Sanjana V M, Johnston P A, Robertson C R, Jamison R L
Am J Physiol. 1976 Aug;231(2):313-8. doi: 10.1152/ajplegacy.1976.231.2.313.
We recently demonstrated that net fluid uptake occurs in the capillary system of the inner medulla. To define the site of fluid uptake, the concentration of protein was determined in plasma from descending vasa recta at the base and tip of the exposed papilla in Munich-Wister rats. The vasa recta plasma-to-arterial plasma protein concentration ratio (VR/P) was 1.43 +/- 0.09 at the base and 1.66 +/- 0.09 at the tip. These results, which indicate fluid loss from the descending vasa recta, are difficult to explain on the basic of hydraulic and oncotic forces alone. The osmolality of the contents of descending vasa recta increased between base and tip (delta = 72 +/- 30 mosmol/kg H2O). If the increase in osmolality of plasma in descending vasa recta lags behind that of the adjacent medullary interstitium, a transcapillary osmotic driving force exists favoring water loss from descending vessels. It is concluded that fluid uptake by the inner medullary circulation occurs beyond descending vasa recta in interconnecting capillaries or ascending vasa recta. In our view the most likely interpretation of these results is that fluid movement across vasa recta in the inner medulla is influenced by three forces: those owing to transcapillary differences in osmotic, oncotic, and hydraulic pressures.
我们最近证实，内髓质的毛细血管系统存在净液体摄取。为了确定液体摄取的部位，我们测定了慕尼黑-维斯特大鼠暴露乳头基部和尖端下行直小血管血浆中的蛋白质浓度。直小血管血浆与动脉血浆蛋白质浓度比（VR/P）在基部为1.43±0.09，在尖端为1.66±0.09。这些结果表明下行直小血管有液体丢失，仅靠水力和胶体渗透压是难以解释的。下行直小血管内容物的渗透压在基部和尖端之间升高（Δ=72±30毫摩尔/千克H₂O）。如果下行直小血管血浆渗透压的升高滞后于相邻髓质间质的升高，则存在有利于下行血管失水的跨毛细血管渗透驱动力。得出的结论是，内髓质循环的液体摄取发生在下行直小血管之外的相互连接的毛细血管或上行直小血管中。我们认为，对这些结果最可能的解释是，内髓质中液体通过直小血管的移动受三种力的影响：由于跨毛细血管渗透压、胶体渗透压和液压压力差异产生的力。
