Quantitative SEM analysis of injury to the endothelium of rabbit aorta and carotid artery during experimental atherosclerosis.

The luminal surface of the aorta and the carotid artery in normal and cholesterol-fed rabbits (3 weeks, 6 weeks, and 8 months of alimentary hypercholesterolemia) was studied by scanning electron microscopy (SEM). To study endothelial injury the vessels were perfused and stained under physiological pressure. The frequency of large and small endothelial defects was determined per surface unit of endothelium in the normal and experimental groups of rabbits. Loss of endothelial cells was regarded as a large defect, argyrophilic cells, craters, and stomata were regarded as small ones. It was found that the percentage of regions without endothelial cells was similar in both control rabbits and in rabbits with experimental atherosclerosis (0.005--0.04% of the total surface examined). The frequency of small endothelial defects increased in rabbits after 3 weeks of hypercholesterolemia but decreased to the control level after 6 weeks of hypercholesterolemia. In rabbits with 8 months of hypercholesterolemia the frequency and area of defects outside plaques did not differ from the control group. In the group with hypercholesterolemia for 8 months 39.2% of the plaque surface contained endothelial cells in which there were no distinct silver-stained cell borders. Kevex X-ray spectrometric data of silver topography indicated that the plaque surface without distinct cell borders was not an area devoid of cells. The data obtained do not support the assumption that morphological endothelial injury is the structural precursor of plaque formation.