Bell A W, Wilkening R B, Meschia G
J Dev Physiol. 1987 Feb;9(1):17-29.
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.
在妊娠约45天至120天期间，将怀孕母羊持续暴露于高温环境（每天9小时38 - 40摄氏度，15小时30 - 32摄氏度，相对湿度40 - 50%），并在132 - 137天进行研究。将结果与在孕期任何阶段均未受热的相似孕周母羊的结果进行比较。热暴露并未降低食欲，但导致胎盘重量出现不同程度的减轻。胎儿体重减轻程度较小，且与胎盘重量相关。子宫和脐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氧分压差增大、胎儿动脉血氧分压和氧饱和度降低以及胎儿低血糖。子宫胎盘的氧和葡萄糖利用率以及胎儿血液中果糖浓度均与胎盘重量显著相关。研究表明，胎盘生长受限是母体慢性热应激的主要影响，而与之相关的胎儿生长迟缓代表胎儿对胎盘供氧和营养能力下降的一种适应。
