Generation of active oxygen species in blood platelets--spin trapping analysis

Generation of active oxygen species by bovine blood platelets was examined by the electron spin resonance (ESR) spin trapping technique with 5,5-dimethyl-1-pyroline-1-oxide (DMPO). The hydroxyl spin-trapped adduct 5,5-dimethyl-2-hydroxyl-1-pyrolidinyloxy (DMPO-OH) was formed in the presence of platelets, indicating the generation of hydroxyl radicals (.OH) by the platelets. Generation of .OH was observed even with platelets in the resting state, but was markedly enhanced when the platelets were activated with stimulants. Stronger stimulants such as the calcium ionophore ionomycin, induced greater radical generation than the weaker stimulant ADP. When the platelets were stimulated by thrombin, generation of .OH was greatest after 1.5 min, and depended on the dose of the stimulant. It was inhibited by inhibitors of platelet activation such as forskolin and phenolic antioxidants.