Cyclical cervical function in the mare involves remodelling of collagen content, which is correlated with modification of oestrogen receptor 1 abundance

This study was conducted to elucidate mare cervical dilation mechanisms by testing two hypotheses: (i) the proportion of collagen staining in histological samples of mare cervices and (ii) the abundance of hormone receptors in the equine cervix differ with stage of the oestrous cycle and site within the cervix. Tissues and jugular vein blood samples were collected from 15 mares. Collagen content was assessed using Masson's Trichome staining. Receptor abundance was assessed using RT-PCR, qRT-PCR and immunohistochemistry. In sub-epithelial stroma, there was less collagen during the follicular than luteal phase, in the caudal- (P =  0.029), mid- (P =  0.0000) and cranial (P =  0.001) cervical tissue. In the deep stroma, there was less collagen staining during the follicular stage in the mid- (P =  0.004) and cranial- (P =  0.041) cervical regions. There were PTGER2, PTGER3, PGR and ESR1 mRNA transcripts in the cervix. A greater proportion of cells were positive for ESR1 protein during the follicular phase in sub-epithelial (P =  0.019) and deep (P =  0.013) stroma. The abundance of ESR1 in the epithelium was negatively correlated with collagen staining in sub-epithelial (P =  0.007) and deep (P =  0.005) stroma. The results of the study provide new information about the cervical biology of mares by increasing the knowledge about collagen content and the relationship between collagen content and ESR1 protein abundance during the oestrous cycle which indicates the ESR1 receptor is a candidate for involvement in control of cervical dilation.