Time-dependent effect of pneumonectomy on alveolar epithelial fluid clearance in rat lungs

Objective: Because pneumonectomy initiates compensatory growth of the remaining lung,we determined the time-dependent effects of pneumonectomy on alveolar fluid clearance capacity. Methods: Alveolar fluid clearance capacity with the Evans blue-labeled albumin concentration was measured in rats 3 hours, 2 days. 7 days, 14 days, and 28 days after left pneumonectomy. The mechanisms responsible for the increase in alveolar fluid clearance were explored. Results: Alveolar fluid clearance in the remaining lung was normal through 7 days and then increased 14 and 28 days after pneumonectomy. The increase in alveolar fluid clearance at 28 days after pneumonectomy was accounted primarily by an increase in amiloride-sensitive transport. The expression of epithelial sodium channel messenger RNA was increased in the remaining lung and in type 11 alveolar epithelial cells isolated from rats 28 days after pneumonectomy, The number of isolated type II cells was larger in pneumonectomized rats than in control rats. Also, beta-adrenergic agonist therapy increased the rate of alveolar fluid clearance at the 3-hour and 28-day time points. Conclusions: The capacity to remove alveolar fluid in the remaining lung is maintained at a normal level for up to 7 days after pneumonectomy in a rat, and then there is a marked increase in amiloride-sensitive alveolar fluid transport capacity that might depend, at least in part, on increased expression of epithelial sodium channels in type 11 cells and in part on the increased number of type 11 cells.