Effect of different ratios of dietary N-6 and N-3 fatty acids on fatty acid composition, prostaglandin formation and platelet aggregation in the rat.

Five groups of male Sprague-Dawley rats (150 g) were fed a fat-free diet supplemented with 10% by weight of evening primrose oil (Efamol, rich in linoleic acid and gamma-linolenic acid) and/or marine oil (Polepa, rich in eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) combined in several ratios (Efamol/Polepa; 10.0%/0%; 7.5%/2.5%; 5.0%/5.0%; 2.5%/7.5%; 0%/10.0%). The n-6 fatty acid levels in aortic, platelet and plasma phospholipids decreased in proportion as Efamol was replaced with Polepa. The exception in phospholipids was dihomo-gamma-linolenic acid (20:3n-6), which increased when marine oil was provided in the diet with Efamol. The ratio of 20:3n-6 to arachidonic acid (20:4n-6) was positively correlated with 20:5n-3, docosapentaenoic acid (22:5n-3) or 22:6n-3 in aortic, platelet and plasma phospholipids under these dietary conditions. In contrast, 20:3n-6 in plasma cholesterol esters, triglycerides and free fatty acids did not show any increase in the presence of Polepa. Aortic prostaglandin (PG) production (6-keto-PGF1 alpha, PGE2 and PGE1) was reduced as Efamol was progressively replaced with Polepa. Aortic PG production was positively correlated with 20:4n-6 content in aortic phospholipids. Thrombin-induced thromboxane B2 production in whole blood was related to 20:4n-6 content in platelet phospholipids. However, ADP-induced platelet aggregation was significantly decreased only in the 7.5% Efamol/2.5% Polepa group as compared to the other 4 groups. These results suggest that combined treatment with Efamol and Polepa increases the ratio of 20:3n-6 to 20:4n-6 in tissue and plasma phospholipids. An appropriate ratio of these oils favorably affects aortic PG production and platelet ADP aggregation.