AN ELECTRON MICROSCOPIC STUDY ON HEALING PROCESS OF HYPERTENSIVE ARTERIAL LESIONS IN RATS

Abstract

From hypertensive rats with bilaterally constricted renal arteries, the constricting clamps were removed by the Sekiguchi's method, and the healing process of the arterial lesions of the rats was studied light and electron microscopically and enzyme-histochemically.After the removal of the clamps, blood pressure of the rats dropped, and nodular lesions in the mesenteric arteries were shrunken and scared.The fibrinoid substance, deposited in the intima began to disappear on the luminal side, and intimal cells appeared in the subendothelium. They entered, with protruding cytoplasmic processes, the remaining fibrinoid substance to lyze it. In the granules of the cellular processes were found acid phosphatase reaction products. These granules were considered to be lysosomes, the enzyme of which seemed to be directly involved in the lysis of the fibrinoid substance.In the course of healing of intimal fibrinoid degeneration, intimal cells made their first appearance directly beneath the endothelium, and they were morphologically similar to endothelial cells. Moreover, observation of the longitudinal sections often disclosed migration of endothelial cells into the subendothelium. On account of these, most of the intimal cells were considered to be derived from endothelial cells.After complete healing of the fibrinoid degeneration, the intima came to exhibit cellulofibrous intimal thickening, which consisted of typical smooth muscle cells, collagen, elastica and basement membrane-like substance.Medial smooth muscle cells which were damaged by hypertension showed partly or totally necrotized cell bodies, and they were consequently decreased in number. And the persisting muscle cells had turned into modified smooth muscle cells. After the removal of the clamps, the tendency to necrosis of muscle cells was invisible, and around the nuclei of the modified smooth muscle cell, lysosomes were increased, which were assumed to digest ganulo-vesicular cell debris deposited between the cells. With advance in healing, the cell debris diminished, and basement membrane-like substance and collagen were increased. Myofilaments of the modified smooth muscle cell were increased.After the complete healing of the media, it exhibited the so-called fibrosis, that is, increased collagen and basement membrane-like substance, and muscle cells turned into smooth muscle cells with the typical cytoplasmic structure, though irregular in shape.The adventitial granulation tissue, seen in the nodular arterial lesions of hypertensive rats, consisted of active fibroblasts, capillaries, and blood cells. After the removal of the clamps, the tissue was shrunken, and in association with this, radially disposed active fibroblasts turned into inactive fibroblasts, which were arranged concentrically around the arteries. In such adventitia, typical or modified smooth muscle cells were observed. It was consequently assumed that the adventitial fibroblasts might be converted into smooth muscle cells in the course of shrinking of the adventitial granulation tissue.