Ventilation enhances pulmonary alveolar clearance of radioactive dipalmitoyl phosphatidylcholine in liposomes.

We examined the clearance from lungs of dipalmitoyl phosphatidylcholine (DPPC), the main component of pulmonary surfactant, after instillation in the form of radioactively labeled liposomes (small unilamellar vesicles) in anesthetized rabbits breathing spontaneously. There were 2 protocols: normal ventilation in control animals, and ventilation increased 100% by augmentation of the dead space in experimental animals. Liposomes containing 20% phosphatidylglycerol were also tested in animals breathing normally. We examined the stereospecificity of clearance with levo 14C-DPPC and dextro 3H-DPPC isomers. We measured phospholipid content and plotted curves of radioactivity versus time (0 to 5 h) for alveolar material obtained by lavage and for the whole lung. In the control animals (n = 15), alveolar clearance of 14C-(L)-DPPC was 7.8%/h, and with increased ventilation (n = 13) it was 13.3%/h (p<0.025). With phosphatidylglycerol (n = 9) alveolar clearance during normal breathing was 13.9%/h (p<0.001). Alveolar clearance rates of 14C-(L)-DPPC and 3H-(D)-FPPC were not significantly different. Clearance from the whole lung did not differ between control and experimental animals or between isomers, and it averaged 3.1%/h.