Effect of antenatal thyrotropin-releasing hormone, antenatal corticosteroids, and postnatal ventilation on surfactant mobilization in premature rabbits

OBJECTIVE: The effects of antenatal hormones on postnatal surfactant mobilization were evaluated in preterm rabbits. STUDY DESIGN: Pregnant rabbits were treated with vehicle, betamethasone, or thyrotropin-releasing hormone for 2 days before cesarean section at 29 days' gestation (term 31 days). Newborns were mechanically ventilated or allowed to spontaneously breathe, and groups were compared by analysis of variance. RESULTS: Neither antenatal corticosteroids nor thyrotropin-releasing hormone increased radiolabeled precursor incorporation, alveolar wash or total lung saturated phosphatidylcholine pools, lung clearance of radiolabeled rabbit surfactant, or estimated net secretion of saturated phosphatidylcholine. However, saturated phosphatidylcholine pools in alveolar wash increased 2.7-fold during the first 24 hours in spontaneously breathing rabbits versus 2.1-fold in mechanically ventilated thyrotropin-releasing hormone-treated and control rabbits (p < 0.05). In addition, estimated net secretion of precursor-derived saturated phosphatidylcholine was 50% higher after 24 hours in spontaneously breathing rabbits. CONCLUSION: Mechanical ventilation may have hindered the mobilization of surfactant saturated phosphatidylcholine pools to the alveolar space after birth in preterm rabbits, but maternal hormonal therapies did not appear to influence this adaptive process or change surfactant metabolism.