VENTILATION ENHANCES PULMONARY ALVEOLAR CLEARANCE OF RADIOACTIVE DIPALMITOYL PHOSPHATIDYLCHOLINE IN LIPOSOMES

Abstract

Clearance from lungs of dipalmitoylphosphatidylcholine (DPPC), the main component of pulmonary surfactant, was examined 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 tested in animals breathing normally. Stereospecificity of clearance was examined with levo 14C-DPPC and dextro 3H-DPPC isomers. Phospholipid content was measured and curves of radioactivity vs. time (0-5 h) were plotted for alveolar material obtained by lavage and for the whole lung. In the control animals (n [number] = 15), alveolar clearance of 14C-L-DPPC was 7.8% per h, and with increased ventilation (n = 13) it was 13.3% per h (P < 0.025). With phosphatidylglycerol (n = 9) alveolar clearance during normal breathing was 13.9% per h (P < 0.001). Alveolar clearance rates of 14C-L-DPPC and 3H-D-DPPC 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% per h.