Corpus Luteum and Early Pregnancy in Ruminants

Abstract

This review examines the function of the corpus luteum (CL) with emphasis on pregnancy in ruminant models and the possible impact of pregnancy in conferring luteal resistance to prostaglandin F2α (PGF2α). Critical processes involved with formation of the CL impact the capacity to secrete progesterone. Similarly, complete luteolysis is critically important in the event that pregnancy does not occur so that a new ovulation and opportunity for pregnancy is established. It is well known that serum progesterone must reach a critical nadir if ovulation and fertilization are to occur. Following fertilization, the function of the CL in providing adequate progesterone is critical in setting up an endometrial environment so that pregnancy is maintained. Benefits of supplemental progesterone during early pregnancy are inconsistent in ruminants. However, recent studies indicate that supplemental progesterone following artificial insemination (AI) may depend on the presence of the CL and the amount of progesterone released from the CL. The primary signal for maternal recognition of pregnancy, interferon-tau (IFNT), is secreted from the ruminant conceptus (embryo proper and extraembryonic membranes). IFNT disrupts release of PGF2α from the endometrium and is antiluteolytic through inhibiting uterine expression of the estradiol receptor (ESR1) or the oxytocin receptor (OXTR). Endocrine action of IFNT on peripheral blood mononuclear cells and on the CL may also contribute to immunomodulatory function and longer-term sustainability and function of the CL as pregnancy progresses.