Platelet Adhesion in the Rabbit Abdominal Aorta Following the Removal of the Endothelium: A Scanning and Transmission Electron Microscopical Study

The initial reactions of the blood components and the intima of the rabbit abdominal aorta have been observed following mechanical trauma. The endothelium was removed by the insertion of a roughened metal probe into the lumen of the vessel, thus exposing the subendothelial fibres and the internal elastic lamina. On restoration of the blood flow, platelets and later leucocytes adhered to the injured surface. Only small clumps of platelets or single cells adhered to the surface. Under these conditions it was possible to study the morphology of the cells and vessel surface by scanning electron microscopy, as no large mass of thrombus material was present to obscure the picture. The platelets developed long branched projections on adhering to the injured surface. Platelets were found in larger numbers in areas where much collagen was present, such as the fenestrations of the internal elastic lamina, but were sometimes seen at sites where these fibres were absent. It was possible to observe that platelets were sometimes attached to endothelial basement membrane, but often they adhered to sites where neither basement membrane nor collagen could be seen. It would seem therefore that some other component from the damaged intima may be necessary for platelets to adhere to the injured surface. The presence of a subendothelial mucopolysaccharide layer was demonstrated with the dye ruthenium red. At no time was it possible to observe a complete covering of platelets over the whole injured area.