Intimal healing. The pattern of reendothelialization and intimal thickening

Studies were undertaken to investigate further the basis of intimal proliferation and the identity of the surface lining cell in rabbit aortas subjected to extensive deendothelialization. Endothelial cells were selectively removed by passage of an inflated balloon catheter through the arterial lumen. The healing response was evaluated at intervals up to 36 weeks by several techniques: 1) permeability to Evans blue, 2) reappearance of endothelial cells as indicated by the specific marker, adsorbed goat anti-rabbit tissue factor-horseradish peroxidase, 3) planimetric measurements of intimal thickness, and 4) electron microscopy. The results indicate that endothelial cell recovery progressed slowly and that it extended only from areas spared denudation. The regions not covered by endothelial cells were lined by cells of smooth muscle cell origin. Such areas were permeable to Evans blue-protein complex, and their luminal smooth muscle cells were associated with connective tissue-like material at their luminal surface; this material apparently acted as a base for platelet accumulation. The present findings indicate that the lumen of the extensively denuded vessel is lined by either endothelial or smooth muscle cells and that intimal healing is related to restoration of endothelial cell cover. In addition, intimal thickening reached a maximum well before reendothelialization was complete.