Effects of electrolyte disorders on renal structure and function

A case of pseudo-Bartter/Gitelman syndrome caused by long-term laxative abuse, leading to end-stage kidney disease

Pseudo-Bartter/Gitelman syndrome (PBS/PGS) is a disorder that presents with hypokalemia and metabolic alkalosis resembling Gitelman syndrome (GS) due to secondary factors, such as lifestyle and /or medicines. Notably, PBS/PGS is more likely to cause renal dysfunction than GS. We report the first case of PBS/PGS due to long-term laxative abuse leading to end-stage kidney disease (ESKD). The patient was a 49-year-old woman with a history of constipation since school, who had used excessive doses of laxatives on her own judgment for nine years at least from 22 years of age. Two years later, blood tests revealed hypokalemia (serum K 3.1 mEq/L), and nine years later, the patient's renal function began to deteriorate (Cr-eGFR 48.7 mL/min/1.73 m2). Since abuse of laxatives was suspected as the cause, it was changed to the proper dosage of laxatives. At 33 years, the patient developed acute kidney injury (AKI), due to a urinary tract infection, and required intensive treatment, including hemodialysis. Although the patient was eventually weaned off dialysis, the renal function did not recover to pre-AKI levels. In suspected GS, comprehensive genetic testing for renal disease-related genes was performed; however, no obvious pathogenic variants were identified. Thereafter, despite decreasing the laxative doses and potassium supplementation, her renal function continued to decline. At 49 years, the patient developed ESKD and was started on maintenance hemodialysis. PBS/PGS is a disease that can lead to ESKD. An early diagnosis of PBS/PGS is crucial to prevent renal function deterioration, and the underlying causes should be removed immediately.

Improvement in Tubulointerstitial Nephritis With Glucocorticoid Therapy in an Anorexia Nervosa Patient

Anorexia nervosa is a psychiatric disorder that is often diagnosed in adolescents and young adults. Renal-related complications of anorexia nervosa include abnormal water metabolism, electrolyte abnormalities, and nephrocalcinosis, which may lead to irreversible renal damage. Furthermore, tubulointerstitial nephritis has been reported as a renal pathological feature of anorexia nervosa. Immunosuppressive therapy, such as with glucocorticoids, has been recommended for idiopathic interstitial nephritis treatment; however, the effectiveness of immunosuppressive therapy for interstitial nephritis in patients with anorexia nervosa remains unestablished. Here, we report a case of interstitial nephritis in a patient with anorexia nervosa whose renal function was successfully improved with glucocorticoid therapy. The patient was a 38-year-old woman who was referred for renal dysfunction (estimated glomerular filtration rate: 7.6 mL/min/1.73 m2). She had anorexia nervosa and repeated episodes of vomiting. Hypokalemia (K: 2.1 mEq/L) and metabolic alkalosis (HCO3-: 54.2 mEq/L) were observed. Fluid therapy and potassium supplementation did not improve renal function; therefore, a percutaneous renal biopsy was performed. The renal pathology results revealed interstitial fibrosis, inflammatory cell infiltration in the interstitium, and tubulitis, suggesting a diagnosis of tubulointerstitial nephritis. Glucocorticoid therapy improved the patient's renal function to an estimated glomerular filtration rate of 19.91 mL/min/1.73 m2, and the renal function remained stable thereafter. This case suggests that glucocorticoid therapy may be considered for the treatment of interstitial nephritis in patients with anorexia.

Potassium Metabolism and Management in Patients with CKD

Potassium (K), the main cation inside cells, plays roles in maintaining cellular osmolarity and acid-base equilibrium, as well as nerve stimulation transmission, and regulation of cardiac and muscle functions. It has also recently been shown that K has an antihypertensive effect by promoting sodium excretion, while it is also attracting attention as an important component that can suppress hypertension associated with excessive sodium intake. Since most ingested K is excreted through the kidneys, decreased renal function is a major factor in increased serum levels, and target values for its intake according to the degree of renal dysfunction have been established. In older individuals with impaired renal function, not only hyperkalemia but also hypokalemia due to anorexia, K loss by dialysis, and effects of various drugs are likely to develop. Thus, it is necessary to pay attention to K management tailored to individual conditions. Since abnormalities in K metabolism can also cause lethal arrhythmia or sudden cardiac death, it is extremely important to monitor patients with a high risk of hyper- or hypokalemia and attempt to provide early and appropriate intervention.

Non-uniform Progression of Chronic Tubulointerstitial Nephritis and Widespread Nephrocalcification in a Patient with Anorexia Nervosa

Although patients with anorexia nervosa (anorexia) are known to show tubulointerstitial nephritis (TIN), the pathophysiology of its progression is not fully understood. We herein report a 31-year-old woman with anorexia who showed acute exacerbation of chronic kidney disease. Renal biopsy showed non-uniform chronic TIN; some areas were obsolete lesions and other areas were active lesions. In addition, many calcium-containing crystals were widely deposited in the distal tubules. The results suggest that chronic TIN in the setting of anorexia does not uniformly progress and that not only TIN but also widespread calcification of distal tubules might aggravate the renal function of anorexia patients.

Risk factors, complication and measures to prevent or reverse catastrophic sodium overcorrection in chronic hyponatremia

Hyponatremia is the most common electrolyte disorder encountered in clinical practice. Patients who develop this condition for more than 48 hours are at risk for severe neurological sequelae if correction of the serum sodium occurs too rapidly. Certain medical disorders are known to place patients at an increased risk for rapid correction of serum sodium concentration. Large-volume polyuria in this setting is an ominous sign. For these patients, early identification of risk factors, close monitoring of serum sodium correction and the use of 5% dextrose with or without desmopressin to prevent or reverse overcorrection are important components of treatment.

Two novel genotypes of the thiazide-sensitive Na-Cl cotransporter (SLC12A3) gene in patients with Gitelman's syndrome

Gitelman's syndrome is an autosomal recessive disorder marked by salt wasting and hypokalaemia resulting from loss-of-function mutations in the SLC12A3 gene that codes for the thiazide-sensitive Na-Cl cotransporter. Gitelman's syndrome is usually distinguished from Bartter's syndrome by the presence of both hypomagnesaemia and hypocalciuria. Although recent advances in molecular genetics may make it possible to both diagnose and differentiate these diseases, the phenotypes sometimes overlap. Here we report two sporadic cases of Gitelman's syndrome and two novel genotypes of SLC12A3. Patient 1 was a compound heterozygote with a known missense mutation, L849H, and a novel mutation, R852H in exon 22. Patient 2 was homozygous for the missense mutation L849H. To our knowledge, this is the first report of a patient homozygous for 849H. Interestingly, both patients were affected with autoimmune thyroid disease. Patient 1 was affected with Hashimoto's disease, and Patient 2 was affected with Graves' disease. The symptoms of Patient 2 were more serious than those of Patient 1. Although the patients both carried the 849H allele (Patient 1 as a heterozygote and Patient 2 as a homozygous), their clinical symptoms differed. The difference in the clinical features may have been due both to phenotypic differences and the fact that Gitelman's syndrome is a complicated disorder.

Impaired osmoregulation in anorexia nervosa: a case-control study

BACKGROUND

Anorexia nervosa (AN) has been associated with abnormal osmoregulation and impaired urinary concentrating capacity. Conflicting results suggest that the disorder may be related to hypothalamic dysfunction and/or a primary renal defect. The role of antidepressants, which are increasingly prescribed in AN patients, has not been evaluated.

METHODS

We analysed renal function as well as electrolyte disturbances and osmoregulation parameters at baseline and following a water deprivation test in 12 well-defined AN patients (all females, 10 taking antidepressants) vs 12 age-matched controls and 11 young female patients taking antidepressants.

RESULTS

In comparison with matched controls, patients with AN were characterized by a significant alteration of osmoregulation both at baseline [lower plasma sodium and osmolality, abnormally high levels of antidiuretic hormone (ADH) and tendency towards more concentrated urine] and after water deprivation (impaired ADH reaction and lower urinary concentrating ability). The AN patients had no electrolyte abnormalities. The two patients with the shortest duration of AN showed a normal urinary concentrating ability. Patients taking antidepressants showed similar but less marked changes than AN patients, including a lower urinary concentrating ability.

CONCLUSIONS

These results show that AN patients are characterized by abnormal osmoregulation at baseline and a lack of reactivity of ADH with a significant urinary concentrating defect after water deprivation. The origin of these defects in AN patients is probably multifactorial, but the duration of the disease and the prescription of antidepressants could play a role.

Possible liposomal amphotericin B-induced nephrogenic diabetes insipidus

OBJECTIVE

To report the development of nephrogenic diabetes insipidus (NDI) associated with the use of high-dose liposomal amphotericin B.

CASE SUMMARY

A 38-year-old white man with relapsed acute myelogenous leukemia underwent a matched unrelated donor allogeneic bone marrow transplant with adequate engraftment and mild graft-versus-host disease responding to corticosteroids. Approximately 11 months after transplant, the patient was admitted to the hospital with suspected fungal pneumonia and started on liposomal amphotericin B (baseline serum creatinine 1.4-1.5 mg/dL). The dose was increased due to his immunosuppression and poor response, as the fungal etiology was identified as Torulopsis glabrata. The patient required mechanical ventilation due to biopsy-proven bronchiolitis olbiterans organizing pneumonia. Additionally, he developed diffuse alveolar hemorrhage and received intravenous desmopressin, with a reduction in bloody secretions. He also developed hypernatremia (serum sodium 155 mEq/L) on day 3 of the desmopressin and had an inappropriately increased urine output consistent with NDI. The most likely etiology for the NDI was liposomal amphotericin B and its associated hypokalemia.

DISCUSSION

The observation of worsening hypernatremia (serum sodium increased from 135 to 164 mEq/L) with polyuria was associated with an increasing cumulative dosage of liposomal amphotericin B for fungal pneumonia despite the concurrent use of intravenous desmopressin. Aggressive water replacement was an effective treatment option in this patient. The Naranjo probability scale classified this as a possible adverse reaction because of the temporal sequence of NDI after high-dose liposomal amphotericin B and previously reported cases of NDI associated with amphotericin B desoxycholate.

CONCLUSIONS

Amphotericin B desoxycholate has been implicated as an etiology for NDI, and the use of the newer liposomal amphotericin B reportedly avoids this rare complication. We observed the development of NDI despite the use of liposomal amphotericin B in a critically ill patient with bone marrow transplant.

The role of growth factors and ammonia in the genesis of hypokalemic nephropathy

Hypokalemia is a common electrolyte abnormality encountered in clinical practice. It can be identified in an asymptomatic patient undergoing routine electrolyte screening or can manifest itself as part of a number of functional abnormalities in a variety of organs and systems. Among the most commonly recognized complications are profound effects on the cardiovascular and neuromuscular systems, together with abnormalities in acid-base regulation. In humans, hypokalemia contributes to the development of hypertension and predisposes patients to a variety of ventricular arrhythmias, including ventricular fibrillation. Commonly recognized neuromuscular complications include weakness, cramping, and myalgia. Hypokalemia also affects systemic acid-base homeostasis by interfering with multiple components of the renal acid-base regulation and is a frequent cause of metabolic alkalosis. Less known, however, is the role of potassium deficiency in causing progressive renal failure. In animals, potassium deficiency stimulates renal enlargement because of cellular hypertrophy and hyperplasia. If potassium deficiency persists, interstitial infiltrates appear in the renal interstitial compartment, and eventually tubulointerstitial fibrosis develops. In humans, longstanding hypokalemia is associated with the development of renal cysts, chronic interstitial nephritis, and progressive loss of renal function, the so-called hypokalemic nephropathy. This review focuses on the potential mechanisms involved in the development of the hypokalemic nephropathy with emphasis on the role of ammonia and growth factors in its pathogenesis.

Might distal renal tubular acidosis be a proximal tubular cell disorder?

Incomplete renal tubular acidosis (RTA) and overt distal RTA may be different stages of the same underlying pathophysiology in certain individuals. The rationale that draws these conditions together is the relatively alkaline pH of the urine, hypocitraturia, and a possible familial association. The rate of excretion of ammonium (NH4+), on the other hand, suggests that these conditions stem from fundamentally different lesions. To explain this difference, we suggest that two possible disorders may result in the evolution from incomplete RTA to overt distal RTA. One subgroup could have gradient-limited distal RTA, while the other subgroup may have a lower pH of the intracellular fluid of the proximal convoluted tubular epithelium. Indices of proximal intracellular pH (rates of excretion of NH4+, NH3, and citrate) were culled from the literature spanning the years 1959 to 1991 on patients with incomplete RTA and overt distal RTA. Three points emerge: (1) the rate of excretion of NH4+ was lower in patients with overt distal RTA than in normals following an acute acid load (23 +/- 1 v 49 +/- 3 mumol/min); (2) the concentration of NH3 in the urine was almost 25-fold higher in incomplete RTA than in normals (69 +/- 14 v 3 +/- 0.4 nmol/min); and (3) in incomplete RTA, the pH of the urine fell to very low values (4.9 +/- 0.1) when high urine flows were induced with furosemide. The low pH of the urine would therefore suggest that many of these patients do not gradient-limited distal RTA, but more likely have proximal renal epithelial cell acidosis. We hypothesize that this high rate of excretion of NH4+ and low rate of excretion of citrate in the absence of acidosis or hypokalemia is consistent with proximal cell acidosis. To explain a transition from incomplete RTA to overt distal RTA, we speculate that toxicity of high concentrations of NH3 in the medullary interstitium as well as nephrolithiasis and nephrocalcinosis due to low urinary citrate and possibly an alkaline medullary interstitium may lead to damage of structures in this region.

Reversible low-molecular-weight proteinuria in patients with distal renal tubular acidosis

Four patients with untreated renal tubular acidosis had a urinary excretion of low-molecular-weight (LMW) proteins which was restored to normal by alkali therapy. Hypokalaemic proximal tubular damage in untreated patients with distal renal tubular acidosis is believed to be the cause of LMW proteinuria. An examination of urinary excretion of LMW proteins is useful for determining hypokalaemic proximal tubular dysfunction, as well as the efficiency of alkali therapy.

Reversal of diuretic-induced secondary hyperaldosteronism and hypokalemia by trilostane, an inhibitor of adrenal steroidogenesis

Correction of diuretic-induced hypokalemia is usually accomplished by potassium supplementation or antagonism of aldosterone's renal action. This study sought to determine if inhibition of aldosterone biosynthesis could reverse diuretic-induced hypokalemia and whether trilostane would be clinically useful in this regard. Essential hypertensives (n = 22) were treated with hydrochlorothiazide (HCTZ) 50 mg/d, and patients who became hypokalemic were randomly assigned to receive in addition to HCTZ either a placebo (n = 7), trilostane 240 mg/d (Trilo 240) (n = 7), or trilostane 60 mg/d (Trilo 60) (n = 3). Following 12 weeks of therapy the placebo patients remained hypokalemic with hyperaldosteronism, while the patients who received Trilo 240 had a correction of hypokalemia and hyperaldosteronism (P less than .05) along with a reduction in diastolic blood pressure (P less than .05). The Trilo 60 patients, however, remained hypokalemic with no significant reduction in aldosterone excretion or blood pressure compared with HCTZ. Body weight and urinary free cortisol levels along with routine biochemical tests were unchanged during this study. Three Trilo 240 patients developed diarrhea but did not discontinue the study. These results demonstrate that trilostane can correct diuretic-induced hypokalemia by lowering aldosterone secretion. Furthermore, this reduction in aldosterone may enhance the antihypertensive effects of diuretic therapy.

Potassium homeostasis and hypokalemia

Potassium, largely an intracellular cation, contributes to the regulation of cellular volume, to tissue growth and metabolic synthesis of proteins and nucleic acids, and to the integrity of electrical properties of excitable tissues as well as nonexcitable, transporting epithelia. Potassium balance is closely regulated by a variety of nonrenal and renal mechanisms. When potassium losses are sufficient to induce hypokalemia, either through nonrenal or renal causes, profound adverse effects on neuromuscular, cardiac, vascular, and renal tissues may ensue. The diagnostic approach is straightforward, and therapy must be directed to replenish losses without inducing a rapid, excessive, and potentially fatal increase in the potassium concentration of the serum.

Hypokalemic nephropathy in the rat. Role of ammonia in chronic tubular injury

Chronic potassium deficiency results in progressive tubulointerstitial injury, associated with augmented renal ammoniagenesis. We investigated the role of elevated renal ammonia levels and the interaction of ammonia with the complement system in this injury. Potassium deficiency was induced in rats by feeding a low potassium diet. Experimental animals received 150 mM NaHCO3 or equimolar NaCl, as drinking water. After 3 wk, NaHCO3 supplemented rats demonstrated decreased ammonia production, less renal hypertrophy, less histologic evidence of injury, and less proteinuria. In in vitro studies on normal cortical tubular fragments, the addition of ammonia to serum in concentrations comparable to renal cortical levels in potassium-deficient animals significantly increased tubular deposition of C3 as quantitated by a radiolabeled antibody binding technique. Thus, alkali supplementation reduced chronic tubulointerstitial disease in a rat model of hypokalemic nephropathy. We propose that increased cortical ammonia levels contribute to hypokalemic nephropathy through ammonia-mediated activation of the alternative complement pathway.

Diuretic use in the elderly: potential for diuretic-induced hypokalemia

The more potent "loop" diuretics are being used with increasing frequency. The elderly constitute a growing portion of the population undergoing treatment with diuretics. The alterations in renal function and pharmacokinetics in the elderly (over 60 years of age) may result in the development of certain adverse effects. In patients over 70 years old, there is a progressive decline in overall renal function, resulting in a more than 50% decrease in glomerular filtration rate. Most of the pharmacokinetic changes in the elderly consist of alterations resulting in enhanced plasma levels of any given drug; diminished hepatic drug extraction, detoxification/metabolism or prodrug conversion; decreased renal excretion of drug; and diminished volume of distribution of drug. Adverse reactions to diuretics may be grouped into metabolic changes (e.g., hypokalemia), physiologic alteration (e.g., volume contraction), toxic manifestation (e.g., interstitial nephritis) and allergic or idiosyncratic phenomena (e.g., rash or thrombocytopenia). There is general agreement that significant hypokalemia, particularly among elderly patients receiving digitalis glycosides, is significant and requires therapy. Diuretic-associated hypokalemia reflects the potency and duration of action of a diuretic, factors modulating potassium balance including dietary intake and concurrent medical processes. The short duration of action and greater natriuresis relative to kaliuresis characteristic of loop diuretics may result in a lesser degree of hypokalemia than that seen with traditional thiazide diuretics.

Potassium homeostasis and clinical implications

The clinical estimation of potassium balance generally depends on the level of serum potassium. Since the extracellular fluid contains only 2 percent of the total body potassium, it must be recognized that potassium deficits are usually large before significant hypokalemia occurs, whereas smaller surfeits of potassium will cause hyperkalemia. The total body potassium is regulated by the kidney in which distal nephron secretion of potassium into the urine is enhanced by aldosterone, alkalosis, adaptation to a high potassium diet, and delivery of increased sodium and tubular fluid to the distal tubule. However, the distribution of potassium between the intracellular and extracellular fluids can markedly affect the serum potassium level without a change in total body potassium. Cellular uptake of potassium is regulated by insulin, acid-base status, aldosterone, and adrenergic activity. Hypokalemia, therefore, may be caused by redistribution of potassium into cells due to factors that increase cellular potassium uptake, in addition to total body depletion of potassium due to renal, gastrointestinal, or sweat losses. Similarly hyperkalemia may be caused by redistribution of potassium from the intracellular to the extracellular fluid due to factors that impair cellular uptake of potassium, in addition to retention of potassium due to decreased renal excretion. An understanding of the drugs that affect potassium homeostasis, either by altering the renal excretion of potassium or by modifying its distribution, is essential to the proper assessment of many clinical potassium abnormalities. Both hypokalemia and hyperkalemia may cause asymptomatic electrocardiographic changes, serious arrhythmias, muscle weakness, and death. Hypokalemia has also been associated with several other consequences, including postural hypotension, potentiation of digitalis toxicity, confusional states, glucose intolerance, polyuria, metabolic alkalosis, sodium retention, rhabdomyolysis, intestinal ileus, and decreased gastric motility and acid secretion.

Reversal of diuretic-induced secondary hyperaldosteronism and hypokalemia by enalapril (MK-421): a new angiotensin-converting enzyme inhibitor

The study reported here prospectively evaluated the prevention of diuretic-induced secondary hyperaldosteronism and hypokalemia by a converting enzyme inhibitor, enalapril (MK 421). Eighteen normal subjects were randomized into three groups: (1) a HCTZ group (hydrochlorothiazide (HCTZ) 50 mg/day); (2) a MK-421 group (MK-421 10 mg/day); and (3) a HCTZ + MK-421 group [HCTZ 50 mg/day plus MK-421 10 mg/day]. Following a five-day control and a 28-day treatment period, the HCTZ group demonstrated an attenuated but persistent secondary hyperaldosteronism and hypokalemia, the MK-421 group manifested a gradual decline in aldosterone secretion, and the HCTZ + MK-421 group had a delayed but effective correction of secondary hyperaldosteronism and hypokalemia at 28 days but not before. In conclusion, MK-421 reversed diuretic-induced secondary hyperaldosteronism and hypokalemia after 28 days of hydrochlorothiazide therapy. Therefore, converting enzyme inhibitors, such as enalapril, provide useful adjunctive therapy in diuretic-treated patients, but potassium supplementation may be required before the start of four weeks of combined therapy.

The therapeutic use of a new potassium-sparing diuretic, amiloride, and a converting enzyme inhibitor, MK-421, in preventing hypokalemia associated with primary and secondary hyperaldosteronism

This presentation is a summary of our recent clinical studies on the therapeutic use of a new potassium-sparing diuretic, amiloride, and a converting enzyme inhibitor, MK-421, in preventing hypokalemia associated with primary and secondary hyperaldosteronism. These drugs are quite different in their physiologic action but they both may be effective in preventing the potassium depletion associated with increased aldosterone production. Amiloride, which blocks the sodium channels in distal renal tubular cells, was administered to 10 patients with primary hyperaldosteronism and five patients with Bartter's syndrome (secondary hyperaldosteronism). Amiloride, at doses of 10-40 mg/day, increased mean plasma potassium levels in both primary hyperaldosteronism (3.2-4.5 mEq/L) and, to a lesser extent, in Bartter's syndrome (2.5-3.6 mEq/L). The blood pressure fell slightly but significantly in primary hyperaldosteronism (171/112 vs 150/97 mm Hg) and remained unchanged in Bartter's syndrome (116/80 vs 117/71 mm Hg). The plasma renin activity and plasma aldosterone rose in primary aldosteronism (PRA 0.39-2.21 ng A1/m1/h and PA 28.4-54.3 ng/d1); but in Bartter's syndrome, the PRA declined (25.3-11.9 ng A1/m1/h) and the PA rose (19.5-38.0 ng/d1). The discrepancy in the PRA between primary aldosteronism and Bartter's syndrome may be due to the effects of potassium repletion on suppressing renin and stimulating aldosterone; while in primary aldosteronism, a mild diuretic effect could explain the rise in PRA. In both of these disorders, despite the rise in plasma potassium levels, amiloride produced a counter-therapeutic rise in PA which could potentiate further potassium losses. Therefore, we undertook a study to evaluate the prevention of diuretic-induced hypokalemia and secondary hyperaldosteronism using a new converting enzyme inhibitor, MK-421. Eighteen normal subjects were randomized into three groups receiving either (1) hydrochlorothiazide alone (50 mg/day), (2) MK-421 alone (10 mg/day), or (3) hydrochlorothiazide (50 mg/day) plus MK-421 (10 mg/day). Although MK-421 did not prevent diuretic-induced hypokalemia or hyperaldosteronism in the first week, after that time hypokalemia was reversed and ASR returned to normal. In these studies, it therefore appears that while potassium-sparing diuretics may remain the medical mainstay in treating primary aldosteronism, new converting enzyme inhibitors such as MK-421 may be more effective in treating secondary hyperaldosteronism, since potassium levels can be normalized without increasing aldosterone secretion.

Cancer and the kidney: complications of neoplasms

Various renal complications occur during the course of neoplastic disease. The therapeutic and prognostic implications differ according to the reversibility of both the underlying malignancy and the superimposed complications in the kidney. Since the mechanisms of renal failure vary significantly in patients with different types of malignancy, it is essential to avoid generalizations about etiologic factors or likely outcomes of the disease processes. The pathophysiologic abnormalities should be determined in each patient, and the reversibility of both the neoplastic and problems assessed before therapeutic decisions are made. This often requires a team effort by the internist, oncologist, nephrologist, urologist and, most importantly, the patient.

Urine concentration and dilution in hypokalemic and hypercalcemic dogs

The urine-concentrating mechanism was studied in chronic hypokalemia (seven dogs given a low K(+), high NaCl diet plus injections of deoxycorticosterone acetate [DOCA]) and chronic hypercalcemia (seven dogs given vitamin D). In the potassium-depleted dogs, muscle, serum, and urine K(+) fell markedly, but glomerular filtration rate (GFR) and body weight varied little. Maximum urine osmolality fell in all dogs (mean decrease = 45%); however, solute-free water reabsorption (T(CH2O)) at high rates of solute excretion remained normal in three of four dogs. Free water excretion (C(H2O)) increased normally or supranormally as a function of increasing Na(+) delivery to Henle's loop in six dogs so tested. Hypercalcemia of several weeks duration caused a decrease in both GFR (mean 36%) as well as in maximum urine osmolality (mean 57%). Maximum T(CH2O) was not invariably depressed; in fact, when the values were adjusted for the reduced number of functioning nephrons (T(CH2O)/C(In)), four of seven studies were normal. C(H20)/C(In) increased normally (or supranormally) with increasing fractional Na delivery to Henle's loop in four of five dogs.I conclude that the lowered maximum urine osmolality in these hypokalemic and hypercalcemic dogs was not related to abnormal water reabsorption from the collecting ducts. Although not specifically measured in this study, it is very likely that solute accumulation in the renal medulla was reduced. This probably was not caused by abnormal delivery of sodium to, nor reabsorption of sodium from Henle's loop. It is likely that a more subtle defect exists in the countercurrent mechanisms for establishing a steep concentration gradient in the renal medulla. In the few hypercalcemic dogs in whom GFR was very low, I believe that injury to, and blockage of medullary tubules could account for most of the reduction in maximum U(Osm). Although not specifically ruled out, there is no evidence here to suggest that high serum Ca(+) or low serum K(+) per se causes a defect in sodium and water reabsorption in the mammalian nephron.