Limited adaptation in chronically hypertrophied hearts from aortic constricted rats: increased inhomogeneity in cross-sectional area of cardiomyocytes and intercapillary distance.

To study the sequential changes of myocardial structure in pressure-overloaded heart, rats were subjected to banding of ascending aorta at 8 weeks of age, and electron-microscopical morphometry was performed at weeks 1, 2, 4, 8, 16, and 24 postoperatively. Not only was the cross-sectional area of cardiomyocyte greater in banded rats but the degree of inhomogeneity increased in correspondence with development of hypertrophy. Intercapillary distance was significantly longer in banded rats than in controls. In banded rats, the distance around larger-than-normal cells (with a cross-sectional area exceeding 600 microns 2) was significantly longer than that around normal-sized cells (with a cross-sectional area under 600 microns 2) at 4, 16, and 24 weeks following surgery. Morphologically, intracellular capillaries were shown to develop; however, single or several necrotic cells were observed in 8- to 16-week banded rats and were attributed to acute ischemia. In 24-week banded rats, advanced interstitial fibrosis as well as collapsed intracellular capillaries were observed.