Ovine cervical function and gene expression during the natural and artificially-induced oestrous cycle
Laparoscopy is used for artificial insemination (AI) and multiple embryo transfer (MOET) in sheep. This technique is unacceptable due to welfare concerns and expense but is a necessary alternative to the low fertilisation rates achieved by cervical AI. The cervix is the natural route to access the uterus and by understanding its anatomy and physiology, new techniques may be developed to provide acceptable fertilisation rates by cervical AI. Cervical dilation is necessary for atraumatic transcervical AI in the sheep. During parturition, cervical dilation occurs via inflammation. The hypothesis that inflammation also occurs in the cervix at oestrus to facilitate trans-cervical semen transport and that this process is inhibited by artificial synchronisation of oestrus is tested using a combination of immunocytochemistry and semi quantitative in situ hybridisation. Leukocyte infiltration and expression of interleukin-8 (IL-8), a pro-inflammatory cytokine were used as markers of inflammation. Expression of gonadal steroid receptors, c-fos and proteinase activated receptors (PARs), which participate early in inflammation were also investigated throughout the oestrous cycle. In the cervix of ewes, increased accumulation of leukocytes, IL-8, PAR-1 and PAR-2 gene expression correlated with elevated c-fos and oestrogen a and progesterone B receptor expression at oestrous confirming relatively high levels of inflammation at this time. An inhibition of inflammation marked by significantly lower levels of IL-8 gene expression followed hormonal synchronisation of the oestrous cycle providing a potential mechanism for low rates of fertilisation following AI and artificial synchronisation. Induced cervical dilation using nitric oxide (NO) donors counteracted the inhibitory effects of hormonal synchronisation on IL-8 expression, as did insemination. However, NO treatment led to low fertility rates. PAR-2 expression was not inhibited by hormonal synchronisation of the oestrous cycle, indicating that PAR agonists, which are small synthetic peptides, may be used to induce cervical dilation following artificial synchronisation of oestrus.