The origin of subendothelial cells in developing coronary collaterals

Using NPase as a specific and differential marker of endothelial cells and some blood-borne cells, we attempted to provide information on the origin of cells contributing to the formation of the intimal thickening occuring during coronary collateral growth in the dog. NPase reactive endothelial cells, polymorphonuclear and mononuclear blood cells and NPase unreactive smooth muscle cells and modified smooth muscle cells were seen in variable proportions in the subendothelial space during the early period of vascular growth and in the intimal thickening, formed a few weeks later. The medial smooth muscle cell appeared to be the main progenitor of cells present in this zone.