Effect of regenerated endothelium on lipid accumulation in the arterial wall

We tested the hypothesis that loss of endothelium results in increased transport of lipoprotein into the arterial wall, favors accumulation of lipid, and thus predisposes to atherosclerosis. In rabbits initially fed a diet low in lipid, the aortas were de-endothlialized with an intraarterial balloon catheter; 28 days later, the animals were divided into two groups. Group I animals were continued on a diet low in lipid and sacrificed at 8, 11, 13, and 15 weeks after de-endothelialization. Group II animals were fed the same diet supplemented with 0.5% cholesterol and sacrificed at comparable intervals. Aortas of group I animals revealed proliferative fibromuscular intimal thickening in both de-endothelialized and re-endothelialized areas, with little or no fatty change in the intima. In contrast, aortas of group II animals revealed slight to marked fatty change in the intima, characterized by accumulation of oil red O-positive material with anisotropic lipid inclusions. The greatest quantity of lipid was present in intimal thickening beneath regenerated endothelium, and not in adjacent intimal thickening lacking an endothelial lining. These results do not support the hypothesis that the absence of endothelium favors accumulation of lipid and predisposes to atherosclerosis. The experiments indicate that lipid accumulates preferentially in areas of intimal thickening covered by regenerated endothelium.