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Glucocorticoid regulation of surfactant‐associated proteins in rabbit fetal lung in vivo

The effects of a maternally administered synthetic glucocorticoid, betamethasone, on the levels of mRNA for the surfactant proteins SP‐A, SP‐B, and SP‐C and on the levels of SP‐A protein were investigated in day 27 gestational age rabbit fetal lung tissue. Betamethasone administration to the pregnant rabbit caused approximately a twofold increase in the fetal lung level of SP‐A protein and a threefold increase in fetal lung SP‐A mRNA levels when compared to levels in fetuses obtained from saline‐treated or uninjected animals. SP‐B mRNA was increased fourfold in fetal lung tissue obtained from glucocorticoid‐treated pregnant does when compared to levels in fetuses of uninjected pregnant does. However, SP‐B mRNA levels in fetal lung tissue from saline‐injected controls were also significantly elevated, ∼twofold, when compared to fetal lung SP‐B mRNA levels in the uninjected control condition. SP‐C mRNA levels in lung tissue of fetuses from both saline‐injected and betamethasone‐injected pregnant does were increased similarly, ∼twofold, over SP‐C mRNA levels in fetal lung tissue obtained from uninjected control does. These data are suggestive that betamethasone treatment increases fetal lung SP‐A and SP‐B mRNA levels and that maternal stress alone can increase the expression of SP‐B and SP‐C mRNA in rabbit fetal lung tissue. Using in situ hybridization, SP‐A mRNA was shown to be present primarily in alveolar type II cells in fetuses of control and saline‐injected does. However, SP‐A mRNA was easily detected in both alveolar type II cells and bronchiolar epithelial cells of rabbit fetal lung tissue following maternal betamethasone treatment. In contrast, SP‐B and SP‐C mRNA were present only in alveolar type II cells of lung tissue obtained from fetuses of control, saline, or betamethasone‐treated does. Thus maternal administration of glucocorticoids increased SP‐A protein as well as SP‐A and SP‐B mRNA levels in rabbit fetal lung tissue. SP‐A mRNA was localized to both alveolar type II cells and in smaller amounts in bronchiolar epithelial cells of rabbit fetal lung tissue. However, SP‐B and SP‐C mRNA were detected only in alveolar type II cells. © 1993 Wiley‐Liss, Inc.