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Studies on thrombin-induced endothelium-dependent vascular effects
1Institute of Pharmacology and Toxicology, Medical Academy Erfurt, GDR.
The clotting enzyme thrombin induces not only blood coagulation but it also receptor-mediated cellular events. In our studies, thrombin at nanomolar concentrations caused irreversible aggregation of washed human platelets which was inhibited by the naturally occurring tight-binding inhibitor hirudin. Thrombin within the same concentration range caused concentration-dependent transient relaxation of PGF2 alpha-precontracted pig coronary artery ring segments with intact endothelium. The relaxant response was neither affected by indomethacin nor by verapamil and was only slightly inhibited by exposure to calcium-free medium. Methylene blue enhanced the PGF2 alpha-induced contraction and diminished the thrombin-induced relaxation. Hirudin inhibited the relaxant effect of thrombin in a concentration-dependent manner. After removal of the endothelium by mechanical rubbing the thrombin-induced relaxation was absent. The present studies suggest that thrombin generated during coagulation is able to modify the vascular smooth muscle tone.
The clotting enzyme thrombin induces not only blood coagulation but it also receptor-mediated cellular events. In our studies, thrombin at nanomolar concentrations caused irreversible aggregation of washed human platelets which was inhibited by the naturally occurring tight-binding inhibitor hirudin. Thrombin within the same concentration range caused concentration-dependent transient relaxation of PGF2 alpha-precontracted pig coronary artery ring segments with intact endothelium. The relaxant response was neither affected by indomethacin nor by verapamil and was only slightly inhibited by exposure to calcium-free medium. Methylene blue enhanced the PGF2 alpha-induced contraction and diminished the thrombin-induced relaxation. Hirudin inhibited the relaxant effect of thrombin in a concentration-dependent manner. After removal of the endothelium by mechanical rubbing the thrombin-induced relaxation was absent. The present studies suggest that thrombin generated during coagulation is able to modify the vascular smooth muscle tone.