Differential immunostaining of adenohypophysial cells with antisera to ACTH and beta-endorphin

Three antisera, raised in rabbits against human beta-endorphin were denoted Y-10, Y-18 and R-230 and tested for their ability to immunohistochemically stain cells in teh adenohypophysis of the rat and dog. By radioimmunoassay Y-10 was highly specific towards beta-endorphin with minimal cross-reactivity against beta-LPH while Y-18 and R-230 cross-reacted with both beta-endorphin and beta-LPH on an equimolar basis. In the rat pituitary, Y-18 and R-230 antisera stained cells identified as corticotrophs. With the dog, however, beta-endorphin-staining cells in the anterior pituitary and infundibulum did not necessarily co-stain for ACTH-like material. When the beta-endorphin antiserum, Y-10, was applied to rat anterior pituitary tissues, the subsequent positive immunocytochemical staining was associated not only with corticotrophs but also with somatotrophs. The findings are consistent with (a) a differential processing of the 31K pro-opiocortin and (b) the presence in rat somatotrophs of determinants that cross-react immunologically with some beta-endorphin antisera.