Scanning electron-microscope studies of the endothelium of aortic allografts in the rabbit: morphological observations.

Segments of aorta were transplanted between male rabbits using a cuff technique for anastomosis. The endothelial surfaces of recipient and donor aortas were observed by scanning electron microscopy following silver staining and pressure fixation at 1/2, 5, 24, 48 hr and 10 and 20 days after transplantation. Five hours after transplantation the endothelium was intact and only occasional cells were adherent to the surface. After 24 hr the endothelium was still intact, but showed breaks and small holes in the intercellular junction. There were many round cells adherent to the surface and lying in the sub-endothelium especially in association with the holes. Light microscopy showed that the intima was packed with cells, but they had not penetrated the internal elastic lamella into the media. Twenty days after transplantation the outlines of endothelial cells were no longer discernible and the surface was carpeted by leukocytes, platelets and thrombotic material.