胎羊体外循环对胎盘肾素-血管紧张素系统的影响

The impact of fetal cardiac bypass on the placental rennin-angiotensin system

目的探讨胎羊体外循环中胎盘肾素-血管紧张素系统（RAS）的变化。方法8头孕羊（孕120～140d）怀有9头胎羊，随机分为对照组（n=4）和胎羊体外循环组（转流组，n=5）。对照组胎羊开胸，不建立体外循环。转流组应用离心泵和胎盘建立胎羊体外循环，转流30min。分别于转流前、转流30min、转流结束后1h、转流结束后2h采集胎羊平均动脉压、心率和动脉血气值。超声流量仪测量脐动脉流量，计算胎盘血管阻力。并分别检测转流前后胎盘血管紧张素-Ⅱ（Ang-Ⅱ）含量和血管紧张素转化酶（ACE）mRNA的表达。结果两组胎羊平均动脉压、心率没有显著变化。转流组胎羊脱离体外循环后出现高碳酸血症和酸中毒，BE负值进行性增高（P〈0．05）。对照组胎羊血气值没有明显变化。转流组胎羊体外循环结束后胎盘血管阻力上升（P〈0．05）。转流组转流后胎盘Ang-Ⅱ较对照组升高，ACEmRNA表达上调，与对照组比较差异有统计学意义（P〈0．05）。结论胎羊体外循环激活胎盘RAS系统，影响胎盘血流，导致胎与脐-胎盘循环状况不良。

Objective To evaluate the response of placental rennin-angiotensin system（RAS） to fetal cardiac bypass. Methods Nine ovine fetuses of gestational age 120 to 140 days were randomized into control group （n = 4） and bypass group （n = 5）. The control group underwent fetal sternotomy. The bypass group underwent fetal cardiac bypass. The hemodynamic and blood gas data of the ewes and the fetuses were recorded before, during, 1 and 2 hour after the bypass. The umbilical flow was measured with ultrasonic flowmeter and the placental vascular resistance was calculated. The level of angiotensin-Ⅱ（Ang-Ⅱ） and angiotensin converse enzyme （ACE） mRNA in placenta were assayed. Resuits The fetal mean blood pressure and heart rate of the two groups showed no significant change during the study period. The fetuses in bypass group developed hypercarbia and acidosis after the cessation of bypass（P〈0. 05）. The fetal arterial oxygen tension of both groups remained normal, but fetal BE value of the bypass group rose significantly compared with control group（P〈0. 05）. Placenta vascular resistance of bypass group increased significantly （P〈0. 05）. The levels of ACE mRNA and Ang-II also increased simultaneously （P〈0. 05） in bypass group（P〈0. 05）. Conclusions Fetal cardiac bypass activates the placental RAS and adversely affect the fetalplacental circulation.