The effect of a fish oil diet on the fatty acid composition of individual phospholipids and eicosanoid production by rat platelets

When rats were fed a diet containing chow or fish oil for six weeks, the platelet phospholipid content and percent distribution were similar. In the fish oil fed animals there was a 54, 40, 41, and 24% reduction, respectively, in the levels of 20∶4(n−6) in the choline-, ethanolamine-, inositol-and serine-containing glycerophospholipids. Dietary fish oil increased the total (n−3) polyunsaturated fatty acid content in all lipids. This effect was most pronounced in the ethanolamine glycerophospholipids which now contained 26, 11, and 4 nmols of 20∶5(n−3), 22∶5(n−3), and 22∶6(n−3) in 10⁹ cells. Ionophore A23187 stimulation of platelets from the chow fed rats resulted in the synthesis of 7, 64, and 3.5 nmols of 12-hydroxy-5,8,10-heptadecatrienoic acid, 12-hydroxy-5,8,10,14-eicosatetraenoic acid and 12-hydroxy-5,8,10,14,17-eicosapentaenoic acid, respectively, from 1×10⁹ cells. The values from animals fed fish oil were 4, 18, and 27 nmol/10⁹ platelets. It was not possible to detect any lipoxygenase products from 22∶5(n−3) or 22∶6(n−3), even though both acids are readily metabolized by lipoxygenase when added directly to platelets. These findings suggest that 22-carbon (n−3) fatty acids are not liberated when phospholipases are activated by calcium mobilization.