Inhibitory effect of vitamin E (alpha-tocopherol) on spontaneous platelet aggregation in whole blood

Vitamin E (D-alpha-tocopherol) inhibited spontaneous human platelet aggregation in whole blood in the 20-200 micrograms/ml range. When alpha-tocopherol (20 micrograms/ml) and aspirin (0.5 mM), or alpha-tocopherol and the mixture of phosphocreatine (1.5 mM) and creatine phosphokinase (50 U/ml) (CP/CPK) were added to this reaction system, a synergic inhibitory effect on aggregation was observed. On the other hand, when both alpha-tocopherol and the specific inhibitor of platelet activating factor (CV-3988; 0.38 mM) were added to this system, the inhibition was the same as that caused by the addition of CV-3988 alone, suggesting there was no synergism, i.e., that the effect of alpha-tocopherol is related to the inhibition of platelet activating factor (PAF)-induced platelet aggregation in whole blood. However, alpha-tocopherol (20 or 50 micrograms/ml) did not inhibit PAF (10 nM) induced platelet aggregation in platelet rich plasma (PRP). These results suggest that the inhibition of platelet aggregation in whole blood by alpha-tocopherol is due to the inhibition of PAF synthesis, and is unrelated to adenosine diphosphate (ADP) or thromboxane A2.