Postnatal stimulation of rat surfactant protein A synthesis by dexamethasone

The effects of postnatal dexamethasone treatment in vivo on the synthesis of surfactant protein A (SP-A) were examined at the protein and RNA levels. Rats ranging from 1 day old to adult were injected with 200 μg of dexamethasone/kg body wt or with vehicle alone and were killed 24 h after injection. One portion of the lung was metabolically labeled with [³⁵S]methionine, the proteins immunoprecipitated using an antiserum to SP-A, and analyzed electrophoretically. Both newly synthesized intracellular and secreted SP-A levels were increased by dexamethasone, reaching averages of 2.3 and 4.5 times control values, respectively. Another portion of the lung tissue was used for RNA analysis. SP-A mRNA levels were also elevated an average of 1.4 times control values by hormone treatment. Dose-response experiments using 16-day-old pups showed that both total SP-A, as measured by enzyme-linked immunosorbent assay, and total SP-A mRNA levels were elevated with dexamethasone treatment, reaching maximal stimulation at 2 mg. We conclude that postnatal dexamethasone treatment in vivo results in increased levels of both newly synthesized SP-A and SP-A mRNA, suggesting that pretranslational events may in part contribute to this process.