterified in TG is rapidly redistributed within blood lipoproteins and the albumin fra ction and that its incorporation in lipid species bound to albumin inf luences its uptake by target tissues.