Morphologic Platelet Changes During Thrombus Formation in the Rat

Abstract

The film presents observations in small mesenteric vessels (diameter 10-20 μm) of the rat using high power Nomarski optics. Under stasis conditions platelets appear as flat discs. Leucocytes are often seen creeping slowly along the intact vessel wall. Vascular lesions are produced with a focused laser beam (Hadron 513 biolaser). Immediately after the lesion platelets stick to the site of the microburn either in their native disc like shape without apparent morphologic changes or with protrusions. Within seconds these platelets swell and form protrusions. After 3-10 min, depending on the size of the lesion the vessel is occluded by a platelet thrombus. Platelets undergo further swelling. Later the thrombus is partially or completely swept away and the vessel is recanal i zed. Irreversible fusion of platelets is rarely observed. . New, usually smaller thrombi form at the damaged vessel wall. The morphologic platelet changes observed differ markedly from the changes observed during aggregation in vitro. After injection of a new antithrombotic substance (Bay G 7565) the adhesion of platelets to the damaged area is remarkably diminished. The few platelets which adhere to the site of injury show the same swelling and transformation like in untreated animals. The film demonstrates that it is possible to investigate morphologic changes of single platelets during thrombus formation. It seems possible to adapt this model for the in vivo study of antithrombotic drugs.