Sustained Hyperoxia Inhibits the Postnatal Increase in Na,K-ATPase Activity in Distal Lung Epithelial Cells From Chronically Ventilated Preterm Baboons• 1649

Abstract

Lung epithelial cell Na,K-ATPase activity increases at birth in association with clearance of fluid from the potential airspaces. We hypothesized that the pulmonary edema that occurs in preterm baboons after sustained hyperoxia and mechanical ventilation might be associated with inhibition of the perinatal increase in Na,K-ATPase activity. To test this hypothesis, we measured Na,K-ATPase activity in distal lung epithelial cells, and we assessed Na,K-ATPase immunoreactivity and α1 and β1subunit mRNA content in whole lung tissue harvested from neonatal baboons that were delivered prematurely (140d gestation, term=180d) and mechanically ventilated for 6-10d with either 100% O2 (hyperoxia) or sufficient O2 to maintain normal PaO2 (normoxia). Results were compared with those from gestation-matched control fetuses. Na,K-ATPase activity, determined by measurement of ouabain-sensitive 86Rb uptake (nmol/106 cells/h), averaged 14 ± 3 in cells from 8 control fetuses, 24 ± 3(significantly different from control, p<0.05) in cells from 10 newborns with normoxia, and 14 ± 2 in lung epithelial cells from 14 newborns with hyperoxia. These results demonstrate that ventilation with 100% O2 is associated with inhibition of the normal postnatal increase in lung epithelial cell Na,K-ATPase activity that occurs after premature birth without subsequent hyperoxia. Immunohistochemistry, performed with antisera to Na,K-ATPase holoenzyme, showed localization to the epithelial membrane in all groups, but there was decreased signal intensity in lung sections from the hyperoxia group compared to the normoxia group and to fetal controls. mRNA content for the α1 and β1 Na,K-ATPase subunits was determined in whole lung tissue by northern blot analysis and quantified by phosphorimagery. A 6-fold increase (p<0.05, n=3) in α1 subunit mRNA content was observed in the hyperoxic group relative to normoxic newborns and control fetuses. No significant difference was observed between the groups in mRNA content for the β1subunit. Thus, sustained postnatal hyperoxia enhanced α1 subunit mRNA abundance, but inhibited Na,K-ATPase activity in the lungs of preterm baboons. We speculate that the failure of epithelial cell Na,K-ATPase activity to increase postnatally in non-human primates that are mechanically ventilated with 100% O2 probably contributes to the postnatal lung edema and associated respiratory distress that occurs in these animals.