Background

Cardiac disease is the major cause of death in hemodialysis patients (HD). It is now clear that aldosterone has deleterious effects in the cardiovascular system. In the present study, we evaluated the effects of an aldosterone-antagonist, spironolactone, on the extrarenal regulation of potassium in HD patients. Furthermore, to validate the effectiveness of the spironolactone dose-design, we measured the expression of Na⁺-channel (ENaC alpha subunit) in peripheral blood mononuclear cells (PBMC), before and after a two-week course of spironolactone.

Methods

The study design included a two-week baseline period, followed by spironolactone treatment (50 mg three times weekly for 15 days), and by a two-week washout period and then a two-week placebo period. An oral K⁺ load (0.3 mEq/K⁺ kg body weight plus carbohydrates) was administered at the end of each period, and time-course of plasma potassium was evaluated. ENaC expression in PBMC was assessed before and after spironolactone.

Results

The maximal increase in plasma potassium after the K⁺ carbohydrate load was: control 5.33 0.88 mEq K⁺/L; spironolactone 5.23 0.68 mEq K⁺/L; placebo 5.38 0.61 mEq K⁺/L (N = 9). No patients developed hyperkalemia during the spironolactone treatment period. ENaC expression was significantly higher in all six HD patients studied, compared to control subjects (P < 0.05). Treatment with spironolactone in HD patients reduced alpha subunit mRNA expression to values similar to those of normal subjects.

Conclusion

Spironolactone may be considered for the treatment of selected chronic HD patients. The effect of the drug on a known target of aldosterone, the ENaC, demonstrates the effectiveness of the drug to block aldosterone effects in nonepithelial tissues.

METHODS

Patients

Study participants were recruited from the Nephrology Dialysis Unit at Clínica Dávila Center. Subjects were anuric and had been in chronic HD therapy three times per week, for at least 18 months. Subjects were excluded if they were experiencing symptomatic congestive heart failure, uncontrolled hypertension (blood pressure greater than 170/100 mm Hg), cirrhosis or chronic liver disease, diabetes mellitus, or treatment with ACEIs, angiotensin receptor antagonist (ATR), or beta-blockers. HD patients who had serum potassium >6 mEq/L were excluded. None of the patients used ion-exchange resins before or during the study. All the patients were under standard diet, and no dietary changes were indicated during the study. Besides our routine procedures and controls, the protocol in this study included a dietary survey and blood potassium measurements before each HD session during the study period. The protocol was approved by the Ethics Committees of both the Faculty of Medicine, Universidad Los Andes, and of Clínica Dávila. Written informed consent was obtained from each subject prior to study participation.

Study design

The design was a sequential, fixed-dose, doubled-blind, and single-center trial. The study design included an initial baseline period as illustrated in Figure 1, followed by a two-week treatment period with 50 mg spironolactone (Aldactone^®; Pharmacia AG, Peapack, NJ, USA). After a two-week washout period, placebo was administered for 15 days. Aldactone or placebo was taken three times/week immediately after the HD session to ensure treatment adherence. At the end of the drug period and just before a new HD session, an oral potassium load was administered to test potassium tolerance of the patients during basal, spironolactone, or placebo period. Aldactone or placebo was given by the nurses in charge—not related to the investigator team—according to the schedule, three times/week immediately after the HD session to ensure treatment adherence. Throughout the study, measurements of serum potassium were performed before each dialysis session in the three aforementioned conditions.

Figure 1.

Study design. Black bars denote administration of 50 mg aldactone, three times a week, or placebo, as indicated. Washout period in between study medications was two weeks in duration. Potassium-carbohydrate load was given at the end of each period. Blood samples were taken as indicated in Methods.

Full figure and legend (8K)

Standard dialysis conditions included polysulfone filters 1.8 m² (F8), Qs = 300 mL/min, Qd = 500 mL/min; 140 mEq/L Na⁺, 2 mEq/L K⁺, 32 mEq/L HCO₃^-, and 100 mg/dL of glucose.

Oral potassium load

After a fasting period of 12 hours, each subject received an oral mixed load of carbohydrates (Ensure Plus, 0.5 g/kg body weight) with 0.3 mEq K⁺/kg of dry body weight. The potassium load was administered before the midweek HD session. Plasma samples were collected at -30, 0, 30, 60, 120 minutes before dialysis started. Also, a final sample was taken at the end of the dialysis (360 minutes) to measure serum potassium. Plasma aldosterone, insulin, and glucose were measured at the times indicated in Results. Plasma renin activity (PRA) was measured before potassium load.

Laboratory analysis

Serum electrolytes were measured by ion selective electrodes. Plasma aldosterone, insulin, and PRA levels were assessed by radioimmunoassay.

Preparation of peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMC) from patients and healthy donors were separated from venous blood collected in EDTA for preservation. Blood samples were diluted in phosphate-buffered saline at 1 part blood to 1 part buffer. PBMC were isolated by Histopaque 1077 (Sigma, St. Louis, MO, USA) density centrifugation, according to instructions by the manufacturer (Boyum). The interface mononuclear cell layer was washed twice with phosphate-buffered saline.

ENaC mRNA expression of alpha subunit

To assess alpha mRNA expression, we isolated total RNA from PBMC of a group of HD patients before and after two weeks of aldactone treatment. Also, blood samples were taken from a group of healthy volunteers. Total RNA was isolated from PBMC using Trizol (Invitrogen-Life Technologies, Carlsbad, CA, USA) per specifications of the manufacturer. RNA concentration was determined by spectrophotometry, and integrity of the RNA was assessed by agarose gel electrophoresis. Total RNA (1 g) was reverse transcribed with random hexamers and Improm II™ Reverse Transcriptase (Promega Corporation, Madison, WI, USA) at 42°C for 60 minutes. The synthesized cDNA was immediately stored at -20°C. Double-stranded cDNAs for the sodium channel (ENaC) subunit were amplified as follows: 2 L was mixed with 23 L of 1 buffer solution [Tris-HCl 75 mmol/L, pH 8,8, (NH₄)₂SO₄ 20 mmol/L, Tween 20 0.01%] containing 0.2 mmol/L dNTP, a pair of flanking PCR primers (0.1 mol/L each), 2.5 U of Taq DNA polymerase (Fermentas, Hanover, MD, USA), and 2.5 mmol/L MgCl₂. Primer sequences: sense primer (5'- GAA CAA CTC CAA CCT CTG GAT GTC) and antisense primer (5'- TCT TGG TGC AGT CGC CAT AAT C -3') amplified a 257 bp fragment. As an internal control, universal 18S ribosomal RNA (Ambion, Austin, TX, USA) was used for PCR amplification, to yield a 315-bp product. PCR conditions were 94°C for 3 minutes, 94°C for 30 seconds, 60°C for 30 seconds, and 72°C for 30 seconds for 30 cycles for EnaC, and 13 cycles for 18S in a DNA Thermal Cycler (Mastercycler personal; Eppendorf, Hamburg, Germany). The PCR products were subjected to electrophoresis on 2.0% agarose gels containing Gel star fluorescent dye for densitometry analysis (EDAS 120; Kodak Digital Science, Rochester, NY, USA).

Statistical analysis

The results were expressed as mean SE. Comparison between the three different treatment conditions was performed using one-way analysis of variance (ANOVA) and Student t test. Statistical significance was assessed at values of P < 0.05.

To estimate the distribution of the potassium load translocated to the intracellular space, first we calculated the maximal rise in the measured plasma potassium after the potassium load (K⁺_max). The amount of potassium present in the extracellular space was calculated by multiplying K⁺_max by extracellular fluid space, estimated as 20% of the body weight. Assuming no potassium loss during the experimental period, the percentage of the retained potassium translocated to the intracellular space was calculated¹⁷.

RESULTS

Patient characteristics

Nine patients that fulfilled the clinical criteria indicated in Methods were included in the study (four female and five males). All of them completed the three periods. They had been in dialysis for at least 18 months (mean dialysis time 39 months). Mean age was 43.1 years (range 16 to 76 years old). Mean plasma creatinine values were 9.2 0.3 mg/dL during the study period.

Table 1 includes baseline clinical predialysis values of the nine patients before the oral potassium load at the end of each treatment. No side effects were noted during the eight-week study period, and no patients required discontinuation of the study for spironolactone-related adverse events. Predialysis serum potassium levels were measured throughout the study before each dialysis. Measurements of serum potassium, performed before each dialysis session, demonstrated no significant differences in predialysis plasma potassium levels in the study period; plasma potassium with spironolactone treatment fluctuated between 4.2 to 5.5 mEq K⁺/L during the two weeks of drug administration. (Mean value SD: 4.52 0.44).

Table 1 - Baseline predialysis parameters at the end of each treatment period.

Full table

Potassium load

An oral potassium and carbohydrate load (0.3 mEq K⁺/kg of dry body weight) was administered to each patient before the midweek dialysis session under three different conditions: predrug treatment, spironolactone, and placebo, in order to compare extrarenal potassium handling. As shown in Figure 2, plasma potassium values were elevated from 4.54 0.15 mEq/L up to 5.33 0.3 after 90 minutes of potassium-carbohydrate load during the predrug period. Similar results were obtained at the end of the spironolactone period, when a second oral potassium-carbohydrate load was administered. During the third phase, after a two-week washout period each patient received placebo for two weeks, and finally, a third potassium load was administered. Plasma potassium time courses after the potassium-carbohydrate load are included in Figure 2. As expected, the oral potassium load induced a significant increase in plasma potassium levels, reaching peak values after two hours. No significant differences in the maximal plasma potassium increments were observed between the three conditions: predrug, spironolactone, or placebo period. The percentage of the oral potassium load translocated to the intracellular compartment was calculated as a way to estimate extrarenal potassium tolerance in our patients in order to evaluate the potential effect of spironolactone. Results were similar in the three experimental conditions: 44.6 6.2% in the predrug period, 48.8 9.3% after spironolactone, and 47.9 9.6% after placebo.

Figure 2.

Time course levels of plasma potassium during the oral potassium and carbohydrate load. Results are the mean SEM in nine hemodialysis (HD) patients during basal conditions, after two-week spironolactone (50 mg three times weekly) and at the end of two-week placebo. The oral load administered was 0.3 mEq potassium and 0.5 g of Ensure Plus, per kg body weight.

Full figure and legend (26K)

As expected, plasma glucose was significantly elevated after potassium-carbohydrate load. Peak values at 60 minutes were: predrug 105.6 4.0 mg/dL; spironolactone 111.0 7.8 mg/dL; and placebo 110.4 6.0 mg/dL. Also, insulin levels were elevated with the oral potassium-glucose load; a maximal value was obtained at 60 minutes. No significant differences were observed between the three conditions; peak plasma insulin levels at 60 minutes were: predrug 57.5 6.3 U/mL; spironolactone 43.9 6.6 U/mL; and placebo 54.4 10.1 U/mL.

Aldosterone and potassium load

The plasma levels of aldosterone were measured under basal and potassium load conditions during the predrug period and after aldactone in eight HD patients. High baseline plasma aldosterone levels were detected in four HD patients (range 32.6 to 94.5 ng/dL); four HD patients had aldosterone values in the normal range (mean 12.1 2.9 ng aldosterone/dL). Spironolactone treatment did not have significant effects of basal values in the patients, both with normal or high plasma aldosterone, except for one patient. Figure 3 includes the effect of potassium load on the aldosterone levels before and after spironolactone treatment. As shown in the Figure 3, a tendency to increased plasma aldosterone levels was observed.

Figure 3.

Plasma aldosterone levels of hemodialysis (HD) patients before and after potassium-carbohydrate load. Individual aldosterone levels at baseline and after 60 minutes of K⁺ load in eight patients are represented in the control period (predrug) and at the end of two-week spironolactone treatment, as indicated in Methods.

Full figure and legend (14K)

Sodium channel expression on peripheral blood mononuclear cells

To test the efficacy of the proposed spironolactone dose and administration scheme, we measured the expression of the ENaC alpha subunit, one of the major targets of aldosterone. For this study, we isolated blood mononuclear cells from the blood of six HD patients. Also, a group of four control normal subjects was studied. HD patients had significantly higher mRNA of the alpha subunit of ENaC compared to lymphocytes from normal subjects (P < 0.05). The results are included in Figure 4. In all HD patients studied, spironolactone treatment for two weeks significantly decreased the amount of ENaC alpha subunit mRNA (P< 0.05 vs. predrug treatment).

Figure 4.

Effect of spironolactone treatment on alpha ENaC mRNA expression in peripheral blood mononuclear cells. (A) Representative agarose-gel electrophoresis of semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) studies for 18S and alpha ENaC mRNA abundance in PBMC from control healthy volunteers (N), hemodyalisis patients (HD) and HD patients after 14 days of spironolactone treatment (SPIRO, 50 mg three times a week). (B) ENaC to 18S ratio was calculated for each experiment and results from PBMC of four healthy volunteers and six HD patients before and after spironolactone treatment are presented as mean SE, *P < 0.05 HD vs. HD + SPIRO and HD vs. healthy volunteers.

Full figure and legend (44K)

DISCUSSION

Serious hyperkalemia occurs in 10% of patients undergoing hemodialysis, and it is held responsible for 3% to 5% of deaths in these patients¹⁶. Hyperkalemia is a known side effect of spironolactone^14,27. However, recent studies have shown the safety of low-dose spironolactone administration in dialysis patients^25,26. Hussain et al used 25 mg of spironolactone administered daily for 28 days, whereas Saudan et al utilized 12.5 mg or 25 mg of spironolactone three times a week. However, none of the previous studies used a placebo control period in the same patients. Saudan's drug design is similar to our study, and is based on the bioavailability of spironolactone because its active metabolites canrenone and 7- methylspironolactone have a long half-life (15 to 20 hours) and 95% plasma binding²⁸. Half of the metabolites are eliminated by the kidney; hence, we hypothesized that 50 mg three times per week in nonfunctional kidney patients would be at least equivalent to the low-dose spironolactone used in the RALES study, carried out in patients with normal or slightly impaired renal function¹³. Treatment with spironolactone immediately after the HD session would avoid eventual hyperkalemic episodes after the drug administration.

The results observed indicate that under the present conditions no patients developed hyperkalemia. Further, in nine patients, we administered a load of potassium and carbohydrates equivalent to one regular meal before and after treatment with 50 mg of spironolactone and/or placebo. There were no significant differences in the extrarenal handling of potassium among the three conditions. Intracellular translocation of an ingested potassium load is the major route by which the potassium absorbed after an acute load is retained within the body. A number of hormones have either relatively well defined (e.g., insulin, catecholamines), or more speculative roles, like aldosterone, on the internal potassium balance. The interpretation of the literature regarding the role of mineralocorticoids on extrarenal potassium metabolism is complicated due to the well-known effect of aldosterone in the kidney, and also by the use in other studies of nonphysiologic doses of aldosterone or other mineralocorticoids²⁹. When renal function is compromised, plasma potassium homeostasis involves increased colonic potassium secretion^30,31. The factors responsible for maintaining the colonic epithelium in its K⁺ hypersecretory state are unclear. Early observations suggested that hyperaldosteronism does not contribute to enteric K⁺ secretion in CRF³², and increased rectal K⁺ secretion has been demonstrated in ESRD patients without secondary hyperaldosteronism³³. However, other reports did not exclude a role of aldosterone in mediating K⁺ secretion in large intestine of CRF patients³⁴. Previous studies in anephric patients found unaltered stool potassium excretion after three days of DOCA or spironolactone administration²³. Plasma aldosterone levels have been shown to be normal or high in CRF^30,35,36,37. In the present study, half of the patients exhibited high plasma aldosterone. Nevertheless, no significant differences were detected in extrarenal potassium handling of HD patients with normal or high plasma aldosterone. Further, spironolactone had no effect on the tolerance of HD patients to a potassium load.

Other tissues implicated in potassium homeostasis that could be influenced by aldosterone in CRF patients are sweat and salivary glands. HD patients have decreased sweat and saliva production^38,39, reflecting compromised gland function. Either normal⁴⁰ or increased K⁺ concentration⁴¹ was found in sweat of HD patients. Similarly, normal⁴⁰ or high salivary K⁺ concentration was reported when comparing normal subjects to CRF patients²³.

Aldosterone activates mineralocorticoid receptors in renal tubules, which in turn increase the rate of synthesis of several membrane proteins. It is well known that a major effect of aldosterone in epithelial tissues is to induce the Na-channel (ENaC) alpha subunit expression⁴². In the kidney, aldosterone increases the abundance of ENaC mRNA, but there is no change in the and subunits⁴³. Our group and others have shown the presence of mineralocorticoid receptors in the cardiovascular system and the induction of the Na-pump by aldosterone in rat blood vessels⁴⁴ Recently, it has been shown that aldosteronism is associated with an activation of PBMCs⁴⁵. These cells have mineralocorticoid receptors, and they express sodium channels⁴⁶. All the patients studied had high levels of ENaC alpha subunit mRNAs. Spironolactone treatment produced a dramatic effect in alpha subunit expression in PBMC of HD patients. After two weeks of spironolactone treatment (50 mg three times a week) the amounts of alpha subunit mRNA were similar to those of normal healthy subjects, even though plasma aldosterone levels in HD patients were not significantly modified. In our view, an important target to monitor the dose of spironolactone is ENaC expression in the PBMC, considering the emerging role of aldosterone in mononuclear blood cells. According to this hypothesis, the study dose-design could be considered an effective strategy to ameliorate aldosterone effects in selected HD patients. It is known that a large fraction of hemodialysis patients are diabetics with insulin resistance, and ACE inhibitors or angiotensin receptor blockers are frequently prescribed to HD patients. Diabetes mellitus and serum creatinine are the main predictors of hyperkalemia for patients under treatment with ACEIs⁴⁷. Combination of ACE inhibitors and spironolactone can increase the risk of hyperkalemia in non-HD patients with renal insufficiency⁴⁸, and the use of ACE inhibitors or angiotensin receptor blockers is independently associated with an increased risk of developing hyperkalemia in chronic HD patients⁴⁹. Other studies in azotemic patients have demonstrated modest increases in kalemia associated with the use of ramipril, captopril, or lisinopril^50,51,52. Previous studies from our group have shown enhanced insulin sensitivity in extrarenal potassium handling in uremic rats²¹. Also, extrarenal potassium balance was not significantly altered in non–insulin-dependent hypertensive diabetic patients challenged with a similar potassium-carbohydrate load protocol⁵³. Nonetheless, it would be important to perform future studies to evaluate the safety of low-dose mineralocorticoid receptor blockers in diabetic HD patients and HD patients under ACE inhibitors.

CONCLUSION

Our results on extrarenal potassium regulation demonstrate that spironolactone can be administered safely, under our study design, to stable HD patients. Furthermore, the measurement of the Na-channel alpha subunit expression could be useful to monitor the effectiveness of the treatment with spironolactone, not only for CRF patients on hemodialysis, but also for other pathologic conditions involving high aldosterone levels.

References

1. ROCHA, R, FUNDER, JW: The pathophysiology of aldosterone in the cardiovascular system. Ann N Y Acad Sci 2002 970: 89–100,
2. BRILLA, CG, WEBER, KT: Reactive and reparative myocardial fibrosis in arterial hypertension in the rat. Cardiovasc Res 1992 26: 671–677,
3. NGARMUKOS, C, GREKIN, RJ: Nontraditional aspects of aldosterone physiology. Am J Physiol Endocrinol Metab 2001 281: E1122–1127,
4. YOUNG, M, HEAD, J, FUNDER, JW: Determinants of cardiac fibrosis in experimental hypermineralocorticoid states. Am J Physiol 1995 269: E657–E662,
5. MACFADYEN, RJ, BARR, CS, STRUTHERS, AD: Aldosterone blockade reduces vascular collagen turnover, improves heart rate variability and reduces early morning rise in heart rate in heart failure patients. Cardiovasc Res 1997 35: 30–34,
6. UNITED STATES RENAL DATA SYSTEM: Annual data report: Part VI. Causes of death. Am J Kidney Dis 1999 34: S87–S94,
7. HERZOG, CA, MA, JZ, COLLINS, AJ: Poor long-term survival after acute myocardial infarction among patients on long-term dialysis. N Engl J Med 1998 339: 799–805,
8. SILBERG, JS, BARRE, PE, PRICHARD, SS, SNIDERMANN, SD: Impact of left ventricular hypertrophy on survival in end-stage renal disease. Kidney Int 1989 36: 286–290,
9. COLLINS, AJ, LI, S, MA, JZ, HERZOG, C: Cardiovascular disease in end-stage renal disease patients. Am J Kidney Dis 2001 38: S26–29,
10. SATO, A, FUNDER, JW, SARUTA, T: Involvement of aldosterone in left ventricular hypertrophy of patients with end-stage renal failure treated with hemodialysis. Am J Hypertens 1999 12: 867–873,
11. HOSTETTER, TH, ROSENBERG, ME, IBRAHIM, HN, JUKNEVICIUS, I: Aldosterone in renal disease. Curr Opin Nephrol Hypertens 2001 10: 105–110,
12. EPSTEIN, M: Aldosterone as a mediator of progressive renal dysfunction: Evolving perspectives. Intern Med 2001 40: 573–583,
13. PITT, B, ZANNAD, F, REMME, WJ, et al: The effect of spironolactone on morbidity and mortality in patients with severe heart failure. Randomized Aldactone Evaluation Study Investigators. N Engl J Med 1999 34: 709–717,
14. SCHEPKENS, H, VANHOLDER, R, BILLIOUW, JM, LAMEIRE, N: Life-threatening hyperkalaemia during combined therapy with angiotensin-converting enzyme inhibitors and spironolactone: An analysis of 25 cases. Am J Med 2001 110: 438–441,
15. KNOLL, GA, SAHGAL, A, NAIR, RC, et al: Renin-angiotensin system blockade and the risk of hyperkalemia in chronic hemodialysis patients. Am J Med 2002 112: 110–114,
16. AHMED, J, WEISBERG, LS: Hyperkalemia in dialysis patients. Semin Dial 2001 14: 348–356,
17. ALVO, M, KRSULOVIC, P, FERNANDEZ, V, et al: Effect of a simultaneous potassium and carbohydrate load on extrarenal K homeostasis in end-stage renal failure. Nephron 1989 53: 133–137,
18. KAHN, T, KAJI, DM, NICOLIS, G, et al: Factors related to potassium transport in chronic stable renal disease in man. Clin Sci Mol Med 1978 54: 661–666,
19. PEREZ, GO, PELLEYA, R, OSTER, JR, et al: Blunted kaliuresis after an acute potassium load in patients with chronic renal failure. Kidney Int 1983 24: 656–662,
20. FERNANDEZ, J, OSTER, JR, PEREZ, GO: Impaired extrarenal disposal of an acute oral potassium load in patients with endstage renal disease on chronic hemodialysis. Miner Electrolyte Metab 1986 12: 125–129,
21. GOECKE, IA, BONILLA, S, MARUSIC, ET, ALVO, M: Enhanced insulin sensitivity in extrarenal potassium handling in uremic rats. Kidney Int 1991 39: 39–43,
22. STUDER, A, ZARUBA, K, GRIMM, J, et al: Control of plasma aldosterone during chronic hemodialysis. Clin Nephrol 1980 13: 172–176,
23. SUGARMAN, A, BROWN, RS: The role of aldosterone in potassium tolerance: Studies in anephric humans. Kidney Int 1988 34: 397–403,
24. VLASSOPOULOS, D, SONIKIAN, M, DARDIOTI, V, et al: Insulin and mineralocorticoids influence on extrarenal potassium metabolism in chronic hemodialysis patients. Ren Fail 2001 23: 833–842,
25. SAUDAN, P, MACH, F, PERNEGER, T, et al: Safety of low-dose spironolactone administration in chronic haemodialysis patients. Nephrol Dial Transplant 2003 18: 2359–2363,
26. HUSSAIN, S, DREYFUS, DE, MARCUS, RJ, et al: Is spironolactone safe for dialysis patients? Nephrol Dial Transplant 2003 18: 2364–2368,
27. SICA, DA, GEHR, TW, YANCY, C: Hyperkalemia, congestive heart failure, and aldosterone receptor antagonism. Congest Heart Fail 2003 9: 224–229,
28. BEERMANN, B: Aspects on pharmacokinetics of some diuretics. Acta Pharmacol Toxicol (Copenh) 1984 54: 17–29,
29. STERNS, RH, COX, M, FEIG, PU, SINGER, I: Internal potassium balance and the control of the plasma potassium concentration. Medicine (Baltimore) 1981 60: 339–354,
30. MARTIN, RS, PANESE, S, VIRGINILLO, M, et al: Increased secretion of potassium in the rectum of humans with chronic renal failure. Am J Kidney Dis 1986 8: 105–110,
31. HATCH, M, FREEL, RW, VAZIRI, ND: Local upregulation of colonic angiotensin II receptors enhances potassium excretion in chronic renal failure. Am J Physiol 1998 274: F275–282,
32. HAYES, CP JR., MCLEOD, ME, ROBINSON, RR: An extravenal mechanism for the maintenance of potassium balance in severe chronic renal failure. Trans Assoc Am Physicians 1967 80: 207–216,
33. SANDLE, GI, GAIGER, E, TAPSTER, S, GOODSHIP, TH: Evidence for large intestinal control of potassium homoeostasis in uraemic patients undergoing long-term dialysis. Clin Sci (Lond) 1987 73: 247–252,
34. HAYSLETT, JP, BINDER, HJ: Mechanism of potassium adaptation. Am J Physiol 1982 243: F103–112,
35. WEIDMANN, P, MAXWELL, MH, LUPU, AN: Plasma aldosterone in terminal renal failure. Ann Intern Med 1973 78: 13–18,
36. OLGAARD, K, MADSEN, S: Regulation of plasma aldosterone in anephric and non-nephrectomized patients during hemodialysis treatment. Acta Med Scand 1977 201: 457–462,
37. IBRAHIM, HN, HOSTETTER, TH: Aldosterone in renal disease. Curr Opin Nephrol Hypertens 2003 12: 159–164,
38. MARCZEWSKI, K, JANICKA, L, CUDNY, J: The effect of pilocarpine on electrodermal resistance in chronic hemodialyzed patients. Clin Nephrol 1993 39: 88–91,
39. YOSIPOVITCH, G, REIS, J, TUR, E, et al: Sweat secretion, stratum corneum hydration, small nerve function and pruritus in patients with advanced chronic renal failure. Br J Dermatol 1995 133: 561–564,
40. EARLBAUM, AM, QUINTON, PM: Elevated divalent ion concentrations in parotid saliva from chronic renal failure patients. Nephron 1981 28: 58–61,
41. YOSIPOVITCH, G, REIS, J, TUR, E, et al: Sweat electrolytes in patients with advanced renal failure. J Lab Clin Med 1994 124: 808–812,
42. VERREY, F, LOFFING, J, ZECEVIC, M, et al: SGK1: Aldosterone-induced relay of Na⁺transport regulation in distal kidney nephron cells. Cell Physiol Biochem 2003 13: 21–28,
43. SNYDER, PM: The epithelial Na+ channel: Cell surface insertion and retrieval in Na+ homeostasis and hypertension. Endocr Rev 2002 23: 258–275,
44. MICHEA, L, VALENZUELA, V, BRAVO, I, et al: Adrenal-dependent modulation of the catalytic subunit isoforms of the Na+-K+-ATPase in aorta. Am J Physiol 1998 275: E1072–1081,
45. AHOKAS, RA, WARRINGTON, KJ, GERLING, IC, et al: Aldosteronism and peripheral blood mononuclear cell activation: A neuroendocrine-immune interface. Circ Res 2003 93: 124–135,
46. BUBIEN, JK, WATSON, B, KHAN, MA, et al: Expression and regulation of normal and polymorphic epithelial sodium channel by human lymphocytes. J Biol Chem 2001 276: 8557–8566,
47. AHUJA, TS, FREEMAN, D, JR., MAHNKEN, JD, et al: Predictors of the development of hyperkalemia in patients using angiotensin-converting enzyme inhibitors. Am J Nephrol 2000 20: 268–272,
48. SCHEPKENS, H, VANHOLDER, R, BILLIOUW, JM, et al: Life-threatening hyperkalemia during combined therapy with angiotensin-converting enzyme inhibitors and spironolactone: An analysis of 25 cases. Am J Med 2001 110: 438–441,
49. KNOLL, GA, SAHGAL, A, NAIR, RC, et al: Renin-angiotensin system blockade and the risk of hyperkalemia in chronic hemodialysis patients. Am J Med 2002 112: 110–114,
50. KEILANI, T, DANESH, FR, SCHLUETER, WA, et al: A subdepressor low dose of ramipril lowers urinary protein excretion without increasing plasma potassium. Am J Kidney Dis 1999 33: 450–457,
51. TEXTOR, SC: Managing renal arterial disease and hypertension. Curr Opin Cardiol 2003 18: 260–267,
52. MANGRUM, AJ, BAKRIS, GL: Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in chronic renal disease: Safety issues. Semin Nephrol 2004 24: 168–175,
53. MICHEA, LF, ALVO, M, MORALES, H, et al: Comparison of extra renal potassium management in hypertensive, diabetic and normal subjects. Rev Med Chil 1997 125: 1292–1298,

Acknowledgments

We would like to thank the staff and patients of the Renal Outpatient Dialysis Unit, Clínica Dávila, and especially to Ms. Cecilia Avalos, who undertook the patients' drug administration and blood samples. We also want to thank Drs. J. Morales and A. Fierro for their helpful comments on the study design. This work was supported by grant no. MED 004–03 from University Los Andes and grants from Fondo Nacional InvestigaciÓn Científica, FONDECYT, nos. 1040338 and 1010185.