Morphologic and functional changes of the aortic intima during experimental hypertension.

The morphology and permeability to horseradish peroxidase of the rat aortic intima have been investigated in three experimental models of hypertension having different values of plasma renin content and plasma aldosterone level. During hypertension the aortic endothelium shows three main changes: 1) increased arithmetic mean thickness, with prominent rough endoplasmic reticulum and polyribosomes; 2) the appearance of actin microfilament bundles; and 3) increased permeability to horseradish peroxidase. These changes are not present in all models, do not appear to depend on hypertension per se, and are independent of each other. The subendothelial layer of hypertensive animals shows an increased thickness that appears to be correlated with an increase of endothelial cell volume. Our results suggest that: 1) the aortic intima reacts differently to different types of hypertension, and 2) factors other than hypertension per se play a role in the development of vascular changes observed in animals with elevated blood pressure.