Inhibition of collagen-induced platelet aggregation by argatroban in patients with acute cerebral infarction.

Platelet aggregation induced by collagen is enhanced in patients with cerebral thrombosis [1], and platelet aggregates and activation products such as beta-thromboglobulin appear in the circulation, particularly during the acute phase [2]. It is known that the presence of activated platelets markedly amplifies thrombin generation by the prothrombinase complex. Platelet aggregation, for which thrombin is the most potent stimulator, is effected by the activation of the thrombin receptor. Activated platelets likely provide the principal surfaces on which intrinsic coagulation factors and prothrombinase assemble in vivo. Moreover, the blood coagulation cascade is simultaneously enhanced during the acute phase of cerebral infarction, resulting in thrombin production and fibrin formation [3]. Cerebral arterial thrombosis is thought to be initiated by rupture of atherosclerotic plaque. Platelets adhere to the constituents of the plaque, and platelet aggregation and the formation of thrombin occur rapidly. The presence of activated platelets involving thrombin generation in cerebral infarction remains to be further clarified. The present study in patients with acute cerebral infarction was undertaken to determine whether argatroban, a direct thrombin inhibitor, is effective in inhibiting collagen-induced platelet aggregation. It is well known that argatroban inhibits not only thrombin cleavage of fibrinogen with a Ki of 19 nM, but also thrombin-mediated platelet activation with a Ki of 40 nM [4]. We evaluated whether the sensitivity of platelets to collagen is increased in the presence of a trace amount of thrombin associated on platelets, at a concentration that does not induce platelet aggregation in acute cerebral infarction. The study also measured the inhibitory effect, if any, of the addition of argatroban during platelet hyperactivation induced by collagen.