In vivo models of arterial thrombosis and thrombolysis.

This year approximately 1.5 million Americans will undergo a myocardial infarction (MI). Of those who make it to the hospital (approximately 1.2 million), only about 20% will receive thrombolytic therapy. Multiple factors contribute to this dismaying figure, but most of them are risk/benefit-related. Moreover, of those receiving lytic therapy, the coronary arteries of as many as one-third may not reopen, and of those that do undergo coronary thrombolysis, an unacceptable fraction will experience reocclusion acutely. Thus, despite significant progress, major challenges for antithrombotic and thrombolytic therapy remain. Promising results with aspirin provide some hope that the figures above can be altered favorably. Efforts are under way in industry and academia to develop drugs to accomplish one or more of the following: lower the incidence of MI, prevent the development of unstable angina or retard its progression to frank MI, increase the inclusion window for lytic therapy, raise the percentage of patients undergoing successful thrombolysis, and maintain coronary patency. During the period that thrombolytic agents have come into vogue important advances have been made in our understanding of platelet function, coagulation, and the endogenous fibrinolytic system. These have spurred the development of novel drugs, such as platelet fibrinogen receptor antagonists, plasminogen activators, and inhibitors of factor IIa (thrombin) and XIIIa. Evaluation of these agents for their antithrombotic or profibrinolytic activity requires relevant animal models of thrombosis. Despite appropriate concerns about their clinical relevance, these models bridge the wide gap between test tube assays of aggregation or coagulation and humans.