Sex-steroid receptors, prostaglandin E2 receptors, and cyclooxygenase in the equine cervix during estrus, diestrus and pregnancy: Gene expression and cellular localization.

The cervix is a dynamic structure that undergoes dramatic changes during the estrous cycle, pregnancy and parturition. It is well established that hormonal changes, including estrogens, progestogens and prostaglandins, regulate the expression of key proteins involved in cervical function. The arachidonic acid cascade is important in the remodeling and relaxation of the cervix in the days preceding parturition. Despite the complexity of this mechanism, regulation of cervical function has received little study in the mare. Therefore, the objective of this study was to compare the expression of estrogen receptor α (ESR1) and β (ESR2), progesterone receptor (PGR), prostaglandin E2 type 2 (PTGER2) and type 4 (PTGER4) receptors as well as cyclooxygenase-1 (PTGS1) and -2 (PTGS2) in the equine cervical mucosa and stroma during estrus, diestrus and late pregnancy using qPCR. Immunohistochemistry was used to localize ESR1, ESR2, PGR, PTGER2 and PTGER4 receptors in these regions of the cervix. Relative mRNA expression of ESR1 and PGR was greater during estrus and diestrus than in late pregnancy in both the mucosa and stroma of the cervix. Expression of PTGER2 was highest in the cervical stroma during late pregnancy compared to either estrus or diestrus. Moreover, PTGS1 expression in mucosa and PTGS2 in stroma was greater during late pregnancy compared with estrus, but not diestrus. Immunostaining for ESR1, ESR2, PGR, PTGER2 and PTGER4 was consistently detected in the nucleus and cytoplasm of epithelium of the endocervix as well as the smooth muscle cytoplasm of the cervix in all stages evaluated. Immunolabeling in smooth muscle nuclei was detected for ESR1 and PGR in estrus, diestrus and late pregnancy, and for ESR2 in estrus and late pregnancy stages. The changes noted in late gestation likely reflect preparation of the equine cervix for subsequent parturition.