Scanning Electron Microscope Study on Hemostatic Reaction. Mural Thrombus after the Removal of Endothelium, with Special References to Platelet Behavior, Site of Fibrin Formation and Microhemolysis

Abstract

Hemostatic reaction in the mural thrombus formation (up to 2 h) was examined by scanning electron microscopy after removal of the endothelium in the rabbit carotid artery by the use of a rough-surfaced needle. The endothelium was almost completely removed leaving a network of subendothelial microfilaments which sometimes appeared half embedded in the basement membrane. Platelet adhesion occurred on this subendothelial tissue by attachment of discoid platelets, pseudopod formation and spreading. The subendothelium was covered by a layer of platelets in about 10 min. During adhesion the platelets caught the microfilaments by their pseudopods and never produced hemispherical protrusions. Loose aggregates of the rounded platelets were then formed on them but they were frequently reversible, resulting in 1-2 h, in coverage by only 1 or 2 layers of the adhered platelets. This platelet reaction was weaker than that to collagen in a case of bleeding in a previous report. Leukocyte participation in thrombus formation began at around 30 min. Fibrin strands appeared as tiny fiaments which were attached exclusively to the activated platelets and later grew into thick and long fibers forming a network. Activated platelets seemed to be very important as the base of development of fibrin thrombus. Many erythrocytes were destroyed at the mural thrombus after attaching to the subendothelial components or activated platelets or fibrin strands and being deformed by the blood stream. The Hellem hypothesis of microhemolysis in the hemostatic process was supported. This type of hemostatic reaction was caused by a slight manipulatory pressure on the arterial wall, suggesting the occurrence of thrombus formation in daily life.