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This thesis involved the investigation of luteal, endometrial and embryonic putative gene regulators in the maternal recognition of pregnancy in the horse, with an emphasis on understanding the role of oxytocin and oxytocinase in early pregnancy. The first objective was to validate the safety and health outcomes of mares following a transvaginal ultrasound-guided ovarian (TVOB) and serial luteal biopsy (TVLB), which was utilized as a means to obtain luteal tissue for gene expression studies without affecting pregnancy. The TVLB technique was determined to be safe and did not to affect pregnancy rate even after serial biopsy of the equine corpus luteum. The accuracy of the luteal biopsy technique was validated with histology, serial serum progesterone analysis and by gene expression studies using Aromatase, which is only expressed in luteal tissue and not in the adjacent ovarian stroma. We concluded TVLB was a safe and useful tool when studying luteal events in equine pregnancy. The second objective was to determine the effect of intrauterine administration of plant oils, such as coconut oil, on equine luteal function. A previous report using intrauterine infusion of a bioidentical coconut oil, product prolonged luteal function. The infusion of coconut oil during diestrus shortened the luteal phase in the mare, demonstrating that plant oil was not effective in keeping mares out of heat. The third objective was to characterize serum and tissue oxytocinase (LNPEP) in mares, especially during early and late pregnancy and to characterize the expression of oxytocin (OXT) in reproductive tissues. Serum LNPEP did not differ between pregnant and nonpregnant mares, or between late prepartum and immediately post-partum period. Tissue LNPEP was widely distributed among the reproductive tissues of the mare, including the placenta. Oxytocin was demonstrated to be expressed in the equine corpus luteum, but not in the endometrium or myometrium. This chapter described the presence of oxytocin and oxytocinase and their importance in reproductive function in the mares. The fourth objective was to compare the equine endometrial and luteal gene expression in mares that either were treated pharmacologically or naturally induced to have prolonged or shortened luteal phases. This series of experiments included six groups: pregnant mares, nonpregnant diestrous mares, estrous mares, mares treated with carbetocin, oxytocin, and meclofenamic acid. Both OXT and LNPEP were expressed in the equine luteal tissue. Carbetocin-treated mares had similar gene expression profiles to estrous mares and had an increased expression of endometrial phospholipase A2 (PLA2G2C) and a decreased expression of both endometrial and luteal prostaglandin E synthase (PTGES). Furthermore, PTGES expression was higher in diestrous, pregnant and oxytocin treated mares, suggesting that prostaglandin E (PGE) may have a luteoprotective role. To further characterize the gene expression during expected time of MRP, the fifth objective focused on comparing endometrial and luteal gene expression of pregnant and nonpregnant mares in different days of the cycle: Day (D)8, D10, 12 and 15. Endometrial and luteal PTGES have an increased mRNA abundance in both diestrous and pregnant mares, further supporting the luteotrophic role of PGE for luteal maintenance. Lastly, the sixth objective was to compare the trophoblastic gene expression on Day 8 through D21 and to immunolocalize OXT and LNPEP in the equine embryo. Prostaglandin synthase 2 (PTGS2) was increased in D14, D15 and D21 embryos; prostaglandin F receptor (PTGFR) was increased from D8 to D12-21; and LNPEP was increased at D15 compared to D10. Oxytocin was not detected by either immunohistochemistry (IHC), the RNAscope technique or by liquid chromatography tandem mass spectrometry (LC-MS/MS). The presence of LNPEP was confirmed with IHC and LC-MS/MS.



Equine, Conceptus, Corpus luteum, Embryo, Endometrium, Glucose transporters, Neurophysin/Oxytocin I, Oxytocinase, Prostaglandins, Steroid receptors



Doctor of Philosophy (Ph.D.)


Large Animal Clinical Sciences


Large Animal Clinical Sciences


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