Morphometric analysis of collagen network and plasma perfused capillary bed in the myocardium of rats during evolution of cardiac hypertrophy

Abstract

In order to investigate the consequences of different types of cardiac hypertrophy on myocardial capillary and fibrosis density in rats we describe here, in the same hearts, the pattern of capillary bed density visualized by fluoresceine isothiocyanate dextran (FITC-dextran) and the pattern of fibrosis density as determined by automated image analysis. Pressure overload was induced by clipping one renal artery in rats (one-clip, two-kidney Goldblatt hypertension, RHV). Volume overload was induced by creation of an arteriovenous shunt between the abdominal aorta and the vena cava (aorto-caval fistula model ACF). Animals were sacrified at 1, 3 and 6 months following surgical procedure. Immediately prior to sacrifice, FITC-dextran (MW 150,000) was injected with the animal under ether anesthesia. Five minutes later, cardiac diastolic arrest was induced by the i.v. injection of potassium chloride. The heart was rapidly excised and placed in a formaldehyde solution. The degree of cardiac hypertrophy was calculated after measurement of cardiac weight. Left ventricular wall thickness and cavity area were measured by microscopic methods. Capillary density and geometry were determined by morphometric methods, under ultraviolet light microscopy, using a graphic tablet connected to a microcomputer. The degree of myocardial fibrosis, visualized with Sirius Red, was estimated by the use of automated image analysis using light microscopy. In renovascular hypertension, cardiac hypertrophy was maximum at one month (36%) and persisted through the six months of the study. This increase in cardiac mass was concentric, due to a significant increase in ventricular wall thickness and was associated with a marked increase in fibrosis and a significant decrease in subendocardial capillary density. These effects existed already one month and did not change with time. In the aorto-caval fistula model, cardiac hypertrophy was also maximum at one month (+56%), but this eccentric increase in cardiac mass was associated with no significant change in left ventricular wall thickness, but rather with a significant increase in the surface area of the left ventricular cavity. This volume overload hypertrophy was associated with a decrease in subendocardial capillary density which was negatively correlated with time. In contrast to concentric hypertrophy there was no increase in the fibrosis density compared to the sham-operated groups. Despite the identical degrees of hypertrophy, pressure and volume cardiac overload differed in a significant manner in both left ventricular wall thickness and cavity surface area. The observed changes in capillary bed and fibrosis density seem to be influenced predominantly by this change in geometry of the left ventricle.