Surfactant treatment and ventilation effects on surfactant SP-A, SP-B, and SP-C mRNA levels in preterm lamb lungs.

The effects of exogenous surfactant treatment combined with postnatal ventilation on surfactant protein (SP)-A, SP-B, and SP-C steady-state mRNA levels were evaluated in preterm sheep at 120, 132, and 139 days gestation. Three groups were studied at each gestation period: animals ventilated and treated with 100 mg/kg natural sheep surfactant, animals ventilated and not treated with surfactant, and a comparison group of lambs that were neither ventilated nor treated with surfactant. In unventilated lambs, SP-A and SP-C mRNA levels measured by densitometry from Northern blots increased between 120 and 132 days gestation (P < 0.05). At 120 days gestation, no differences in SP-A, SP-B, or SP-C mRNA levels were noted among the three groups. At 132 days gestation, SP-A mRNA levels increased in both ventilated groups (P < 0.01), but no additional surfactant effect on SP-A mRNA expression was detected. There were no changes in SP-B or SP-C mRNA levels among the groups at 132 days gestation. At 139 days gestation, mRNA levels for both SP-A and SP-B increased after ventilation, compared with the unventilated groups (P < 0.05). Furthermore, an additional effect of surfactant treatment to increase SP-A mRNA levels relative to animals undergoing ventilation alone was noted (P < 0.05). We conclude that postnatal changes in mRNA levels for the surfactant proteins are gestationally regulated and protein specific.