The cellular pathology of experimental hypertension. VI. Alterations in retinal vasculature.

The ultrastructure of retinal arterial vessels from rats with severe renal hypertension has been studied. The permeability of retinal vessels has also been examined by means of vascular labeling technics utilizing horseradish peroxidase and microperoxidase as tracer substances. Small retinal arteries and arterioles exhibit foci of smooth muscle necrosis characterized initially by fragmentation of medial smooth muscle cells, and subsequently by loss of myofilaments and release of free vesicles, vacuoles and other cytoplasmic organelles extracellularly. Evidence for increased permeability is observed occasionally in retinal capillaries and less frequently in arteries and arterioles. The enzymatic tracers penetrate the tight junctions of the endothelial cells and are found in the basement membranes adjacent to endothelial and smooth muscle cells, as well as in expanded extracellular spaces around the capillaries. The alterations in the ultrastructure and permeability of retinal vessels in experimental hypertension have been compared with that of visceral and cerebral cortical vessels.