Changes in adrenal corticosteroid secretion result in changes in lung liquid production in the late-gestation fetus. To testfor the presence of mineralocorticoid receptor (MR) in fital pulmonary epithelium, lungsfrom fetal sheep of 120 to 130 days'gestation (term about 148 days) were collected andfrozenfor identfication of mRNA for MR in homogenates by reverse transcriptase polymerase chain reaction (RT-PCR) orfor determination of 3H-cortisol binding at MR. Other samples offetal lungs werefixedfor localization of MR and Na,+, K+ adenosine triphosphatase (ATPase) α by immunohistochemistry. MR mRNA was identified in lung tissuefromfetuses and newborn lambs, but notfrom pregnant ewes; MR-regulated genes, including SGK1 and ENaCα were also expressed infital and newborn lungs. Immunoreactive MR was found in pulmonary epithelial cells and to be colocalized with Na+, K+ ATPase α in many sites. These results indicate that the molecular apparatus for mineralocorticoid-stimulated lung liquid reabsorption is present in epithelium by 120 day's gestation.
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