Cardiovascular effects of dobutamine during exercise in dogs

To test the hypothesis that stimulation of adrenergic receptors in the heart is maximal during maximal exercise, and to determine whether generalized stimulation of adrenergic receptors during strenuous exercise produces significant alterations in the normal regional distribution of blood flow that occurs during exercise, we evaluated the cardiovascular effects of the infusion of dobutamine (40 micrograms.kg-1.min-1) in mongrel dogs during treadmill running. During maximal exercise, the dobutamine infusion resulted in a significant (P less than 0.05) increase in heart rate. Exercise capacity, total body O2 consumption (VO2), and maximal arteriovenous O2 difference, however, each were reduced during the infusion of this drug. A concomitant reduction in maximal blood flow to locomotive skeletal muscle occurred. The infusion of dobutamine also resulted in an increase in heart rate at a strenuous level of submaximal exercise. However, unlike during maximal exercise, VO2 was unchanged. Blood flow to locomotive skeletal muscle increased, and there was a concomitant reduction in arteriovenous O2 difference. Blood flow reductions that normally occur in splanchnic circulations during strenuous and during maximal exercise were generally somewhat attenuated during the infusion of this drug. Thus, dobutamine, a sympathomimetic agent, produces significant cardiovascular effects when infused in high doses during exercise. Our results demonstrate that beta-adrenergic receptor reserve exists in the heart during maximal exercise in dogs. In addition, the peripheral responses that occur during the infusion of the drug provide additional evidence that different degrees of adrenergic receptor reserve normally appear to be present within different regional circulations during strenuous and during maximal exercise.