Abstract
During the periovulatory period, the cervix relaxes in response to changes in circulating concentrations of reproductive hormones. The present study investigated the role of gonadotrophins in cervical function by examining the expression of follicle-stimulating hormone receptor (FSHR) and luteinizing hormone receptor (LHR) and their mRNAs following intracervical treatment with either FSH or LH. Eighteen ewes were assigned to four groups, and they were then treated with progestagen sponges and PMSG to synchronize their oestrous cycles. Intracervical treatments were given 24h after sponge removal as follows: Group 1: FSH 2mg; Group 2: LH 2mg; Group 3: Vehicle and Group 4: Control. Cervices were collected 54h after sponge removal and then divided into three regions. The expression of FSHR and LHR was determined by immunohistochemistry and FSHR mRNA and LH mRNA by in situ hybridization. The expression of LHR, FSHR and their respective mRNAs was compared in six tissue layers (luminal epithelium, subepithelial stroma, circular, longitudinal and transverse muscle and serosa) and in three cervical regions (vaginal, mid and uterine). The results showed that FSH increased transcription of the FSHR gene and the levels of its receptor, but only in subepithelial stroma of the cervix. FSH also increased the levels of LHR in the cervix, but only in the muscle layers. LH had no effect on the levels of FSHR despite the fact that it did increase the level of transcription of the FSHR gene and LH also increased the levels of its own receptor in the cervix, but only in the muscle layers, and this action was independent of increased levels of transcription of the LHR gene. These findings suggest multiple levels of regulation of cervical LH and FSH receptors and that the gonadotrophins may have a role in relaxation of the cervix during oestrus by regulating their own receptors.
Highlights
One of the main purposes of artificial insemination in sheep breeding is to increase the rate of genetic improvement
There were no significant interactions of cervical layer with either hormonal treatment or the region of the cervix for any of the 4 endpoints (FSHR, LH receptor (LHR), Follicle stimulating hormone (FSH) mRNA and LHR mRNA)
The results showed that the cervical levels of FSH receptor (FSHR), LHR and their receptors can be altered by the intra-cervical application of FSH
Summary
One of the main purposes of artificial insemination in sheep breeding is to increase the rate of genetic improvement. Conventional trans-cervical insemination in sheep gives poor fertility mainly because of the unusual anatomy of the sheep cervix. There is a degree of natural relaxation at oestrus (Leethongdee et al, 2007b) that is probably regulated by the peri-ovulatory changes in reproductive hormones (Kershaw et al, 2004). The cervix contains receptors for oestradiol, progesterone, oxytocin (Fuchs et al, 1996) as well as those for Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) (Mizrachi and Shemesh, 1999b, 1999a; Fields and Shemesh, 2004) suggesting that the gonadotrophins may have a functional role in cervical physiology at oestrus. There is good evidence indicating that cervical relaxation is mediated by Prostaglandin E2
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