Developmental and glucocorticoid regulation of surfactant protein mRNAs inpreterm lambs

Glucocorticoid treatment increases content of surfactant protein (SP) A and SP-B in lung tissue and lavage fluid of preterm lambs. To investigate this process, we determined the ontogeny and glucocorticoid induction of SP mRN As. In separate treatment protocols, each with its own controls, sheep were injected with betamethasone 15 h, 48 h or weekly for 1-4 doses before pret erm delivery. Using ovine SP cDNAs, we found an increase equal to or more t han threefold in basal levels of all three SP mRNAs between 125 days and te rm. After betamethasone treatment, SP-B and SP-C mRNA levels increased by 1 5 h and all SP mRNAs were elevated after 24 h (greater than or equal to 2-f old); mRNA levels in fetuses delivered 1-3 wk after betamethasone were not different from control. me conclude that in vivo betamethasone rapidly indu ces a coordinated increase in SP mRNAs, which is fully reversible within 7 days despite repetitive doses of betamethasone. Similar increases in mRNA a nd protein contents for SP-A and SP-B suggest that glucocorticoid regulatio n of these SPs in vivo is primarily pretranslational.