RADIOIMMUNOCYTOCHEMICAL LOCALIZATION OF CORTICOTROPIN-RELEASING FACTOR AND ADRENOCORTICOTROPIN IN THE HYPOTHALAMO HYPOPHYSEAL SYSTEM OF THE RAT - EFFECTS OF ADRENALECTOMY

Various radioimmunocytochemical approaches have been utilized to localize primary antibody-antigen complexes. Here we examined the binding properties of three different radioiodinated compounds for their ability to label the antibody-antigen complex, including: donkey anti-rabbit immunoglobulin, donkey anti-rabbit F(ab')2-IgG, and a biotinylated goat anti-rabbit secondary antibody followed by [I-125]-avidin. These probes were used to localize rabbit primary antisera against corticotropin-releasing factor (CRF) and adrenocorticotropin-releasing hormone (ACTH) in the hypothalamo-hypophyseal system of the rat. The pattern of labeling with each radiolabeled probe was consistent with the light microscopic immunocytochemical staining for CRF and ACTH. The utility of the radioimmunocytochemical method for quantitative analyses was further tested by studying the effects of adrenalectomy (ADX) on the levels of immunoreactive CRF and ACTH in the hypothalamo-hypophyseal system. Computer-assisted microdensitometric analysis of immunoreactive CRF levels in the median eminence indicated that there was a 33% decrease 24 h after ADX. Immunoreactive ACTH levels in the anterior pituitary were significantly decreased from 1 day (38%) to 1 week (36%) after ADX and were increased at 2 weeks (89%). The changes in CRF and ACTH levels, as measured radioimmunocytochemically after ADX, were consistent with previous biochemical studies. These results indicate that computer-assisted radioimmunocytochemical analysis can be used quantitatively to measure immunoreactivity in tissue sections. The high resolution and high sensitivity provided by this method should make it widely applicable.