Inhibitors of "spontaneous" platelet aggregation in whole blood

In vitro 'spontaneous' platelet aggregation has been studied in whole blood. The spectrum of activity of materials known to influence platelet aggregation in platelet-rich plasma proved different in whole blood. Thus dipyridamole and one of its analogues SH1242 had a striking effect in whole blood whilst aspirin, chlorpromazine and K3920 had little or no effect. The combination of aspirin and dipyridamole as currently employed in clinical practice had no greater inhibitory effect than dipyridamole alone. The possible clinical relevance of these findings is discussed.