Exercise, dobutamine, and combined atropine, norepinephrine, and epinephrine compared

We compared the cardiovascular effects evoked in conscious dogs by 1) submaximal exercise; 2) infusion of dobutamine (40 μg·kg^-1·min¹); and 3) infusion of a combination of atropine (0.15 mg/kg), norepinephrine (0.19 μg·kg^-1·min¹), and epinephrine (0.05 μg·kg^-1·min^-1). Myocardial O₂ demand, as estimated by the double product (heart rate x systolic blood pressure), was similar during all three interventions. Cardiac output and heart rate increased significantly (P < 0.05) during each of the three interventions. Arteriovenous O₂ difference and total body O₂ consumption, however, increased only during submaximal exercise. Although myocardial blood flow increased similarly during each of the three interventions, blood flow to skeletal muscle and the tongue increased only during exercise. Exercise and the combined infusion of atropine, norepinephrine and epinephrine produced similar increases in blood flow to the diaphragm and similar decreases in blood flow to the stomach. These changes in blood flow were associated with appropriate changes in vascular resistance. Additionally, blood flow to the brain, kidney, adrenal glands, liver, and intestine did not change during any of the three interventions. Thus, in dogs, submaximal exercise, infusion of dobutamine, and infusion of a combination of atropine, norepinephrine, and epinephrine to evoke a given level of estimated myocardial O₂ consumption produce similar increases in cardiac output, heart rate, and myocardial blood flow. In contrast, the changes in total body O₂ consumption, arteriovenous O₂ difference, regional blood flow, and regional vascular resistance that occur during each of these three interventions are different.