THE F-2-ISOPROSTANE 8-EPIPROSTAGLANDIN F2-ALPHA INCREASES PLATELET-ADHESION AND REDUCES THE ANTIADHESIVE AND ANTIAGGREGATORY EFFECTS OF NO

F-2-isoprostanes are prostaglandin (PG) isomers produced in vivo throu gh free radical-catalyzed peroxidation of arachidonic acid, which may affect platelet function. The current Study investigated the effects o f 8-epiprostaglandin F-2 alpha (8-epi-PGF(2 alpha)) on critical events of platelet activation. A dose-dependent increase in platelet adhesio n to fibrinogen- and plasma-coated microwells by 8-epi-PGF(2 alpha) (1 to 1000 nmol/L) was observed when resting platelets (plasma from 1.3/-0.2% to 5.5+/-0.2%, ECS, of 48 nmol/L, fibrinogen from 3.3+/-0.3% to 6.4+/-0.2%, EC50 of 35 nmol/L; mean+/-SEM, n=8, P<0.001) and thrombin -stimulated human platelets were used. The expression of the adhesion molecule glycoprotein Ilb/IIIa was increased by 10 to 1000 nmol/L 8-ep i-PGF(2 alpha),, in resting platelets (from 64.8+/-2.1% to 83.9+/-1.3% ; n=5, P<0.01) and in stimulated platelets. The secretion of the glyco protein GMP-140 increased only in the presence of both thrombin and 10 to 1000 nmol/L 8-epi-PGF(2 alpha),, (from 48.5+/-3.1% to 63.1+/-2.0%, P<0.05). The antiaggregatory effects of both the NO donor NOR-3 (basa l, 21.4+/-4.6%; with 8-epi-PGF(2 alpha), 30.8+/-6.9%; n=14, P<0.05) an d endothelial cells that release NO (basal, 18.5+/-4.6%; with 8-epi-PG F(2 alpha), 30.7+/-5,3%; n=15, P<0.001) were also reduced. All of thes e effects were prevented by the thromboxane receptor antagonist GR3219 1 but not affected by acetylsalicyclic acid. An increase in free intra cellular calcium concentration, measured with the use of fura 2, was o bserved with 8-epi-PGF(2 alpha). In conclusion, F-2-isoprostanes may p articipate in oxidative injury by inducing platelet activation and by reducing the antiplatelet activity of NO: increased platelet adhesiven ess and expression of the fibrinogen receptor are induced by nanomolar amounts of 8-epi-PG-F-2 alpha,,. Platelet secretion and aggregation c an also be induced in the presence of platelet agonists.