A Scanning Electron Microscope Study on Hemostatic Reaction. Early Hemostatic Plug Formation and the Effect of Aspirin

In order to clarify the mechanism of the hemostatic plug formation from the morphologic standpoint, scanning electron microscope observation was made on the inner surface of the rabbit carotid arteries 1, 5, 15, 30 and 45sec after stabbing with a needle. The arteries were first fixed in situ by an infusion of glutaraldehyde and then, after being excised, by immersion in glutaraldehyde and in osmium tetroxide. The critical point-dried and gold-palladium covered specimens were examined in a field emission type scanning electron microscope.Stabbing made a hole, about 0.25mm in diameter, in the arterial wall, and the ruptured endothelial cell shrank and retracted. Thus the subendothelial collagen fibers were exposed and hung on the wall of the holes. Some of the fibers were single and wavy and others were compactly packed in bundles, forming a network.The first step of the hemostatic process was adhesion of discoid platelets which were attached, with their bodies or frequently with their pseudopods, to the collagen fibers especially at the marginal and hanging part.On the adhered platelets other free platelets subsequently came to be attached. A thin layer of the platelet aggregates thus formed grew thicker, though somewhat distorted by the blood stream. At this second stage some erythrocytes were found hanging from the collagen fibers or undergoing collapse, suggesting its contribution to platelet aggregation by releasing ADP through hemolysis. The aggregate layer became so thick that it almost obliterated the hole and rose on the arterial lumen 45 sec after the stabbing.Aspirin which has been shown to affect platelet aggregation in the second phase was demonstrated to lower the rate of aggregate formation to half to one-third.