Effect of intravenously injected collagenase on the concentration of circulating platelets in rats.

An enzymatically induced irritation of the vessel wall by intravenous injection of collagenase (1.5 U per kg body weight) into rats resulted in a transient decrease of the platelet concentration in the flowing blood. This may be caused by an occurrence of inter-endothelial gaps distributed throughout the total area of the circulatory system, as could be observed by electron-microscopic studies. Subendothelial structures, at the sites of those gaps, induce a formation of multilocal microthrombi of platelets. At some gaps within the endothelial layer a deposit of fibrin could also be observed hinting at a participation of the blood coagulation system in the sealing processes.