VASOPRESSIN CONTRIBUTES TO THE CARDIOVASCULAR-RESPONSE TO DYNAMIC EXERCISE

Vasopressin is a powerful vasoconstrictor that is released into the sy stemic circulation during exercise. We tested the hypothesis that this peptide contributes to the cardiovascular response during treadmill e xercise in the pig. Seventeen miniswine were instrumented with epicard ial electrocardiogram leads, left atrial and aortic catheters, and a l eft ventricular pressure transducer for measurement of heart rate (HR) , regional blood flow, arterial blood pressure (MAP), and myocardial c ontractility [first derivative of left ventricular pressure (dP/dt) at 40 mmHg developed pressure] at rest and during exercise. At a work in tensity of 80% of each animal's maximal HR reserve, exercise-induced i ncreases in MAP, HR, dP/dt at 40 mmHg developed pressure, and cardiac output were measured. On a separate day, the workload performed by eac h animal was replicated in the presence of selective vasopressin V1-re ceptor inhibition using the specific V1 antagonist, [d(CH2)5Tyr(Me)]ar ginine vasopressin (10-14 mug/kg iv). During exercise, MAP was lower ( 96 +/- 3 vs. 104 +/- 2 mmHg) and cardiac output was higher (13.5 +/- 0 .6 vs. 12.6 +/- 1.0 l/min) in the presence of V1-receptor blockade tha n during unblocked conditions, respectively. Furthermore, we observed an attenuation of exercise-induced decreases in blood flow to the colo n. Increases in vascular resistance in the stomach, small intestine, c olon, and pancreas also were diminished by V1-receptor inhibition. How ever, HR and myocardial contractile responses to exercise were not aff ected. These results suggest that vasopressin contributes to increases in MAP and to the redistribution of cardiac output during dynamic exe rcise in the miniswine.