Maternal treatments with corticosteroids and/or T3 change lung volumes and rupture pressures in preterm rabbits.
Pregnant does were treated with betamethasone, T3, the combination of beta-methasone and T3 or vehicle control on days 24 and 25 of gestation. At 26 days gestational age, pressure-volume curves and lung rupture pressures and volumes were measured in the various groups of rabbits randomized to receive saline or surfactant by tracheal injection. Alveolar wash and lung tissue quantities of saturated phosphatidylcholine were comparable across the hormone-treated and control groups. Corticosteroids increased maximal lung volumes more than did T3. Corticosteroids augmented the lung volumes of surfactant-treated lungs more than did T3, and no additive effects on lungs treated with both hormones and surfactant were noted. Both corticosteroids and surfactant decreased lung rupture pressures from 51.7 +/- 4.1 to about 44 cm H2O. T3 decreased lung rupture pressure to 48.9 +/- 3.9 cm H2O and the combination of T3 and corticosteroids resulted in rupture pressures comparable to T3 alone. There were no additive effects of the combined use of T3 and corticosteroids and T3 antagonized the decreased lung rupture pressures caused by corticosteroids. While T3 did not alter the increase in lung volumes noted with corticosteroids, lung structure as assessed by lung rupture was differentially affected by the two hormones.