de Rouffignac C, Morel F
J Clin Invest. 1969 Mar;48(3):474-86. doi: 10.1172/JCI106005.
The mechanism by which the osmotic pressure increases in tubular fluid along the descending limb of the loop of Henle was examined in Psammomys undergoing salt diuresis. In two series of experiments, micropuncture samples were collected either from proximal and distal convolutions at the surface of the cortex, or from loops of Henle and collecting ducts at the surface of the extrarenal part of the papilla. Inulin-(3)H, urea-(14)C, Na(+), and K(+) concentrations, as well as osmotic pressure, were determined in all micropuncture samples.Net movements of water along the descending and ascending limbs of the loop could not be deduced by comparing inulin data obtained from convoluted tubules and from loops of Henle, since there appeared to be a large difference in the filtration rate of the superficial glomeruli (9 nl/min) and the deep ones (21.4 nl/min) under the conditions of these experiments. The results indicate that no large net movement of water occurred along the loop since a) only 23% of the filtrate was reabsorbed along the loop of Henle (including pars recta) of superficial nephrons despite the fact that all these loops reached markedly hypertonic regions; b) there was no positive correlation between (F/P)(In) in early distal samples and the simultaneous osmotic pressure of the urine; c) when (F/P)(In) and (F/P)(Osm) in loop samples were correlated, the increase in inulin concentration accounted only for 15% of the increase in osmotic pressure. Therefore, 85% of the concentrating process taking place along the descending limb must have resulted from net addition of solutes; this was directly supported by Na(+) and K(+) measurements in the loop samples, which showed that, at the tip of the loops, the Na(+) and K(+) flow rates were correlated to the osmotic pressure. Moreover, since the load of Na(+) urea flow rate in superficial early distal tubules was constant and independent of the urinary osmotic pressure, it is suggested that a medullary recycling of both ions occurred between ascending and descending limbs.Urea-(14)C concentration in the loop samples indicates a net addition of urea into the descending limb; the mean and K(+) delivered to the distal superficial tubules was 4.18 times its filtration rate, suggesting a recycling of urea from collecting ducts to Henle's loops. The permeability properties of the wall of the thin descending limb are discussed in relation to the obtained results.
在盐利尿状态下的沙地鼠中，研究了沿亨利氏袢降支肾小管液渗透压升高的机制。在两组实验中，微穿刺样本要么取自皮质表面的近曲小管和远曲小管，要么取自乳头肾外部分表面的亨利氏袢和集合管。测定了所有微穿刺样本中的菊粉 -（³H）、尿素 -（¹⁴C）、Na⁺和K⁺浓度以及渗透压。由于在这些实验条件下，浅表肾小球（9 nl/min）和深部肾小球（21.4 nl/min）的滤过率似乎存在很大差异，所以无法通过比较取自曲小管和亨利氏袢的菊粉数据来推断沿袢降支和升支的水的净移动情况。结果表明，沿袢没有发生大量的水的净移动，因为：a）尽管所有这些袢都到达明显高渗区域，但浅表肾单位的亨利氏袢（包括直部）仅重吸收了23%的滤液；b）早期远曲小管样本中的（F/P）（菊粉）与同时的尿液渗透压之间没有正相关；c）当袢样本中的（F/P）（菊粉）和（F/P）（渗透压）相关时，菊粉浓度的增加仅占渗透压增加的15%。因此，沿降支发生的浓缩过程的85%一定是由于溶质的净添加导致的；这在袢样本中的Na⁺和K⁺测量中得到了直接支持，测量结果表明，在袢的顶端，Na⁺和K⁺流速与渗透压相关。此外，由于浅表早期远曲小管中Na⁺尿素流速的负荷是恒定的，且与尿液渗透压无关，所以提示在升支和降支之间发生了两种离子的髓质再循环。袢样本中的尿素 -（¹⁴C）浓度表明尿素净添加到降支中；输送到远曲浅表小管的平均K⁺是其滤过率的4.18倍，提示尿素从集合管再循环到亨利氏袢。结合所得结果讨论了细降支壁的通透性特性。
