Effect of amiloride with or without hydrochlorothiazide on urinary calcium and saturation of calcium salts

Coupling of renal sodium and calcium transport: a modeling analysis of transporter inhibition and sex differences

Ca2+ transport along the nephron occurs via specific transcellular and paracellular pathways and is coupled to the transport of other electrolytes. Notably, Na+ transport establishes an electrochemical gradient to drive Ca2+ reabsorption. Hence, alterations in renal Na+ handling, under pathophysiological conditions or pharmacological manipulations, can have major effects on Ca2+ transport. An important class of pharmacological agent is diuretics, which are commonly prescribed for the management of blood pressure and fluid balance. The pharmacological targets of diuretics generally directly facilitate Na+ transport but also indirectly affect renal Ca2+ handling. To better understand the underlying mechanisms, we developed a computational model of electrolyte transport along the superficial nephron in the kidney of a male and female rat. Sex differences in renal Ca2+ handling are represented. Model simulations predicted in the female rat nephron lower Ca2+ reabsorption in the proximal tubule and thick ascending limb, but higher reabsorption in the late distal convoluted tubule and connecting tubule, compared with the male nephron. The male rat kidney model yielded a higher urinary Ca2+ excretion than the female model, consistent with animal experiments. Model results indicated that along the proximal tubule and thick ascending limb, Ca2+ and Na+ transport occurred in parallel, but those processes were dissociated in the distal convoluted tubule. Additionally, we conducted simulations of inhibition of channels and transporters that play a major role in Na+ and Ca2+ transport. Simulation results revealed alterations in transepithelial Ca2+ transport, with differential effects among nephron segments and between the sexes.NEW & NOTEWORTHY The kidney plays an important role in the maintenance of whole body Ca2+ balance by regulating Ca2+ reabsorption and excretion. This computational modeling study provides insights into how Ca2+ transport along the nephron is coupled to Na+. Model results indicated that along the proximal tubule and thick ascending limb, Ca2+ and Na+ transport occur in parallel, but those processes were dissociated in the distal convoluted tubule. Simulations also revealed sex-specific responses to different pharmacological manipulations.

Acute decrease of urine calcium by amiloride in healthy volunteers under high sodium diet

BACKGROUND

Amiloride is a competitive blocker of the epithelial sodium channel (ENaC) in the renal collecting duct. It is a less potent diuretic than thiazides or loop diuretics, but is often used in association for its potassium-sparing profile. Whether amiloride has hypocalciuric effect similar to thiazides remains unclear. Animal studies and experiments on cell lines suggested that amiloride increases calcium reabsorption in the distal nephron, but human studies are scarce.

METHODS

We performed a post hoc analysis of a study with 48 healthy males (age, 23.2 ± 3.9 years) who were assigned to a high sodium (Na)/low potassium (K) diet for 7 days before receiving 20 mg of amiloride p.o. Urinary excretions of electrolytes were measured at 3 and 6 hours afterward; we calculated the relative changes in urinary excretion rates after amiloride administration.

RESULTS

The high Na/low K diet led to an expected suppression of plasma renin and aldosterone. Amiloride showed a mild natriuretic effect associated with a decreased kaliuresis. Urinary calcium excretion dropped substantially (by 80%) 3 hours after amiloride administration and remained low at the 6th hour. At the same time, fractional excretion of lithium decreased by a third, reflecting an increased proximal tubular reabsorption.

CONCLUSION

During a high Na/low K diet, amiloride had a strong acute hypocalciuric effect, most probably mediated by increased proximal calcium reabsorption, even though distal effect cannot be excluded. Further studies should establish if chronic amiloride or combined amiloride/thiazide treatment may decrease calciuria more efficiently and be useful in preventing kidney stones.

Use of calcimimetics in children with normal kidney function

The calcium-sensing receptor (CaSR) plays an important role in the homeostasis of serum ionized calcium by regulating parathyroid hormone (PTH) secretion and tubular calcium handling. Calcimimetics, which act by allosteric modulation of the CaSR, mimic hypercalcemia resulting in suppression of PTH release and increase in calciuria. Mostly used in children to treat secondary hyperparathyroidism associated with advanced renal failure, we have shown that calcimimetics can also be successfully used in children with bone and mineral disorders in which elevated PTH plays a detrimental role in skeletal pathophysiology in the face of normal kidney function. The current review briefly discusses the role of the CaSR and calcimimetics in calcium homeostasis, and then addresses the potential applications of calcimimetics in children with normal kidney function with disorders in which suppression of PTH is beneficial.

Changes in selected metabolic parameters in patients over 65 receiving hydrochlorothiazide plus amiloride, atenolol or placebo in the MRC elderly trial

Background

Treatment of hypertension reduces incidence of stroke, myocardial infarction and heart failure perhaps partly by controlling different metabolic parameters. There is limited information regarding the changes in potassium, sodium, weight, cholesterol and glucose levels in patients using anti-hypertensives. This study aimed to determine changes in potassium, sodium, glucose, cholesterol, weight, urea and urate levels in patients using anti-hypertensives. Furthermore, to describe these changes and differences between the atenolol, hydrochlorothiazide plus amiloride and placebo arms of the Medical Research Council (MRC) elderly randomised controlled trial.

Methods

Patients were randomly allocated to one of the three treatment arms. Measurements were taken at baseline, end of year one and end of year two in 4396 subjects. Linear Mixed Models (LMM) were used to determine the longitudinal profiles of sodium, potassium, weight, cholesterol, glucose, urea and urate. Estimates of changes within groups and difference between groups were obtained.

Results

Patients randomised to receive hydrochlorothiazide + amiloride experienced a significantly greater mean reduction in potassium, sodium and weight compared to placebo at end of year one - mean differences in change −0.18 mmol/L, (95 % CI: −0.21, −0.15); −1.45 mmol/L, (95 % CI: −1.62, −1.29) and −0.46 kgs (95 % CI: −0.73, −0.20) respectively, and greater increases in cholesterol, urea and urate - mean differences in change 0.16 mmol/L, (95 % CI: 0.10,0.22); 0.77 mmol/L, (95 % CI: 0.68, 0.87) and 53.10 μmol/L, (95 % CI: 49.35, 56.85) respectively. Changes were in the same direction but smaller in the atenololarm except for potassium and weight (increases). No group differences in glucose were found.

Conclusion

Results were in line with expectation except for lack of change in glucose in the hydrochlorothiazide + amiloride arms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12872-016-0368-2) contains supplementary material, which is available to authorized users.

Personalizing the diuretic treatment of hypertension: the need for more clinical and research attention

Neither randomized controlled trials nor efforts to identify genetic markers have been helpful with regard to the goal of individualizing diuretic therapy in the treatment of hypertension, a goal that receives little clinical or research attention. This review will examine, and bring attention to, the considerable yet overlooked information relevant to individualizing diuretic therapy. It will bring attention to clinical, biochemical, and pharmacological clues that can be helpful in identifying who is likely to respond to a diuretic, who needs a stronger diuretic regimen, which diuretic to prescribe, and how to minimize adverse effects. New directions for clinical research aimed at individualizing use in hypertension will be explored. Research and clinical attention to the goal of individualizing diuretic treatment in hypertension need to be renewed, to help us achieve greater hypertension control with fewer adverse effects and lower costs.

Effect of thiazides on bone mineral density in children with idiopathic hypercalciuria

To determine the effect of thiazide treatment on bone mineral density (BMD) in children with idiopathic hypercalciuria (IH) and osteopenia, we reviewed the case notes of 22 children aged 11.7 ± 2.7 years diagnosed with IH and osteopenia who had received thiazides for 2.4 years. The data on this group were compared with those of 32 IH children with osteopenia aged 11.2 ± 2.7 years who had not received thiazide treatment. By the end of the follow-up period, the z-BMD had improved spontaneously in 23 of the 32 control children (72%) and in 12 of the 22 patients on thiazides (54%). Although treated patients had a higher body mass index (BMI) and a higher BMD following treatment, the differences became statistically negligible when these parameters were expressed as z-BMD or as bone mineral apparent density (BMAD). In contrast, within the control group, there were significant differences in BMAD and z-BMD at the end of the follow-up. Patients who had an improved z-BMD at the end of the treatment also showed an increase in their BMI. Based on these results, we conclude that thiazide treatment does not improve the z-BMD in children with IH. More than half of the children suffering from IH enrolled in our study showed a spontaneous improvement in their z-BMD, which was more evident when the initial BMAD was not low and when their BMI increased during the follow-up period.

Essential oil terpenes: adjunctive role in the management of childhood urolithiasis

Essential oil preparation of the terpenic type was introduced for the first time in the 1930s for the management of urolithiasis. Although essential oil preparations are registered in 50 countries, including some developed countries such as the United Kingdom, Italy, and Japan, for use in urolithiasis, no literature has been published in a peer-reviewed English (Anglo-American) medical journal. Recently the use of these terpenes has been investigated in children with urolithiasis and underlying metabolic abnormalities. The aim of this article is to extract the useful and worthy information about the use of these terpenes in urolithiasis from the previous literature as many of these articles are now considered of poor quality for a thorough systematic scientific review. The main disadvantages of most of the old literature about terpenes are the treatment was not followed radiologically and most of these articles represent anecdotal reports of spontaneous passage of calculi and symptomatic improvement of colic in association with the use of terpenes. The other aim is to discuss the possible role of essential oil terpenes in the management of childhood urolithiasis.

Modulation of renal calcium handling by 11 beta-hydroxysteroid dehydrogenase type 2

Reduced concentration of serum ionized calcium and increased urinary calcium excretion have been reported in primary aldosteronism and glucocorticoid-treated patients. A reduced activity of the 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta HSD2) results in overstimulation of the mineralocorticoid receptor by cortisol. Whether inhibition of the 11 beta HSD2 by glycyrrhetinic acid (GA) may increase renal calcium excretion is unknown. Serum and urinary electrolyte and creatinine, serum ionized calcium, urinary calcium excretion, and the steroid metabolites (THF+5 alpha THF)/THE as a parameter of 11 beta HSD2 activity were repeatedly measured in 20 healthy subjects during baseline conditions and during 1 wk of 500 mg/d GA. One week of GA induced a maximal increment of 93% in (THF+5 alpha THF)/THE. Ambulatory BP was significantly higher at day 7 of GA than at baseline (126/77 +/- 10/7 versus 115/73 +/- 8/6 mmHg; P < 0.001 for systolic; P < 0.05 for diastolic). During GA administration, serum ionized calcium decreased from 1.26 +/- 0.05 to 1.18 +/- 0.04 mmol/L (P < 0.0001), and absolute urinary calcium excretion was enhanced from 29.2 +/- 3.6 to 31.9 +/- 3.1 micromol/L GFR (P < 0.01). Fractional calcium excretion increased from 2.4 +/- 0.3 to 2.7 +/- 0.3% (P < 0.01) and was negatively correlated to the fractional sodium excretion during GA (R = -0.35; P < 0.001). Moreover, serum potassium correlated positively with serum ionized calcium (R = 0.66; P < 0.0001). Inhibition of 11 beta HSD2 activity is sufficient to significantly increase the fractional excretion of calcium and decrease serum ionized calcium, suggesting decreased tubular reabsorption of this divalent cation under conditions of renal glucocorticoid/mineralocorticoid excess. The likely site of steroid-regulated renal calcium handling appears to be the distal tubule.

Human cortical distal nephron: distribution of electrolyte and water transport pathways

The exact distributions of the different salt transport systems along the human cortical distal nephron are unknown. Immunohistochemistry was performed on serial cryostat sections of healthy parts of tumor nephrectomized human kidneys to study the distributions in the distal convolution of the thiazide-sensitive Na-Cl cotransporter (NCC), the beta subunit of the amiloride-sensitive epithelial Na channel (ENaC), the vasopressin-sensitive water channel aquaporin 2 (AQP2), and aquaporin 3 (AQP3), the H(+) ATPase, the Na-Ca exchanger (NCX), plasma membrane calcium-ATPase, and calbindin-D28k (CaBP). The entire human distal convolution and the cortical collecting duct (CCD) display calbindin-D28k, although in variable amounts. Approximately 30% of the distal convolution profiles reveal NCC, characterizing the distal convoluted tubule. NCC overlaps with ENaC in a short portion at the end of the distal convoluted tubule. ENaC is displayed all along the connecting tubule (70% of the distal convolution) and the CCD. The major part of the connecting tubule and the CCD coexpress aquaporin 2 with ENaC. Intercalated cells, undetected in the first 20% of the distal convolution, were interspersed among the segment-specific cells of the remainder of the distal convolution, and of the CCD. The basolateral calcium extruding proteins, Na-Ca exchanger (NCX), and the plasma membrane Ca(2+)-ATPase were found all along the distal convolution, and, in contrast to other species, along the CCD, although in varying amounts. The knowledge regarding the precise distribution patterns of transport proteins in the human distal nephron and the knowledge regarding the differences from that in laboratory animals may be helpful for diagnostic purposes and may also help refine the therapeutic management of electrolyte disorders.

Medical therapy, calcium oxalate urolithiasis

The development of diagnostic protocols that identify specific risk factors for calcium oxalate nephrolithiasis has led to the formulation of directed medical regimens that are aimed at correcting the underlying metabolic disturbances. Initiation of these treatment programs has reduced markedly the rate of stone formation in the majority of patients who form stones. This article discusses the rationale that underlies the choice of medical therapy for the various pathophysiologic causes of calcium oxalate nephrolithiasis and the appropriate use of available medications.

Stimulation of calcium transport by amiloride in mouse distal convoluted tubule cells

This study examined the mechanism by which amiloride dissociates Na and Ca transport in distal convoluted tubules. Control rates of Na uptake averaged 288 nmol/(min mg protein) and were inhibited 39% by microM amiloride. Amiloride had no effect on Cl uptake. Resting membrane voltage, measured with the voltage-sensitive dye DiOC6 (3), averaged -70 mV. Amiloride hyperpolarized cells in a reversible manner by 18 mV. Control rates of Ca uptake averaged 2.8 nmol/(min mg protein) and increased by 39% in the presence of amiloride. Alterations of intracellular Ca activity were measured in single cells loaded with Fura2-AM. Control intracellular Ca activity averaged 100 nM. Amiloride increased intracellular Ca activity in a concentration-dependent manner to a maximum of 330 nM at microM amiloride. Amiloride analogues ethylisopropyl amiloride (EIPA) and dimethylbenzamil (DMB), which preferentially block Na/H and Na/Ca exchange, respectively, had no effect on Na or Ca influx or on intracellular Ca activity. The dihydropyridine Ca channel blocker nifedipine inhibited amiloride-stimulated Ca uptake and the rise of intracellular Ca activity but had no effect on membrane voltage. It is concluded that amiloride blocks Na entry mediated by Na channels. Inhibition of Na entry results in membrane hyperpolarization, which activates Ca entry by dihydropyridine-sensitive Ca channels.

Etiology and treatment of urolithiasis

Nephrolithiasis is a heterogeneous disorder, with varying chemical composition and pathophysiologic background. Although kidney stones are generally composed of calcium oxalate or calcium phosphate, they may also consist of uric acid, magnesium-ammonium phosphate, or cystine. Stones develop from a wide variety of metabolic or environmental disturbances, including varying forms of hypercalciuria, hypocitraturia, undue urinary acidity, hyperuricosuria, hyperoxaluria, infection with urease-producing organisms, and cystinuria. The cause of stone formation may be ascertained in most patients using the reliable diagnostic protocols that are available for the identification of these disturbances. Effective medical treatments, capable of correcting underlying derangements, have been formulated. They include sodium cellulose phosphate, thiazide, and orthophosphate for hypercalciuric nephrolithiasis; potassium citrate for hypocitraturic calcium nephrolithiasis; acetohydroxamic acid for infection stones; and D-penicillamine and alpha-mercaptopropionylglycine for cystinuria. Using these treatments, new stone formation can now be prevented in most patients.

Hydrochlorothiazide versus spironolactone: long-term metabolic modifications in patients with essential hypertension

The metabolic side effects of thiazide diuretics are believed to be responsible for the failure of thiazide diuretics to reduce cardiovascular morbidity in patients with hypertension. However, the decrease in the incidence of osteoporotic fractures that are associated with thiazide administration may be relevant in elderly patients with arterial hypertension. Spironolactone (SP) appears not to influence the metabolic risk profile of the patient with hypertension, and no studies have examined its effect on calcium metabolism. Therefore, in 22 patients with mild to moderate essential hypertension, the authors performed a parallel, randomized, double-blind, placebo-controlled study that compared the effects on serum urate and lipid, potassium, magnesium, and calcium metabolism of hydrochlorothiazide (HC) (mean [+/- SD] dose, 72 +/- 26 mg/d) and SP (144 +/- 53 mg/d) during a 52-week period. As compared with placebo, HC significantly increased serum urate and total cholesterol concentrations, and decreased serum potassium levels. SP did not affect serum urate or cholesterol levels but increased serum potassium concentrations. Neither diuretic significantly modified magnesium metabolism. Little changes were seen in serum calcium levels during HC or SP treatment, whereas urinary calcium excretion was significantly decreased by HC (mean decrease, 45%; P less than .01) or SP (40%; P less than .01). The authors conclude that SP, in addition to its potassium-sparing properties, has a calcium-sparing effect that may be beneficial for patients in whom reduction of urinary calcium excretion has a therapeutic value.

The pharmacology and therapeutics of diuretics in the pediatric patient

Selection of appropriate diuretic therapy in children is hampered by a lack of age-specific pharmacokinetic and pharmacodynamic data, especially in premature neonates. Well-designed clinical trials in neonates, infants, and younger children are necessary prerequisites to safer and more efficacious diuretic therapy.

The effect of verapamil and thiazide in the prevention of renal stone formation

The effect of the calcium antagonist verapamil, and of thiazide, a well accepted treatment in the prevention of calcium oxalate renal stones, were examined in an experimental renal stone model. Calcium oxalate stones were induced by the synthetic metabolite of vitamin D3, the alpha-OH-vitamin D3 plus ethylene glycol fed rats. A significant decrease in urinary calcium and oxalate was observed following verapamil treatment. Thiazide significantly decreased urinary calcium, but unlike verapamil, did not decrease urinary oxalate. However, no differences in the radiological findings or in the calcium or magnesium content of the kidneys were observed. Although several animal models have been described for the study of calcium oxalate stones, none has yet been proven useful for the evaluation of stone therapy.

Urolithiasis in children: current medical management

The mechanism of stone formation in the urinary tract is reviewed. Diet, urinary tract infection and metabolic disorders account for the different epidemiological patterns of stone formation. The diagnosis and management of renal tract calculi are discussed. Calcium stones are associated with hypercalciuria, urine acidification defects, the use of furosemide in premature babies, hypercalcaemia, hyperoxaluria, hyperuricosuria, an alkaline urine and hypocitraturia. Uric acid stones occur in acid urine, from increased purine synthesis with lympho- or myeloproliferative disorders or from several inborn errors of purine metabolism which can also cause xanthine or dihydroxyadenine stones. Cystinuria, inherited as an autosomal recessive disorder is best treated with a low sodium diet, a fluid intake exceeding 40 ml/kg per day maintaining urine pH between 7.5 and 8 and, if necessary, with oral penicillamine. Oxalate stones occur in relation to diet, bowel disease and primary inherited defects in oxalate metabolism. Urinary tract infection causing struvite and carbonate apatite formation is the commonest cause of stones in Europe.

Dissolution of staghorn calculus associated with amiloride-hydrochlorothiazide, sulfamethoxazole and trimethoprim, and ascorbic acid

We report a case of a large staghorn calculus of the right kidney that was treated with sulfamethoxazole and trimethoprim, and amiloride-hydrochlorothiazide. The patient, who had refused any surgical intervention, also elected to take ascorbic acid. Without any other treatment x-rays revealed dissolution of the staghorn calculus 8 weeks later.

An inheritable anomaly of red-cell oxalate transport in "primary" calcium nephrolithiasis correctable with diuretics

We measured the rate of oxalate flux across the red-cell membrane in the steady state in 114 patients with a history of calcium oxalate kidney stones and in 25 controls. Of the patients, 98 had recurrent, "idiopathic" kidney stones, 8 had primary hyperparathyroidism, 7 had renal or urinary tract malformations, and 1 had primary hyperoxaluria. Oxalate exchange was significantly higher in the 98 patients with idiopathic stone formation than in the controls (-1.10 +/- 0.95 [SD] X 10(-2) min-1 vs. -0.31 +/- 0.12 X 10(-2); P less than 0.001); it was above the upper limits of normal in 78 of these patients. All 8 patients with hyperparathyroidism and the patient with primary hyperoxaluria had values in the normal range; 2 of the patients with renal or urinary tract malformation had values at the upper normal limit. A study of five families indicated that the abnormality is an autosomal monogenic dominant trait with complete penetrance and variable expressivity. Oxalate-tolerance tests were carried out in five pairs of brothers. One brother in each pair had the abnormality in oxalate flux, and had a significantly higher percentage of oxalate excretion at two hours after oxalate loading (18.09 +/- 3.07 [SD] vs. 10.37 +/- 3.08 percent; t = 3.97; P less than 0.005) and four hours (14.87 +/- 2.91 vs. 9.89 +/- 2.93 percent; t = 2.70; P less than 0.05). Treatment with oral hydrochlorothiazide (50 mg per day) or amiloride (5 mg per day) or both restored normal or nearly normal red-cell oxalate exchange in all of 33 patients who initially had increased rates. We conclude that an inherited cellular defect in oxalate transport may be a factor in "primary" calcium oxalate stone formation and that this defect may be corrected with diuretics.

Correction of hypocitraturia and prevention of stone formation by combined thiazide and potassium citrate therapy in thiazide-unresponsive hypercalciuric nephrolithiasis

Thirteen patients with hypercalciuric calcium nephrolithiasis continued to form calcium stones when treated with thiazide (4.69 +/- 6.62 [mean +/- SD] stones per patient-year to 5.12 +/- 10.87 stones per patient-year), despite adequate hypocalciuric response (a reduction in urinary calcium levels from 303 +/- 119 mg per day to 193 +/- 88 mg per day, p less than 0.01). Because they had hypocitraturia (250 +/- 86 mg per day versus 643 +/- 236 mg per day in normal subjects, p less than 0.001), potassium citrate (10 to 20 meq three times per day) was added to the ongoing treatment program. During combined treatment with thiazide and potassium citrate, urinary pH significantly rose, and normal levels of urinary citrate were restored. Ten patients stopped forming new stones and all 13 had reduced stone formation rate. Thus, potassium citrate supplementation should be considered in patients requiring thiazide therapy for the control of hypercalciuric nephrolithiasis, especially if they have concurrent hypocitraturia or if it develops during thiazide therapy.

Diuretics and calcium metabolism

In this review the normal renal tubular handling of calcium is briefly described. A detailed examination follows of the sites and modes of action of furosemide and thiazide diuretics on renal calcium handling and overall calcium metabolism. The clinical applications of these effects are also considered. Finally, the use of diuretics with different tubular sites of action on calcium transport as probes to study disorders of calcium excretion is discussed.