The role of the low-molecular weight (less than or equal to 15,000 daltons) apoproteins of pulmonary surfactant.

An artificial surfactant was prepared by combining synthetic dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol and the low-molecular weight (less than or equal to 15,000 daltons) surfactant apoproteins in the proportions 80:20:5. In the Wilhelmy balance, this surfactant formed a film with an equilibrium surface tension of 29 mN/m; surface tension was reduced to nearly zero during cyclic film compression, with effective respreadability during multiple compression-expansion cycles; similar surface properties were recorded with a pulsating bubble. When instilled into the airways of artificially ventilated immature newborn rabbits, the apoprotein-based artificial surfactant produced a five-fold increase in tidal volumes at insufflation pressure 25 cm H2O; this effect is similar to that obtained in previous experiments with natural surfactant phospholipids, administered in equal concentration (5 mg/ml). Higher concentration of the apoprotein-based surfactant could not be evaluated in vivo due to the high viscosity of the material. Systematic studies should be undertaken to find out whether an even more effective artificial surfactant could be prepared from the low-molecular weight apoproteins and other combinations of synthetic phospholipids.