beta-Adrenergic induced synthesis and secretion of phosphatidylcholine by isolated pulmonary alveolar type II cells

Rat pulmonary alveolar type II cells isolated by trypsinization and discontinuous density gradient ultracentrifugation were maintained in primary culture for 48 hours. The cultured type II cells responded to beta-adrenergic, but not cholinergic, agonists by an increase in the rate of synthesis and also secretion of 3H-phosphatidylcholine. The beta-adrenergic agonists, isoproterenol and terbutaline, 10 microM, caused a 1.7-fold increase in the rate of synthesis of 3H-phosphatidylcholine after a 4-hour incubation. At this time, there was also an increase in the cAMP content of the cultured cells. Terbutaline, 10 microM, caused a 4.9-fold increase in the rate of secretion of 3H-phosphatidylcholine after a 1-hour incubation. The beta-adrenergic effect on both synthesis and secretion by type II cells was blocked by propranolol. 8-Br-cAMP, 100 microM, but not 8-Br-cGMP, mimicked the beta-adrenergic effect on both synthesis and secretion of 3H-phosphatidylcholine. The increased rate of 3H-phosphatidylcholine induced by beta-adrenergic agonists was unaffected by colchicine. These data are consistent with the hypothesis that both synthesis and secretion of pulmonary surfactant are under adrenergic control operating through a beta-receptor and the adenylate cyclase system. These data also suggest that synthesis and secretion of pulmonary surfactant are independent processes. The possibility of other neural or hormonal mechanisms is not excluded.