The effects of highly purified eicosapentaenoic acid (97% pure) on the arachidonic acid cascade in isolated murine vascular cells and platelets were studied. The incorporation of eicosapentaenoic acid was not as active as that of arachidonic acid in platelets. The ratio of incorporation of eicosapentaenoic acid to arachidonic acid into platelet phospholipids was about 0.7. Analysis of the phospholipid fractions of platelets after labeling with 14C-eicosapentaenoic acid and 14C-arachidonic acid revealed that the incorporation of 14C-eicosapentaenoic acid into the fraction is significantly less than that of 14C-arachidonic acid, while the incorporation of both fatty acids into other phospholipid fractions was almost the same. On the other hand, no significant difference between either fatty acid in incorporation rate, kinetics or distribution in cellular phospholipids was found in cultured aortic smooth muscle cells. Following treatment with eicosapentaenoic acid, cells produced less prostacyclin from endogenous arachidonic acid than did control cells. This was not due to the decrease in fatty acid cyclooxygenase activity, but rather, due to the decrease in arachidonic acid content in cellular phospholipids. In addition, eicosapentaenoic acid was neither converted to prostaglandin I3 by the vascular cells nor to thromboxane A3 by platelets. Furthermore, similar results were also obtained by in vivo experiments in which rats were fed with eicosapentaenoic acid enriched diet.
