Light and scanning electron microscopic and immunohistochemical studies on permeability of hypertensive rat mesenteric arteries.

Experimental hypertensive rats were intravenously injected with carbon and iron as tracers, and their mesenteric arteries exhibiting hypertensive arterial lesions were observed by light and scanning electron microscopy and immunohistochemistry. Early arterial lesions showing intense medial damages, deposition of fibrinoid substance consisting of fibrin in the intima and/or media, and granulation tissue in the adventitia were characterized by marked insudation of intravenously injected tracers. Scanning electron microscopy demonstrated numerous leukocytes and platelets adhering to endothelial surface, opened endothelial cell junctions, and desquamation of these cells. Immunohistochemistry revealed laminin and low stainability of fibronectin in the subendothelium. Advanced lesions showed deposition of a large amount of fibrinoid substance and no insudation of tracers in the intima, but scanning electron microscopy manifested opening of endothelial cell junctions, desquamation of endothelial cells, and adherence of leukocytes and platelets. Immunohistochemistry revealed fibronectin in the intima and laminin just beneath the endothelium. In the healed lesions disclosing fibrocellular intimal thickening, there was no insudation of tracers. Scanning electron microscopy showed opened endothelial cell junctions, endothelial cell defects, and adherence of leukocytes and platelets. There were fibronectin in the intima and laminin beneath the endothelium. It was suggested that the opening of endothelial cells junctions and desquamation of endothelial cells would be necessary for the arterial increased permeability in hypertensive rats, and that fibrin-fibronectin complex, fibronectin-acid mucopolysaccharide complex, and basement membrane would together inhibit the increased permeability in the mesenteric arteries of hypertensive rats in spite of endothelial cell injuries and their defects.