Hypothalamic Ghrelin suppresses pulsatile secretion of luteinizing hormone via beta-endorphin in ovariectomized rats.
OBJECTIVE
Ghrelin, an endogenous growth hormone secretagogue, is a known accelerator of feeding behavior and suppresses pulsatile secretion of luteinizing hormone (LH) in ovariectomized rats. However, the mechanisms underlying this action remain unclear. We examined the effects of naloxone (NAL), a specific opioid antagonist, on the suppression of pulsatile LH secretion by ghrelin to determine whether beta-endorphin (beta-END) is involved in this suppressive effect.


METHODS
Ghrelin was administered intracerebroventricularly, and NAL was injected intravenously in ovariectomized rats; then, serum LH concentrations were measured by radioimmunoassay in blood samples drawn every 6 min for 2 h to analyze pulsatile secretion.


RESULTS
Administration of ghrelin significantly reduced mean LH concentration and pulse frequency. Coadministration of NAL with ghrelin significantly restored mean LH concentration and pulse frequency.


CONCLUSIONS
Suppressive effect of intracerebroventricular injection of ghrelin on pulsatile LH secretion was mediated by beta-END, suggesting that hypothalamic ghrelin suppressed pulsatile gonadotropin-releasing hormone secretion via beta-END in female rats.
Ogata
Rie
R
Department of Obstetrics and Gynecology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan. r-ogata @ pop21.odn.ne.jp
Matsuzaki
Toshiya
T
Iwasa
Takeshi
T
Kiyokawa
Machiko
M
Tanaka
Naoko
N
Kuwahara
Akira
A
Yasui
Toshiyuki
T
Irahara
Minoru
M
D000818:Animals; D001835:Body Weight; D002404:Catheterization; D005260:Female; D054439:Ghrelin / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010052:Ovariectomy; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D001615:beta-Endorphin / Q000378:metabolism*
D054439:Ghrelin; D009292:Narcotic Antagonists; D009270:Naloxone; D001615:beta-Endorphin; D007986:Luteinizing Hormone