Glucocorticoid receptor immunoreactivity in the rat intermediate lobe

Abstract Cells containing Type II glucocorticoid receptor (GR) immunoreactivity were identified in the rat pituitary gland by immunocytochemistry using a specific monoclonal antibody. At light microscopic level, GR immunoreactive cells were located in the intermediate lobe in addition to the well known GR-containing cell population in the anterior lobe. In both groups of cells GR appeared predominantly in the cell nuclei. Adrenalectomy resulted in a decrease in staining intensity of the anterior lobe and changed the pattern of fluorescence in a minority of cells where cytoplasmic staining became predominant. These changes appeared less marked in the intermediate lobe. Dexamethasone administration reversed the adrenalectomy-induced alterations of GR staining in both lobes. At the electron microscopic level, GR immunoreactive sites were revealed by the protein A-gold technique. In contrast to the distribution of fluorescence, GR was localized in cell nuclei as well as in the cytoplasm in both lobes. Quantitative estimates indicate that about 40% more immunoreactive sites are present in the anterior lobe than in the intermediate lobe. The presence of GR in the intermediate lobe suggests that this pituitary region, like the anterior lobe, is influenced by glucocorticoid hormones.