Role of lysosomes in mesenteric arterial lesions of renal hypertensive rats.

The acid phosphatase activities of arterial cells in the mesenteric arteries of renal hypertensive rats were investigated by both light and electron microscopy. Light microscopically, strongly positive acid phosphatase reactions were confirmed in endothelial cells, intimal cells, medial cells and adventitial cells of the mesenteric arteries, together with considerable deposition of fibrinoid substance in the intima and media in contrast to the appearance in control rats. Electron microscopically, lysosomes with acid phosphatase-positive reaction products were increased in number in endothelial cells, intimal smooth muscle cells, medial smooth muscle cells and adventitial neutrophils or macrophages. The lysosomes in intimal smooth muscle cells and those which were extracellularly discharged were responsible for lysis of the fibrinoid substance. In the media, acid phosphatase-positive lysosomes of medial cells and extracellularly discharged matrix lysosomes with acid phosphatase-positive reactions were also involved in the hydrolysis of necrotic substances and extracellular matrix. These acid phosphatase-positive reactions were diminished both light and electron microscopically in endothelial cells, intimal cells, medial muscle cells and adventitial cells in the regions of healing arteries where fibrinoid substance had been degradated and the intima showed cellulofibrous thickening. The possible role of this acid phosphatase activation for the clearance of cell debris as well as exudative substances in the healing of damaged arterial tissue was discussed.