Iwamoto H S, Rudolph A M, Mirkin B L, Keil L C
Am J Physiol. 1983 Nov;245(5 Pt 1):H767-72. doi: 10.1152/ajpheart.1983.245.5.H767.
In fetal sheep, hypoxemia causes arterial hypertension, bradycardia, a redistribution of blood flow, and an increase in plasma vasopressin and catecholamine concentrations. To assess the role of the sympathetic nervous system in mediating these responses, we administered 6-hydroxydopamine to 11 chronically catheterized fetal sheep. Some of the responses to acute hypoxemia, achieved by administration of a low-O2 gas mixture to the ewe, were similar to those in intact fetal sheep. Fetal arterial O2 tension decreased from 22 +/- 3 to 12 +/- 3 (SD) Torr; fetal heart rate decreased transiently; combined ventricular output and umbilical-placental blood flow, as measured by the radionuclide-labeled microsphere technique, were maintained; cerebral, myocardial, and adrenal blood flow increased, and pulmonary blood flow decreased. However, there was no significant change in arterial pressure or blood flow to the peripheral, renal, and splanchnic circulations in the chemically sympathectomized fetuses in response to hypoxemia. The sympathetic nervous system is important in certain fetal vascular responses to hypoxemia but is not necessary for vascular responses in certain critical organs and thus is not crucial for fetal survival during hypoxia.
在胎羊中，低氧血症会导致动脉高血压、心动过缓、血流重新分布以及血浆血管加压素和儿茶酚胺浓度升高。为了评估交感神经系统在介导这些反应中的作用，我们对11只长期插管的胎羊给予了6-羟基多巴胺。通过向母羊给予低氧气体混合物实现的急性低氧血症的一些反应与完整胎羊中的反应相似。胎羊动脉血氧张力从22±3降至12±3（标准差）托；胎心率短暂下降；通过放射性核素标记微球技术测量的心室联合输出量和脐-胎盘血流量得以维持；脑、心肌和肾上腺血流量增加，而肺血流量减少。然而，化学性交感神经切除的胎儿在低氧血症时动脉血压或外周、肾脏和内脏循环的血流量没有显著变化。交感神经系统在某些胎儿对低氧血症的血管反应中很重要，但在某些关键器官的血管反应中并非必需，因此对胎儿在缺氧期间的存活并不关键。
