Dennis V W
Kidney Int. 1976 Nov;10(5):373-80. doi: 10.1038/ki.1976.123.
Segments of the proximal tubule of the rabbit kidney were perfused in vitro in order to examine the influence of bicarbonate on the reduction in fluid absorption that occurs following the acute administration of parathyroid hormone (PTH). Studies were performed using either normal ultrafiltrate as perfusion fluid and normal rabbit serum as bath or low bicarbonate ultrafiltrate as perfusion fluid and low bicarbonate rabbit serum as bath. Low bicarbonate fluids were prepared by replacement of bicarbonate with chloride. In the presence of normal concentrations of bicarbonate, the addition of PTH to the bath (1 U/ml) resulted in a decrease in the fluid absorption rate (Jv) from 1.13 +/- 0.08 to 0.60 +/- 0.04 nl/mm X min (p is less than 0.001) in 23 convoluted segments and from 0.64 +/- 0.05 to 0.46 +/- 0.05 nl/mm - mm (P less than 0.01) in ten straight portions. Simultaneous with the PTH-induced reduction in Jv, the chloride concentration in the collected fluid changed from 119.0 +/- 2.0 to 113.4 +/- 1.1 mEq/liter (P less than 0.01) in the pars convoluta and from 117.7 +/- 0.6 to 114.0 +/- 1.9 mEq/liter (P less than 0.01) in the pars recta. However, there was no change in the net flux of chloride which averaged 42.58 +/- 5.00 pEq/mm - min during the control periods. Additional studies were performed in eight convoluted segments during perfusion on a randomized basis with low bicarbonate fluids as well as during perfusion with fluids having normal levels of bicarbonate. As before, in the presence of normal levels of bicarbonate, PTH reduced Jv from 1.16 +/- 0.15 to 0.68 +/- 0.07 nl/mm - min (P less than 0.001) and the chloride concentration in the collected fluid ([Cl]o) from 118.6 +/- 2.9 to 111.6 +/- 1.3 mEq/liter (P less than 0.005). Substitution of low bicarbonate fluids for normal bicarbonate fluids resulted in a decrease in Jv from 1.16 +/- 0.15 to 0.74 +/- 0.10 nl/mm - min (P less than 0.001). In the presence of low bicarbonate fluids, the addition of PTH resulted in no further decrease in Jv (0.74 +/- 0.10 vs. 0.72 +/- 0.10 nl/mm - min). These data indicate that in the proximal tubule the PTH-induced reduction in fluid absorption may be mediated by changes in bicarbonate absorption.
为了研究碳酸氢盐对急性给予甲状旁腺激素（PTH）后液体吸收减少的影响，对兔肾近端小管节段进行了体外灌注实验。实验采用正常超滤液作为灌注液、正常兔血清作为浴液，或低碳酸氢盐超滤液作为灌注液、低碳酸氢盐兔血清作为浴液。低碳酸氢盐溶液通过用氯离子替代碳酸氢盐来制备。在正常碳酸氢盐浓度存在的情况下，向浴液中添加PTH（1 U/ml）导致23个曲段的液体吸收率（Jv）从1.13±0.08降至0.60±0.04 nl/mm×min（p＜0.001），10个直段的液体吸收率从0.64±0.05降至0.46±0.05 nl/mm - mm（P＜0.01）。与PTH诱导的Jv降低同时，在曲部收集液中的氯离子浓度从119.0±2.0变为113.4±1.1 mEq/升（P＜0.01），在直部从117.7±0.6变为114.0±1.9 mEq/升（P＜0.01）。然而在对照期，氯离子的净通量没有变化，平均为42.58±5.00 pEq/mm - min。在另外8个曲段上进行了额外研究，随机使用低碳酸氢盐溶液灌注以及用正常碳酸氢盐水平的溶液灌注。如前所述，在正常碳酸氢盐水平存在时，PTH使Jv从1.16±0.15降至0.68±0.07 nl/mm - min（P＜0.001），收集液中的氯离子浓度（[Cl]o）从118.6±2.9变为111.6±1.3 mEq/升（P＜于0.005）。用低碳酸氢盐溶液替代正常碳酸氢盐溶液导致Jv从1.16±0.15降至0.74±0.10 nl/mm - min（P＜0.001）。在低碳酸氢盐溶液存在时，添加PTH未导致Jv进一步降低（0.74±0.10对比0.72±0.10 nl/mm - min）。这些数据表明，在近端小管中，PTH诱导的液体吸收减少可能由碳酸氢盐吸收的变化介导。
