Lung deflation impairs alveolar epithelial fluid transport in ischemic rabbit and rat lungs

Background. Because the fluid transport capacity of the alveolar epithelium after lung ischemia with and without lung deflation has not been well stud ied, we carried out experimental studies to determine the effect of lung de flation on alveolar fluid clearance. Methods, After 1 or 2 hr of ischemia, we measured alveolar fluid clearance using I-125-albumin and Evans blue-labeled albumin concentrations in in viv o rabbit lungs in the presence of pulmonary blood flow and in ex vivo rat l ungs in the absence of any pulmonary perfusion, respectively. Results. The principal results were: (1) lung deflation decreased alveolar fluid clearance while inflation of the lungs during ischemia preserved alve olar fluid clearance in both in vivo and ex vivo studies; (2) alveolar flui d clearance was normal in the rat lungs inflated with nitrogen (thus, alveo lar gas composition did not affect alveolar fluid clearance); (3) amiloride -dependent alveolar fluid clearance was preserved when the lungs were infla ted during ischemia; (4) terbutaline-simulated alveolar fluid clearance was preserved in the hypoxic rat lungs inflated with nitrogen; (5) lecithinize d superoxide dismutase, a scavenger of superoxide anion, and N-omega-nitro- L-arginine methyl ester, an inhibitor of nitric oxide, preserved normal alv eolar fluid clearance in the deflated rat lungs. Conclusion. Lung deflation decreases alveolar fluid clearance by superoxide anion- and nitric oxide-dependent mechanisms.