Corticotropin-releasing factor stimulates the release of adrenocorticotropin from domestic fowl pituitary cells

Abstract

The effect of synthetic ovine CRF on ACTH secretion of dispersed, domestic fowl pituitary cells was investigated. Cells preincubated for 2 h, 16 h, or after 48-h culture were incubated briefly with CRF (up to 4 h). ACTH was bioassayed using isolated rat adrenocortical cells; ACTH-(1-24) served as the standard for expressing the data. Results with 16-h preincubated cells were as follows: CRF induced ACTH secretion in a concentration-dependent manner: ED50 and maximal stimulatory concentrations were 1.0 nM and 5.0 nM, respectively. CRF (10 nM) induced significant ACTH secretion within 10 min of incubation; maximal secretion (370% over basal value) was attained at 2 h. Dexamethasone (DEX) inhibited basal and CRF-induced ACTH secretion in a concentration-dependent manner; half-maximal inhibitory and maximal inhibitory concentrations were approximately 10 nM and 1 microM, respectively. In addition, DEX (10 microM) acutely (within 2 h) inhibited maximal CRF-induced ACTH secretion by 46%. 8-Bromo-cAMP (1 mM) also induced ACTH secretion, and DEX inhibited this secretion with a potency equivalent to that for CRF-induced ACTH secretion. In contrast to the effect of CRF, high concentrations (100 nM) of ovine LHRH, TRH, and synthetic human pancreatic GH-releasing factor (1-32) failed to induce significant ACTH secretion, thus suggesting that the effect of CRF was peptide specific. Domestic fowl pituitary cells cultured for 48 h before treatment also responded to CRF but not to any greater extent than that of 16-h preincubated cells. In contrast to 16-h preincubated cells or 48-h cultured cells, 2-h preincubated cells had high basal values of ACTH secretion that may have partially diminished or masked the actions of CRF. These data suggest that 1) CRF is a potent and specific stimulator of ACTH secretion by domestic fowl pituitary cells and 2) 16-h preincubated cells or 48-h cultured cells are amenable for other in vitro investigations on the regulation of avian ACTH secretion.