Opioids regulation of human chorionic gonadotropin release from trophoblast tissue is mediated by gonadotropin releasing hormone

In the hypothalamic-pituitary axis opioid regulation of luteinizing hormone secretion occurs via gonadotropin hormone-releasing hormone (GnRH). Trophoblast gonadotropic hormone human chorionic gonadotropin (hCG) and locally produced GnRH in human placenta are similar in structure and biological functions to luteinizing hormone and GnRH from hypothalamic- pituitary axis. In addition, placental kappa receptors mediate opioid regulation of hCG release from trophoblast tissue in vitro and placental GnRH plays a role in regulation of hCG secretion as well. The purpose of this investigation was to determine whether opioids regulation of hCG release from trophoblast tissue is mediated by GnRH. Opioid agonists at their concentrations causing maximal release of hCG from the tissue also stimulated GnRH secretion. Antagonists inhibited the release of hCG and GnRH and totally reversed the effect of agonists, i.e., their effect is kappa receptor mediated. GnRH antagonist inhibited both opioids and GnRH stimulation of hCG release from trophoblast tissue. Neither GnRH nor its antagonist bind to placental kappa receptors. These data suggest that in vitro opioids regulation of hCG release from term trophoblast tissue is mediated by GnRH.