Inactivation of vascular prostacyclin synthetase by platelet lipoxygenase products

The sensitivity of prostacyclin synthetase to inactivation by hydroperoxy-fatty acids suggests that vascular prostacyclin synthesis might be modulated by the platelet lipoxygenase product 12-hydroperoxyeicosatetraenoic acid (12-HPETE). On incubation of a lipoxygenase source from lysed platelets, a prostacyclin synthetase source from bovine aortic microsomes, and arachidonic acid, rapid inactivation of prostacyclin synthetase resulted. This was reflected by failure to convert exogenous prostaglandin H₂ to 6-keto prostaglandin F_1α, and the inactivation was prevented by the lipoxygenase inhibitor eicosatetraynoic acid. Prostacyclin synthetase inactivation did not occur when whole platelets were used as the lipoxygenase source unless concentrations of arachidonic acid high enough to induce platelet lysis were employed. Vascular prostacyclin synthesis is thus not likely to be influenced by 12-HPETE released from platelets.