Lin S H, Cheema-Dhadli S, Gowrishankar M, Marliss E B, Kamel K S, Halperin M L
Renal Division, National Defense Medical Center, Taipei, Taiwan, Republic of China.
Am J Physiol. 1997 Nov;273(5):F796-800. doi: 10.1152/ajprenal.1997.273.5.F796.
A deficit of K+ of close to 300 mmol develops in the first 2 wk of fasting, but little further excretion of K+ occurs, despite high levels of aldosterone and the delivery of ketoacid anions that are not reabsorbed in the distal nephron. Our purpose was to evaluate how aldosterone could have primarily NaCl-retaining, rather than kaliuretic, properties in this setting. To evaluate the role of distal delivery of Na+, four fasted subjects received an acute infusion of NaCl to induce a natriuresis. To assess the role of distal delivery of HCO3-, five fasted subjects were given an infusion containing NaHCO3. The natriuresis induced by an infusion of NaCl caused only a small rise in the rate of excretion of K+ (0.8 +/- 0.1 to 1.9 +/- 0.3 mmol/h); in contrast, when HCO3- replaced Cl- in the infusate, K+ excretion rose to 8.3 +/- 2.2 mmol/h, despite little excretion of HCO3- (urine, pH 5.8) and similar rates of excretion of Na+. The transtubular K+ concentration gradient was 19 +/- 3 with HCO3- and 6 +/- 2 with NaCl. We conclude that the infusion of NaHCO3 led to an increase in K+ excretion, likely reflecting an increased rate of distal K+ secretion. With a low distal delivery of HCO3-, aldosterone acts as a NaCl-retaining, rather than a kaliuretic, hormone.
禁食的前2周会出现近300 mmol的钾缺乏，但尽管醛固酮水平较高且有酮酸阴离子进入远曲小管且不被重吸收，钾的进一步排泄却很少。我们的目的是评估在这种情况下醛固酮如何主要具有保氯化钠而非促尿钾排泄的特性。为评估远曲小管钠的输送作用，4名禁食受试者接受了一次急性氯化钠输注以诱导利钠作用。为评估远曲小管碳酸氢根的输送作用，5名禁食受试者接受了含碳酸氢钠的输注。输注氯化钠诱导的利钠作用仅使钾排泄率小幅升高（从0.8±0.1 mmol/h升至1.9±0.3 mmol/h）；相比之下，当输注液中碳酸氢根替代氯离子时，尽管几乎没有碳酸氢根排泄（尿液pH 5.8）且钠排泄率相似，但钾排泄率升至8.3±2.2 mmol/h。碳酸氢根时的跨肾小管钾浓度梯度为19±3，而氯离子时为6±2。我们得出结论，输注碳酸氢钠导致钾排泄增加，可能反映了远曲小管钾分泌率增加。在远曲小管碳酸氢根输送量低的情况下，醛固酮起到保氯化钠而非促尿钾排泄激素的作用。
