Thrombostatin inhibits induced canine coronary thrombosis

Thrombostatin (RPPGF), an angiotensin converting enzyme metabolite of bradykinin, is an inhibitor of alpha-thrombin's ability to activate platelets. We examined the in vivo pharmacokinetics and pharmacodynamics of thrombostatin in rabbits and its ability to inhibit coronary thrombosis induced by electrolytic injury in dog;. Plasma half-life of thrombostatin had a t(1/2)alpha of 2.6 min and a t(1/2)beta of 24 min in rabbits. Ligating the renal arteries did not prolong clearance (t(1/2)alpha = 2.4 min; t(1/2)beta = 12 min). Thrombostatin produced a prolonged in vivo antiplatelet effect. At 30 min after a single intravenous administration in rabbits, thrombostatin's plasma concentration was <8.7 mu M (5 mu g/ml). However ex vivo 20 and 40 nM gamma-thrombin-induced platelet aggregation of these rabbits' platelets was inhibited 40% for 2.75 and 1 h, respectively. In vitro, flow cytometry studies revealed that thrombostatin specifically bound to human platelets and washed human platelets treated with thrombostatin were less responsive to gamma-thrombin than control platelets. Using electrolytic injury to induce coronary artery thrombosis, dogs treated with thrombostatin. aspirin, or combined thrombostatin and aspirin occluded in 62 +/- 25 (mean +/- SD), 62 +/- 36, or 89 +/- 32 min versus untreated animals which occluded at 39 +/- 27 min, (p <0.01. p <0.01 and p <0.001, respectively). These studies show that thrombostatin binds to platelets and can delay coronary occlusion in vivo.