ABSTRACT
Maternal recognition of pregnancy requires signaling between the conceptus (embryo and its associated membranes) and the maternal system which is essential for maintenance of the corpus luteum (CL) and for production of progesterone, which is essential for endometrial functions required for early embryonic development, implantation, placentation and fetal/placental development (see Bazer et al., 1998). Pregnancy recognition signals can be luteotrophic, luteal protective or antiluteolytic. Luteotrophic signals include chorionic gonadotrophin (CG), produced by primate conceptuses, which acts directly on the CL via Luteinizing Hormone (LH) receptors to insure CL maintenance. The ovarian cycle of primates is independent of the uterus, as regression of the CL results from intra-ovarian effects of prostaglandins, oxytocin or other undefined luteolytic agents; therefore, it follows that CG acts directly on the CL to abrogate the intra-ovarian luteolytic mechanism (see Stouffer and Hearn, 1998). Luteolytic agents induce structural and functional demise of the CL, and prostaglandin F2α (PGF2α) is the luteolytic signal in most, if not all, mammals. Luteal protective signals, e.g. prostaglandin E2 (PGE2) may antagonize luteolytic effects of PGF.
