Lipid peroxide makes rabbit platelet hyperaggregable to agonists through phospholipase A2 activation

Treatment of rabbit platelets with tert-butyl hydroperoxide and Fe2+ caused increasing arachidonic acid release, lysophosphatidylcholine formation, and aggregation with increasing concentrations of Fe2+. A combination of tert-butyl hydroperoxide and a low concentration of Fe2+, which by itself causes slight or no such activation, elicited synergistic release of arachidonic acid and aggregation under stimulation with a suboptimal concentration of collagen or arachidonic acid as an agonist. These responses were inhibited by pretreatment of the platelets with vitamin E or mepacrine in a concentration-dependent manner, but not by uric acid. The arachidonic acid release was dependent on the presence of Ca2+ in the medium. Synergistic formation of lysophosphatidylcholine, but not diacylglycerol, was also observed under this condition. The aggregation was also inhibited by indomethacin, a cyclooxygenase inhibitor. Cyclooxygenase activity was not affected by the oxidative treatment. These results suggest that lipid peroxide formed in membranes causes phospholipase A2 to become hypersusceptible to the agonist used, making the platelets hyperaggregable.