Jang P R, Brace R A
Department of Reproductive Medicine, University of California, San Diego, La Jolla 92093-0802.
Am J Obstet Gynecol. 1992 Dec;167(6):1732-41. doi: 10.1016/0002-9378(92)91768-6.
Recently an intramembranous pathway was reported in the ovine fetus as a route for the rapid exchange of water, ions, and molecules between the amniotic fluid and the fetal blood that perfuses the fetal surface of the placenta and the fetal membranes. Our study was designed to test the hypothesis that the amniotic fluid composition would gradually equilibrate with fetal plasma when the major flows to and from the amniotic compartment were eliminated.
Eleven near-term fetal sheep underwent ligation of the urachus to eliminate the allantoic fluid. An inflatable cuff was placed around the esophagus and trachea, and catheters were placed in the fetal urinary bladder, fetal circulation, and maternal circulation. At > or = 5 days after surgery the animals were subjected to either a control experiment or a continuous urine drainage plus tracheoesophageal occlusion for 8 hours.
During the urine drainage plus occlusion study, amniotic fluid osmolality (p < 0.0001), Na+ (p < 0.0001), K+ (p < 0.01) Cl- (p < 0.001), and lactate (p < 0.001) increased compared with the control experiment. These corresponded to 50% reductions in the gradients for osmolality and Na+ between fetal plasma and amniotic fluid; the K+ gradient increased, and the Cl- gradient reversed. The percentage increases in amniotic Na+, K+, Cl-, and lactate were all 10% at 8 hours.
These observations suggest that water is absorbed from the amniotic fluid through the intramembranous pathway into the fetal circulation at a rate of 1.25% of the total amniotic volume per hour or approximately 240 ml/day.
最近有报道称，在绵羊胎儿中存在一种膜内途径，作为羊水与灌注胎盘胎儿表面和胎膜的胎儿血液之间水、离子和分子快速交换的途径。我们的研究旨在检验以下假设：当进出羊膜腔的主要流量被消除时，羊水成分将逐渐与胎儿血浆达到平衡。
11只近足月的胎儿绵羊接受脐尿管结扎以消除尿囊液。在食管和气管周围放置一个可充气的袖带，并将导管分别置于胎儿膀胱、胎儿循环和母体循环中。术后≥5天时，将动物分为对照组或进行8小时持续尿液引流加气管食管闭塞实验。
在尿液引流加闭塞实验期间，与对照实验相比，羊水渗透压（p<0.0001）、Na+（p<0.0001）、K+（p<0.01）、Cl-（p<0.001）和乳酸（p<0.001）升高。这相当于胎儿血浆与羊水之间渗透压和Na+梯度降低了50%；K+梯度升高，Cl-梯度逆转。8小时时，羊水中Na+、K+、Cl-和乳酸的增加百分比均为10%。
这些观察结果表明，水以每小时羊水总体积的1.25%或约240毫升/天的速率通过膜内途径从羊水吸收进入胎儿循环。
