Iwamoto H S, Teitel D F, Rudolph A M
Cardiovascular Research Institute, University of California, San Francisco 94143-0544.
Pediatr Res. 1991 Aug;30(2):158-64. doi: 10.1203/00006450-199108000-00007.
At birth, changes in utilization of metabolic substrates occur as the fetus, dependent upon carbohydrates and amino acids available continuously from the placenta, becomes a neonate, dependent primarily upon fat obtained intermittently by suckling. In addition to changes in substrates, at birth, metabolic rate increases dramatically as the activity of several organs and thermoregulatory mechanisms increase. To determine whether metabolic changes are related to certain events that occur at birth, we studied 15 fetal sheep instrumented chronically with vascular catheters and an endotracheal tube at 133 to 137 d gestational age. We measured blood flow with radionuclide-labeled microspheres and arteriovenous concentration differences for oxygen content, blood glucose, and lactate across the placental, cerebral, myocardial, and hindlimb circulations at rest, during in utero ventilation of the fetal lungs with 3% O2, during in utero ventilation with 100% O2, and during ventilation with 100% O2 and umbilical cord occlusion. Ventilation with 3% O2 decreased oxygen uptake by the fetus and by the cerebral circulation but produced no other significant changes. Ventilation with the low and high oxygen gas mixture reduced glucose uptake by the fetus from the placental circulation dramatically to zero. In contrast, blood glucose concentrations increased and glucose uptake by the fetal brain, heart, and hindlimb were not altered significantly. These data indicate that, for a short time at least, complete cessation of glucose supply to the fetus from the placenta is not associated with decreases in blood glucose concentrations or utilization of glucose by a major portion of the fetal body.
出生时，代谢底物的利用发生变化，因为依赖于从胎盘持续获得碳水化合物和氨基酸的胎儿变成了新生儿，主要依赖于通过哺乳间歇性获得的脂肪。除了底物的变化外，出生时，随着几个器官的活动和体温调节机制的增加，代谢率急剧上升。为了确定代谢变化是否与出生时发生的某些事件有关，我们研究了15只妊娠133至137天的慢性植入血管导管和气管内导管的胎羊。我们用放射性核素标记的微球测量血流量，并测量在静息状态下、用3%氧气对胎儿肺进行宫内通气时、用100%氧气进行宫内通气时以及用100%氧气通气并阻断脐带时，胎盘、脑、心肌和后肢循环中氧含量、血糖和乳酸的动静脉浓度差。用3%氧气通气会降低胎儿和脑循环的氧摄取，但没有产生其他显著变化。用低氧和高氧混合气体通气会使胎儿从胎盘循环中的葡萄糖摄取急剧降至零。相比之下，血糖浓度升高，胎儿脑、心脏和后肢的葡萄糖摄取没有显著改变。这些数据表明，至少在短时间内，胎盘对胎儿葡萄糖供应的完全停止与血糖浓度的降低或胎儿身体大部分对葡萄糖的利用无关。
