Remodeling of the rat aortic endothelial layer during experimental hypertension. Changes in replication rate, cell density, and surface morphology.

Three models of hypertension were induced in Wistar rats: (1) aortic ligature between renal arteries, (2) uninephrectomy and Na-rich diet, (3) uninephrectomy, 0.9 per cent NaCl as drinking fluid and subcutaneous administration of desoxicorticosterone acetate (DOCA). We studied the aortic endothelium during the early (7 to 10 days) and late (40 days) phases of these models and quantified: (1) thymidine index and cell density using autoradiography on en face preparations, and (2) internal aortic circumference by planimetry. We also examined by means of scanning electron microscopy the surface morphology of the aorta in rats with aortic ligature. Thymidine index was constantly increased in the early phases of all models; it reverted to normal levels in the late phases. Endothelial cell density was slightly but significantly increased in the early and late phases after aortic ligature and in the early phase after Na-rich diet; it increased strikingly in the early and late phases after DOCA. There were no significant correlations between the variations of the internal aortic circumference and blood pressure, thymidine index, or cell density. Scanning electron microscopy showed no discontinuity of the endothelial cell layer either in the early or late phases after aortic ligature; bulging of endothelial cells into the lumen and appearance of cell clusters with numerous surface projections were seen during the early phase after aortic ligature. These changes produce a remodeling of the aortic endothelial layer which is maximal in the early phase after aortic ligature and in the early and late phases after DOCA and correlates with the previously reported increase of endothelial permeability to horseradish peroxidase in the same hypertensive situations.