Equine Embryonic, Luteal and Endometrial Interactions in Pregnancy Recognition

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Luteal, uterine and embryonic tissues are involved in the maternal recognition of pregnancy (MRP) in mares, but the detailed mechanism of how this occurs, remains unsolved. Early pregnancy failure in horses is a cause of economic loss and affects more than 10% of equine pregnancies. This high rate of equine pregnancy loss is a compelling cause for research in pregnancy recognition. An understanding of the factors involved in the maternal recognition of pregnancy (MRP) in mares, and their regulation, is required to prevent early pregnancy losses. ******Our research has concentrated on examining the role of oxytocin (Oxy), and the enzyme that metabolizes Oxy, called oxytocinase (OTase) in equine MRP. We reported that OTase is present in serum in non-pregnant and pregnant mares. We determined that levels of OTase are not regulated by progesterone (P4), as levels do not vary as P4 levels decline. There are high levels of OTase (U/g tissue) in tissues, and immunohistochemistry reveals that OTase is present in endometrial epithelium; myometrium; and placental tissue. Oxytocin has a central role in: maternal behaviour, milk ejection, uterine contraction, and placental delivery. Systemic levels of Oxy are tightly regulated by rapid clearance mechanisms involving OTase. We will study the conversion of OTNP-1 to Oxy, and further clarify the role of Oxy in MRP. Oxytocin acting through its receptor, is know to increase prostaglandin (PG) secretion in other tissues. ******Embryo mobility from day 5-15 post-ovulation is required for MRP. Oxytocin, OTase and PG are likely involved in embryo mobility. We will compare pregnant mares that are treated with different PG inhibitors known to effect embryo mobility. We will apply: molecular studies of endometrial, embryonic and luteal tissues; ultrasound imaging tools; and hormone assays. We will study non-pregnant mares on day 10 after ovulation, treated with intrauterine pulses of: saline, estrogen, Oxy, PGF, PGE, and PGE and PGF to mimic nature. Intercepting or changing the pulses of PG, or the PGE PGE ratio, is thought to affect luteal function, which is key for MRP. The effects of treatment on P4, luteal tissue, hormones, gene expression and proteins will be determined. We will also identify MRP regulatory signals by using in vitro cultures of luteal and endometrial cells from different days post-ovulation. Cells will be treated with conceptus conditioned media, hormones, inhibitors and agonists. Treatment effects will be examined using molecular analyses of genes and proteins, and secretion of various hormones. Possible regulatory substances will then be explored for their underlying molecular mechanism of action. We will, through these diverse approaches, be able to identify regulatory factors that influence embryo mobility, luteal function and the regulatory pathways associated with MRP. This information will be applied to develop therapies aimed at decreasing early pregnancy loss in mares. **