Some aspects of placental function in chronically heat-stressed ewes.
Some aspects of placental function in chronically heat-stressed ewes.
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发表时间：
1987-02
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通讯作者：
A. Bell;R. Wilkening;G. Meschia
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作者：
A. Bell;R. Wilkening;G. Meschia
妊娠母羊在妊娠约45天和120天之间连续暴露于高环境温度（38-40 ℃持续9小时，30-32 ℃持续15小时，相对湿度40-50%），并在132-137天进行研究。结果进行了比较与那些母羊的相似胎龄，没有暴露在任何阶段的怀孕热。热暴露并不抑制食欲，但引起胎盘重量的可变减少。胎仔体重降低程度较小，与胎盘重量相关。子宫和脐带血流量以及胎盘葡萄糖转运能力均显著降低，且与胎盘重量高度相关。这些影响伴随着子宫和脐静脉血之间的PO 2差异的扩大，在PO 2和胎儿动脉血的氧饱和度的下降，和胎儿低血糖。子宫胎盘的氧和葡萄糖利用率和胎儿血液中果糖的浓度与胎盘重量均显着相关。这表明，减少胎盘生长是一个主要的影响，慢性母体热应激和相关的胎儿生长迟缓代表胎儿适应胎盘供应氧气和营养物质的能力下降。
Pregnant ewes were exposed continuously to high ambient temperature (38-40 degrees C for 9 h, 30-32 degrees C for 15 h daily, relative humidity 40-50%) between about 45 days and 120 days of gestation and studied at 132-137 days. Results were compared with those of ewes of similar gestational age which were not exposed to heat at any stage of pregnancy. Heat exposure did not depress appetite but caused variable reductions in placental weight. Fetal weight was reduced to a lesser extent and correlated with placental weight. Uterine and umbilical blood flows and placental glucose transfer capacity were all significantly reduced and highly correlated with placental weight. These effects were accompanied by an enlargement of the PO2 difference between uterine and umbilical venous blood, a decrease in the PO2 and oxygen saturation of fetal arterial blood, and fetal hypoglycemia. Uteroplacental rates of oxygen and glucose utilization and the concentration of fructose in fetal blood were each significantly correlated with placental weight. It is suggested that reduced placental growth is a primary effect of chronic maternal heat stress and that the associated retardation of fetal growth represents a fetal adaptation to a decreased placental ability to supply oxygen and nutrients.