Cardiac function and morphology with aging in the spontaneously hypertensive rat

Abstract

To determine the effects of a chronic pressure load on cardiac function and morphology, spontaneously hypertensive rats (SHR) and 2 normotensive strains of Wistar rats (WKY and NWR) were studied under ether anesthesia at 13, 25, 25, 52 and 90 wk of age. Resting cardiac index of the SHR was comparable to that of WKY and NWR at all ages but the peak cardiac output and peak stroke volume per gram of left ventricle determined during a rapid infusion of Tyrode solution were markedly reduced in the SHR only at 90 wk old age. Autonomic inhibition did not alter the peak stroke volume attained, but reduced peak cardiac output at all ages in each of the strains. Absolute left ventricular dimensions in the SHR increased out of proportion to body growth, consistent with concentric hypertrophy. As peak pumping ability markedly declined from 52-90 wk in the SHR, the free wall of the left ventricle greatly thickened but the septum remained unchanged. At this time the right ventricle also hypertrophied. This disproportionate thickening of the walls of the left ventricle and the hypertrophy of the right ventricle were reflected in measurements of their fiber diameters. Changes in ventricular architecture may contribute to the decrease in pumping ability seen in long-standing hypertension.