Investigation of the interrelationship between coagulation and thrombin-induced EDRF-dependent relaxation in dog coronary artery

Abstract

Little is known about the possible interrelationships between thrombin-induced EDRF-dependent vascular relaxation and coagulant activity. We have now studied the effects of the anticoagulant zymogen protein C, on EDRF-dependent relaxation in isolated canine coronary arteries. Low concentrations of activated protein C (0.1–30 ng/ml) had no significant effect, but higher concentrations caused relaxation (E max−39.2 ± 7.2%; 100 – 1000 ng/ml). To determine whether relaxation was dependent on coagulation complexes associated with endothelial cell membranes, the coumarin, brodifacoum was given three days before in vitro experiments were carried out in order to inhibit production of active vitamin K1-dependent clotting factors. Brodifacoum (10 mg/kg i.p.) increased prothrombin time from 8.5 ± 0.24 sec (control), to 46.2 ± 2.4 sec (p< 0.05), but had no effect on thrombin-induced relaxation (E max >90%; ED50 0.026 ± 0.004 units/ml control; 0.025 ± 0.004 unit/ml brodifacoum). In the final group of studies, we investigated the effects of the concomitant administration of protein C (1000 ng/ml) and thrombin in vitro. Protein C (1000 ng/ml) increased relaxant sensitivity to thrombin after partial desensitization of the relaxant response by previous thrombin administration, (−60.2 ± 7.1% thrombin alone; −77.9 ± 7.2% thrombin + protein C), but had no effect after complete desensitization of the relaxant response. In conclusion, the data appear best explained by protein C and thrombin-induced EDRF dependent relaxation being due to proteolytic actions.