Contractile function and myofibrillar ATPase activity in the exercise-trained dog heart

Myocardial contractility and the enzymatic (ATPase) activity of cardiac contractile proteins were examined after exercise training using the chronically instrumented, unanesthetized dog as an experimental model. Before training, heart rate and the maximum rate of left ventricular pressure development (max dP/dt) were measured at rest and during submaximal exercise. Animals were then subjected to an 8- to 10-wk treadmill running program. Training was verified by the establishment of a 10- to 20-beat/min reduction in heart rate during submaximal exercise. After training max dP/dt was within normal limits at rest, but significantly elevated during submaximal exercise. When max dP/dt was plotted as a function of heart rate, either with the animal standing quietly on the treadmil or during submaximal exercise, a marked elevation in max dP/dt at any given heart rate was observed following training. Myofibrillar protein yield and ATPase activity values were nearly identical in left ventricles from exercise-trained and sedentary control dogs. Although exercise training by treadmill running improved contractile function in the unanaesthetized dog myocardium, this response does not appear to involve alterations in myofibrillar ATPase activity.