The Effect of Tiace Amounts of'Tissue Fastor on Thr.ombin Generation ' in Platelet Rich Plasma, its Inhibition by Heparin

Amounts of human brain thromboplastin that do not stimulate thrombin generation in platelet poor plasma, were shown to advance by about 4 min an explosive formation of thrombin that occurs after recalcification in the presence of blood platelets. This synergistic effect is inhibited by the specific thrombin inhibitor hirudin and mimicked by adding low concentrations (< 5 nM) of thrombin to platelet r ich phsma. I t is our conclusion that small amounts of thrombin, generated under the inf luence of thrombo-plastin induced procoagulant act ivi ty in the blood platelets. This activi tv is most l ikely mainly due to procoagulant phospholipids. Heparin inhibits this effect and retards the explosive thrombin formation. I t does not, however, diminish the peak amount of thrombin eventual lv formed. because heparin neutral izing mate-r ial released irom the activated platelets quenches the heparin e ffect