Heparin neutralization by platelet-rich thrombi. Role of platelet factor 4.

Abstract

Extracts prepared from platelet-rich arterial thrombi significantly inhibit the in vitro anticoagulant potency of heparin but not of hirudin. This antiheparin effect appears to be mediated by platelet factor 4. These results are consistent with the hypothesis that localized inhibition of heparin at sites of platelet activation may reduce its antithrombotic efficacy. In addition, they suggest an additional mechanism for the apparent superiority of hirudin over heparin as a thrombin inhibitor at sites of arterial injury.