Enrichment of plasma lipid subfractions with varying dietary levels of N-3 fatty acids in the canine model

Abstract

In an attempt to better understand how varying levels of dietary n-3 fatty acids affected enrichment of plasma lipid subfractions, the current study was undertaken. Adult dogs were fed one of two basal diets with the addition of beef tallow, safflower oil, linseed oil, or menhaden fish oil at 18.0 g/100 g diet or beef tallow or safflower oil at 5.65 g/100 g diet. Plasma was collected on the day oil supplementation began (day 0) and on the day oil supplementation concluded (day 28). No change in plasma total cholesterol or triacylglycerol was observed on day 28. Plasma free cholesterol was depressed in all groups suggesting plasma cholesterol esterification. However, plasma esterified cholesterol was significantly decreased on day 28 in the group supplemented with menhaden fish oil. This finding may be due to the fact that n-3 highly unsaturated fatty acids II-IUFAI act as poor substrates for the lecithin: cholesterol acyltransferase reaction. Plasma triacylglycerol (TG) and phospholipid (PL) fatty acid compositions reflected dietary fatty acids. When actual plasma PL and TG fatty acids were compared with values predicted by the Lands' equations, some modifications of constants were necessary to achieve an equation that better predicted values for the percent n-6 HUFA in PL. However, n-3 HUFA was not accurately predicted, and studies delineating more precisely the competitive effects of n-3 fatty acids on lipid metabolism will permit further modification of the hyperbolic PL equation. After minor adjustments to Lands' linear equations that predict linoleum acid (LA) and linolenic acid (ALA) in plasma TG, algebraic equations with improved ability to estimate LA and ALA in plasma TG resulted. Fatty acid profiles of plasma phosphatidylcholine (PC) reflected oil supplementation. However, n-3 FIUFA were not incorporated into cholesterol ester (CE) at the same proportion as found in the PC fraction. While the PC fraction did contain docosapentaenoic acid (DPA), it was not significantly present in plasma CE. These findings are consistent with the possibility that DPA is transported only on plasma TG and PL lipoprotein lipid subfractions and that this transport is unidirectional.