| Abstract: | We describe a slice model for the study of pulmonary surfactant secretion in newborn rabbits. Full term rabbits were delivered by cesarean section and injected intraperitoneally with [Me-3H]choline. Four hours later they were killed, the lungs were perfused to remove blood, slices (0.5 mm thick) were prepared and incubated in buffer at 37 degrees C. The composition of the lipids initially released into the medium resembled those of lung tissue rather than surfactant. Following 3 changes of medium, however, the composition of the lipids released was very similar to that of lung lavage. Phosphatidylcholine accounted for over 70% of the total while phosphatidylethanolamine and sphingomyelin accounted for only 7% and 4%, respectively. 52% of the phosphatidylcholine was disaturated. Less than 5% of the tissue lactate dehydrogenase was released into the medium. The rate of phosphatidyl[Me-3H]choline release during this period was, therefore, measured. Release of phosphatidyl[Me-3H]choline was linear with time and was temperature-dependent. Prostaglandin E2 stimulated its rate of release by 20% while indomethacin and flufenamic acid, inhibitors of prostaglandin synthesis, inhibited it by 52% and 37%, respectively. The calcium ionophore A23187 in the presence of Ca2+ stimulated release by 40% while colchicine an cytochalasin B inhibited it by 36% and 32%, respectively. These data suggest that both prostaglandins and Ca2+ are involved in surfactant release and that intact microtubular and microfilament systems may also be necessary. |
