Effect of oxotremorine and epinephrine on lung surfactant secretion in neonatal rabbits

The phosphatidylcholine (PC) content (mg/g dry lung weight; mean +/- S.E.) of lung washes of 1 to 3-day-old rabbits was significantly greater 30 min after the injection of the muscarinic agonist oxotremorine (0.2 mg/kg; 50.5 +/- 2.9 mg/g; 2 P < 0.01) or epinephrine (50 micrograms/kg; 78.0 +/- 14.8 mg/g; 2 P < 0.001) than saline (25.7 +/- 1.9 mg/g). Injection of atropine (2 mg/kg), dl-propranolol (1 mg/kg) but not d-propranolol (1 mg/kg) at 40 min or adrenalectomy at 45 min before killing abolished the increase produced by oxotremorine (2 P < 0.001). Also, dl-propranolol antagonized the increase produced by epinephrine. Palmitic and myristic acids were the major fatty acids in the lung wash PC of control and oxotremorine-treated rabbits. The residual lung tissue PC content following atropine (2 mg/kg; 104.4 +/- 18.5 mg/g) was significantly greater (2 P < 0.05) than following saline (72.6 +/- 6.0 mg/g) but not different (2 P > 0.05) in other treatment groups. The total lung content of PC was 55% greater (2 P < 0.001) than controls 30 min after epinephrine (50 micrograms/kg). The surface activity of lung washes (mg/g dry lung weight; mean +/- S.E.), assayed on a surface tension balance using dipalmitoyl-phosphatidylcholine as standard, was significantly greater (2 P < 0.05) 30 min following injection of oxotremorine (0.2 mg/kg; 73.8 +/- 9.9 mg/g) or epinephrine (50 micrograms/kg; 72.2 +/- 10.2 mg/g) than saline (42.8 +/- 2.0 mg/g). Ten-min infusions of oxotremorine (0.34 micrograms/ml) into isolated, ventilated, perfused neonatal rabbit lung preparations failed to alter the PC content of the subsequent wash, but this was significantly (2 P < 0.05) raised from 3.7 (+/- 0.8) to 4.8 (+/- 0.8) mg/g dry lung wt by a 10 min infusion of epinephrine (3.4 micrograms/ml).