The Permeability Pathways in the Walls of Intestinal Submucosal Arterioles in Acute Angiotensin‐induced Hypertension in Rats

In rats with acute angiotensin‐induced hypertension, segments from intestinal submucosal arterioles dilated and permeable to plasma components were studied in the electron microscope. The permeability pathways were found to be endothelial gaps measuring from 900 Å to 29 microns, discontinuities of the endothelial basement membrane, fenestrae in the internal elastic lamina and discontinuities of the luminal basement membrane of the media. Most of the endothelial gaps were shown to be dilated endothelial junctions, and colloidal carbon and formed elements of the blood were found passing through the gaps. In media, carbon was found extra‐ and intracellularly if the smooth muscle cells were severely damaged. Penetration of carbon into the adventitia was not found when the adventitial basement membrane of the media was intact. The changes are probably caused by mechanical factors secondary to the development of dilatations.