Magnitude and duration of lung response to dexamethasone in fetal sheep

Some cases of respiratory distress syndrome (RDS) occur after optimal prenatal exposure to glucocorticoids. To explore whether some of these cases might be due to a transient effect of glucocorticoids on developing fetal lung, we studied nine chronically catheterized sheep fetuses after infusion of 500 micrograms of dexamethasone phosphate. Daily efflux of disaturated phosphatidylcholine (DSPC) from fetal tracheal fluid was measured. Three cases showed no response, two showed an early sustained rise in DSPC, and four showed an unsustained response. We interpret these data as indicating that the fetus may respond in a variety of ways to glucocorticoids, depending possibly on such factors as stage of maturity, sex, dose, and duration of exposure.