Effects of maternal dexamethasone therapy on fetal lung development in the rhesus monkey.

A large body of evidence demonstrates that antenatal glucocorticoids can accelerate fetal lung maturation. The purpose of this study was to delineate the optimal dose of dexamethasone and to determine whether a single- or multiple-injection regimen of the same total dexamethasone dosage was more effective in accelerating pulmonary development. Pregnant rhesus monkeys were injected with varying doses of dexamethasone or vehicle as either a single-bolus injection or as four separate injections, each spaced 12 hours apart. All maternal treatments were begun exactly 72 hours prior to delivery, and all fetuses were delivered by cesarean section at 135 +/- 1 days gestation. When a single injection of dexamethasone was used, fetal liver weight increased in a dose-related fashion. Fetal and maternal cortisol and fetal blood glucose concentrations were also influenced by increasing dexamethasone dosages. Fetal pulmonary phospholipids, however, were unchanged at all steroid doses examined. Multiple injections of dexamethasone generally produced more pronounced effects, even though the total dexamethasone dose remained the same. Thus, liver weight and fetal and maternal cortisol, glucose, and insulin levels were significantly influenced by the multiple administration of dexamethasone. In addition, total lung phosphatidylcholine, surfactant phosphatidylcholine, the surfactant-phosphatidylcholine-to-total-phosphatidylcholine ratio, and the surfactant-disaturated-phosphatidylcholine-to-total-lung-disaturated- phosphatidylcholine ratio were elevated after the multiple-injection regimen. A total dose of 0.5 mg dexamethasone/kg maternal body weight given in four separate injections appeared to produce the most beneficial results. These data suggest that low-dose, antenatal glucocorticoid treatment can effectively accelerate the biochemical maturation of the fetal lung.