11β-Hydroxysteroid Dehydrogenase Type 1: A New Regulator of Fetal Lung Maturation

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Abstract
Glucocorticoids (GCs) induce surfactant synthesis in the late fetal lung. Deficient GC action causes respiratory distress syndrome. 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) converts inert cortisone (11-dehydrocorticosterone in rodents) into active cortisol (corticosterone), thus amplifying intracellular GC action. We investigated 11β-HSD1 in the late fetal lung using the licorice-derived inhibitor, glycyrrhetinic acid (GE), in pregnant rats (day 13 of gestation until term). Control fetal mice and rats showed high 11β-HSD activity in the late fetal lung; levels of plasma 11-dehydrocorticosterone were also high. Reduction/loss of pulmonary 11β-HSD1 activity in GE-treated rats substantially impaired fetal lung maturation. Lungs from GE-exposed rats had lower surfactant protein-A (mRNA and protein) levels and reduced amniotic fluid lecithin/sphingomyelin ratios. There was a marked depletion of lung surfactant before and after birth, as detected by both light and electron microscopy. The data emphasize the importance of 11β-HSD1 in amplifying key GC-dependent maturational processes in the late fetal lung.

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