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 10(9) 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 X 10(9) cells. The values from animals fed fish oil were 4, 18, and 27 nmol/10(9) 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.