Late-onset renal hypertension in old rats alters myocardial microvessels

We tested the hypothesis that late-onset hypertension in middle-aged (15 mo) and senescent (24 mo) rats would adversely affect the coronary microvasculature. Morphometric analyses were performed on coronary capillaries and arterioles from rats with one-kidney, figure-8 renal wrap hypertension of 3-mo duration. Compared with control rats, wall-to-lumen ratios of arterioles with lumen diameters less than 25 microns were higher in the two hypertensive groups by approximately 30%; larger arterioles did not show consistent intergroup differences. A comparison of the two control groups revealed that wall-to-lumen ratio of arterioles with lumen diameters less than 50 microns tended to be greater in the senescent rats. Capillary numerical density was markedly reduced in the hypertensive animals of both age groups and caused an increase in the mean Krough cylinder radius and in the mean capillary domain. The latter increased by 28-63%; the largest increment occurred in the endomyocardium of the senescent group. A trend toward increased heterogeneity of capillary spacing was also noted in the hypertensive rats. The observed microvascular alterations occurred in the absence of an absolute increase in left ventricular mass but in the presence of cardiocyte hypertrophy. Thus the decrements in capillary numerical density are not only due to inadequate growth but reflect an absolute reduction in the number of these vessels associated with cardiocyte loss. It is concluded that late-onset hypertension in middle-aged and senescent rats is characterized by left ventricular wall remodeling that includes microvascular alterations that would be expected to limit maximal myocardial flow and O2 supply to the cardiocyte.