Mann S E, Fresquez M, Ross M G
Perinatal Research Laboratories, Department of Obstetrics and Gynecology, University of California Los Angeles School of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA.
Am J Obstet Gynecol. 2000 Oct;183(4):933-6. doi: 10.1067/mob.2000.109051.
Human pregnancy results in a reduction in plasma osmolality and thus a reduction in the osmotic threshold for arginine vasopressin secretion. Although the functional characteristics of the osmoregulatory system controlling arginine vasopressin secretion have been carefully defined, determination of the osmotic threshold requires a complex, labor-intensive protocol of an intravenous hypertonic saline infusion. To aid in studies of osmotic threshold resetting in pregnancy, we sought to develop a simplified method for determination of this value.
Ten healthy nonpregnant women between the ages of 18 and 40 years were studied over 2 days. All patients were hospitalized, and morning euhydration was ensured by oral water hydration (5-10 mL/kg) the evening before the study. On the first study day, patients were fed a standard no-salt-added diet; plasma osmolality and sodium values were checked just before and 1 and 2 hours after meals. On the second study day, after fasting blood samples were obtained, patients received an intravenous infusion (0.06 mL. kg(-1). min(-1) for 120 minutes) of hypertonic (5%) saline to gradually increase the plasma sodium level. Blood samples were obtained every 15 minutes for measurement of plasma electrolytes and arginine vasopressin. Plasma arginine vasopressin concentrations were regressed against plasma osmolality and sodium concentration to calculate the osmotic threshold for arginine vasopressin secretion.
Hypertonic saline injection significantly increased plasma sodium (from 139 +/- 1 to 149 +/- 1 mEq/L) and osmolality (from 284 +/- 2 to 304 +/- 2 mOsm/kg H(2)O). Plasma arginine vasopressin significantly increased (from 5 +/- 1 to 30 +/- 10 pg/mL). The mean sodium and osmolality thresholds for arginine vasopressin secretion were calculated as 137 +/- 2 mEq/L and 285 +/- 15 mOsm/kg H(2)O. The mean morning fasting sodium level was nearly identical to the calculated sodium threshold, whereas the morning fasting osmolality value was significantly different.
The morning fasting, euhydrated sodium level can be used as a simplified index for the plasma osmotic threshold for arginine vasopressin secretion. This index may provide a useful predictive measure for pregnant women in whom the plasma volume does not expand.
人类妊娠会导致血浆渗透压降低，从而降低精氨酸加压素分泌的渗透阈值。尽管已经仔细定义了控制精氨酸加压素分泌的渗透调节系统的功能特征，但测定渗透阈值需要一套复杂且耗费人力的静脉输注高渗盐水方案。为了辅助妊娠中渗透阈值重置的研究，我们试图开发一种简化方法来测定该值。
对10名年龄在18至40岁之间的健康非妊娠女性进行了为期2天的研究。所有患者均住院，在研究前一晚通过口服补水（5 - 10 mL/kg）确保早晨处于正常水合状态。在第一个研究日，患者食用标准无盐饮食；在进餐前以及进餐后1小时和2小时检查血浆渗透压和钠值。在第二个研究日，在采集空腹血样后，患者接受静脉输注（0.06 mL·kg⁻¹·min⁻¹，持续120分钟）高渗（5%）盐水，以逐渐提高血浆钠水平。每15分钟采集血样以测量血浆电解质和精氨酸加压素。将血浆精氨酸加压素浓度与血浆渗透压和钠浓度进行回归分析，以计算精氨酸加压素分泌的渗透阈值。
注射高渗盐水显著提高了血浆钠水平（从139 ± 1 mEq/L升至149 ± 1 mEq/L）和渗透压（从284 ± 2 mOsm/kg H₂O升至304 ± 2 mOsm/kg H₂O）。血浆精氨酸加压素显著升高（从5 ± 1 pg/mL升至30 ± 10 pg/mL）。精氨酸加压素分泌的平均钠和渗透压阈值经计算分别为137 ± 2 mEq/L和285 ± 15 mOsm/kg H₂O。早晨空腹钠水平均值与计算出的钠阈值几乎相同，而早晨空腹渗透压值则有显著差异。
早晨空腹、处于正常水合状态下的钠水平可作为精氨酸加压素分泌的血浆渗透阈值的简化指标。该指标可能为血浆容量未增加的孕妇提供有用的预测指标。
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