MODULATION OF ARGININE-VASOPRESSIN SECRETION FROM CULTURED OVINE HYPOTHALAMIC CELLS BY GLUCOCORTICOIDS AND OPIOID-PEPTIDES

In sheep, arginine vasopressin (AVP) appears to be a more potent ACTH- releasing factor than ovine corticotrophin-releasing hormone. In order to investigate the neuroendocrine regulation of AVP secretion we have developed a novel system for maintaining fetal ovine hypothalamic neu rones in serum-free culture. Hypothalamic neurones derived from fetal sheep at day 70 gestation (term = 145 days) secreted AVP under basal c onditions and in response to repeated potassium-induced depolarization s, for up to 35 days in vitro. AVP secretion was time- and calcium-dep endent. AVP secreted from ovine hypothalamic cells co-eluted with synt hetic AVP on a Sephadex chromatography column and diluted in parallel with AVP standard in the radioimmunoassay. The addition of coritisol ( 150 nM) to medium bathing ovine hypothalamic cells significantly inhib ited basal, and potassium-induced AVP secretion without altering the A VP content of the cell cultures. Furthermore, the opioid peptide [D-Pr o(10)]Dynorphin(1-11) which acts via the kappa opioid receptor, signif icantly inhibited basal and potassium-stimulated AVP secretion, an eff ect which was abolished when cells were cultured in the presence of co rtisol. These data show that hypothalamic AVP is a site for negative f eedback regulation within the ovine hypothalamic-pituitary-adrenal axi s. Furthermore, these data suggest that the kappa opioid system inhibi ts AVP secretion from ovine hypothalamic neurones, a response which is modulated by glucocorticoids.