EFFECT OF VASOACTIVE INTESTINAL POLYPEPTIDE ON THE CANINE CARDIOVASCULAR-SYSTEM

  • 1 January 1985
    • journal article
    • research article
    • Vol. 106  (5) , 542-550
Abstract
Our purpose was to determine the effect of vasoactive intestinal polypeptide (VIP) on the cardiovascular system with special emphasis on coronary vascular effects. In section I, VIP was infused into six healthy and six cobalt-cardiomyopathic dogs at two infusion rates (0.02 and 0.05 .mu.g/kg/min). Left ventricular end diastolic pressure and mean systemic pressure fell significantly in both groups. Heart rate rose in both, and maximum systolic dP/dt increased in the myopathic group. Cardiac output and regional blood flows were determined by serial left atrial injections of radioactive 15 .+-. 3 .mu.m (mean .+-. SD) microspheres. In both groups, blood flow increased significantly to the esophagus, pancreas, atria, and ventricles and to the endocardial and epicardial regions of the left ventricular free wall. Blood flow to the brain decreased. In section II, VIP was infused intravenously at 0.1 .mu.g/kg/min into six anesthetized dogs with coronary sinus flow, pulmonary artery, and systemic artery catheters inserted. Cardiac index rose from baseline (3.1 .+-. 0.5 to 4.8 .+-. 1.3 L/min/m2, P < 0.005), as did coronary blood flow (90 .+-. 25 to 159 .+-. 54 ml/min, p < 0.005) during the VIP infusion. Myocardial oxygen consumption rose from 14.1 .+-. 3.9 to 19.8 .+-. 5.4 ml/min (P < 0.001), but the aorta-to-coronary sinus O2 difference decreased from 157 .+-. 19 ml/L to 132 .+-. 42 ml/L (P < 0.05), and the percent O2 extracted from coronary blood also decreased significantly. In section III, the beating hearts of 12 anesthetized dogs were removed, and the coronary arteries excised, cut into helical strips, placed in a tissue bath, and put at a resting tension of 500 mg. The K+ concentration of the bath was manipulated to concentrations of 2 mmol/L, 10 mmol/L, and 20 mmol/L; resulting coronary tensions were 480 .+-. 34, 601 .+-. 110, and 835 .+-. 54 mg, respectively. Strips were washed and then bathed with VIP at one of the following final concentrations: 1.5 .times. 10-9, 1.5 .times. 10-8, 1.5 .times. 10-7, and 1.5 .times. 10-6 mol/L. The various K+ concentrations were restored to the bath, and six observations were made at each K+ and VIP concentration. VIP decreased coronary arterial tone most significantly at the higher K+ concentrations. At 10 mmol/L K+, VIP decreased tension by 45 .+-. 41 (P < 0.05), 75 .+-. 19 (P < 0.005), 71 .+-. 76 (P < 0.05), and 55 .+-. 63 mg (P < 0.05) at rising VIP concentrations of 10-9, 10-8, 10-7, and 10-6 mol/L. At 20 mmol/L K+, VIP decreased tension by 52 .+-. 95, 93 .+-. 33 (P < 0.005), 128 .+-. 49 (P < 0.05), and 112 .+-. 46 mg (P < 0.005), respectively. Thus, although the physiologic role of VIP in the coronary and peripheral vascular system is not known, VIP is potentially important to regional blood flow especially in the heart.