Jones C T, Parer J T
J Physiol. 1983 Oct;343:525-37. doi: 10.1113/jphysiol.1983.sp014907.
The distribution of the cardiac output and the maternal placental blood flow has been measured in guinea-pigs at days 49-51 of pregnancy using radioactively labelled microspheres. In some instances uterine blood flow was reduced chronically by ligating one uterine artery at day 30 of pregnancy. Between 3 and 4% of the cardiac output passed normally to placenta, and this could be reduced to less than 2% after uterine artery ligation. The result of the ligation was to reduce fetal and placental weight by up to 70%. Fetal and placental weight showed a close linear correlation in controls and in pregnancies with uterine artery ligation. However, when placental size was reduced below 60% of control, fetal weight was less affected by a reduction in placental weights than normal. Placental blood flow and placental size exhibited a close linear relationship over the whole range of values, but there was limiting placental weight which approached 1.3 g as placental blood flow approached zero. Thus a reduced placental size, particularly below about 50%, was associated with a proportionately greater reduction in maternal placental blood flow. Maternal placental blood flow or the percentage of maternal cardiac output to the placenta and fetal weight also showed a well-correlated linear relationship. However, when placental blood flow was below about 50% of control values further reduction had a less than normal effect upon fetal growth. Small fetuses were hypoglycaemic and hypoinsulinaemic and the degree of each was dependent upon the extent of the reduction in fetal weight and in maternal placental blood flow. In fetuses that were below about 40% of normal size, and in which placental blood was below about 30% of control, fetal weight was less sensitive to falls in blood glucose, which in turn was more sensitive than normal to a fall in maternal placental blood flow. The results indicate that over the range of 50-100% of normal fetal growth, maternal placental blood flow and probably nutrient supply to the fetus vary in parallel. Hence over this range fetal and placental growth rates are determined in part by placental blood flow. At placental blood flow rates and fetal growth rates below 40% of normal fetal growth is less dependent upon placental blood flow than usual, presumably because of a reduced dependence upon glucose metabolism for growth. This would appear to be essential, since as maternal placental blood flow is reduced to low values the placenta has to utilize an increasing proportion of the available glucose.
在妊娠49 - 51天的豚鼠中，使用放射性标记的微球测量了心输出量和母体胎盘血流量的分布。在某些情况下，在妊娠第30天结扎一条子宫动脉，使子宫血流量长期减少。正常情况下，心输出量的3% - 4%流向胎盘，子宫动脉结扎后，这一比例可降至2%以下。结扎的结果是使胎儿和胎盘重量减少多达70%。在对照组和子宫动脉结扎的妊娠中，胎儿和胎盘重量呈密切的线性相关。然而，当胎盘大小降至对照组的60%以下时，胎盘重量的减少对胎儿体重的影响小于正常情况。在整个数值范围内，胎盘血流量和胎盘大小呈密切的线性关系，但当胎盘血流量接近零时，胎盘重量有一个极限值，接近1.3克。因此，胎盘大小的减小，尤其是降至约50%以下时，与母体胎盘血流量的相应更大减少有关。母体胎盘血流量或母体心输出量流向胎盘的百分比与胎儿体重也呈良好的线性相关。然而，当胎盘血流量低于对照组值的约50%时，进一步减少对胎儿生长的影响小于正常情况。小胎儿出现低血糖和低胰岛素血症，其程度取决于胎儿体重和母体胎盘血流量减少的程度。在大小约为正常大小40%以下且胎盘血流量低于对照组约30%的胎儿中，胎儿体重对血糖下降的敏感性较低，而血糖对母体胎盘血流量下降的敏感性则比正常情况更高。结果表明，在正常胎儿生长的50% - 100%范围内，母体胎盘血流量以及可能对胎儿的营养供应是平行变化的。因此，在此范围内，胎儿和胎盘的生长速度部分由胎盘血流量决定。当胎盘血流量和胎儿生长速度低于正常胎儿生长的40%时，胎儿生长对胎盘血流量的依赖程度比通常情况低，推测是因为对生长的葡萄糖代谢依赖性降低。这似乎是至关重要的，因为随着母体胎盘血流量降至低值，胎盘不得不利用越来越多的可用葡萄糖。
