Production of immunoreactive adrenocorticotropin and beta-endorphin by hypothalamic and extrahypothalamic brain cells

Despite many in vivo studies, little is known about brain regulation of POMC synthesis or regulation of secretion of POMC-related peptides. To test the hypothesis that dissociated brain cells in culture can produce and release POMC-related peptides, immunoreactive (IR)-adrenocorticotropin (ACTH) and beta-endorphin were measured in cells and media of dissociated cell cultures incubated up to 38 days. Fetal rat hypothalamic and extrahypothalamic forebrain cells were maintained in serum free medium. IR-ACTH and beta-endorphin were measured by radioimmunoassay in concentrated cells and media after various incubation times using two ACTH (mid-portion = R4; carboxy-portion directed = KEND) antisera and a beta-endorphin antiserum. IR-ACTH and IR-beta-endorphin in hypothalamic and extrahypothalamic cells and in media (cumulative) were greater than quantities in cells before culture. Peak hypothalamic cellular content of IR-ACTH (5.3 fmol/10(6) cells-R4; 4.7 fmol/10(6) cells-KEND) and content of IR-beta-endorphin (32.0 fmol/10(6) cells) occurred on days 16, 9 and 23, respectively. Peak extrahypothalamic content of IR-ACTH (2.9 fmol/10(6) cells-R4; 1.0 fmol/10(6) cells-KEND) and content of IR-beta-endorphin (10.8 fmol/10(6) cells) was also seen on different days, was lower than hypothalamic content and was not always concurrent with peak hypothalamic content. Gel filtration chromatography revealed that the predominant forms of IR-ACTH and IR-beta-endorphin in hypothalamic cell extracts co-eluted with synthetic ACTH1-39 and beta-endorphin. Changes in molar ratios of IR-ACTH and IR-beta-endorphin also suggested a differential regulation of different POMC derivatives.

(1) IR-ACTH and IR-beta-endorphin are produced by hypothalamic and extrahypothalamic forebrain cells in culture: and (2) dissociated brain cell cultures can be used as a potential model for studying regulation of POMC-related peptides in brain.