Smooth muscle cell proliferation in the rat coronary artery induced by vitamin D.

Ultrastructural changes induced in rat coronary arteries by oral administration of a large dose of vitamin D2 were examined by transmission and scanning electron microscopy. Our observations were that smooth muscle cell proliferation occurred without endothelial denudation and without exposure of the subendothelium. While the endothelial cells did show evidence of degeneration, the adjoining endothelial cells migrated beneath so that these degenerated cells could become detached without exposing the subendothelium. Therefore, factors other than platelets seem to participate in the phenotypic modulation and proliferation of the smooth muscle cell. Medial degeneration may be a prerequisite for formation of the lesion.