Foetal lung maturation in 11β-hydroxysteroid dehydrogenase type 1 knockout mice

Glucocorticoids (GCs) induce surfactant synthesis in the late foetal lung. Deficient GC action causes respiratory distress syndrome (RDS). 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) converts inert cortisone (11-dehydrocorticosterone in rodents) into active cortisol (corticosterone), thus amplifying intracellular GC action. Reduction or loss of pulmonary 11β-HSD1 activity in glycyrrhetinic acid-treated rats substantially impaired foetal lung maturation (Hundertmark et al., Horm Metab Res, this issue). To test these data, we investigated 11β-HSD1 activity and lung maturity in the late foetal lung using 11β-HSD1 knock-out mice. Control foetal mice showed high 11β-HSD activity in the late foetal lung and levels of plasma 11-dehydrocorticosterone were high. Lungs from 11 β-HSD1 -/- mice had lower surfactant protein-A (mRNA and protein) levels and significant depletion of lung surfactant according to both light and electron microscopy, and also had reduced amniotic fluid lecithin/sphingomyelin ratios. These results support the previous experiments with glycyrrhetinic acid and emphasize the importance of 11β-HSD1 in foetal lung maturation.