α-Linolenic acid does not contribute appreciably to docosahexaenoic acid within brain phospholipids of adult rats fed a diet enriched in docosahexaenoic acid

Authors


Address correspondence and reprint requests to Stanley I. Rapaport, Brain Physiology and Metabolism Section, National Institute on Aging, National Institutes of Health, Building 9, Room 1S128, Bethesda, MD 20892–0947, USA. E-mail: sir@helix.nih.gov

Abstract

Adult male unanesthetized rats, reared on a diet enriched in both α-linolenic acid (α-LNA) and docosahexaenoic acid (DHA), were infused intravenously for 5 min with [1-14C]α-LNA. Timed arterial samples were collected until the animals were killed at 5 min and the brain was removed after microwaving. Plasma and brain lipid concentrations and radioactivities were measured. Within plasma lipids, > 99% of radioactivity was in the form of unchanged [1-14C]α-LNA. Eighty-six per cent of brain radioactivity at 5 min was present as β-oxidation products, whereas the remainder was mainly in ‘stable’ phospholipid or triglyceride as α-LNA or DHA. Equations derived from kinetic modeling demonstrated that unesterified unlabeled α-LNA rapidly enters brain from plasma, but that its incorporation into brain phospholipid and triglyceride, as in the form of synthesized DHA, is ≤ 0.2% of the amount that enters the brain. Thus, in rats fed a diet containing large amounts of both α-LNA and DHA, the α-LNA that enters brain from plasma largely undergoes β-oxidation, and is not an appreciable source of DHA within brain phospholipids.

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