Methods in laboratory investigation. Autoradiographic demonstration of the specific binding and nuclear localization of 3H-dexamethasone in adult mouse lung.

This report describes the first autoradiographic demonstration of specific nuclear localization of 3H-dexamethasone in different cell types of the lung. Adult mouse lung tissue was incubated in vitro for 90 minutes with 17 nM 3H-dexamethasone in the presence or absence of various nonradioactive steroids. After extensive washing to remove any nonspecifically bound ligand, the specimens were processed for autoradiography using the thaw-mount method. In the absence of competing steroids, silver grains were localized in the nuclei of alveolar type II cells, bronchiolar and arteriolar smooth muscle cells, fibroblasts, and endothelial cells of the pulmonary vasculature. No significant nuclear concentration of label was observed in the bronchiolar epithelium, however. The specificity of 3H-dexamethasone labeling was demonstrated by incubating 17 nM 3H-dexamethasone with a 600-fold excess of either unlabeled dexamethasone, estrogen, dihydrotestosterone, or progesterone. These autoradiographic binding and steroid competition studies were confirmed by quantifying with liquid scintillation counting the specific 3H-dexamethasone binding in nuclear and cytosolic fractions prepared from lung tissues that had undergone identical incubation and washing procedures as those for autoradiography. These results demonstrate that many cell types in adult lung are targets for glucocorticoids and may respond to physiologic concentrations of this hormone.