Depressed in vivo myocardial reactivity to dobutamine in streptozotocin diabetic rats: influence of exercise training

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Abstract
To assess the effects of chronic diabetes on in vivo myocardial reactivity to beta1 adrenergic receptor stimulation and to evaluate the therapeutic effect of exercise training in preventing the cardiac abnormalities induced by diabetes four groups of rats were studied: sedentary control, trained control, sedentary diabetic, and trained diabetic. Trained rats were adapted to treadmill running before the induction of diabetes with streptozotocin 55 mg·kg−1 iv. The duration, speed, and grade of exercise were then progressively increased during eight weeks of training until the rats could run for 90 min at 18 m/min, 5% grade. A training effect was confirmed by an increase in plantaris muscle cytochrome oxidase activity. In vivo cardiac contractile performance was assessed by intracardiac catheterisation. Heart rate, left intraventricular peak systolic pressure, and positive and negative dP/dt were measured under basal conditions and after the intravenous administration of dobutamine 10−10 to 5 × 10−7 mol·kg−1 body weight. Under basal conditions, there were no differences among the four groups in left intraventricular peak systolic pressure, positive dP/dt, and heart rate, but negative dP/dt was lower in both diabetic groups. The response to dobutamine of the sedentary diabetic group, as reflected in the measured cardiodynamic variables, was significantly attenuated compared with that of the sedentary control group. Exercise training tended to improve cardiac function towards the level detected in the sedentary controls; however, the differences between sedentary and trained diabetic groups were not statistically significant. Exercise training also did not significantly alter the response of the control group to dobutamine. These findings suggest that myocardial reactivity to betai adrenergic stimulation is impaired in diabetic rats. Exercise training at the intensity used failed significantly to improve this condition.