CHANGES IN EXOGENOUS SURFACTANT IN VENTILATED PRETERM LAMB LUNGS

Preterm lambs were treated with either a surfactant from bovine lung ( Survanta(R)) or three synthetic surfactants (Exosurf(R)), a 69:22:9 mi xture of dipalmitoylphosphatidylcholine, phosphatidylglycerol, and pal mitic acid prepared by heat annealing (Lipid Mixture 1) or with glass beads (Lipid Mixture 2). After 5 h of ventilation, large and small agg regate surfactant fractions were isolated f rom alveolar washes by cen trifugation. SP-A was used as an indicator for the association of endo genous surfactant components with the treatment surfactants. The large aggregate fraction from Survanta-treated iambs contained more SP-A th an did the fractions from the lambs treated with the other surfactants (p < 0.05). The surfactants used to treat the sheep and the large agg regate surfactants from alveolar washes increased compliances when tes ted in surfactant-deficient, immature rabbits, relative to that in con trol animals. The large aggregate fractions in alveolar washes from la mbs treated with Survanta, Lipid Mixture 1, and Lipid Mixture 2 improv ed compliances in the preterm rabbits to a greater extent than did the surfactants used to treat the lambs. The small aggregate fractions we re inactive as surfactants. The function of exogenous surfactant can b e improved after exposure to the preterm lung. The improvement may res ult from the association of exogenous surfactant with components of en dogenous surfactant.