Alveolar metabolism of natural vs. synthetic surfactants in preterm newborn rabbits

We compared the recoveries of four surfactant preparations: two natural [te rm fetal rabbit surfactant (FRS) and adult rabbit surfactant (ARS)] and two commercially available preparations [apoprotein-based Survanta (S) and syn thetic Exosurf (E)] from 27-day gestation rabbit pups treated at birth and ventilated up to 120 min. At 5, 60, and 120 min, we measured the recovery o f the heavy-aggregate, metabolically active form (H) and the light-aggregat e, nonsurface active metabolic breakdown form (L) of alveolar surfactant an d determined the phospholipid content and composition of the intracellularl y stored lamellar body (LB) pool. Pups treated with FRS had <15% loss of H by 2 h. ARS-treated pups had a >50% loss of H by 1 h, and E- and S-treated pups had similar to 50% loss by 5 min, with a slower rate of continuing los s of up to 80% by 2 h. The major losses of H phospholipid were not explaine d by the L-form recovery. LB phospholipid significantly increased only in t he E-treated pups and only at 2 h. FRS provides a biologically active form (H) of surfactant that appeared to remain in the airway for a significantly longer time than the other surfactant preparations. The unique properties of FRS merit further study.