Upregulated liver conversion of α-linolenic acid to docosahexaenoic acid in rats on a 15 week n-3 PUFA-deficient diet

Abstract

We quantified incorporation rates of plasma-derived α-linolenic acid (α-LNA, 18:3n-3) into "stable" liver lipids and the conversion rate of α-LNA to docosahexaenoic acid (DHA, 22:6n-3) in male rats fed, after weaning, an n-3 PUFA-adequate diet (4.6% α-LNA, no DHA) or an n-3 PUFA-deficient diet (0.2% α-LNA, no DHA) for 15 weeks. Unanesthetized rats were infused intravenously with [1-14C]α-LNA, and arterial plasma was sampled until the liver was microwaved at 5 min. Unlabeled α-LNA and DHA concentrations in arterial plasma and liver were reduced >90% by deprivation, whereas unlabeled arachidonic acid (20:4n-6) and docosapentaenoic acid (22:5n-6) concentrations were increased. Deprivation did not change α-LNA incorporation coefficients into stable liver lipids but increased synthesis-incorporation coefficients of DHA from α-LNA by 6.6-, 8.4-, and 2.3-fold in triacylglycerol, phospholipid, and cholesteryl ester, repectively. Assuming that synthesized-incorporated DHA even tually would be secreted within lipoproteins, calculated liver DHA secretion rates equaled 2.19 and 0.82 μmol/day in the n-3 PUFA-adequate and -deprived rats, respectively. These rates exceed the published rates of brain DHA consumption by 6- and 10-fold, respectively, and should be sufficient to maintain normal and reduced brain DHA concentrations, respectively, in the two dietary conditions.