Suppression of endogenous hormones alters fetal lung mechanics and gas trapping
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Static pulmonary mechanics were studied prior to air breathing in 64 rabbit fetuses at 30 days gestational age in four groups: (1) control (n=20), (2) thyroid suppression by propylthiouracil (PTU) (n=20), (3) inhibition of corticosteroids by metyrapone (MP) (n=13), and (4) combined suppression of both hormones by PTU + MP (n=11). Both agents were given to the does and cross readily through the placental barrier. Single and combined treatments induced a significant increase (p<0.05) in appropriate gland wt/body wt ratio, indicating substantial hormonal suppression. MP increased lung volume slightly at high pressures, but PTU and PTU + MP decreased volume significantly (p<0.05) at low pressures. Volume (% TLC) at a pressure of 10 cm H2O (V10) was significantly reduced by PTU + MP (p<0.01), suggesting synergistic effects. Trapped gas volume (VTG) correlated well (r=0.87) with V10 by curvilinear regression, but did not correlate significantly with lung wet/dry weight ratio. The data suggest that fetuses deficient in both thyroid and glucocorticoid hormones might be particularly vulnerable to respiratory distress syndrome. VTG is related more to lung mechanical properties than to lung fluid content.
Key wordsRabbit fetuses Lung pressure-volume curves Pulmonary fluid content
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