Gowrishankar M, Lenga I, Cheung R Y, Cheema-Dhadli S, Halperin M L
Renal Division, St. Michael's Hospital, University of Toronto, Canada.
Kidney Int. 1998 Jan;53(1):159-66. doi: 10.1046/j.1523-1755.1998.00750.x.
We evaluated whether altering the rate of excretion of sodium (Na) and chloride (Cl) when antidiuretic hormone (ADH) acts would cause urea to behave as an 'effective' or 'ineffective' urinary solute. Urine composition was compared to that in the excised papillary tip in rats treated with DDAVP while on a normal or a low electrolyte diet; half the rats were given a urea load. Studies were also carried out in humans who were water restricted for 12 to 16 hours and given DDAVP. One group had a high rate of NaCl excretion induced by a thiazide diuretic, while the other group consumed a low salt diet to decrease the rate of excretion of electrolytes. Urea (3 mmol/kg) was ingested after the control urine samples were collected. On the high salt protocols, the urine flow rate was directly proportional to the rate of excretion of electrolytes ('non-urea' osmoles) and there was no change in the 'non-urea' osmolality despite large changes in Na and Cl excretion rates. After urea was administered, there was no change in urine flow rate, 'non-urea' osmolality, or 'non-urea' osmole excretion rate, whereas the urinary urea concentration, urine osmolality and the rate of excretion of urea were higher. The papilla of the salt-loaded rats had a similar urea concentration to that in the urine. In contrast, in the low electrolyte excretion protocols, the sum of the concentrations of 'non-urea' osmoles in the urine was much lower than that in the excised papilla, and the converse applied to urea. Similar changes were observed in the composition of the urine in human subjects with high and low rates of excretion of electrolytes. We conclude that urea appears to be an 'ineffective' urine osmole when there is a high rate of salt excretion, whereas urea is an 'effective' osmole when there is a low rate of excretion of electrolytes.
我们评估了在抗利尿激素（ADH）起作用时改变钠（Na）和氯（Cl）的排泄速率是否会使尿素表现为“有效”或“无效”的尿溶质。将正常或低电解质饮食的大鼠用去氨加压素（DDAVP）处理后，比较其尿液成分与切除的乳头尖端的尿液成分；一半的大鼠给予尿素负荷。还对禁水12至16小时并给予去氨加压素的人类进行了研究。一组通过噻嗪类利尿剂诱导高NaCl排泄率，而另一组食用低盐饮食以降低电解质排泄率。在收集对照尿液样本后摄入尿素（3 mmol/kg）。在高盐方案中，尿流率与电解质（“非尿素”渗透摩尔）排泄率成正比，尽管Na和Cl排泄率有很大变化，但“非尿素”渗透压没有变化。给予尿素后，尿流率、“非尿素”渗透压或“非尿素”渗透摩尔排泄率没有变化，而尿尿素浓度、尿渗透压和尿素排泄率更高。高盐负荷大鼠的乳头尿素浓度与尿液中的相似。相反，在低电解质排泄方案中，尿液中“非尿素”渗透摩尔浓度之和远低于切除的乳头中的浓度，而尿素则相反。在电解质排泄率高和低的人类受试者的尿液成分中也观察到了类似的变化。我们得出结论，当盐排泄率高时，尿素似乎是一种“无效”的尿渗透摩尔，而当电解质排泄率低时，尿素是一种“有效”的渗透摩尔。
