Summanen Milla, Bäck Susanne, Voipio Juha, Kaila Kai
Department of Biosciences, University of Helsinki, Helsinki, Finland.
Neuroscience Center and HiLife, University of Helsinki, Helsinki, Finland.
Front Cell Neurosci. 2018 Jan 19;12:2. doi: 10.3389/fncel.2018.00002. eCollection 2018.
Mammalian birth is accompanied by a period of obligatory asphyxia, which consists of hypoxia (drop in blood O levels) and hypercapnia (elevation of blood CO levels). Prolonged, complicated birth can extend the asphyxic period, leading to a pathophysiological situation, and in humans, to the diagnosis of clinical birth asphyxia, the main cause of hypoxic-ischemic encephalopathy (HIE). The neuroendocrine component of birth asphyxia, in particular the increase in circulating levels of arginine vasopressin (AVP), has been extensively studied in humans. Here we show for the first time that normal rat birth is also accompanied by an AVP surge, and that the fetal AVP surge is further enhanced in a model of birth asphyxia, based on exposing 6-day old rat pups to a gas mixture containing 4% O and 20% CO for 45 min. Instead of AVP, which is highly unstable with a short plasma half-life, we measured the levels of copeptin, the C-terminal part of prepro-AVP that is biochemically much more stable. In our animal model, the bulk of AVP/copeptin release occurred at the beginning of asphyxia (mean 7.8 nM after 15 min of asphyxia), but some release was still ongoing even 90 min after the end of the 45 min experimental asphyxia (mean 1.2 nM). Notably, the highest copeptin levels were measured after hypoxia alone (mean 14.1 nM at 45 min), whereas copeptin levels were low during hypercapnia alone (mean 2.7 nM at 45 min), indicating that the hypoxia component of asphyxia is responsible for the increase in AVP/copeptin release. Alternating the O level between 5 and 9% (CO at 20%) with 5 min intervals to mimic intermittent asphyxia during prolonged labor resulted in a slower but quantitatively similar rise in copeptin (peak of 8.3 nM at 30 min). Finally, we demonstrate that our rat model satisfies the standard acid-base criteria for birth asphyxia diagnosis, namely a drop in blood pH below 7.0 and the formation of a negative base excess exceeding -11.2 mmol/l. The mechanistic insights from our work validate the use of the present rodent model in preclinical work on birth asphyxia.
哺乳动物出生时会经历一段强制性窒息期，其中包括缺氧（血液中氧含量下降）和高碳酸血症（血液中二氧化碳含量升高）。长时间、复杂的分娩会延长窒息期，导致病理生理状况，在人类中则会被诊断为临床分娩窒息，这是缺氧缺血性脑病（HIE）的主要原因。分娩窒息的神经内分泌成分，特别是精氨酸加压素（AVP）循环水平的升高，在人类中已经得到了广泛研究。在此，我们首次表明，正常大鼠出生时也伴随着AVP激增，并且在分娩窒息模型中，基于将6日龄大鼠幼崽暴露于含4%氧气和20%二氧化碳的混合气体中45分钟，胎儿的AVP激增会进一步增强。由于AVP高度不稳定且血浆半衰期短，我们测量了 copeptin 的水平，copeptin 是前体 AVP 的 C 末端部分，其生化稳定性更高。在我们的动物模型中，大部分 AVP/copeptin 释放发生在窒息开始时（窒息15分钟后平均为7.8 nM），但即使在45分钟实验性窒息结束90分钟后仍有一些释放（平均为1.2 nM）。值得注意的是，仅在缺氧后测量到最高的 copeptin 水平（45分钟时平均为14.1 nM），而仅在高碳酸血症期间 copeptin 水平较低（45分钟时平均为2.7 nM），这表明窒息的缺氧成分是导致 AVP/copeptin 释放增加的原因。以5分钟的间隔将氧气水平在5%和9%之间交替（二氧化碳为20%）以模拟长时间分娩期间的间歇性窒息，导致 copeptin 的上升较慢但在数量上相似（30分钟时峰值为8.3 nM）。最后，我们证明我们的大鼠模型满足分娩窒息诊断的标准酸碱标准，即血液pH值降至7.0以下且负碱剩余超过-11.2 mmol/l。我们工作中的机制见解验证了当前啮齿动物模型在分娩窒息临床前研究中的应用。
