Derivation of intimal cells appearing in spontaneous healing process of hypertensive arterial lesions.

Light and electron microscopic and autoradiographic studies were made on the process of spontaneous organization of fibrinoid substance deposited in the intima, that is, spontaneous healing of intimal fibrinoid degeneration of the hypertensive rat mesenteric arteries at 8–24 weeks after the constriction of the bilateral renal arteries.The organization of the intimal fibrinoid substance by intimal cells was performed mainly from the luminal side and infrequently from the medial side. Indigenous intimal cells and circulating blood cells were not positively involved in the organization.During the organization of fibrinoid substance, the endothelial cells turned into smooth muscle cell-like cells in situ, and there was a picture suggesting the migration of these smooth muscle cell-like endothelial cells into the intima or their incorporation into the intima by the covering of adjacent endothelial cells. Experiments with intravenous administration of ³H-proline revealed that endothelial cells and intimal and medial smooth muscle cells resembled each other functionally. It can therefore be said that the majority of the cells that participate in the organization of intimal fibrinoid substance are intimal smooth muscle cells derived from endothelial cells, and a part of the cells is derived from medial smooth muscle cells. The cellulofibrous tissue of the intima after the complete organization of intimal fibrinoid substance resulted from the proliferation of the endothelial cellderived intimal smooth muscle cells and from the fiber and ground substance formation by these.