Effects of arginine vasopressin on hemodynamics and lung fluid balance in lambs

The purpose of this project was to study the effects of increased plasma concentrations of arginine vasopressin (AVP) on hemodynamics and lung fluid balance in lambs. We studied 16 unanesthetized newborn lambs during a base-line period and while infusing AVP into a hindlimb vein at 1.65 ± 0.12 and 2.98 ± 0.15 mU·kg^-1·min^-1. We measured aortic, pulmonary arterial, and left atrial pressures and heart rate continuously and cardiac output at frequent intervals. In five additional experiments, we collected samples of pure lung lymph during a base-line period and while infusing AVP at 2.02 ± 0.15 mU·kg^-1·min^-1. AVP infusion increased plasma concentrations of AVP to 11.3 ± 5.2 and 19.9 ± 5.2 μU/ml at the low and high rates of infusion, respectively. Both aortic and left atrial pressures increased at the low rate of infusion (11 and 3 Torr, respectively) but remained unchanged at the higher rate. Systemic vascular resistance increased, and heart rate and cardiac output decreased at each rate of infusion. In fact, at the higher rate of infusion cardiac output decreased 38% when compared with base line. Neither pulmonary artery pressure nor pulmonary vascular resistance was affected by infusion of AVP. Despite the increase in left atrial pressure, the rate of lung lymph flow was not affected by the infusion of AVP, whereas the lymph-to-plasma protein ratio decreased slightly but significantly from 0.64 ± 0.02 to 0.60 ± 0.02. We conclude that at plasma concentrations similar to those seen clinically AVP has profound effects on the systemic circulation, increasing systemic resistance and reducing both heart rate and cardiac output but has little effect on the pulmonary vascular tone or the net rate of fluid filtration in the lung.