In vitro and in vivo effects of vitamin E on arachidonic acid metabolism in rat platelets.

Preincubating platelet-rich plasma (PRP) of vitamin E-deficient rats with RRR-alpha-tocopherol prior to the aggregation induced by collagen suspension resulted in inhibition of the formation of endoperoxide metabolites derived from endogenous arachidonic acid (AA). This inhibition was not dose dependent at concentrations above the plasma level of RRR-alpha-tocopherol of vitamin E-supplemented rats. Preincubating the vitamin E-deficient PRP with RRR-alpha-tocopherol did not affect the formation of 12-hydroxyeicosatetraenoic acid, the platelet lipoxygenase product. Concentrations of endoperoxide metabolites in diluted whole blood challenged with collagen suspension were significantly greater in the vitamin E-deficient group than the supplemented group. The level of AA in platelet or plasma phospholipids was not different between the two groups. However, blood platelet counts in the deficient group were significantly greater than those of the supplemented group. Concentrations of endoperoxide metabolites in PRP samples in which platelet concentrations were equalized were still greater in vitamin E-deficient group; however, the difference was not statistically significant. There was also no difference in the degree of maximal platelet aggregation between the two groups. These results indicated that vitamin E deficiency can slightly stimulate the formation of cyclooxygenase products derived from endogenous AA, but it did not affect the formation of lipoxygenase product in rat platelets.