Mineralocorticoid receptor expression in late-gestation ovine fetal lung

Changes in adrenal corticosteroid secretion result in changes in lung liquid production in the late-gestation fetus. To test for the presence of mineralocorticoid receptor (MR) in fetal pulmonary epithelium, lungs from fetal sheep of 120 to 130 days' gestation (term about 148 days) were collected and frozen for identification of mRNA for MR in homogenates by reverse transcriptase polymerase chain reaction (RT-PCR) or for determination of 3H-cortisol binding at MR. Other samples of fetal lungs were fixed for localization of MR and Na+, K+ adenosine triphosphatase (ATPase) alpha by immunohistochemistry. MR mRNA was identified in lung tissue from fetuses and newborn lambs, but not from pregnant ewes; MR-regulated genes, including SGK1 and ENaCalpha were also expressed in fetal and newborn lungs. Immunoreactive MR was found in pulmonary epithelial cells and to be colocalized with Na+, K+ ATPase alpha in many sites. These results indicate that the molecular apparatus for mineralocorticoid-stimulated lung liquid reabsorption is present in epithelium by 120 days' gestation.