Cardiac function in hypertrophied hearts from chronically exercised female rats

Abstract

Physiological cardiac hypertrophy was produced in female rats by subjecting them to a swimming program for 8 wk. Conditioned rats (C) had body weights similar to sedentary control rats (S), but hearts from C weighed 33% more than hearts from S. Heart function was assessed in an isolated working-heart apparatus at similar heart rates and aortic diastolic pressures and over a range of 5-20 cm H2O left atrial filling pressure (LAP). At any given LAP, absolute values for cardiac output and coronary flow were greater (P < 0.001) in C than S, but when these values were normalized for dry left ventricular (LV) weight, no differences were observed. Peak LV systolic pressure and ejection fraction were greater (P < 0.01) in C than S at all LAP. Derived measures of contractility calculated at the midwall demonstrated greater (P < 0.01) velocity and extent of circumferential fiber shortening in C compared to S. Chronic swimming in female rats leads to enhanced contractile performance of the left ventricle despite a marked degree of hypertrophy. These results contrast with previous observations in female rats trained by running where hypertrophy and enhanced function were not observed.