The role of the endometrial oxytocin receptor in determining the length of the sterile oestrous cycle and ensuring maintenance of luteal function in early pregnancy in ruminants.

The oxytocin receptor, a seven transmembrane domain, G protein-linked receptor molecule, plays a central role in determining the endocrine function of the ruminant uterine endometrium. During nonpregnant cycles the control of this molecule by circulating steroid hormones leads to regression of the corpora lutea. The kinetics of the mechanisms involved determine the time at which luteolysis occurs, and therefore the length of the oestrous cycle. In pregnancy, secretions of the trophoblast block endometrial oxytocin receptor gene expression and lead to luteal maintenance. An understanding of the molecular mechanisms involved in the steroidal control of oxytocin receptor gene expression will provide an explanation for the relative constancy of oestrous cycle lengths in non-pregnant animals. Unravelling the way in which trophoblast products block expression of the oxytocin receptor gene will lead to a better understanding of the reasons for the high rate of embryonic loss in domestic ruminants.