Cardiac function and actomyosin ATPase activity in hearts of conditioned and deconditioned rats

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Abstract
Rats were assigned to 4 groups: sedentary for 8 wk (SH), conditioned by a swimming program for 8 wk (CH), conditioned by the swimming program for 8 wk followed by 2 wk of inactivity (DC) and sedentary for 10 wk (DS). The hearts of these animals were perfused in an isolated working rat heart apparatus at fixed heart rates, and atrial perfusion pressures were varied. After perfusion the hearts were analyzed for actomyosin ATPase activity. The conditioning program caused an increase in ventricular function as measured by cardiac output and negative dP/dt [change in pressure with time]. Coronary flow, myocardial O2 consumption and actomyosin ATPase activity were also significantly higher in hearts of conditioned animals. After 2 wk of deconditioning, the hearts of previously conditioned animals and of sedentary controls had the same cardiac output, coronary flow, myocardial O2 consumption and negative dP/dt. Actomyosin ATPase activity was the same in the 2 groups. The effects of physical training, which produces enhanced cardiac function and biochemical activity in the hearts of physically trained rats, apparently are reversed by a 2-wk deconditioning program.