Dipyridamole potentiates the anti-aggregating effect of endothelium-derived relaxing factor

One effector of the anti-aggregatory property of endothelium is thought to be endothelium-derived relaxing factor. The best characterized of these, nitric oxide, inhibits platelet aggregation by increasing cyclic GMP levels. The effects of nitric oxide and dipyridamole (a cyclic GMP phosphodiesterase inhibitor), alone and in combination, on in vitro platelet aggregation were evaluated. Dipyridamole had no effect per se on platelet aggregation but potentiated the inhibition of aggregation due to nitric oxide. This was concomitant with an increase in platelet cyclic GMP concentration. The author suggests an alternative mechanism for the clinical efficacy of dipyridamole as an antiplatelet agent.