Role of hypothalamus nociceptin/orphanin FQ in pre-ovulatory luteinizing hormone surge of estrogen and progesterone-primed, ovariectomized rats.
OBJECTIVE
To investigate the role of hypothalamus nociceptin/orphanin FQ (OFQ) and its endogenous receptor, the opioid receptor-like1 receptor (ORL1 receptor) in the estrus cycle of female rats.


METHODS
Radioimmunoassay was used to detect the effect of the intracerebroventricular (icv) administration of OFQ and/or the ORL1 receptor antagonist [Nphe1]Nociceptin(1-13)NH2, that is, NC13 on luteinizing hormone (LH) levels of estrogen- and progesterone (EBP)-primed, ovariectomized (OVX) rats (EBP-primed OVX rats). RT-PCR, Western blotting, and immunohistochemistry techniques were adopted to observe the changes of OFQ and the ORL1 receptor in the pre-optic area (POA) and the medial basal hypothalamus (MBH) of the estrus cycle of female rat.


RESULTS
Pre-ovulatory LH surges in EBP-primed, OVX rats were significantly reduced by icv administration of 20 and 200 nmol OFQ (P<0.05), and the effect of 20 nmol OFQ could be abolished by pretreatment with 20 nmol NC13. The OFQ mRNA level in the POA on pro-estrus was lowered markedly compared to diestrus and estrus (P<0.05), while the mRNA and protein levels of the ORL1 receptor showed no significant changes in the POA and MBH across the estrus cycle. Meanwhile, the number of OFQ-immunoreactive neurons in the medial POA, ventromedial hypothalamus, and the arcuate nucleus on pro-estrus was significantly decreased compared to diestrus and estrus (P<0.05).


CONCLUSIONS
The inhibitory effect of OFQ on the LH surge of EBP-primed, OVX rats and its downregulation in POA and MBH on pro-estrus suggests that it might play a negative modulatory role in the estrus cycle.
An
Xiao-fei
XF
Department of Endocrinology, Jiangsu Province Hospital of Traditional Chinese Medicine, Nanjing, China. anxiaofei2000@hotmail.com
Yu
Jiang-yi
JY
Feng
Yi
Y
Chen
Bo-ying
BY
Zhang
Su-lin
SL
D000818:Animals; D015153:Blotting, Western; D004967:Estrogens / Q000494:pharmacology*; D004971:Estrus / Q000378:metabolism*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D007031:Hypothalamus / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D018847:Opioid Peptides / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D010052:Ovariectomy; D011374:Progesterone / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000032:analysis / Q000235:genetics; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D004967:Estrogens; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D018847:Opioid Peptides; D011374:Progesterone; D012333:RNA, Messenger; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C000722285:Oprl1 protein, rat