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Impact of thermal stress on placental function and fetal physiology

机译：热应激对胎盘功能和胎儿生理的影响

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In ruminants, prolonged exposure to high ambient temperatures negatively affects placental development and function. The pursuing limitations in placental oxygen and nutrient supply between the mother and fetus slow fetal growth lowering birth weights and postnatal performance. The pregnant ewe is a long-standing animal model for the study of maternal-fetal interactions and is susceptible to naturally occurring heat stress, which causes fetal growth restriction. In the pregnant ewe, studies show that the fetus adapts to hyperthermia-induced placental insufficiency to preserve placental transport capacity of oxygen and nutrients. These adaptive responses are at the expense of normal fetal development and growth. Enlarged transplacental gradient for oxygen and glucose facilitates diffusion across the placenta, but develops by lowering fetal blood oxygen and glucose concentrations. Fetal hypoxemia and hypoglycemia slow growth and alter their metabolic and endocrine profiles. Deficits in amino acids transport across the placenta are present but are overcome by reduced fetal clearance rates, likely due to fetal hypoxemia or endocrine responses to hypoxic stress. Here, we provide an overview of the performance limitations observed in ruminants exposed to heat stress during pregnancy, but we focus our presentation on the sheep fetus in pregnancies complicated by hyperthermia-induced placental insufficiency. We define the characteristics of placental dysfunction observed in the fetus of heat stressed ewes during pregnancy and present developmental adaptations in organogenesis, metabolism, and endocrinology that are proposed to establish maladaptive situations reaching far beyond the perinatal period.
机译：在反刍动物中，长时间暴露在高温下会对胎盘发育和功能产生负面影响。母亲和胎儿之间的胎盘氧气和营养供应的持续限制限制了胎儿的生长，从而降低了出生体重和产后表现。怀孕母羊是研究母婴相互作用的长期动物模型，易受自然热应激的影响，从而引起胎儿生长受限。研究表明，在怀孕的母羊中，胎儿适应了高热引起的胎盘功能不全，从而保持了胎盘中氧气和养分的转运能力。这些适应性反应是以正常胎儿发育和成长为代价的。胎盘中氧气和葡萄糖的梯度增大，促进了整个胎盘的扩散，但通过降低胎儿血液中的氧气和葡萄糖浓度而发展。胎儿低氧血症和低血糖症会减慢生长并改变其代谢和内分泌特征。氨基酸在整个胎盘中的运输存在缺陷，但可以通过降低胎儿的清除率来克服，这可能是由于胎儿低氧血症或内分泌对低氧应激的反应。在这里，我们提供了在妊娠期间暴露于热应激的反刍动物中观察到的性能局限性的概述，但我们将介绍的重点放在妊娠并发高热引起的胎盘功能不全的绵羊胎儿上。我们定义了在妊娠期热应激母羊的胎儿中观察到的胎盘功能异常的特征，并提出了器官发生，代谢和内分泌学方面的发育适应性建议，以建立远超过围产期的适应不良情况。

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