Morphometry of cardiac hypertrophy induced by experimental renal hypertension

Abstract

A method for determining the mean volume of cells within a tissue has been applied to the measurement of endocardial and epicardial myocytes in the left ventricle of normal and hypertensive rats. The technique is based on nuclear counts per unit area in tissue slices of different known thicknesses. It measures the mean cell volume per nucleus and has been combined with electron microscopic morphometry. Compared with the epicardial regions, the normal endocardial regions contained 30 percent more myocytes, 27 percent less interstitial space, 48 percent less capillary volume, 17 percent less capillary surface and the same capillary length per unit of tissue volume. In terms of both the relative and absolute volumes and surface areas of their organelles, the cytoplasmic composition of normal endocardial and epicardial myocytes was nearly identical. After 1 to 4 weeks of hypertension induced by renal arterial constriction, endocardial myocytes enlarged from 10,370 ± 410 to 12,520 ± 490 μ m 3 whereas epicardial myocytes enlarged from 12,600 ± 1,600 to 17,300 ± 1, 100 μm 3. The number of myocytes and the total length of capillaries remained constant. The epicardial region enlarged 37 percent with proportional increases of myocyte and interstitial volumes. In contrast, the endocardial enlargement was only 26 percent, consisting of 21 percent hypertrophy of myocytes and a 55 percent increase in interstitial components. Expansion of capillary lumens accounted for much of the interstitial enlargement throughout the myocardium. Hypertrophy of myocytes in the epicardial region was accompanied by a reduced mitochondria to myofibril ratio and disproportionately large increases (two- to three-fold) in both smooth endoplasmic reticulum and T system volume and surface area. On a cell basis the morphometric characteristics of myocytes from hypertensive rats are significantly different from normal, and significant differences occur between the inner and outer layers of the myocardium for practically every cytoplasmic component.