Adrenergic mediation of the naloxone-induced GnRH release from hypothalami of ovariectomized, steroid-treated immature rats.
The present study examines the effect of naloxone on GnRH release in vitro under different steroid milieus. Naloxone (6.1 mumol/kg) administered 30 min before decapitation was highly effective in evoking GnRH release from superfused hypothalamic tissues derived from ovariectomized, estradiol- and progesterone-treated immature rats, while ineffective in altering GnRH release from intact, ovariectomized and vehicle- or estradiol-treated rats. To further explore the possible involvement of catecholamines in the naloxone-stimulated GnRH release, diethyldithiocarbamic acid (2.9 mmol/kg), an inhibitor of noradrenalin synthesis, was administered ip 30 min before naloxone injection into ovariectomized, estradiol- and progesterone-treated rats. Diethyldithiocarbamic acid markedly reduced the naloxone-evoked GnRH release, although it was ineffective in modifying the spontaneous release of GnRH. A blockade of alpha-adrenergic receptor with phenoxybenzamine significantly suppressed the naloxone-stimulated GnRH release, whereas treatment with propranolol, a beta-adrenergic receptor blocker, failed to alter GnRH release. The present data suggest that the endogenous opioid peptide may participate in the regulation of GnRH release under a particular steroid milieu, and the inhibitory action of endogenous opioid peptide seems to require the mediation of adrenergic neurotransmission, presumably through alpha-adrenergic receptor.
Kim
K
K
Department of Molecular Biology, College of Natural Sciences, Seoul National University, Korea.
Lee
B J
BJ
Lee
C C
CC
Cho
W K
WK
Ramirez
V D
VD
D000320:Adrenergic Fibers / Q000502:physiology*; D000818:Animals; D004050:Ditiocarb / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000097:blood*; D007031:Hypothalamus / Q000378:metabolism* / Q000648:ultrastructure; D007267:Injections; D009270:Naloxone / Q000032:analysis / Q000494:pharmacology*; D010052:Ovariectomy; D010643:Phenoxybenzamine / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000187:drug effects / Q000502:physiology
D004967:Estrogens; D011941:Receptors, Adrenergic; D010643:Phenoxybenzamine; D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D011374:Progesterone; D004050:Ditiocarb; D011433:Propranolol