COMPARISON OF THE PLATELET AGGREGATION INDUCED BY THREE THROMBIN-LIKE ENZYMES OF SNAKE VENOMS AND THROMBIN

Abstract

Acutin was isolated from Agkistrodon acutus venom and batroxobin and thrombocytin were isolated from Bothrops atrox venom. These three thrombin-like enzymes had different specificity for platelet activation and fibrinogen clotting. The clotting activities were 700, 170 and 7 μ/mg for batroxobin, acutin and thrombocytin, respectively. They induced aggregation and ATP release of washed rabbit platelets. The aggregating activities were 102, 104 and 105 times less than that of thrombin for thrombocytin, acutin and batroxobin, respectively basing on the clotting unit. The platelet -activating potency was correlated with their effectiveness on the retractility and elasticity of the clots. Platelet aggregation induced by thrombin or thrombocytin could be inhibited by heparin with antithrombin III while that by acutin or batroxobin could not. The thrombin-like enzymes did not induce aggregation of thrombin-degranulated platelets even fibrinogen was added. Indomethacin showed weak inhibition on the aggregation while the ADP - scavenging system, creatine phosphate/creatine phosphokinase, or apyrase inhibited the aggregation induced by the three thrombin-like enzymes but not that by thrombin. In the presence of EGTA, only thrombin could induce ATP release from platelets. It is concluded that the aggregation induced by thrombin-like enzymes is different from that of thrombin and mainly due to ADP released from platelets.