The aortic intima. II. Repair of the aortic lining after mechanical denudation.

This article reports the ultrastructure of the aortic lining during the repair of mechanically denuded aortic intima in the rat. Three main features were observed: a) Although platelets form a pavement on the exposed components of the aortic intima, platelet thrombi do not form on the denuded surface. b) During the first weeks after injury, a temporary false endothelial lining is formed by modified intimal smooth muscle cells. While the modified smooth muscle cells do not constitute a continuous cell layer, they are like true endothelial cells in that platelets do not adhere to the cell membrane of either cell type. c) A continuous layer of true endothelial cells is formed within 2 months after the original injury. Even after reestablishment of a continuous endothelium, however, abnormalities persist in the form of incompletely formed intercellular junctions. This abnormal endothelium is associated with areas of intimal smooth muscle cell proliferation. These observations are compatible with two alternative interpretations of the role of endothelial injury in the intimal proliferation seen following injury to the vessel wall: a) persistent defects in the endothelium may result in proliferation of underlying arterial smooth muscle cells or b) the proliferation, in converse, may in some manner delay the healing process of the overlying endothelium.