Mujais S K, Chekal M A, Jones W J, Hayslett J P, Katz A I
J Clin Invest. 1985 Jul;76(1):170-6. doi: 10.1172/JCI111942.
The purpose of this study was to determine the nephron site, time course, and mechanism of mineralocorticoid action on renal tubular Na-K-ATPase in rats and rabbits, without dietary manipulation and by using the natural mineralocorticoid aldosterone. Sustained, high physiologic levels of circulating aldosterone mimicking those produced endogenously during potassium loading or sodium deprivation were provided by constant delivery of the hormone in doses of 5 or 50 micrograms/100 g body wt per 24 h, respectively, from osmotic minipumps implanted subcutaneously. In adrenal-intact rats receiving the 5-microgram dose, aldosterone levels were similar to those seen in animals fed a high K diet and produced a time-dependent increase in Na-K-ATPase activity in the cortical-collecting tubule (CCT) to a level 103% higher than in controls after 7 d (2,007 +/- 178 vs. 989 +/- 72 pmol/mm per h, P less than 0.001); the enzyme activity in the proximal convoluted tubule, medullary thick ascending limb, and the inner stripe of the medullary-collecting tubule did not change significantly. The increment in CCT Na-K-ATPase was larger (142%) in animals receiving for the same period of time the 50-micrograms dose, which produced circulating aldosterone levels similar to those of sodium-deprived rats. A significant stimulation of Na-K-ATPase activity was seen in the CCT of adrenalectomized rats after 24 h of treatment with either dose of the hormone, and at 12 h only in animals receiving the 50 micrograms/100 g per 24 h regimen. To determine whether the enhanced Na-K-ATPase activity produced by aldosterone is due to synthesis of new enzyme units or to alteration in its kinetics, we examined the ouabain-binding capacity and the affinity for Na and K of the enzyme from CCT of rabbits treated with 5 micrograms/100 g body wt per 24 h aldosterone for 3 d. These experiments revealed a parallel increment on Na-K-ATPase activity and specific [3H]ouabain binding in aldosterone-treated rabbits, while the affinity of the enzyme for either sodium or potassium was unaltered. The results of this study indicate that high physiologic levels of aldosterone simulating those measured during K loading or Na deprivation lead to a segment-specific increase in Na-K-ATPase activity in the CCT. This effect was time-and dose-dependent and was due to an increase in the number of active enzyme units. The segmental specificity and time course of the increase in enzyme activity suggest that modulation of Na-K-ATPase by aldosterone plays a role in the chronic adaptation of the CCT to altered availability of sodium and potassium, and therefore in the homeostasis of these cations by the kidney.
本研究的目的是在不进行饮食干预的情况下，通过使用天然盐皮质激素醛固酮，确定大鼠和兔子体内盐皮质激素对肾小管钠钾ATP酶作用的肾单位部位、时间进程及作用机制。通过皮下植入的渗透微型泵，分别以每24小时5或50微克/100克体重的剂量持续输注激素，从而提供持续的、高生理水平的循环醛固酮，模拟钾负荷或钠缺乏时内源性产生的醛固酮水平。在接受5微克剂量的肾上腺完整大鼠中，醛固酮水平与喂食高钾饮食的动物相似，并使皮质集合管（CCT）中的钠钾ATP酶活性随时间增加，7天后比对照组高103%（2,007±178对989±72皮摩尔/毫米每小时，P<0.001）；近端曲管、髓袢升支粗段和髓质集合管内带的酶活性没有显著变化。在相同时间段内接受50微克剂量的动物中，CCT中钠钾ATP酶的增加幅度更大（142%），该剂量产生的循环醛固酮水平与钠缺乏大鼠相似。用任一剂量的激素治疗24小时后，在肾上腺切除大鼠的CCT中可见钠钾ATP酶活性有显著刺激，而仅在接受每24小时50微克/100克方案的动物中，12小时时可见该刺激。为了确定醛固酮产生的增强的钠钾ATP酶活性是由于新酶单位的合成还是其动力学改变，我们检测了用每24小时5微克/100克体重醛固酮处理3天的兔子CCT中酶的哇巴因结合能力以及对钠和钾的亲和力。这些实验显示，在醛固酮处理的兔子中，钠钾ATP酶活性和特异性[3H]哇巴因结合平行增加，而酶对钠或钾的亲和力未改变。本研究结果表明，模拟钾负荷或钠缺乏时测得的高生理水平醛固酮会导致CCT中钠钾ATP酶活性出现节段特异性增加。这种作用具有时间和剂量依赖性，且是由于活性酶单位数量增加所致。酶活性增加的节段特异性和时间进程表明，醛固酮对钠钾ATP酶的调节在CCT对钠和钾可用性改变的慢性适应中起作用，因此在肾脏对这些阳离子的稳态维持中也起作用。
