Yang D, Lang U, Greenberg S G, Myatt L, Clark K E
Division of Maternal-Fetal Medicine, University of Cincinnati College of Medicine, OH 45267-0526, USA.
Am J Obstet Gynecol. 1996 Feb;174(2):573-7. doi: 10.1016/s0002-9378(96)70430-1.
Nitric oxide is a potent vasodilator released by endothelial cells that may play an important role in modulating maternal and fetal vascular tone in normal pregnancy. The current study was designed to evaluate whether plasma or urine nitrite and nitrate (the metabolites of nitric oxide) concentrations are elevated in pregnant compared with those of nonpregnant sheep and whether the nitrate concentrations in the fetal circulation were increased in comparison with the maternal circulation.
Eleven pregnant sheep and seven nonpregnant oophorectomized sheep were instrumented with catheters in the maternal and fetal femoral arteries and veins, uterine and umbilical veins, and amniotic cavity. Blood, urine, and amniotic fluid samples were collected for nitrate determination at least 5 days after surgery. After extraction nitrate was reduced to nitrite and quantitated with the Greiss reagent.
Arterial plasma nitrate concentrations in the pregnant sheep were significantly elevated compared with those of nonpregnant sheet (5.0 +/- 0.9 vs 2.5 +/- 0.6 micromol/L, p < 0.05). The urinary nitrate concentrations were also significantly increased in the pregnant sheep compared with those of nonpregnant sheet (89.9 +/- 16.3 vs 23.1 +/- 4.5 nmol/mg creatinine, p < 0.01). Fetal plasma nitrate concentrations were ninefold higher than the maternal nitrate concentrations (43.9 +/- 7 vs 5.0 +/- 0.9 micromol/L, p < 0.01), whereas amniotic fluid concentrations were extremely high (133.8 +/- 13.8 micromol/L, n = 3). No venous-arterial differences were measurable across either the maternal or fetal sides of the placenta.
Nitrate concentrations in pregnant sheet and their fetuses are increased. The increased nitrate concentrations in the maternal and fetal circulations may reflect the increased nitric oxide synthesis, which may in part mediate the cardiovascular adaptations to normal pregnancy and the low systemic and umbilical vascular resistance in the fetus.
一氧化氮是一种由内皮细胞释放的强效血管舒张剂，在正常妊娠中调节母体和胎儿血管张力方面可能发挥重要作用。本研究旨在评估与未怀孕绵羊相比，怀孕绵羊血浆或尿液中亚硝酸盐和硝酸盐（一氧化氮的代谢产物）浓度是否升高，以及与母体循环相比，胎儿循环中的硝酸盐浓度是否增加。
对11只怀孕绵羊和7只未怀孕的去卵巢绵羊进行手术，在母体和胎儿的股动脉和静脉、子宫和脐静脉以及羊膜腔内插入导管。术后至少5天采集血液、尿液和羊水样本用于硝酸盐测定。提取后，硝酸盐被还原为亚硝酸盐，并用格里斯试剂进行定量。
与未怀孕绵羊相比，怀孕绵羊的动脉血浆硝酸盐浓度显著升高（5.0±0.9对2.5±0.6微摩尔/升，p<0.05）。与未怀孕绵羊相比，怀孕绵羊的尿液硝酸盐浓度也显著增加（89.9±16.3对23.1±4.5纳摩尔/毫克肌酐，p<0.01）。胎儿血浆硝酸盐浓度比母体硝酸盐浓度高9倍（43.9±7对5.0±0.9微摩尔/升，p<0.01），而羊水浓度极高（133.8±13.8微摩尔/升，n = 3）。在胎盘的母体或胎儿侧均未检测到静脉-动脉差异。
怀孕绵羊及其胎儿的硝酸盐浓度升高。母体和胎儿循环中硝酸盐浓度的增加可能反映了一氧化氮合成的增加，这可能部分介导了对正常妊娠的心血管适应以及胎儿低全身和脐血管阻力。
