Developmental differences in catalase activity and hypoxic-hyperoxic effects on fluid balance in isolated lamb lungs

The effects of hypoxia (95% N₂/5% CO₂) followed by hyperoxia (95% O₂/5% CO₂) were determined in isolated lungs of premature (gestational age 128 to 135 d) and full-term (postnatal age 0 to 5 d) lambs perfused with autologous blood (100 mL·min^-1 kg body weight^-1). In full-term lungs, hypoxia-hyperoxia compared with hypoxia alone decreased pulmonary artery pressure and increased weight gain and extravascular lung water. In premature lungs, the increase in weight gain was greater and was associated with hemorrhage and increased pulmonary arterial and peak airway pressures. Papaverine eliminated reoxygenation-induced differences in pulmonary artery pressure, peak airway pressure, and weight gain in both age groups. Osmotic reflection coefficients for total protein and albumin, measured by a modification of the filtered volume technique, averaged 0.591 ± 0.054 (SEM) and 0.465 ± 0.054 (SEM), respectively, and were not altered by reoxygenation or age. Catalase activity in lung tissue and erythrocytes was lower in premature lambs, but there were no age-related differences in superoxide dismutase or glutathione peroxidase activities. These results demonstrate that hypoxia-hyperoxia in isolated lamb lungs increased lung weight due to edema formation in full-term lamb lungs and hemorrhage in premature lamb lungs and that this increase was greater in premature lamb lungs. We speculate that the weight gain caused by reoxygenation was due to a vasodilation-induced increase in surface area in full-term lamb lungs and a vasoconstriction-induced increase in vascular pressure in premature lamb lungs. The mediators of this developmental difference in vasomotor tone are unknown, but lower catalase activity in premature lungs suggests that hydrogen peroxide may have played a role.