Fig. 3
From: Early pregnancy in the horse revisited – does exception prove the rule?
Schematic representation of interactions between the conceptus and the uterus as currently proposed at the time of maternal recognition of pregnancy on days 12/13 after ovulation: The conceptus propels through the uterine lumen dependent on the action of conceptus-derived prostaglandins on the myometrium. In addition, the conceptus secretes estrogens and arginine into the uterine lumen. Endometrial oxytocin (OT) stimulates conceptus growth by action on OT receptors (OTR) in the trophectoderm. Due to down-regulation of cyclooxygenase 2 (COX2) in the endometrial epithelium, endometrial oxytocin cannot stimulate endometrial synthesis of prostaglandin F2α, therefore corpus luteum function is maintained