Endurance training in the rat. II. Performance of isolated and intact heart

The effects of isotonic physical training and detraining on cardiac function were studied in young and adult male rats trained by graded treadmill running and compared with sedentary controls. Absolute left ventricular mass was not increased, and ventricular compliance was not altered by training. Ventricular function curves that plotted peak systolic pressure, maximum rate of rise of left ventricular pressure, cardiac output, coronary flow, or stroke work as a function of atrial filling height in the isolated perfused heart did not demonstrate a training effect in either age group. The cardiac response to hypoxia was also comparable in the trained and sedentary rats. The base-line heart rate of anesthetized rats, in which in situ cardiac function was studied, was lower in the trained rats (321 +/- 14 vs. 377 +/- 8, P less than 0.005). Resting hemodynamics and left ventricular function curves generated from pressure-flow data during volume infusion did not differentiate between the hearts of trained and sedentary rats. In conclusion, a moderate level of endurance training did not enhance cardiac contractility when this was assessed under nonexercise conditions in both the isolated perfused heart and intact in situ heart preparations.