Endothelial injury induced by thrombin or thrombi.

A variety of blood constituents was injected into an isolated segment of rabbit aorta to determine which elements might be involved in early endothelial injury. Test materials consisted of platelet-rich plasma (PRP) alone; PRP plus adenosine diphosphate (ADP); PRP plus tendon extract; PRP plus thrombin; ultrasonicated PRP alone; platelet-poor plasma alone; and thrombin in saline. Each experimental mixture was left in the aorta for 15 minutes, followed by reflow for 20 minutes. The vessel was then fixed by glutaraldehyde perfusion. Thick sections of the entire circumference of the aorta were taken for phase contrast microscopy and representative arease were selected for electron microscopy. In control PRP alone, platelet-poor plasma alone and with PRP plus ADP there were occasional subendothelial vesicles. When PRP plus thrombin and platelet-poor plasma plus thrombin were injected separately to form a thrombus or when thrombin in saline was used, there was extensive subendothelial vesiculation with focal ulceration and adherence of thrombus to endothelium. Severe injury was associated with the presence of thrombin initiating the polymerization of fibrinogen to fibrin. Electron micrographs demonstrate the earliest lesion as a disruption of the superficial fibrilliary elastica with separation of overlying endothelium.