Effect of dipyridamole and aspirin on the platelet-neutrophil interaction via the nitric oxide pathway.

This study was designed to determine the influence of the combination of aspirin and dipyridamole on the interaction in vitro between neutrophils and platelets through the nitric oxide (NO) pathway. Collagen-induced platelet aggregation (impedance method) was determined in platelet-rich plasma and in platelet-rich plasma+neutrophils, and cGMP (enzyme immunoanassay) and NO levels (electrochemical method, with a ISO-200 electrode) were also measured. The 50% inhibitory concentration (IC(50)) of aspirin was 139+/-11 microM in platelet-rich plasma, 367+/-21 microM in platelet-rich plasma+L-N(G)-nitro-arginine-methyl-ester (L-NAME), and 42+/-3 microM in platelet-rich plasma+L-arginine. The IC(50) for dipyridamole in platelet-rich plasma was not affected by L-NAME or L-arginine; the combination of aspirin with 20 microM dipyridamole (which has no effect per se) led to an IC(50) of 51+/-2 microM in platelet-rich plasma, 101+/-7 microM in platelet-rich plasma+L-NAME, and 13+/-2 microM in platelet-rich plasma+L-arginine. The cGMP levels showed the greatest increases in the aspirin plus dipyridamole group. Dipyridamole and aspirin increased the leukocyte production of NO: 50% increases were obtained at concentrations of 285+/-31 microM aspirin, 110+/-9 microM dipyridamole, and 16+/-2 microM aspirin+dipyridamole. Dipyridamole alone at a concentration of 20 microM had no significant effect on NO levels. We conclude that the combination of aspirin and dipyridamole significantly increases the antiplatelet effect of leukocytes, through an increase of NO, and that this effect is further evidence of the therapeutic benefits of this combination of drugs.