Immunocytochemical identification of the proopiocortin-producing cells in the chum salmon pituitary with antisera to endorphin and NH2-terminal peptide of salmon proopiocortin.

The proopiocortin-containing cells were identified immunocytochemically in the chum salmon pituitary using specific antibodies raised against NH2-terminal peptide (sNPP) and COOH-terminal peptide, endorphin (sEP), of salmon proopiocortin. Immunoreactivity for both sNPP and sEP was observed in the same cells, melanotrops, in the pars intermedia. In the pars distalis, on the other hand, corticotrops were stained only with antibody to sNPP but not with that to sEP. The present results indicate that proopiocortin or a precursor molecule for NH2-terminal peptide and endorphin is biosynthesized in both melanotrops of the pars intermedia and corticotrops of the pars distalis. However, the absence of immunoreactivity of corticotrops with sEP antibody suggests that the processing of the precursor molecule in the pars distalis differs significantly from that in the pars intermedia in the chum salmon pituitary as the processings established in the two lobes in the mammalian pituitaries.