Ovine surfactant protein cDNAs: use in studies on fetal lung growth and maturation after prolonged hypoxemia

cDNAs for ovine surfactant-associated protein (SP) A, SP-B, and SP-C have b een cloned and shown to possess strong similarity to cDNAs for surfactant a poproteins in other species. These reagents were employed to examine the ef fect of fetal hypoxia on the induction of surfactant apoprotein expression in the fetal lamb. Postnatal lung function is dependent on adequate growth and maturation during fetal development. Insulin-like growth factor (IGF) I and ICF-II, which are present in all fetal tissues studied, possess potent mitogenic and proliferative actions, and their effects can be modulated by IGF-specific binding proteins (IGFBPs). Hypoxia can lead to increases in c irculating cortisol and catecholamines that can influence lung maturation. Therefore, the effects of mild hypoxia in chronically catheterized fetal la mbs at gestational days 126-130 and 134-236 (term 145 days) on the expressi on of pulmonary surfactant apoproteins and IGFBPs were examined. Mild hypox ia for 48 h resulted in an increase in plasma cortisol that was more pronou nced at later gestation, and in these animals, there was a twofold increase in SP-A mRNA. SP-B mRNA levels also increased twofold, but this was not si gnificant. SP-C mRNA was not altered. No significant changes in apoprotein mRNA were observed with the younger fetuses. However, these younger animals selectively exhibited reduced IGFBP-5 mRNA levels. IGF-I mRNA was also red uced at 126-130 days, although this conclusion is tentative due to low abun dance. IGF-II levels were not affected at either gestational age. We conclu de that these data suggest that mild prolonged fetal hypoxia produces alter ations that could affect fetal cellular differentiation early in gestation and can induce changes consistent with lung maturation closer to term.