Abstract 1302 Neonatal Disease Oriented Research: Ductus and Surfactant Platform, Sunday, 5/2

Background: SP-C mRNA and the pro SP-C protein are present in the distal branching airway epithelium of human lung from early gestation, and SP-C mRNA levels are similar to term (31d) levels by about 24d gestation in the rabbit (Ohashi et al. A.J. Physiol., 267:L46, 1994). Pro-SP-C is processed in the mature lung in the trans-golgi and the mature 3700 kDa protein is found in lamellar bodies. The amount of mature SP-C present in late fetal lung and alveoli is not known. Question: We asked how much mature SP-C was present in alveolar washes of preterm rabbit fetuses and if the amount of SP-C increased after ventilation. Methods We delivered time mated preterm rabbits at 27, 28, and 29d gestation and ventilated half of the rabbits in each litter for 15 min using tidal volumes of about 8 ml/kg as previously described. The other rabbits were killed without ventilation. Large aggregate surfactant fractions were recovered by centrifugation from pooled alveolar washes from 1-4 animals. Membrane fractions also were isolated from lung homogenates by differential centrifugation. The amount of Saturated Phosphatidylcholine (Sat PC) was estimated using Sat PC recovered from 0s04 treated lipid extracts and expressed as µmol/kg. SP-C was measured from Western blots using a newly available antibody raised to recombinant human SP-C and also expressed as µmol/kg. Values for 6-10 pooled alveolar washes at each gestation ± ventilation were compared to measurements for 7 - one day old spontaneously breathing newborn rabbits. Results: Sat PC increased from 0.05±0.02 in unventilated 27d rabbits to 13.6±1.0 µmol/kg in newborns, a 286 fold increase. Ventilation increased alveolar Sat PC at 29d gestation by 3 fold but not at earlier gestations. SP-C was not detectable in 20% of alveolar wash pools at both 27 and 28d gestation. Where measurable the values were very low (1/400 of the term values of 0.011±0.003 µmol/kg). SP-C increased 3.5 fold with ventilation at 29d gestation, (p<0.00) but not at earlier gestations. At 29d and term, there were about 1000 Sat PC molecules per SP-C molecule in the alveolar washes. The membrane fractions from lung homogenates contained much more pro-SP-C than the trace amount of mature SP-C at 27 and 28d gestation. By 29d gestation, pro-SP-C was less evident and mature SP-C predominated in the lung membrane fraction. Conclusions: Despite high levels of SP-C mRNA from 24d gestation, preterm rabbits have very low levels of mature SP-C until 29d gestation and short term ventilation does not stimulate release of SP-C at earlier gestations. Surfactant lipid deficient preterm airways are also severely SP-C deficient, despite high tissue levels of SP-C mRNA and pro-SP-C protein.

Funded by HD-12714