The expression of ERα, OTR, cPLA2, COX-2, and PPARγ in the cervix of the ewe during the estrous cycle

Abstract

The ovine cervix relaxes at estrus allowing easier entry of spermatozoa into the uterus. The mechanism responsible for this relaxation is not fully elucidated and we hypothesized that cervical relaxation at estrus is induced by ovarian and pituitary hormones stimulating the local production of prostaglandin E2 via a biosynthetic pathway involving a number of mediators including oxytocin, phospholipase A2 (cPLA2), cyclooxygenase-2 (COX-2), and peroxisome proliferator-activated receptor gamma (PPARγ). The aim of this study was to investigate the cervical expression of estradiol receptor alpha (ERα), oxytocin receptor (OTR), cPLA2, COX-2, and PPARγ at three stages of the estrous cycle (the luteal phase and two times during the follicular phase, just before and just after the LH surge). An experiment was conducted during the breeding season, in 25 ewes to test this hypothesis. Samples of cervical tissue were collected from groups of ewes at three stages of the estrous cycle: the luteal (N = 8), “pre-LH surge” (N = 8), and “post-LH surge” (N = 9) stages. Cervical tissue from uterine, mid, and vaginal regions of the cervix were analyzed by Western immunoblot analysis for ERα, OTR, cPLA2, COX-2, and PPARγ. The results showed that the levels of all five proteins were lowest during the luteal phase of the estrous cycle in all regions of the cervix. The levels of all except cPLA2, increased significantly during the “pre-LH surge” stage. The levels of cPLA2 and ERα increased in the “post-LH surge” stage and those for OTR and PPARγ were unchanged and those for COX-2 were lower. These data show that the cervical levels of all five of the intermediates in the synthesis of prostaglandin E2 that were examined in this study were higher in the “pre-” and “post-LH surge” stages compared with the luteal phase of the estrous cycle and these findings are consistent with our hypothesis.