Häberle D A, von Baeyer H
Am J Physiol. 1983 Apr;244(4):F355-66. doi: 10.1152/ajprenal.1983.244.4.F355.
Glomerulotubular balance (GTB) is defined as the ability of each successive segment of the proximal tubule to reabsorb a constant fraction of glomerular filtrate and solutes delivered to it. For maintenance of GTB the coupling of peritubular blood flow and intratubular fluid flow to the process of glomerular filtration seems to be of functional importance since tubular fluid reabsorption is significantly altered when either or both parameters are experimentally changed. In the case of peritubular blood flow, variations of tubular fluid reabsorption have been ascribed to variations of the mean net colloid osmotic pressure in the peritubular blood and its effects on the paracellular backleak of tubular resorbate. This relationship has, however, been clearly demonstrated only in volume expansion, when GTB is impaired. Under nondiuretic conditions, in which GTB typically occurs, the importance of the peritubular colloid osmotic pressure in control of tubular fluid reabsorption is less clear since variations of peritubular colloid osmotic pressure within a physiologic range exert only a negligible influence on tubular fluid transport. Pharmacologically induced alterations of peritubular hemodynamics or mean net colloid osmotic pressure can affect tubular fluid reabsorption without consistently altering the net interstitial pressure. In the case of intratubular flow rate, variations of tubular fluid reabsorption are comparable to changes seen with GTB. Such an interrelation is found only in tubules perfused by natural tubular fluid. In individual nephrons flow-dependent reabsorption cannot always be observed even when it appears that GTB is preserved in that kidney. Flow dependency of tubular fluid reabsorption might be attributed to some properties or constituents in tubular fluid rather than to some intrinsic characteristics of the tubular epithelium. Because flow dependence and tubular fluid transport are homogeneous along the tubule, fluid reabsorption might be controlled by a mechanism akin to a flow reactor. As yet it is not possible to explain GTB exclusively by peritubular or luminal control alone.
球管平衡（GTB）的定义是近端小管的每个连续节段重吸收输送至该节段的肾小球滤过液和溶质的恒定比例的能力。为维持球管平衡，肾小管周围血流和管内液流与肾小球滤过过程的耦合似乎具有重要功能意义，因为当其中一个或两个参数经实验改变时，肾小管液重吸收会发生显著变化。就肾小管周围血流而言，肾小管液重吸收的变化归因于肾小管周围血液中平均净胶体渗透压的变化及其对肾小管重吸收物细胞旁回漏的影响。然而，这种关系仅在容量扩张导致球管平衡受损时得到明确证实。在通常发生球管平衡的非利尿条件下，肾小管周围胶体渗透压在控制肾小管液重吸收中的重要性尚不清楚，因为在生理范围内肾小管周围胶体渗透压的变化对肾小管液转运仅产生可忽略不计的影响。药物诱导的肾小管周围血流动力学或平均净胶体渗透压的改变可影响肾小管液重吸收，而不会持续改变净间质压力。就管内流速而言，肾小管液重吸收的变化与球管平衡时所见的变化相当。这种相互关系仅在由天然肾小管液灌注的小管中发现。在单个肾单位中，即使在该肾脏似乎保持球管平衡的情况下，也并非总能观察到流速依赖性重吸收。肾小管液重吸收的流速依赖性可能归因于肾小管液中的某些特性或成分，而非肾小管上皮的某些内在特征。由于沿小管的流速依赖性和肾小管液转运是均匀的，液体重吸收可能由类似于流动反应器的机制控制。迄今为止，仅靠肾小管周围或管腔控制来解释球管平衡是不可能的。
