EXOGENOUS SURFACTANT PHOSPHOLIPIDS STIMULATE ENDOGENOUS SATURATED PHOSPHATIDYCHOLINE SYNTHESIS

Surfactant treatments result in increased synthesis and secretion of endogenous saturated phosphatidylcholine (Sat.PC) in adult rabbits. To elucidate the contribution to these effects of surfactant associated proteins and surfactant phospholipids in surfactant preparations we studied a mixture (MPCG) of dipalmitoylphosphatidyl choline and phosphatidyl glycerol (9:1), a lipid extract of natural surfactant (LENS), a phospholipid fraction of natural surfactant (PLNS) and a reconstituted natural surfactant (RNS). These surfactants were injected into the left mainstem bronchus after induction of oxygen resorption atelectasis of the left lower lobe of adult rabbits. Surfactant metabolism was studied by injecting 32P-orthophosphate 30 min and 3H palmitic acid i.v. 6 h after the injections, followed by sacrifice at 10 h after the injections with subsequent alveolar wash and processing of the right lung and left lower lobe separately. For the 32P incorporation into Sat.PC the ratios of the left lower lobe to right lung were: 0.87±0.15 (MPCG), 0.74±0.14 (LENS), 0.90±0.11 (PLNS), 0.86±0.14 (RNS) significantly higher than unmanipulated controls: 0.47±0.05 (mean±SD) (P<0.05). LENS tended to decrease the secretion of Sat.PC. These results suggest that Sat.PC synthesis is stimulated aspecificially by phospholipids from exogenous surfactant.