Melatonin inhibits naloxone-induced luteinizing hormone release in ovariectomized estrogen-primed rats.
J Neuroendocrinol
; 9(11): 849-57, 1997 Nov.
Article
em En
| MEDLINE
| ID: mdl-9419836
ABSTRACT
The present study aimed to examine the effect of melatonin on naloxone-induced luteinizing hormone (LH) secretion in ovariectomized estrogen-primed rats. A single intracerebroventricular (i.c.v.) injection of naloxone (mu opioid receptor blocker, 15 micrograms) or an intravenous (i.v.) injection of LH-releasing hormone (LHRH, 50 ng/kg) elicited a transient and significant increase in the serum LH concentration within 10 min. While an i.c.v. injection of 100 ng melatonin by itself did not change the basal LH release, it almost completely inhibited the naloxone-induced LH release. Melatonin (10 ng) also significantly reduced the effect of naloxone. However, an i.c.v. injection of 100 ng melatonin did not affect the LHRH-induced LH release. In separate experiments, the effect of melatonin on naloxone-induced pulsatile LH secretion was studied in estrogen-treated rats. A continuous i.v. infusion of naloxone (20 mg/kg/h) induced LH pulses in rats treated i.c.v. with saline. An i.c.v. administration of 100 ng melatonin, which by itself did not affect basal LH secretion, significantly reduced the frequency, but not the amplitude, of LH pulses induced by the naloxone infusion. These results show that melatonin has a suprapituitary site of action to inhibit naloxone-induced LH release, and suggest that melatonin has an effect in inhibiting the activity of the hypothalamic LHRH pulse generator, either directly or indirectly, in female rats.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Hormônio Luteinizante
/
Ovariectomia
/
Melatonina
/
Naloxona
Limite:
Animals
Idioma:
En
Revista:
J Neuroendocrinol
Assunto da revista:
ENDOCRINOLOGIA
/
NEUROLOGIA
Ano de publicação:
1997
Tipo de documento:
Article
País de afiliação:
Japão