Myocardial contractility and energetics in cardiac hypertrophy and its regression

The changes in myocardial contractility and ventricular myosin isoenzymes were investigated in rats with pressure-overload cardiac hypertrophy as well as during its regression. Hypertrophic myocardium was obtained from rats with renovascular hypertension (Goldblatt rats), rats with abdominal aortic constriction (AC), and spontaneously hypertensive rats (SHR). Regression of cardiac hypertrophy was induced by lowering the blood pressure through nephrectomy on the affected side in Goldblatt rats, by opening the clip which constricted the abdominal aorta in AC rats, and by the administration of antihypertensive agents to SHR. The isometric developed tension of isolated left ventricular papillary muscles and the maximum rate of increase in the tension (dT/dtmax) were measured. Left ventricular myosin isoenzymes were separated by pyrophosphate gel electrophoresis. Isometric developed tension remained unchanged, but dT/dtmax was decreased in hypertrophic myocardium, although it recovered along with the regression of cardiac hypertrophy. The left ventricular myosin isoenzyme pattern was shifted towards V3 in hypertrophic myocardium, and shifted back again towards V1 with the regression of cardiac hypertrophy. These results indicate that relief of hemodynamic overload is one of the most important elements in the regression of cardiac hypertrophy and the associated physiological or biochemical alterations. However, other factors such as neurohumoral influences must also be taken into consideration.