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.

Glucocorticoid Receptor Function in Rat Pituitary Intermediate Lobe is Inhibited by an Endogenous Protein

“…Interestingly, in these studies at the electron microscopic level using a protein A-gold technique, a difference in the cellular distribution of ir-GR between AL and IL was observed, in that AL GR was predominantly nuclear localized whereas IL GR was evenly distributed between the nucleus and cytoplasm. In contrast, immunofluorescent staining was predominantly nuclear localized in IL, with the authors speculating that the discrepancy in the localization of ir-GR between the two techniques was likely due to a loss of IL cytoplasmic receptor during fixation for the immunofluorescent procedure (14); similarly, the differences between this study in which GR was detected in IL (14) and other studies (11,12) that failed to detect IL may also be due to differences in methodology, and thus preservation of GR in IL. Apart from methodological limitations, another possible explanation why several immunocytochemical techniques have failed to detect substantial GR in IL maybe due to masking of the immunoreactive sites by a tissue-specific protein or a con- formation of the receptor that 'hides' the antigenic site.…”

“…A likely explanation for the low levels of IL ir-GR detected by immunocytochemistry (11,12) may be the methodology used. In a more recent study using fixation techniques more likely to preserve G R protein, ir-GR was detected in melanotroph cells of the IL, at levels only slightly less than those observed in the AL (14). Interestingly, in these studies at the electron microscopic level using a protein A-gold technique, a difference in the cellular distribution of ir-GR between AL and IL was observed, in that AL GR was predominantly nuclear localized whereas IL GR was evenly distributed between the nucleus and cytoplasm.…”

“…In addition, immunocytochemical studies were unable to detect immunoreactive G R (ir-GR) in rat IL tissue (1 1,12), though the presence of the receptor became obvious in vivo following denervation of the IL or after in vitro culture of IL cells (13). More sensitive immunocytochemical studies using a protein A-gold labelling technique have demonstrated the presence of ir-GR in the melanotroph cells of the normal rat IL (14), though the intracellular distribution differed from cells in the AL. In the IL there was an equal distribution of ir-GR staining in the nucleus and cytoplasm, while in the AL more labelling was found in the nucleus.…”

Cytological Differences in the Localization of Glucocorticoid Receptor‐Like Imnunoreactivity in the Normal and Transplanted Pituitary Pars Intermedia

“…2 stained for -MSH. Dark cells (1,2,3,4,5) can be seen. Notice that these cells are the ones that in Fig.…”

Can Endocrine Dysfunction Be Reliably Tested in Aged Horses That Are Experiencing Pain?

“…It is not known to what degree these cells might be influenced by stress and pain, as they are not usually involved in the stress response. Glucocorticoid receptors, mediating the stress response, have been found in the pars intermedia of the pituitary gland in rats, suggesting a potential responsiveness of melanotropes to stress [ 15 , 16 , 17 , 18 , 19 ]. The present study was intended to measure the ACTH and cortisol levels in endocrinologically healthy horses in different pain states.…”