Selective screening for distal renal tubular acidosis in recurrent kidney stone formers: initial experience and comparison of the simultaneous furosemide and fludrocortisone test with the short ammonium chloride test.

BACKGROUND: Distal renal tubular acidosis (dRTA) is associated with renal stone disease, and it often needs to be considered and excluded in some recurrent calcium kidney stone formers (KSFs). However, a diagnosis of dRTA, especially when 'incomplete', can be missed and needs to be confirmed by a urinary acidification (UA) test. The gold standard reference test is still the short ammonium chloride (NH4Cl) test, but it is limited by gastrointestinal side effects and occasionally failure to ingest sufficient NH4Cl. For this reason, the furosemide plus fludrocortisone (F+F) test has been proposed as an easier and better-tolerated screening test. The aim of the present study was to assess the usefulness of the F+F test as a clinical screening tool for dRTA in a renal stone clinic. METHODS: We studied 124 patients retrospectively in whom incomplete dRTA was suspected: 71 had kidney stones only, 9 had nephrocalcinosis only and 44 had both. A total of 158 UA tests were performed: 124 F+F and 34 NH4Cl; both tests were completed in 34 patients. RESULTS: The mean age was 45.4 ± 15 years, and 49% of patients were male. The prevalence of complete and incomplete dRTAs was 7 and 13.7%, respectively. Of the 34 patients tested using both tests, 17 (50%) were abnormal and 4 (12%) were normal. Thirteen (39%) patients were abnormal by F+F, but normal by NH4Cl [sensitivity 100% (95% CI 80-100), specificity 24% (95% CI 7-50), positive predictive value 57% (95% CI 37-75), negative predictive value 100% (95% CI 40-100)]. CONCLUSIONS: The F+F test is characterized by an excellent sensitivity and negative predictive value, and the diagnosis of incomplete dRTA can be excluded reliably in a patient who acidifies their urine normally with this test. However, its lack of specificity is a drawback, and if there is any doubt, an abnormal F+F test may need to be confirmed by a follow-up NH4Cl test. Ideally, a prospective blinded study in unselected KSFs is needed to accurately assess the reliability of the F+F test in diagnosing, rather than excluding, dRTA.

Renal ammonium excretion after an acute acid load: blunted response in uric acid stone formers but not in patients with type 2 diabetes.

Idiopathic uric acid nephrolithiasis is characterized by elevated urinary net acid excretion and insufficient buffering by ammonium, resulting in excessively acidic urine and titration of the relatively soluble urate anion to insoluble uric acid. Patients with type 2 diabetes have similar changes in urinary pH, net acid excretion, and ammonium in 24-h urine collections at baseline, even after controlling for dietary factors, and are at increased risk for uric acid nephrolithiasis. However, not all patients with type 2 diabetes develop kidney stones, suggesting that uric acid stone formers may have additional urinary defects, perhaps not apparent at baseline. We performed a metabolic study of 14 patients with idiopathic uric acid nephrolithiasis, 13 patients with type 2 diabetes, and 8 healthy control subjects of similar body mass index. After equilibration on a fixed diet for 5 days, subjects were given a single oral acid load (50 meq ammonium chloride), and urine was collected hourly for 4 h. Uric acid stone formers had a lower ammonium excretory response to acute acid loading compared with diabetic and nondiabetic nonstone formers, suggesting that an ammonium excretory defect unique to uric acid stone formers was unmasked by the acid challenge. The Zucker diabetic fatty rat also did not show impaired urinary ammonium excretion in response to acute acid challenge. A blunted renal ammonium excretory response to dietary acid loads may contribute to the pathogenesis of idiopathic uric acid nephrolithiasis.

The biochemical and histopathological investigation of amlodipine in ethylene glycol-induced urolithiasis rat model.

BACKGROUND: Urinary calculi are a common and severe problem, which are formed by urolithiasis or by the formation of calcium oxalate (CaOx) crystals in the kidneys. Many treatment options such as drugs, various herbal preparations, surgical removal of the stones, and extracorporeal shock wave lithotripsy have been applied for this condition. The aim of this study is to assess the effects of the drug amlodipine in an experimentally induced urolithiasis rat model. MATERIALS AND METHODS: The effect of 5 mg/kg amlodipine was studied in rats that were first treated with 1% ethylene glycol and 1% ammonium chloride for 21 days to induce urolithiasis. The weight differences and the levels of calcium, magnesium, and phosphate were measured in serum and urine. In addition, urine CaOx level was defined and histopathological analyses were performed on the kidneys. RESULTS: Urolithiasis caused a significant increase in both serum and urine parameters compared with healthy rats. Urolithiasis plus amlodipine administration increased the levels of these same parameters. Urine CaOx level was high in urolithiasis rats and was also increased by urolithiasis plus amlodipine administration. The weight of the rats decreased in the urolithiasis plus amlodipine group when compared with the urolithiasis group. Histopathological examinations revealed extensive intratubular crystal depositions and degenerative tubular structures in the urolithiasis group and the amlodipine treatment group. CONCLUSION: We showed that amlodipine may increase susceptibility to urolithiasis by raising hyperoxaluria and hypercalciuria. Further studies should be performed to elucidate the urolithiasis activity of amlodipine and to confirm the data.

A comparative study on several models of experimental renal calcium oxalate stones formation in rats.

In order to compare the effects of several experimental renal calcium oxalate stones formation models in rats and to find a simple and convenient model with significant effect of calcium oxalate crystals deposition in the kidney, several rat models of renal calcium oxalate stones formation were induced by some crystal-inducing drugs (CID) including ethylene glycol (EG), ammonium chloride (AC), vitamin D(3)[1alpha(OH)VitD(3), alfacalcidol], calcium gluconate, ammonium oxalate, gentamicin sulfate, L-hydroxyproline. The rats were fed with drugs given singly or unitedly. At the end of experiment, 24-h urines were collected and the serum creatinine (Cr), blood urea nitrogen (BUN), the extents of calcium oxalate crystal deposition in the renal tissue, urinary calcium and oxalate excretion were measured. The serum Cr levels in the stone-forming groups were significantly higher than those in the control group except for the group EG+L-hydroxyproline, group calcium gluconate and group oxalate. Blood BUN concentration was significantly higher in rats fed with CID than that in control group except for group EG+L-hydroxyproline and group ammonium oxalate plus calcium gluconate. In the group of rats administered with EG plus Vitamin D(3), the deposition of calcium oxalate crystal in the renal tissue and urinary calcium excretion were significantly greater than other model groups. The effect of the model induced by EG plus AC was similar to that in the group induced by EG plus Vitamin D(3). EG plus Vitamin D(3) or EG plus AC could stably and significantly induced the rat model of renal calcium oxalate stones formation.

Study of urinary acidification in patients with idiopathic hypocitraturia.

Hypocitraturia (HCit) is one of the most remarkable features of renal tubular acidosis, but an acidification defect is not seen in the majority of hypocitraturic patients, whose disease is denoted idiopathic hypocitraturia. In order to assess the integrity of urinary acidification mechanisms in hypocitraturic idiopathic calcium stone formers, we studied two groups of patients, hypocitraturic (HCit, N = 21, 39.5 +/- 11.5 years, 11 females and 10 males) and normocitraturic (NCit, N = 23, 40.2 +/- 11.7 years, 16 females and 7 males) subjects, during a short ammonium chloride loading test lasting 8 h. During the baseline period HCit patients showed significantly higher levels of titratable acid (TA). After the administration of ammonium chloride, mean urinary pH (3rd to 8th hour) and TA and ammonium excretion did not differ significantly between groups. Conversely, during the first hour mean urinary pH was lower and TA and ammonium excretion was higher in HCit. The enhanced TA excretion by HCit during the baseline period and during the first hour suggests that the phosphate buffer mechanism is activated. The earlier response in ammonium excretion by HCit further supports other evidence that acidification mechanisms react promptly. The present results suggest that in the course of lithiasic disease, hypocitraturia coexists with subtle changes in the excretion of hydrogen ions in basal situations.

Relative importance of urinary sulfate and net acid excretion as determinants of calciuria in normal subjects.

In normal subjects fed western-mixed diets, in the fasting state, 39.6% of the variance of calciuria is accounted for by net acid excretion and 4% by sulfaturia. In the postprandial period, net acid accounts for 6.9% and sulfaturia for 11.8% of the variance of calciuria. As expected, after a load of ammonium chloride, net acid excretion exceeded the importance of sulfaturia (36.2% vs. 8.4%) and the opposite was observed after DL-methionine load (1.5% and 46.2%). A group of normal subjects fed vegetarian diets was also investigated. The excretion of the three variables measured were significantly reduced in this group when compared with that of the former group. In the fasting state the variance of calciuria was accounted mainly by net acid excretion (85.7%). In the postprandial state net acid (4.9%) and sulfate (2.2%) had much less importance as determinants of calciuria. It is concluded that in spite of their metabolic relationship, net acid and sulfate excretions are independent determinants of calciuria. The relative importance of each variable changes as a function of metabolic circumstances.

Mechanism by which enhanced ammonia production reduces urinary potassium excretion.

To determine the mechanism whereby an increase in ammonia production decreases urinary potassium excretion, we perfused isolated rat kidneys at a pH of either 7.0 or 7.4. After 45 min of perfusion at either pH, glutamine or ammonium chloride was added to the perfusate to result in concentration of 5 and 0.8 mM, respectively and observations were continued for 50 min. Control kidneys were perfused at both pH's without further additions to the perfusate. At pH 7.0 glutamine increased ammonia production and increased urinary ammonium excretion strikingly; whereas the addition of ammonium chloride did not change ammonia production but increased urinary ammonium excretion to a comparably degree. Both maneuvers resulted in a reciprocal fall in urinary potassium excretion in comparison with control perfusions. The decreases in potassium excretion could not be accounted for by differences in perfusate or urinary acid-base parameters, or by changes in urinary sodium, water, or chloride excretion. At pH 7.4, glutamine also significantly increased ammonia production and perfusate ammonia concentration. In contrast to the studied at pH 7.0 in which the urine pH was acid (5.9), the urine remained alkaline (pH 7.2), and both urinary ammonium excretion and urinary potassium excretion were unaltered. Thus, potassium sparing is not a nonspecific effect of glutamine, its metabolism to ammonia, or perfusate ammonia concentration but is directly related to an increase in urinary ammonium excretion.

Ammonia-nitrogen turnover in the rabbit caecum and exchange with plasma urea-N.

Continuous infusion and single-shot administration of 15NH4Cl into the caecum of the conscious rabbit was used to measure caecal ammonia flux. Continuous infusion of 15NH4Cl and sampling from both the caecal ammonia and blood urea pools indicated that 0.27 of plasma urea-nitrogen was derived from caecal ammonia-N. Values from intravenous [15N]urea and intracaecal 15NH4Cl infusions were used to produce two models of the movement of N between these two metabolic pools. Further analysis of the results suggested an alternative model involving a third pool associated with the caecal mucosa and values for this model are also presented.

Urine electrolytes in the assessment of extracellular fluid volume contraction.

The purpose of this study was to determine which urine electrolytes should be measured to confirm that the extracellular fluid (ECF) volume is depleted. ECF volume contraction was induced by furosemide administration to rats consuming an electrolyte-free diet. An external potassium balance was achieved by replacing potassium losses with KHCO3 and KCl so that the sodium and chloride deficits were comparable (equivalent to a 30% reduction in ECF volume). As expected, the urine sodium and chloride concentrations fell to 2 +/- 0.3 mmol/l and 3 +/- 0.3 mmol/l, respectively. Rats were then randomized to receive 50-75% of their sodium or chloride deficit as either: NaCl (control group), NH4Cl or NaHCO3 to mimic clinical situations associated with ECF volume contraction. In the NaCl group, the urine sodium and chloride concentrations remained low (6 +/- 2 mmol/l and 7 +/- 2 mmol/l), consistent with persistent ECF volume contraction. Although the NH4Cl group continued to have a low urine sodium concentration (2 +/- 0.2 mmol/l), there was now a marked increase in the urine chloride concentration (51 +/- 7 mmol/l; p less than 0.01 vs. NaCl group). In contrast, although the NaHCO3 group continued to have a low urine chloride concentration (2 +/- 1 mmol/l), there was a significant increase in the urine sodium concentration (19 +/- 3 mmol/l; p less than 0.01 vs. NaCl group). We conclude that the clinical assessment of ECF volume by urine electrolytes requires an evaluation of both the urine sodium and chloride concentrations.

Impaired renal tubular potassium secretion in sickle cell disease.

We examined renal tubular function in six patients with sickle cell hemoglobin. All had normal inulin and para-aminohippurate clearances and impaired urinary concentrating and acidifying abilities. After intravenous potassium chloride administration, maximum excretion of potassium (U,V) was significantly lower in sickle cell patients than in control subjects, and the percentage of potassium load excreted in 5 h was markedly reduced. Urinary potassium excretion after sodium sulfate infusion was also markedly reduced in sickle cell patients compared to control subjects. After 40 mg of oral furosemide, U,V was also diminished in sickle cell patients. Plasma aldosterone response to ACTH and intravenous potassium was similar to that of control subjects. Plasma renin activity increased normally after volume contraction. We conclude that sickle cell patients have a defect in their ability to excrete an acute potassium load that cannot be attributed to abnormal renin or aldosterone secretion. Overall potassium homeostasis is maintained by extrarenal mechanisms during acute potassium loading.

Polycystic disease and hepatic fibrosis in children. Renal function studies.

Renal function studies were done in five children with infantile polycystic disease (IPCD)of kidneys and liver and in four with congenital hepatic fibrosis (CHF). Glomerular filtration rate was reduced in all IPCD patients and in two of four CHF patients. Urinary concentrating ability following water deprivation and vasopressin administration was impaired in all IPCD patients and in three of four CHF patients. During control period, all patients had asymptomatic metabolic acidosis with total carbon dioxide content less than or equal to 20.5 millimols/liter, and net acid excretion (NAE) was reduced in all but one. Ammonium chloride was administered to seven patients; NAE increased in all, but the increments were subnormal in four. The inability to excrete maximally concentrated urine and an adequate amount of net acid may best be explained by abnormal tubular structure or alterations in medullary architecture secondary to progressive scarring, or both.

Impaired urinary acidification in the hypothyroid rat.

Since abnormalities in the renal handling of sodium and water in both the proximal and distal tubule have been described in primary hypothyroidism, this study was undertaken to examine renal tubular hydrogen secretion in this disorder. Metabolic acidosis was induced in hypothyroid rats (H) and their age matched controls (C) by the administration of an oral ammonium chloride load of 0.15 g/24 h/kg for three days. On day 3 animals were prepared for clearance and acid-base studies, receiving an infusion of Ringer's solution of 0.6 ml/hr/100 g during surgery and the experimental procedure. A 26% decrease in GFR (P less than 0.005) and a doubling in fractional excretion of sodium (P less than 0.02) were observed in H rats. The lowest blood pH and average bicarbonate concentration and the excretion of chloride were similar in the two groups, indicating that the acid load was reabsorbed and led to similar degrees of systemic acidification. Urine flow also was comparable in the two groups. Minimal urine pH after NH4Cl was 6.21 +/- 0.06 in H and 5.68 +/- 0.09 in C (P less than 0.001). Ammonium excretion was 28% (P less than 0.05) lower in H than in C. The defect in urine acidification in H was only partially corrected after 5 days on a low sodium diet and DOCA administration for 2 days. Fractional bicarbonate excretion at normal blood pH and bicarbonate concentration was not different in the two groups. These data indicate that hypothyroid rats have a mild defect in urine acidification and that it is localized predominantly in the distal tubule.

Effect of acetazolamide on renal metabolism and ammoniagenesis in the dog.

The effect of acetazolamide (ACZ) on renal metabolism and ammoniagenesis was studied in the dog in vivo and in vitro. ACZ was administered to 10 dogs with normal acid-base status and five with chronic metabolic acidosis induced by NH4Cl. In both groups of dogs, the acute administration of ACZ markedly reduced the urinary excretion of ammonium (from 33 to 10 in normal dogs and from 100 to 23 mumoles/100 ml GFR in acidotic dogs) whereas its release into the renal vein was increased in a reciprocal fashion (from 69 to 95 in normal dogs and from 91 to 152 mumoles/100 ml GFR in acidotic dogs). ACZ did not change the total ammonium production nor the renal glutamine utilization. The renal utilization or production of glutamate, alphaketoglutarate, alanine and citrate also remained unchanged. Despite a marked urinary alkalinization, citraturia remained minimal. However, the renal cortical concentrations of glutamine, glutamate, succinate, fumarate, malate, aspartate and phosphoenolpyruvate fell following ACZ administration, especially in acidotic dogs showing rapid renal utilization of glutamine. ACZ had no effect on the same metabolites in the kidney of normal dogs even when lactate utilization was enhanced by lactate infusion. This study demonstrates that an accelerated ammoniagenic flux can proceed in the dog kidney without the renal cortical changes produced by metabolic acidosis in this species. In vitro, using dog tubules, a selective effect of ACZ on glutamine metabolism as compared to lactate was observed. ACZ reduce the rate of the reactions catalyzed by alphaketoglutarate dehydrogenase and by succinyl CoA synthetase. Other enzymes of the ammoniagenic and gluconeogenic pathways (glutaminase, GLDH, malic enzyme, PEPCK) were not changed by ACZ. The metabolic effects of ACZ observed in the intact kidney in vivo or with tubules in vitro may be in part related to the effect of ACZ on these enzymes critical for the ammoniagenic process.

Acute zinc chloride ingestion in a child: local and systemic effects.

A 16-month-old boy ingested liquid zinc chloride/ammonium chloride soldering flux. He developed severe local burns, metabolic acidosis, hepatic damage, hyperamylasemia, lethargy, and hypertension. Peak measured plasma zinc was 1,199 micrograms/dL. Because of persistent signs of systemic toxicity, he was chelated with dimercaprol (BAL) and EDTA. Although clinical improvement was noted coincident with the initiation of chelation, there was no apparent increase in urinary zinc excretion. Scarring in the gastric antrum necessitated an antrectomy. The child recovered without other apparent complications.