Department of Medicine, Baylor College of Medicine, Houston, Texas, USA.
Division of Nephrology, Department of Medicine, Houston Methodist Hospital, Houston, Texas, USA.
Am J Nephrol. 2019;50(1):11-18. doi: 10.1159/000501190. Epub 2019 Jun 19.
The Edelman equation has long guided the expected response of plasma [Na+] to changes in sodium, potassium, and water balance, but recent short-term studies challenged its validity. Plasma [Na+] following hypertonic NaCl infusion in individuals on low-sodium diet fell short of the Edelman predictions supposedly because sodium restriction caused progressive osmotic inactivation of 50% of retained sodium. Here, we examine the validity of this challenge.
We evaluated baseline total body water (TBW) and Na+ space following acute hypertonic NaHCO3 infusion in dogs with variable sodium and potassium stores, including normal stores, moderate depletion (chronic HCl feeding), or severe depletion (diuretics and dietary NaCl deprivation).
TBW (percentage body weight) averaged 65.9 in normals, 62.6 in HCl-induced metabolic acidosis and moderate sodium and potassium depletion, and 57.6 in diuretic-induced metabolic alkalosis and severe sodium and potassium depletion (p < 0.02). Na+ space (percentage body weight) at 30, 60, and 90 min postinfusion averaged 61.1, 59.8, and 56.1, respectively, in normals (p = 0.49); 70.0, 74.4, and 72.1, respectively, in acidotic animals (p = 0.21); and 56.4, 55.1, and 54.2, respectively, in alkalotic animals (p = 0.41). Absence of progressive expansion of Na+ space in each group disproves progressive osmotic inactivation of retained sodium. Na+ space at each time point was not significantly different from baseline TBW in normal and alkalotic animals indicating that retained sodium remained osmotically active in its entirety. However, Na+ space in acidotic animals at all times exceeded by ∼16% baseline TBW (p < 0.01) signifying an early, but nonprogressive, osmotic inactivation of retained sodium, which we link to baseline bone-sodium depletion incurred during acid buffering.
Our investigation affirms the validity of the Edelman construct in normal dogs and dogs with variable sodium and potassium depletion and, consequently, refutes the recent observations in human volunteers subjected to dietary NaCl restriction.
长期以来，埃德尔曼方程一直指导着人们对血浆[Na+]在钠、钾和水平衡变化时的预期反应，但最近的短期研究对其有效性提出了挑战。在接受低钠饮食的个体中，接受高渗 NaCl 输注后，血浆[Na+]低于埃德尔曼的预测值，这是因为钠限制导致保留钠的 50%逐渐发生渗透失活。在这里，我们检查了这一挑战的有效性。
我们评估了接受急性高渗 NaHCO3 输注的具有不同钠和钾储存量的犬的基础总体液（TBW）和 Na+空间，包括正常储存量、中度耗竭（慢性 HCl 喂养）或严重耗竭（利尿剂和饮食性 NaCl 剥夺）。
TBW（体重百分比）在正常情况下平均为 65.9%，在 HCl 诱导的代谢性酸中毒和中度钠钾耗竭时为 62.6%，在利尿剂诱导的代谢性碱中毒和严重钠钾耗竭时为 57.6%（p<0.02）。在正常情况下，输注后 30、60 和 90 分钟的 Na+空间（体重百分比）平均分别为 61.1%、59.8%和 56.1%（p=0.49）；在酸中毒动物中分别为 70.0%、74.4%和 72.1%（p=0.21）；在碱中毒动物中分别为 56.4%、55.1%和 54.2%（p=0.41）。每组中 Na+空间的无逐渐扩张证明保留的钠没有逐渐发生渗透失活。在正常和碱中毒动物中，各时间点的 Na+空间与基础 TBW 无显著差异，表明保留的钠仍保持全部渗透性。然而，酸中毒动物的 Na+空间在所有时间点均超过基础 TBW 的 16%（p<0.01），这表明保留的钠发生了早期但非进行性的渗透失活，我们将其与酸缓冲期间发生的基础骨钠耗竭联系起来。
我们的研究证实了埃德尔曼构念在正常犬和具有可变钠钾耗竭的犬中的有效性，因此反驳了最近在接受饮食性 NaCl 限制的人类志愿者中观察到的结果。
