Thornburg K L, Binder N D, Faber J J
J Dev Physiol. 1979 Feb;1(1):47-60.
Experiments were performed on unanaesthetized ewes in the last third of pregnancy. Fetuses and ewes had indwelling vascular catheters. In some of the experiments fetal urine was drained to the exterior by means of an indwelling vesicular catheter. Placental diffusion permeabilities were measured with 22Na+ and 36Cl- injected into eight fetuses. Volumes of distribution of Na+ and Cl- in the conceptus were Na+: 548 +/- 24, Cl-: 760 +/- 51 (ml/kg fetal wt +/- SEM). Diffusion permeabilities were Na+: 5.2 X 10(-3) +/- 0.3 X 10(-3), Cl-: 9.8 X 10(-3) +/- 0.9 X 10(-3) (ml.s-1.kg-1 +/- SEM). Ultrafiltration-reflection-coefficients of Na+ and Cl- in the placental exchange barrier were measured 17 times in seven fetuses with vesicular catheters. The transplacental e.m.f. was estimated from these results, on the assumption that the individual reflection-coefficients of Na+ should correlate with those of Cl-. The best estimate was -1.0 mV (fetus negative), and the best estimates of the placental reflection-coefficients were Na+: 0.83 and Cl-: 0.79. There was a reliable negative correlation (P < 0.01) between the calculated reflection-coefficients and the osmolality of the urine secreted by the fetus. This suggested that the concentration of vasopressin in fetal plasma affects the membrane characteristics of the placenta. The mean total osmotic force across the placental barrier of the sheep in these experiments was calculated to be 260 Pa (2 mmHg).
实验在妊娠后期未麻醉的母羊身上进行。胎儿和母羊均留置了血管导管。在一些实验中，通过留置的膀胱导管将胎儿尿液引流至体外。向8只胎儿注射22Na+和36Cl-来测量胎盘扩散通透性。胎儿体内Na+和Cl-的分布容积分别为：Na+：548±24，Cl-：760±51（ml/kg胎儿体重±标准误）。扩散通透性分别为：Na+：5.2×10(-3)±0.3×10(-3)，Cl-：9.8×10(-3)±0.9×10(-3)（ml·s-1·kg-1±标准误）。在7只带有膀胱导管的胎儿身上，对胎盘交换屏障中Na+和Cl-的超滤反射系数进行了17次测量。根据这些结果，在假设Na+的个体反射系数应与Cl-的反射系数相关的前提下，估算了经胎盘的电动势。最佳估算值为-1.0 mV（胎儿为负），胎盘反射系数的最佳估算值为：Na+：0.83，Cl-：0.79。计算得到的反射系数与胎儿分泌尿液的渗透压之间存在可靠的负相关（P<0.01）。这表明胎儿血浆中血管加压素的浓度会影响胎盘的膜特性。在这些实验中，计算得出绵羊胎盘屏障上的平均总渗透力为260 Pa（2 mmHg）。
