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- Title
Suppressive Action of Orexin A on Pulsatile Luteinizing Hormone Secretion Is Potentiated by a Low Dose of Estrogen in Ovariectomized Rats.
- Authors
Furuta, Miyako; Funabashi, Toshiya; Kimura, Fukuko
- Abstract
Orexins are hypothalamic neuropeptides which stimulate luteinizing hormone (LH) secretion in estrogen- and progesterone-treated ovariectomized (OVX) rats and suppress it in OVX rats not treated with estrogen, suggesting a modulation by estrogen of the response to orexins. We examined the effects of orexin A on pulsatile LH secretion in OVX rats treated with a very small dose of estrogen so as to maintain the pulsatile secretion of LH. The estrogen treatment was done 24 h before the blood sampling by subcutaneously implanting a silicone tube (id = 1.5 mm, od = 2.5 mm, length = 25 mm) containing 17β-estradiol (E[sub 2] ) dissolved in sesame oil at 20 μg/ml. In OVX rats treated with sesame oil as a control, the intracerebroventricular (icv) injection of orexin A (0.3 nmol, dissolved in 3 μl artificial cerebrospinal fluid) had no significant effect on the parameters of pulsatile LH secretion, i.e., pulse frequency and pulse amplitude, although it caused a small but statistically significant decrease in overall mean LH concentrations within 1 h. In OVX rats treated with E[sub 2] , the icv injection of orexin A significantly suppressed the pulsatile LH secretion; the frequency decreased for more than 2 h, inducing a rapid decline in overall mean LH concentrations. In view of the finding that a much higher dose of orexin A suppresses pulsatile LH secretion in OVX rats not treated with E[sub 2] , we suggest that the suppressive action of orexin A on pulsatile LH secretion is potentiated by estrogen.Copyright © 2002 S. Karger AG, Basel
- Subjects
GONADOTROPIN; LUTEINIZING hormone; ESTROGEN; RATS; PROGESTERONE
- Publication
Neuroendocrinology, 2002, Vol 75, Issue 3, p151
- ISSN
0028-3835
- Publication type
Article
- DOI
10.1159/000048232