Effects of subacute hypoxia on alveolar epithelial ion transport in rats

To study the effects of subacute hypoxia on alveolar epithelial ion transport, alveolar fluid clearance was measured in isolated fluid-filled rat lungs. After instillation of a solution containing about 5% bovine albumin, an increase in alveolar fluid clearance was measured over 2 hours. Alveolar fluid clearance was lower when rats were kept in hypoxic conditions (FiO₂ = 0.1) for 48 hours. Neither 10^-5 M amiloride (a Na⁺-channel blocker) nor 10^-3 M ouabain (an inhibitor of Na⁺-K⁺-ATPase) inhibited fluid clearance in the hypoxia group, but they did in the normoxia group. These results indicate that subacute hypoxia may down-regulate both the Na⁺-channel and Na⁺-K⁺-ATPase, and thus decrease the absorption of excess alveolar fluid.