Neurohumoral control of pulmonary surfactant secretion

The effect of the muscarinic drug, carbamylcholine, on surfactant secretion by hamster lung was examined. Intracellular phosphatidylcholine was prelabeled with tritium by intraperitoneal injection of ³H]choline into adult hamsters. Carbamylcholine (18 µg/100 g body wt.) was administered IP to one group of animals 30 min before sacrifice and isotonic saline was given to another group. Following sacrifice, the lungs were perfused, sliced, and incubated in the presence or absence of 15 µg/ml carbamylcholine for 1 h. Secretion of radiolabeled phosphatidylcholine by the lung tissue slices into the medium was evaluated. Treatment of animals with carbamylcholine was associated with a significant enhancement in the secretion of ³H]phosphatidylcholine into the medium. Administration of the muscarinic antagonist, atropine, in an equimolar dose completely inhibied the stimulatory effect of carbamylcholine on surfactant secretion. Treatment of hamster fetuses with carbamylcholine had no effect on ³H]phosphatidylcholine secretion from fetal lung tissue slices. The results support the concept that surfactant secretion by adult hamster lung is regulated by neurohumoral mechanisms.