Effects of hypoxia on alveolar fluid transport capacity in rat lungs

There is little information regarding the effect of hypoxia on alveolar flu id clearance capacity. We measured alveolar fluid clearance, lung water vol ume, plasma catecholamine concentrations, and serum osmolality in rats expo sed to 10% oxygen for up to 120 h and explored the mechanisms responsible f or the increase in alveolar fluid clearance. The principal results were 1) alveolar fluid clearance did not change for 48 h and then increased between 72 and 120 h of exposure to hypoxia; 2) although nutritional impairment du ring hypoxia decreased basal alveolar fluid clearance, endogenous norepinep hrine increased net alveolar fluid clearance; 3) the changes of lung water volume and serum osmolality were not associated with those of alveolar flui d clearance; 4) an administration of beta -adrenergic agonists further incr eased alveolar fluid clearance; and 5) alveolar fluid clearance returned to normal within 24 h of reoxygenation after hypoxia. In conclusion, alveolar epithelial fluid transport capacity increases in rats exposed to hypoxia. It is likely that a combination of endogenous norepinephrine and nutritiona l impairment regulates alveolar fluid clearance under hypoxic conditions.