Rabkin R, Palathumpat M, Tsao T
Department of Veterans Affairs Medical Center, Palo Alto, California.
Lab Invest. 1993 Apr;68(4):427-38.
Since renal hypertrophy occurs in conditions associated with increased renal ammonia genesis it has been suggested that ammonia may stimulate renal growth. Indeed, quiescent cultured tubular epithelial cells exposed to NH4Cl undergo hypertrophy. However, ammonia inhibits liver regeneration in vivo and proliferation of cultured fibroblasts. This study was designed to evaluate the effect of ammonia (NH3/NH4+) as a regulator of kidney cell hypertrophy and also kidney cell proliferation.
Cultured opossum kidney cells and primary rabbit proximal tubular epithelial cells were grown with or without (controls) NH4Cl present.
After 3 days exposure to 5-20 mM NH4Cl, there was a dose-dependent depression of cell replication that ranged between 8 and 63% compared with controls (p < 0.017). In contrast, cell volume and protein content were significantly greater in the NH4Cl-treated cells. At 20 mM NH4Cl the protein content of treated cells exceeded that of controls by as much of 75%. This difference in protein content could, in part, be related to the disparity in cell density. However, experiments performed with cells at similar density revealed that NH4Cl also has a direct effect on cell protein content that increased by 25%; this appeared to be a consequence of depressed protein breakdown and was not due to altered protein synthesis. Experiments with rabbit kidney cells revealed that inhibition of replication was associated with a decrease in DNA [3H]thymidine incorporation. Cell cycle analysis revealed a fall in the proportion of cells in the S + G2 + M phase compared with controls (22 versus 30%, respectively; p < 0.01). NH4Cl also inhibited the burst of replication that followed chemically induced hypoxic injury of quiescent opossum kidney cells.
We conclude that in addition to inducing hypertrophy, NH4Cl can inhibit tubular cell proliferation. Thus, while heightened ammoniagenesis in vivo may favor hypertrophy, this in vitro study raises the question whether an elevated intrarenal ammonia content might be harmful when cell replication is required. Acute tubular necrosis is a condition in which elevated ammonia levels and a requirement for cell replication coexist and could serve as an important model to study this question.
由于肾肥大发生于肾氨生成增加的情况下，因此有人提出氨可能刺激肾脏生长。实际上，暴露于氯化铵的静止培养肾小管上皮细胞会发生肥大。然而，氨在体内会抑制肝脏再生以及培养的成纤维细胞的增殖。本研究旨在评估氨（NH₃/NH₄⁺）作为肾细胞肥大和肾细胞增殖调节因子的作用。
培养的负鼠肾细胞和原代兔近端肾小管上皮细胞在有或无（对照）氯化铵的情况下生长。
暴露于5 - 20 mM氯化铵3天后，细胞复制出现剂量依赖性抑制，与对照相比，抑制范围在8%至63%之间（p < 0.017）。相反，氯化铵处理的细胞的细胞体积和蛋白质含量显著更高。在20 mM氯化铵时，处理细胞的蛋白质含量比对照高出多达75%。蛋白质含量的这种差异部分可能与细胞密度的差异有关。然而，对密度相似的细胞进行的实验表明，氯化铵对细胞蛋白质含量也有直接影响，蛋白质含量增加了25%；这似乎是蛋白质分解受抑制的结果，而不是由于蛋白质合成改变。对兔肾细胞的实验表明，复制抑制与DNA [³H]胸苷掺入减少有关。细胞周期分析显示，与对照相比，处于S + G₂ + M期的细胞比例下降（分别为22%和30%；p < 0.01）。氯化铵还抑制了静止负鼠肾细胞化学诱导的缺氧损伤后出现的复制爆发。
我们得出结论，除了诱导肥大外，氯化铵还可抑制肾小管细胞增殖。因此，虽然体内氨生成增加可能有利于肥大，但这项体外研究提出了一个问题，即当需要细胞复制时，肾内氨含量升高是否可能有害。急性肾小管坏死是一种氨水平升高和细胞复制需求并存的情况，可作为研究这个问题的重要模型。
