INTRAVENOUS-INFUSION OF TOLAZOLINE REDUCES PULMONARY VASCULAR-RESISTANCE AND NET FLUID FILTRATION IN THE LUNGS OF AWAKE, HYPOXIC NEWBORN LAMBS

Publisher Website
Google Scholar
Abstract
In newborn lambs, alveolar hypoxia increases pulmonary microvascular pressure, causing an increase in lung lymph flow and a decrease in the concentration of protein in lymph. To see if reducing pulmonary vascular resistance during hypoxia might decrease net transvascular filtration of fluid in the newborn lung, vascular pressures and cardiac output were measured and lung lymph from 10 unanesthetized lambs 1-3 wk of age was collected before and during hypoxia, and then during a constant i.v. infusion of tolazoline, an .alpha.-adrenergic blocker. After a 2 h control period in air, the lambs breathed 10-12% O2 in N for 2-3 h; then, during sustained hypoxia, tolazoline (2 mg/kg of body wt) was given by rapid i.v. injection, followed by a constant infusion at a rate of 4 mg/kg per h for 2-3 h. During hypoxia alone, pulmonary vascular resistance increased 69%, lymph flow increased 84% and lymph protein concentration decreased. During persistent hypoxia and infusion of tolazoline, pulmonary vascular resistance decreased 23% and this was associated with a 22% reduction in lymph flow and lymph protein flux. The concentration of protein in lymph was unaffected by tolazoline. In 3 lambs killed during hypoxia and tolazoline infusion, extravascular lung water averaged 3.9 .+-. 0.1 g/g of dry lung, significantly less than the lung water content of lambs killed during hypoxia alone (4.5 .+-. 0.1 g/g). I.v. infusion of tolazoline into hypoxic, newborn lambs reduced pulmonary vasoconstriction and decreased the amount of liquid and protein entering the lungs. The fact that the concentration of protein in lymph did not change as lymph flow decreased during tolazoline infusion suggests that tolazoline reduced extravascular lung water by decreasing the effective vascular surface area for exchange of fluid or by decreasing pulmonary microvascular permeability to protein.