Studies on the site of renal salt loss in a patient with Bartter's syndrome

First-in-Man Demonstration of Direct Endothelin-Mediated Natriuresis and Diuresis

Endothelin (ET) receptor antagonists are potentially novel therapeutic agents in chronic kidney disease and resistant hypertension, but their use is complicated by sodium and water retention. In animal studies, this side effect arises from ETB receptor blockade in the renal tubule. Previous attempts to determine whether this mechanism operates in humans have been confounded by the hemodynamic consequences of ET receptor stimulation/blockade. We aimed to determine the effects of ET signaling on salt transport in the human nephron by administering subpressor doses of the ET-1 precursor, big ET-1. We conducted a 2-phase randomized, double-blind, placebo-controlled crossover study in 10 healthy volunteers. After sodium restriction, subjects received either intravenous placebo or big ET-1, in escalating dose (≤300 pmol/min). This increased plasma concentration and urinary excretion of ET-1. Big ET-1 reduced heart rate (≈8 beats/min) but did not otherwise affect systemic hemodynamics or glomerular filtration rate. Big ET-1 increased the fractional excretion of sodium (from 0.5 to 1.0%). It also increased free water clearance and tended to increase the abundance of the sodium-potassium-chloride cotransporter (NKCC2) in urinary extracellular vesicles. Our protocol induced modest increases in circulating and urinary ET-1. Sodium and water excretion increased in the absence of significant hemodynamic perturbation, supporting a direct action of ET-1 on the renal tubule. Our data also suggest that sodium reabsorption is stimulated by ET-1 in the thick ascending limb and suppressed in the distal renal tubule. Fluid retention associated with ET receptor antagonist therapy may be circumvented by coprescribing potassium-sparing diuretics.

Pathophysiology and clinical presentations of salt-losing tubulopathies

At least three renal tubular segments are involved in the pathophysiology of salt-losing tubulopathies (SLTs). Whether the pathogenesis starts either in the thick ascending limb of the loop of Henle (TAL) or in the distal convoluted tubule (DCT), it is the function of the downstream-localized aldosterone sensitive distal tubule (ASDT) to contribute to the adaptation process. In isolated TAL defects (loop disorders) ASDT adaptation is supported by upregulation of DCT, whereas in DCT disorders the ASDT is complemented by upregulation of TAL function. This upregulation has a major impact on the clinical presentation of SLT patients. Taking into account both the symptoms and signs of primary tubular defect and of the secondary reactions of adaptation, a clinical diagnosis can be made that eventually leads to an appropriate therapy. In addition to salt wasting, as occurs in all SLTs, characteristic features of loop disorders are hypo- or isosthenuric polyuria and hypercalciuria, whereas characteristics of DCT disorders are hypokalemia and (symptomatic) hypomagnesemia. In both SLT categories, replacement of urinary losses is the primary goal of treatment. In loop disorders COX inhibitors are also recommended to mitigate polyuria, and in DCT disorders magnesium supplementation is essential for effective treatment. Of note, the combination of a salt- and potassium-rich diet together with an adequate fluid intake is always the basis of long-term treatment in all SLTs.

Impaired Urine Dilution Capability in HIV Stable Patients

Renal disease is a well-recognized complication among patients with HIV infection. Viral infection itself and the use of some antiretroviral drugs contribute to this condition. The thick ascending limb of Henle's loop (TALH) is the tubule segment where free water clearance is generated, determining along with glomerular filtration rate the kidney's ability to dilute urine. Objective. We analyzed the function of the proximal tubule and TALH in patients with HIV infection receiving or not tenofovir-containing antiretroviral treatment in comparison with healthy seronegative controls, by applying a tubular physiological test, hyposaline infusion test (Chaimowitz' test). Material & Methods. Chaimowitz' test was performed on 20 HIV positive volunteers who had normal renal functional parameters. The control group included 10 healthy volunteers. Results. After the test, both HIV groups had a significant reduction of serum sodium and osmolarity compared with the control group. Free water clearance was lower and urine osmolarity was higher in both HIV+ groups. Proximal tubular function was normal in both studied groups. Conclusion. The present study documented that proximal tubule sodium reabsorption was preserved while free water clearance and maximal urine dilution capability were reduced in stable HIV patients treated or not with tenofovir.

Localization of tubular adaptation to renal sodium loss in Gitelman syndrome

BACKGROUND AND OBJECTIVES

Gitelman syndrome (GS) is a salt-wasting tubulopathy that results from the inactivation of the human thiazide-sensitive sodium chloride cotransporter located in the distal convoluted tubule. Tubular adaptation to renal sodium loss has been described and localized in the distal tubule in experimental models of GS but not in humans with GS.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The tubular adaptation to renal sodium loss is described. Osmole-free water clearance and endogenous lithium clearance with furosemide infusion are used to compare 7 patients with genetically confirmed GS and 13 control participants.

RESULTS

Neither endogenous lithium clearance nor osmole-free water clearance disclosed enhanced proximal fluid reabsorption in patients with GS. These patients displayed significantly lower osmole-free water clearance factored by inulin clearance (7.1 ± 1.9 versus 10.1 ± 2.2; P<0.01) and significantly lower fractional sodium reabsorption in the diluting nephron (73.2% ± 7.1% versus 86.1% ± 4.7%; P<0.005), consistent with the inactivation of the thiazide-sensitive sodium chloride cotransporter. The furosemide-induced reduction rate of fractional sodium reabsorption in the diluting segment was higher in patients with GS (75.6% ± 6.1% versus 69.9% ± 3.2%; P<0.039), suggesting that sodium reabsorption would be enhanced in the cortical part of the thick ascending limb of the loop of Henle in patients with GS.

CONCLUSIONS

These findings suggest that tubular adaptation to renal sodium loss in GS would be devoted to the cortical part of the thick ascending limb of the loop of Henle in humans.

Threading through the mizmaze of Bartter syndrome

The story, described here in detail, started in 1962 with the publication of a seminal paper by Frederic Bartter et al. in the December issue of the American Journal of Medicine. The authors reported two pediatric patients with hitherto undescribed features, namely growth and developmental delay associated with hypokalemic alkalosis and normal blood pressure despite high aldosterone production. It soon became clear that this condition was not so exceptional. The syndrome named after Bartter was actually identified in children as well as in adults, females as well as males and in all five continents. It took almost four decades to clarify the exact nature of the disease. Bartter disease is an autosomal recessive disorder with four genotypes and mainly two phenotypes. Moreover, there are acquired secondary forms of Bartter syndrome as well as pseudo-Bartter syndromes. The history demonstrates the power of genetics but also illustrates the fundamental and irreplaceable contributions from nephrologists and renal physiologists.

Mutation G47R in the BSND gene causes Bartter syndrome with deafness in two Spanish families

Bartter syndrome (BS) is a heterogeneous group of autosomal recessive hypokalaemic salt-losing tubulopathies. Five types of BS caused by different genetic defects have been identified, and one of them is associated with sensorineural deafness (BSND). Mutations in the recently described BSND gene, mapped in chromosome 1p31, have been reported to be associated with BSND. This gene encodes barttin, an essential beta-subunit subunit for ClC-Ka and ClC-Kb channels. Both subunits are co-expressed in basolateral membranes of renal tubules, in the ascending limb of the loop of Henle, and in the stria vascularis of the inner ear. We studied two apparently unrelated Spanish families from the Canary Islands, with five members showing this pathology. Sequence analysis of the BSND gene showed that the affected members were homozygous for a C-to-T transition in exon 1, while their parents were heterozygous. This alteration results in a missense mutation, G47R, which has been previously shown to abolish the stimulatory effect on the subunit barttin of the ClC-Kb channel. Our results indicate that families with the G47R mutation indeed present polyhydramnios, premature birth and salt loss. Nevertheless, glomerular filtration rate was normal in all patients. Clinical manifestations are moderate in patients with the G47R mutation compared to other published data form patients with BSND. This constitutes the first report of BSND cases in Spain.

[Primary molecular changes and secondary biological problems in Bartter and Gitelman syndrome]

Bartter syndrome and Gitelman syndrome are primary hereditary diseases characterized by hypokaliemia, alkalosis, hypertrophy of the juxtaglomerular complex with secondary hyperaldoteronism and normal blood pressure. They result from molecular disorders leading to a defect of sodium reabsorption in respectively the Henle's loop and the distal convoluted tubule. Biological adaptations of downstream tubular segments, i.e. distal convoluted tubule and collecting duct, are responsible for hypokaliemia, alkalosis, renin-aldosterone activation, prostaglandins hypersecretion and dysregulation of the urinary excretion of calcium and magnesium, illustrating the close integration of the regulation of different solutes in the distal tubular structures.

The pathophysiological and molecular basis of Bartter's and Gitelman's syndromes

Molecular defects affecting the transport of sodium, potassium and chloride in the nephron through the ROMK K+ channel, Na+/K+/2Cl- cotransporter, the Na+/Cl- cotransporter and chloride channel have been identified in patients with Bartter's and Gitelman's syndromes. Defects of the angiotensin II type I receptor and CFTR have also being described. These defects are simple (i.e., most are single amino acid substitutions) but affect key elements in tubular transport. The simplicity of the genetic defects may explain why the inheritance of these conditions remains unclear in most kindreds (i.e., not just recessive or dominant) and emphasises the crucial importance of the conformational structure of these channels. Application of this molecular information will allow the early genetic identification of patients with these syndromes and enable us to differentiate between the various disorders at a functional level. It may also identify a subgroup in which the heterozygous form may make patients potentially exquisitely sensitive to diuretics.

Studies on the site of renal tubular defect in Bartter's syndrome

Renal tubular function was studied in an 8-month-old male infant with Bartter's syndrome, which is characterized by hypokalemic metabolic alkalosis, normotensive hyperreninemic hyperaldosteronism, and reduced pressor response to angiotensin II. Chloride transport along the diluting segment (CH2O/CH2O + CCl) was impaired. Furthermore, furosemide did not elicit normal natriuresis, which suggested impaired chloride reabsorptive capacity at the furosemide-sensitive ascending limb of Henle's loop. Loss of antidiuretic hormone-mediated urinary concentration was in support of this. These findings pointed to the thick ascending limb of Henle's loop as the site of the primary defect in this child.

Impaired response to furosemide in hyperprostaglandin E syndrome: evidence for a tubular defect in the loop of Henle

In hyperprostaglandin E syndrome (HPS) renal wasting of electrolytes and water is consistently associated with enhanced synthesis of prostaglandin E2. In contrast to Bartter or Gitelman syndrome (BS/GS), HPS is characterized by its severe prenatal manifestation, leading to fetal polyuria, development of polyhydramnios, and premature birth. This disorder mimics furosemide treatment with hypokalemic alkalosis, hypochloremia, isosthenuria, and impaired renal conservation of both calcium and magnesium. Therefore the thick ascending limb of the loop of Henle seems to be involved in HPS. To characterize the tubular defect we investigated the response to furosemide (2 mg/kg) in HPS (n = 8) and BS/GS (n = 3) 1 week after discontinuation of long-term indomethacin treatment. Sensitivity to furosemide was completely maintained in patients with BS/GS. The diuretic, saluretic, and hormonal responses were similar to those of a control group of healthy children (n = 13), indicating an intact function of the thick ascending limb of the loop of Henle in BS/GS. In contrast, patients with HPS had a marked resistance to this loop diuretic. Furosemide treatment increased urine output by 7.5 +/- 0.7 ml/kg per hour in healthy control subjects but only by 4.4 +/- 1.2 ml/kg per hour (p < 0.5) in children with HPS. In parallel, the latter also had a markedly impaired saluretic response (delta Cl(urine) 0.14 +/- 0.04 mmol/kg per hour vs 0.85 +/- 0.09 mmol/kg per hour, p < 0.001; delta Na(urine) 0.23 +/- 0.06 mmol/kg per hour vs 0.77 +/- 0.09 mmol/kg per hour, p < 0.001). Furosemide therapy further enhanced prostaglandin E2 excretion in patients with HPS (54 +/- 17 to 107 +/- 28 ng/hr per 1.73 m2, p < 0.05), whereas no significant effect was observed in healthy children (20 +/- 3 to 12 +/- 3 ng/hr per 1.73 m2). We conclude that a defect of electrolyte reabsorption in the thick ascending limb of the loop of Henle plays a major role in HPS.

Bartter's syndrome: the unsolved puzzle

Bartter's syndrome is a congenital abnormality characterized by metabolic alkalosis [corrected], hyperreninemic hyperaldosteronism, and hypokalemia. Most patients present early in life with symptoms such as muscle weakness and polyuria, which may be attributed to potassium depletion. Despite the hyperaldosteronism, the patients tend to be normotensive, which is at least partially explained by vascular hyporesponsiveness to pressor hormones. Numerous studies have documented increased renal excretion of prostaglandins. Several different patterns of aberrant renal ion transport have been observed in patients with the syndrome, suggesting that it actually may represent a family of related but distinct tubular disorders. Therapeutic approaches to Bartter's syndrome include potassium supplementation, prostaglandin synthesis inhibitors (nonsteroidal anti-inflammatory agents), aldosterone antagonists, and converting enzyme inhibitors. During the first two decades following its initial description, Bartter's syndrome was the focus of widespread interest, based on the likelihood that its investigation might provide insight into the normal functioning of the renin-angiotensin-aldosterone and prostanoid hormone systems. During the past decade, however, little additional progress has been made in Bartter's syndrome, and its patho-physiology remains poorly understood.

Effects of subclinical hyperthyroidism on renal handling of water and electrolytes in patients with nodular goiter

Evidence is beginning to accumulate that minor degrees of hyperthyroidism lead to adverse effects in various tissues, even though clinically the patients are euthyroid. To determine whether these anomalies in thyroid function have deleterious effects on renal function and electrolyte metabolism, the plasma concentrations of electrolytes, urea, and creatinine, the renal handling of water and sodium, and the urinary excretion of these substances were measured in patients with nodular goiter who were displaying stable subclinical hyperthyroidism. The studies were carried out before and after correcting the thyroid dysfunction. Restoration of euthyroidism did not modify any of the renal function parameters studied and did not cause changes in blood analyte levels. The data show that treatment of minor degrees of hyperthyroidism does not have any effects on renal function and electrolyte metabolism, and confirm the well-known capacity of the kidney to adjust its functions to changes induced by an abnormal secretion of thyroid hormones.

Erythrocyte sodium transport in Bartter's syndrome

Erythrocyte sodium transport was evaluated by measurement of intracellular Na concentration (ICNa), 22Na efflux rate constant (NaERC) and 3H-ouabain binding (BMax) (reflecting the number of Na/K ATPase pump sites) in 9 children with Bartter's syndrome compared to controls (children and adults) and children with various forms of salt wasting disease. There were no differences between control children and adults. In untreated Bartter's syndrome ICNa was significantly increased with NaERC and BMax significantly decreased compared to findings in controls and patients with other salt wasting disease. On prostaglandin synthetase inhibitor (Indomethacin) therapy, ICNa decreased but remained higher than in controls, NaERC increased to normal values but BMax remained low. These data support the view that there is a widespread defect in membrane electrolyte transport in Bartter's syndrome but suggest that the benefit of indomethacin therapy is not manifest via an effect on Na/K ATPase.

The effect of hydropenia and oral water loading on renal lysozyme handling and N-acetyl-beta-D-glucosaminidase excretion in man

To substantiate the effects of urine flow rate on renal lysozyme handling and N-acetyl-beta-D-glucosaminidase (NAG) excretion, experiments were performed in normal human subjects. Urine flow rate was varied by overnight fluid deprivation and progressive diuresis induced by oral water loading. Lysozyme measurements were made using an improved turbidimetric method and NAG determinations using a modified fluorometric assay utilising individual recovery techniques. Fractional lysozyme clearance and lysozyme excretion demonstrated a nearly linear relationship with urine flow rate (r = 0.78, r = 0.80, P less than 0.0005), and both were elevated significantly in samples obtained during diuresis. NAG excretion, however, demonstrated a significant but weak correlation (r = 0.47, P less than 0.005) with fractional urine flow rate. A significant (P less than 0.05) difference in NAG activity occurred only during the period of hydropenia, when a decrease in excretion was observed. These findings suggest that the effect of diuresis on lysozyme excretion should be considered in studies utilising this enzyme as a marker of renal injury.

Urinary prostaglandins in Bartter's and pseudo-Bartter's syndrome

Renal secretion of prostaglandins (PG) in Bartter's syndrome and in different forms of hypokalemic normotensive syndromes (pseudo-Bartter's syndrome) was measured to determine if it is possible to use the measurement of urinary prostaglandins for the discrimination of different etiologies. Prostaglandins E2, F2 alpha, 6-keto-PGF1 alpha and thromboxane B2 (TxB2) were measured after extraction and chromatography by radioimmunoassay in 19 patients and in 26 control healthy subjects. Bartter's syndrome may be characterized as primary renal hyperprostaglandinism with high urinary PGE2 excretion. It can be dissociated from pseudo-Bartter's syndrome because the urinary PGE2 excretion is always in the normal range in the pseudosyndrome. Abuse of loop diuretics may have effects that mimic Bartter's syndrome since these diuretics stimulate urinary prostaglandin excretion. Therefore, loop diuretics should always be excluded prior to the diagnosis of Bartter's syndrome.

Idiopathic hypercalciuria associated with hyperreninemia and high urinary prostaglandin E

A patient with idiopathic hypercalciuria and some features suggestive of Bartter syndrome is reported. Excessive urinary prostaglandin E (PGE) excretion and renal calcium leak were documented in this child. Treatment with aspirin and indomethacin reduced urinary PGE excretion and was associated with a decrease in daily calcium excretion. At the lowest levels of urinary PGE, the renal calcium leak was no longer evident although mild hypercalciuria persisted. These results suggest that PGE may play a role in some cases of idiopathic hypercalciuria.

Erythrocyte Na+ and K+ transport systems in children with Bartter syndrome: increase in passive sodium permeability

Na+ and K+ intracellular content was studied in five children with Bartter syndrome and their age and race-paired controls. Na+ and K+ pump (ouabain sensitive) fluxes, Na+-K+ co-transport (furosemide sensitive), and rate constants of passive Na+ and K+ permeability were determined in each patient and control and also in six parents. The results show that in Bartter syndrome, there is a significant increase in the rate constant of passive Na+ permeability without any change in passive K+ permeability. This increase in the rate constant of passive permeability might explain at least partially the increased intracellular Na+ concentration also found in these patients. Moreover, the maximal rate of ouabain sensitive Na+ efflux was increased slightly, and co-transport fluxes were variable. Parents of patients had normal erythrocyte fluxes.

The role of chloride transport in the thick ascending limb in the pathogenesis of Bartter's syndrome

Fractional chloride reabsorption in the thick ascending limb of the loop of Henle, measured by clearance techniques, is subnormal in patients with Bartter's syndrome. This defect is a marker for the syndrome and, presumably, is the cause of the supranormal tubular secretion of potassium that characterizes the disorder. The potassium depletion that results from excessive potassium excretion is probably the stimulus for the increased synthesis of prostacyclin by blood vessels and prostaglandin E2 by kidneys that occurs in Bartter's syndrome. The overproduction of prostaglandins mediates hyperreninemia, supranormal plasma bradykinin, supranormal plasma norepinephrine and vascular resistance to the pressor effects of angiotensin II and norepinephrine; treatment with a prostaglandin synthetase inhibitor corrects these abnormalities. Increases in angiotensin II and in norepinephrine appear to be compensatory changes, occurring in response to vasodilatation induced by vascular prostaglandins to maintain blood pressure. The hyperreninemia also stimulates production of aldosterone with aggravation of potassium loss.

Surreptitious diuretic ingestion and pseudo-Bartter's syndrome

A patient with profound hypokalemia satisfied the criteria for Bartter's syndrome, including hyperreninemia, aldosteronism, normal blood pressure, and hyperplasia of the juxtaglomerular apparatus. Two screening tests of urine and one of plasma for diuretic agents gave negative results. A third urinary sample gave negative results for thiazide but positive for furosemide; the fourth and fifth samples gave negative results for furosemide but positive for thiazide. Urinary prostaglandin excretion was normal. We conclude that this apparent case of Bartter's syndrome was caused by long term surreptitious diuretic ingestion and suggest this may occur more frequently than is generally appreciated.

Studies on the pathogenesis of Bartter's syndrome

There is no agreement concerning the primary pathogenetic event leading to Bartter's syndrome. Free water clearance and distal fractional chloride reabsorption were abnormally low in our patient with Bartter's syndrome. This series of investigations in this patient with Bartter's syndrome and hypomagnesemia was undertaken to determine if the defect in chloride transport in the ascending limb and the associated renal potassium wasting was specifically related to potassium depletion, increased prostaglandin production or magnesium depletion. Neither potassium repletion, indomethacin administration nor magnesium repletion had an effect on the defect in free water clearance or in distal fractional chloride reabsorption. However, magnesium infusion eliminated renal potassium wasting. These observations suggest that the proximate cause of Bartter's syndrome in this patient is a primary defect in the reabsorption of sodium chloride in the ascending limb and not renal potassium wasting. however, hypomagnesemia may contribute to the renal potassium wasting seen in this syndrome.

Postnatal development of renal sodium handling in premature infants

To estimate the contribution of the specific defect in proximal and distal tubular reabsorption of sodium to renal salt wasting, fractional sodium excretion, distal tubular sodium delivery, and distal tubular sodium reabsorption were determined in 11 healthy premature infants. The study was performed on the seventh day and at weekly intervals thereafter up to the sixth week of life. Sodium clearance and fractional sodium excretion decreased significantly with increasing postnatal age (P less than 0.001). There was no significant alteration in either osmolar or free-water clearances. Distal tubular sodium delivery steadily decreased from 4.96 +/- 0.66 (mean +/- SE) in the first week to 3.3 +/- 0.41 ml/minute/dl GFR in the sixth week of life (P less than 0.05). Distal tubular sodium reabsorption was 69.5 +/- 2.36% in the first week, then rose significantly to reach a value of 83.7 +/- 1.85% in the second week (P less than 0.001) and remained practically unchanged thereafter. It is suggested that the rapid improvement of distal tubular sodium reabsorption in premature infants might result from forced stimulation by the excessively activated renin-angiotensin-aldosterone system.

The acidification defect in the syndrome of renal tubular acidosis with nerve deafness

An 8-year-old boy with renal tubular acidosis and nerve deafness, has been followed for seven years. Repeated studies of his renal acidification defect showed that until the age of six years the tubular defect was mixed, proximal and distal (type 1,2 hybrid). After that age the defect of proximal acidification disappeared and the patient only presented a distal renal tubular acidosis type 1. When this is associated with nerve deafness, it is considered a distinct nosological entity.

Evidence for a prostaglandin-independent defect in chloride reabsorption in the loop of Henle as a proximal cause of Bartter's syncrome

Maximal free-water clearance was measured in five patients with Bartter's syndrome and in five patients with the hypokalemic alkalosis of persistent psychogenic vomiting. Hypokalemic alkalosis, hyperreninemia, hyperaldosteronism and excessive renal production of prostaglandin E2 were present in the patients with both disorders. Maximal free water clearance was abnormally low, in association with a high clearance of chloride, in all the patients with Bartter's syndrome; it was normal in all the patients with psychogenic vomiting. In the patients with Bartter's syndrome, apparent distal delivery of proximal tubular fluid was inversely related to glomerular filtration rate and was excessive only in those patients with a low glomerular filtration rate. Patients with psychogenic vomiting showed mean distal fractional chloride reabsorption of 0.92 +/- 0.04 (standard error [SE]). In the patients with Bartter's syndrome, distal fractional reabsorption of chloride was 0.49 +/- 0.08 and was the same (0.46 +/- 0.06) during inhibition of prostaglandin synthesis with indomethacin therapy. Thus, a prostaglandin-independent defect in chloride reabsorption in the loop of Henle is the most proximal cause for the abnormalities in Bartter's syndrome thus far identified.

Sodium wasting, acidosis and hyperkalemia induced by methicillin interstitial nephritis. Evidence for selective distal tubular dysfunction

A 61 year old male patient was studied who manifested dehydration, azotemia, acidosis and hyperkalemia six weeks after exposure to methicillin. Thyroid and adrenal glucocorticoid and mineralocorticoid function were normal. The dehydration was found to be caused by a profound sodium-losing nephropathy; urinary sodium ranged from 78 to 101 meq/day during a salt restricted diet. A distal renal tubular acidosis and a quantitively impaired ability to excrete potassium were also found. These defects were relatively unresponsive to mineralocorticoid or prednisone therapy. A renal biopsy specimen showed an interstitial nephritis which selectively affected distal tubules and was thought to be secondary to methicillin. The data suggest functional impairment specific for the distal tubule, but with only a modest decrease in the glomerular filtration rate.

Bartter's syndrome: an overview

Bartter's syndrome, which is characterized by hypokalemic hypochloremic alkalosis, renal juxtaglomerular hyperplasia, elevated renin and aldosterone, and normal or low blood pressure, has been ascribed to a variety of etiologies. Most recently, the prostaglandins have been in the forefront of the pathophysiologic discussion. Two cases with appropriate renal biopsies are reviewed, as are the clinicopathologic pathways. It is important that strict criteria be applied, and confirmation by renal biopsy is urged.

The pathogenesis of Bartter's syndrome. Functional and histologic studies

We describe a patient with Bartter's snyndrome. In addition to the well-known characteristic findings by light microscopy, electron micrograms confirmed the presence of juxtaglomerular cell hyperplasia with polymorphous renin secretory granules and dense multivesicular bodies. Volume expansion by albumin infusion decreased plasma renin activity and aldosterone excretion, and improved the pressor response to exogenous angiotensin, suggesting that the renin-angiotensin-aldosterone system was not autonomous but that a decreased extracellular volume might be a major defect in this patient. During hypotonic saline diuresis, moreover, fractional free water clearance per fractional distal sodium delivery, CH2O/CH2O + CNa, was markedly depressed in the patient when compared with the value in the controls. Evidence presented suggests that chronic extracellular volume depletion exists as a consequence of an impaired sodium transport in the ascending limb of Henle's loop.

Prostaglandins and aspirin therapy in Bartter's syndrome

A young patient with Bartter's syndrome was treated for three months with 100 mg/kg/day of aspirin to inhibit prostaglandin synthesis. Clinical symptoms resolved and serum-potassium increased from 2-9 to 3-5 mmol/l. Urinary excretion and plasma concentration of prostaglandins E and F were significantly reduced during aspirin therapy. Plasma-renin activity declined from 85 to 20 ng/ml/h (normal 1-5-4 mg/ml/h) and hyperaldosteronism was corrected. These results suggest that overproduction of prostaglandins has a central role in the pathogenesis of Bartter's syndrome.

Role of prostaglandins in the pathogenesis of Bartter's syndrome

Increased renal prostaglandins activated by beta-catecholamines could produce renal tubular sodium wasting and angiotensin pressor resistance observed in Bartter's syndrome. We therefore measured plasma renin activity (PRA), aldosterone and prostaglandin A (PGA) by radioimmunoassay, and body composition by isotope dilution prior to and following beta-adrenergic blockade with propranolol (200 mg/day for 4 days) and prostaglandin synthesis inhibition by indomethacin (200 mg/day for 4 days) in a patient with Bartter's syndrome on a 250 meq sodium diet. After the administration of propranolol, body weight increased 3 kg, daily urine sodium decreased within 24 hours from 230 to 64 meq, and urine potassium from 102 to 45 meq, but PRA and the aldosterone level remained elevated. With the administration of indomethacin, body weight increased 5 kg, daily urinary sodium decreased within 24 hours to 11meq and urine potassium to 16 meq, PRA (normal less than 3 ng/100 ml/hour) decreased from 55 to 4.3 ng/ml/hour, plasma aldosterone (normal less than 8 ng/100 ml) from 74.1 to 3.6 ng/100 ml, and whole blood PGA (normal 546 +/- 307 pg/ml) decreased from 1,390 and 945 to 86 pg/ml. After the administration of propranolol or indomethacin, exchangeable sodium, total body water, extracellular volume and plasma volume all increased from less than to greater than predicted, and pressor resistance to angiotensin was normalized. These results suggest that Bartter's syndrome results from beta adrenergic and prostaglandin-mediated proximal tubular rejection of sodium leading to increased distal sodium-potassium exchange.

Distal renal tubular acidosis in infancy: a bicarbonate wasting state

Three unrelated infants with apparently distal RTA were investigated. Growth retardation, polyuria, nephrocalcinosis, inappropriately high urinary pH, and marked dependence of bicarbonate excretion on urinary flow were characteristic of the distal or classic form of RTA, but the urinary loss of bicarbonate at normal serum values exceeded that usually found in children or adults with this disorder. Renal tubular function was studied during hypotonic saline diuresis in the three patients and in seven healthy control infants of similar age. Fractional delivery of sodium to the distal nephron was significantly higher in the patients than in control subjects. Sodium transport at the diluting segment was not impaired. The results support the assumption that the bicarbonate wasting was the consequence of an increased delivery of this substance to an already impaired distal nephron and thus further inhibited the distal mechanisms of net acid excretion.