Buerkert J, Martin D, Trigg D, Simon E
J Clin Invest. 1983 Jun;71(6):1661-75. doi: 10.1172/jci110921.
Papillary and surface micropuncture were used to study the handling of ammonium and the formation of net acid by surface nephrons, deep nephrons, and the terminal segment of collecting duct (CD) after renal mass was reduced by two-thirds. Net acid excretion by the remnant kidney (RK) was significantly reduced, averaging 794+/-81 neq/min (SE) compared with 1,220+/-105 neq/min after sham operation (P < 0.001), due to a decrease in ammonium excretion (494+/-54 vs. 871+/-79 nmol/min in controls, P < 0.001). Urinary pH and titratable acid excretion were not different in the two groups of animals. After RK formation, ammonium delivery to the end of the proximal tubule increased nearly threefold and averaged 66.2+/-5.6 compared with 18.4+/-2.9 pmol/min in controls, (P < 0.001). This greater delivery of ammonium was primarily due to renal tubule entry rather than to changes in the filtered load and was only partially related to the differences in flow rate. Ammonium processing by deep nephrons was profoundly affected by a reduction in renal mass. Although absolute delivery of ammonium was greater to the bend of Henle's loop (BHL), the difference could be accounted for on the basis of an increase in nephron size. Thus, fractional delivery (FD(NH+4)) to this site was not different for the two groups of animals, averaging 1,567+/-180% in controls and 1,400+/-181% in the group with the RK. Hydrogen secretion in the proximal segments of deep and surface nephrons did not increase in proportion to the decrease in renal mass and as a consequence bicarbonate delivery to the end of the proximal tubule of surface nephrons and to the BHL of deep nephrons was increased. When renal mass was reduced FD(NH+4) to the base of the terminal CD doubled but did not change by the tip. In both groups FD(NH+4) to the base of the CD was greater than to the end of the distal tubule. However, the increase was the same. On the other hand, the increase in the net acid index between the end of the distal tubule and the base of the CD was profoundly greater in rats with an RK. This difference was primarily due to bicarbonate reabsorption rather than enhanced ammonium reentry. Indeed, >400% of the fractional ammonium delivered to the end of the proximal tubule was lost from the tubule fluid. The data suggest that the decrease in acid excretion by the RK is due to two factors. First, hydrogen secretion in the proximal segments of both nephron populations fails to increase in the proportion to the reduction in renal mass. Second, a reduced reentrapment of ammonia, rather than its impaired production, causes ammonium excretion to decrease.
采用乳头微穿刺和表面微穿刺技术，研究了肾切除三分之二后，浅表肾单位、深部肾单位和集合管终末段对铵的处理及净酸生成情况。残余肾（RK）的净酸排泄显著减少，平均为794±81纳当量/分钟（标准误），而假手术组为1220±105纳当量/分钟（P<0.001），这是由于铵排泄减少（494±54对对照组的871±79纳摩尔/分钟，P<0.001）。两组动物的尿pH值和可滴定酸排泄无差异。RK形成后，近端小管末端的铵输送增加了近三倍，平均为66.2±5.6，而对照组为18.4±2.9皮摩尔/分钟（P<0.001）。铵输送增加主要是由于肾小管重吸收，而非滤过负荷的变化，且仅部分与流速差异有关。深部肾单位对铵的处理受到肾质量减少的显著影响。尽管到达亨氏袢转折处（BHL）的铵绝对输送量更大，但这种差异可归因于肾单位大小的增加。因此，两组动物输送至该部位的分数输送量（FD(NH+4)）无差异，对照组平均为1567±180%，RK组为1400±181%。深部和浅表肾单位近端段的氢分泌并未与肾质量的减少成比例增加，结果是浅表肾单位近端小管末端和深部肾单位BHL的碳酸氢盐输送增加。肾质量减少时，输送至集合管终末段底部的FD(NH+4)增加了一倍，但在顶端未发生变化。两组中，输送至集合管底部的FD(NH+4)均大于输送至远端小管末端的量。然而，增加幅度相同。另一方面，RK大鼠远端小管末端与集合管底部之间的净酸指数增加幅度更大。这种差异主要是由于碳酸氢盐重吸收增加，而非铵再进入增强。实际上，输送至近端小管末端的分数铵中有>400%从肾小管液中丢失。数据表明，RK酸排泄减少是由两个因素导致的。首先，两个肾单位群体近端段的氢分泌未能与肾质量的减少成比例增加。其次，氨的再捕获减少，而非其生成受损，导致铵排泄减少。
