The Role of Oxytocin and Oxytocinase in the Maternal Recognition of Pregnancy in Mares

母马早期妊娠丢失是马业繁殖效率低下和经济损失的重要原因。据报道，这在一定程度上与母亲对怀孕的认识失败(MRP)有关。MRP是一个过程，涉及一系列复杂和复杂的事件，允许母马对胚胎的存在做出反应，导致黄体(CL)的维持和孕酮的持续分泌。在母马中，MRP的细节仍然难以捉摸，但人们认识到，其中涉及一个复杂的信号级联。在反刍动物中，24 kDa的胎盘滋养细胞产物干扰素tau(INFT)是MRP的启动者。已确定1-10 kDa的马胚胎物质可以改变子宫内膜外植体模型中前列腺素(PG)的合成，但其作用机制尚不清楚。越来越多的实验证据表明，小肽激素、催产素和催产素偶联受体事件，如前列腺素H2合成酶(PGHS2)的诱导，是母马MRP的关键调节因素。PGHS2酶将花生四烯酸代谢成前列腺素F2-α，后者是公马体内的黄体素。母马从垂体后叶系统地释放催产素，并在子宫内膜上皮局部合成催产素。与其他物种不同，后叶催产素没有卵巢来源。催产素的生物半衰期非常短。系统和组织中催产素的水平被认为受到严格的调控，因为这种激素参与了重要的生理过程，如：性唤醒、子宫活动、MRP、分娩、母体行为和排乳。目前，对系统释放或局部产生的子宫内膜催产素如何相互作用或代谢缺乏了解。据报道，催产素主要以旁分泌方式起作用。在其他物种中，‘催产素酶’存在于血清中，有些组织具有膜结合的催产素酶/胰岛素调节的氨基肽酶，可降解激素。有证据表明，在大多数物种中，催产素与其受体结合也会刺激催产素酶活性，这是一个负反馈过程。本研究拟研究MRP前后母马催产素受体结合、催产素分泌及催产素代谢之间的关系。给母马注射催产素的途径、持续时间、使用的类似物和剂量都会对黄体功能产生不同的结果，从没有影响到黄体期的缩短或延长。为了了解这些催产素相关的影响，我将研究妊娠母马、催产素或催产素类似物(Carbetocin)处理的怀孕母马的子宫内膜和黄体组织，以及第15天未怀孕母马的子宫内膜和黄体组织。我还将检查与MRP相关的关键时间点(周期的第8-15天)怀孕和未怀孕母马的子宫内膜和黄体组织。我将使用放射自显影技术描述怀孕状态、排卵后天数和组织催产素酶的位置之间的关系。我将测定血清和组织中催产素酶的活性，并评估催产素、催产素酶和其他关键激素、受体和酶在生殖组织中的表达，例如那些与前列腺素级联反应相关的激素、受体和酶。了解与MRP相关的关键过程将使兽医更好地了解马的妊娠成功和失败，并将有助于开发更好的治疗干预措施，以防止怀孕丢失，并提高繁殖效率。这项研究有助于确保马的生殖健康所必需的基础知识。

Early pregnancy loss in mares is a substantial cause of reproductive inefficiency and economic loss in the equine industry. It is reported to be partly related to a failure of the maternal recognition of pregnancy (MRP). MRP is a process that involves a series of complex and complicated events that allow a mare to respond to the presence of an embryo, resulting in maintenance of the corpus luteum (CL) and the continued secretion of progesterone. The details of MRP remain elusive in the mare but it is recognized that an intricate signaling cascade is involved. In ruminants a 24 kDa conceptus trophoblast product, interferon tau (INFT), is the initiator of the MRP. A 1-10 kDa equine conceptus substance has been identified that alters prostaglandin (PG) synthesis in an endometrial explant model, but the mechanism of action is unknown. Mounting experimental evidence shows that the small peptide hormone, oxytocin, and oxytocin coupled receptor events, such as induction of prostaglandin H2 synthase (PGHS2), are key regulators of the MRP in mares. The enzyme PGHS2 metabolizes arachidonic acid to Prostaglandin F2-alpha, the putative luteolysin in the mare. The mare has both systemically released oxytocin from the posterior pituitary and local synthesis of oxytocin in the endometrial epithelium. Unlike other species, there is no ovarian source of oxytocin. Oxytocin has a very short biologic half-life. The systemic and tissue levels of oxytocin are believed to be tightly regulated in the mare, as this hormone is involved in important physiologic processes such as: sexual arousal, uterine activity, MRP, parturition, maternal behaviour, and milk ejection. Currently there is a lack of knowledge of how systemically released or locally produced endometrial oxytocin interact or are metabolized. It is reported that oxytocin primarily functions in a paracrine fashion. In other species ‘oxytocinase’ is present in the serum and there are tissues that have a membrane bound oxytocinase/insulin regulated aminopeptidase that degrades the hormone. There is evidence of a negative feedback process in most species where oxytocin binding to its receptor also stimulates oxytocinase activity. I propose to study the relationship between oxytocin receptor binding, secretion of oxytocin, and metabolism of oxytocin in the mare around the time of MRP. The route, duration, analogue used and dose of oxytocin administered to mares results in different outcomes on luteal function, ranging from no effect to either a shortening or lengthening of the luteal phase. To understand these oxytocin related effects I will study endometrial and luteal tissues from: pregnant mares, oxytocin or oxytocin analog (carbetocin) treated mares, with non-pregnant mares at Day 15. I will also examine endometrial and luteal tissues of pregnant and non-pregnant mares at critical time points (day 8 -15 of the cycle) that are associated with the MRP. I will describe relationships between pregnancy status, number of days post ovulation and the location of tissue oxytocinases using autoradiography. I will determine the activity of serum and tissue oxytocinases, and evaluate the expression of oxytocin, oxytocinases, and other key hormones, receptors, and enzymes, such as those associated with the prostaglandin cascade, in reproductive tissues. An understanding of the critical processes associated with MRP will allow veterinarians a better understanding of pregnancy success and failure in horses and will enable the development of better therapeutic interventions to prevent pregnancy loss, and improve reproductive efficiency. This research contributes to fundamental knowledge essential to ensuring reproductive health in horses.