Superoxide anions enhance platelet adhesion and aggregation

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Abstract
1 Superoxide dismutase (SOD, 60 u ml−1) or ferricytochrome c (70 μm) significantly inhibited thrombin-stimulated platelet adhesion to gelatin-coated plastic, whereas catalase (1000 u ml−1) or mannitol (1 mm) had no effect. 2 The platelet aggregation induced by low concentrations of thrombin (causing less than 45% maximal change in light transmission) was inhibited by SOD. Catalase or mannitol had no effect on platelet aggregation. 3 Pyrogallol (an O2− generator) enhanced both platelet adhesion to gelatin-coated plastic and platelet aggregation induced by thrombin; this enhancement was neutralized by SOD. 4 These results indicate that O2− increase both platelet adhesion and aggregation, whereas other free radicals such as hydrogen peroxide or hydroxyl radicals are not involved.