Superoxide dismutase triggers activation of primed platelets

Abstract Superoxide dismutase (SOD) triggers activation of human platelets exposed to subthreshold concentrations of arachidonic acid and collagen. The subthreshold concentrations used are not able to activate platelets but “prime” platelets to be activated by SOD. The addition of SOD to arachidonic acid- or collagen-primed platelets induced aggregation, thromboxane A 2 production, and release of [ 3 H]serotonin. Superoxide dismutase does not have any effect on resting platelets and ADP-, thrombin-, calcium ionophore A23187-, PAF-, or U46619-stimulated platelets. Furthermore, superoxide dismutase-dependent platelet activation is fully prevented by catalase and/or aspirin, suggesting a role for H 2 O 2 and the involvement of the cyclooxygenase pathway of arachidonic acid in such activation.