NOVEL MECHANISMS OF OXYTOCIN ACTION

描述(由申请人提供)：尽管在美国，催产素被安全地用于引产或增加分娩，但大约一半的有偿产科事故案件涉及其滥用的索赔，安全用药实践研究所将催产素列为高度警戒药物。最近发表了安全使用低剂量和高剂量催产素的临床指南，但作者认识到缺乏证据来支持坚定的建议，并承认个别患者需要的剂量可能高于他们建议的指南。开发最有效的治疗方法将需要详细描述催产素作用模式的基本机制。虽然催产素对子宫收缩强度的影响已有文献记载，但多项研究表明，催产素还能通过增加子宫肌层平滑肌细胞(MSMC)动作电位的产生来调节收缩频率；然而，其发生机制尚不清楚。有趣的是，催产素可以通过产生钠依赖的、对电压门控钠通道阻滞剂河豚毒素不敏感的内向钠电流来去极化迷走神经细胞。最近，在MSMC中发现了一种具有类似性质的钠泄漏通道(NALCN；Na泄漏通道，非选择性)。我们的初步研究表明，人类MSMC表达NALCN并产生类似NALCN的电流，在体外模型中，抑制这一通道会改变人子宫收缩的频率。我们还发现，催产素增加了妊娠妇女子宫肌层细胞中的NALCN样电流，但不增加非妊娠妇女子宫肌层细胞中的NALCN样电流。最后，催产素受体变异体减弱了配体结合，并可能直接或间接地通过NALCN影响子宫对催产素的反应。这项建议的目的是促进对孕妇催产素作用的潜在机制的了解。催产素及其受体对分娩过程都很重要，但为什么催产素会在经历分娩停滞的女性中引起不可预测的反应尚不清楚。最近，已发现催产素受体中具有较弱催产素结合的变体，但这是否会转化为分娩延长或停滞的临床表现尚不清楚。我们的中心假设是，催产素与催产素受体结合调节NALCN通道，该通道是设定子宫自发节律性收缩频率的背景泄漏电流的基础。我们推测，需要更高剂量催产素的女性在催产素受体中存在序列变异，并将在收缩模式中出现频率改变。

DESCRIPTION (provided by applicant): Despite the fact that oxytocin is used safely to induce or augment labor in the majority of births in the United States, roughly half of all paid obstetric malpractice cases involve claims of its misuse, and the Institute for Safe Medication Practices lists oxytocin as a High-Alert medication. Clinical guidelines for safe use of low versus high doses of oxytocin have recently been published, but the authors recognize the paucity of evidence to support firm recommendations and acknowledge that individual patients may require higher doses than their proposed guidelines. Development of the most effective methods of therapy will require detailed characterization of the basic mechanisms underlying oxytocin's mode of action. Although effects of oxytocin on uterine contractile strength are well documented, multiple studies have now indicated its ability to also regulate the frequency of contraction via an increase in the generation of uterine myometrial smooth muscle cell (MSMC) action potentials; however, the mechanism by which this occurs remains unclear. Intriguingly, oxytocin can depolarize vagal neurons by generating an inward Na+ current that is Na+-dependent and insensitive to the voltage-gated Na+ channel blocker tetrodotoxin. Recently, a sodium leak channel (NALCN; Na+ leak channel, non-selective) with similar properties was identified in MSMCs. Our preliminary studies demonstrate that human MSMCs express NALCN and produce a NALCN-like current, and that inhibition of this channel alters the frequency of human uterine contractions in an ex vivo model. We have also discovered that oxytocin increases NALCN-like current in myometrial cells derived from pregnant women, but not in myometrial cells derived from non-pregnant women. Lastly, oxytocin receptor variants that have attenuated ligand binding have been identified and may affect the response of the uterus to oxytocin either directly or indirectly via NALCN. The objective of this proposal is to advance knowledge of the underlying mechanism of oxytocin action in pregnant women. Both oxytocin and its receptor are important to the process of labor, yet why oxytocin elicits an unpredictable response in women who experience labor arrest is unknown. Recently, identified variants in the oxytocin receptor that have weaker oxytocin binding have been identified, but whether this translates into a clinical presentation of labor protraction or arrest is unknown. Our central hypothesis is that oxytocin binding to the oxytocin receptor regulates the NALCN channel, which underlies the background leak current that sets the frequency of spontaneous rhythmic contractions of the uterus. We speculate that women who require higher doses of oxytocin harbor sequence variants in the oxytocin receptor and will present with altered frequency in their contraction patterns.