On the mechanism of polyuria in potassium depletion. The role of polydipsia

Abnormal neonatal sodium handling in skin precedes hypertension in the SAME rat

We discovered high Na⁺ and water content in the skin of newborn Sprague–Dawley rats, which reduced ~ 2.5-fold by 7 days of age, indicating rapid changes in extracellular volume (ECV). Equivalent changes in ECV post birth were also observed in C57Bl/6 J mice, with a fourfold reduction over 7 days, to approximately adult levels. This established the generality of increased ECV at birth. We investigated early sodium and water handling in neonates from a second rat strain, Fischer, and an Hsd11b2-knockout rat modelling the syndrome of apparent mineralocorticoid excess (SAME). Despite Hsd11b2^−/− animals exhibiting lower skin Na⁺ and water levels than controls at birth, they retained ~ 30% higher Na⁺ content in their pelts at the expense of K⁺ thereafter. Hsd11b2^−/− neonates exhibited incipient hypokalaemia from 15 days of age and became increasingly polydipsic and polyuric from weaning. As with adults, they excreted a high proportion of ingested Na⁺ through the kidney, (56.15 ± 8.21% versus control 34.15 ± 8.23%; n = 4; P < 0.0001), suggesting that changes in nephron electrolyte transporters identified in adults, by RNA-seq analysis, occur by 4 weeks of age. Our data reveal that Na⁺ imbalance in the Hsd11b2^−/− neonate leads to excess Na⁺ storage in skin and incipient hypokalaemia, which, together with increased, glucocorticoid-induced Na⁺ uptake in the kidney, then contribute to progressive, volume contracted, salt-sensitive hypertension. Skin Na⁺ plays an important role in the development of SAME but, equally, may play a key physiological role at birth, supporting post-natal growth, as an innate barrier to infection or as a rudimentary kidney.

Rapid development of vasopressin resistance in dietary K+ deficiency

The association between diabetes insipidus (DI) and chronic dietary K+ deprivation is well known, but it remains uncertain how the disorder develops and whether it is influenced by the sexual dimorphism in K+ handling. Here, we determined the plasma K+ (PK) threshold for DI in male and female mice and ascertained if DI is initiated by polydipsia or by a central or nephrogenic defect. C57BL6J mice were randomized to a control diet or to graded reductions in dietary K+ for 8 days, and kidney function and transporters involved in water balance were characterized. We found that male and female mice develop polyuria and secondary polydipsia. Altered water balance coincided with a decrease in aquaporin-2 (AQP2) phosphorylation and apical localization despite increased levels of the vasopressin surrogate marker copeptin. No change in the protein abundance of urea transporter-A1 was observed. The Na+-K+-2Cl- cotransporter decreased only in males. Desmopressin treatment failed to reverse water diuresis in K+-restricted mice. These findings indicate that even a small fall in PK is associated with nephrogenic DI (NDI), coincident with the development of altered AQP2 regulation, implicating low PK as a causal trigger of NDI. We found that PK decreased more in females, and, consequently, females were more prone to develop NDI. Together, these data indicate that AQP2 regulation is disrupted by a small decrease in PK and that the response is influenced by sexual dimorphism in K+ handling. These findings provide new insights into the mechanisms linking water and K+ balances and support defining the disorder as "potassium-dependent NDI."NEW & NOTEWORTHY This study shows that aquaporin-2 regulation is disrupted by a small fall in plasma potassium levels and the response is influenced by sexual dimorphism in renal potassium handling. The findings provided new insights into the mechanisms by which water balance is altered in dietary potassium deficiency and support defining the disorder as "potassium-dependent nephrogenic diabetes insipidus."

Potassium deficiency decreases the capacity for urea synthesis and markedly increases ammonia in rats

Our study provides novel findings of experimental hypokalemia reducing urea cycle functionality and thereby severely increasing plasma ammonia. This is pathophysiologically interesting because plasma ammonia increases during hypokalemia by a hitherto unknown mechanism, which may be particular important in relation to the unexplained link between hypokalemia and hepatic encephalopathy. Potassium deficiency decreases gene expression, protein synthesis, and growth. The urea cycle maintains body nitrogen homeostasis including removal of toxic ammonia. Hyperammonemia is an obligatory trait of liver failure, increasing the risk for hepatic encephalopathy, and hypokalemia is reported to increase ammonia. We aimed to clarify the effects of experimental hypokalemia on the in vivo capacity of the urea cycle, on the genes of the enzymes involved, and on ammonia concentrations. Female Wistar rats were fed a potassium-free diet for 13 days. Half of the rats were then potassium repleted. Both groups were compared with pair- and free-fed controls. The following were measured: in vivo capacity of urea-nitrogen synthesis (CUNS); gene expression (mRNA) of urea cycle enzymes; plasma potassium, sodium, and ammonia; intracellular potassium, sodium, and magnesium in liver, kidney, and muscle tissues; and liver sodium/potassium pumps. Liver histology was assessed. The diet induced hypokalemia of 1.9 ± 0.4 mmol/L. Compared with pair-fed controls, the in vivo CUNS was reduced by 34% (P < 0.01), gene expression of argininosuccinate synthetase 1 (ASS1) was decreased by 33% (P < 0.05), and plasma ammonia concentrations were eightfold elevated (P < 0.001). Kidney and muscle tissue potassium contents were markedly decreased but unchanged in liver tissue. Protein expressions of liver sodium/potassium pumps were unchanged. Repletion of potassium reverted all the changes. Hypokalemia decreased the capacity for urea synthesis via gene effects. The intervention led to marked hyperammonemia, quantitatively explainable by the compromised urea cycle. Our findings motivate clinical studies of patients with liver disease.

Deletion of the serine protease CAP2/Tmprss4 leads to dysregulated renal water handling upon dietary potassium depletion

The kidney needs to adapt daily to variable dietary K⁺ contents via various mechanisms including diuretic, acid-base and hormonal changes that are still not fully understood. In this study, we demonstrate that following a K⁺-deficient diet in wildtype mice, the serine protease CAP2/Tmprss4 is upregulated in connecting tubule and cortical collecting duct and also localizes to the medulla and transitional epithelium of the papilla and minor calyx. Male CAP2/Tmprss4 knockout mice display altered water handling and urine osmolality, enhanced vasopressin response leading to upregulated adenylate cyclase 6 expression and cAMP overproduction, and subsequently greater aquaporin 2 (AQP2) and Na⁺-K⁺-2Cl⁻ cotransporter 2 (NKCC2) expression following K⁺-deficient diet. Urinary acidification coincides with significantly increased H⁺,K⁺-ATPase type 2 (HKA2) mRNA and protein expression, and decreased calcium and phosphate excretion. This is accompanied by increased glucocorticoid receptor (GR) protein levels and reduced 11β-hydroxysteroid dehydrogenase 2 activity in knockout mice. Strikingly, genetic nephron-specific deletion of GR leads to the mirrored phenotype of CAP2/Tmprss4 knockouts, including increased water intake and urine output, urinary alkalinisation, downregulation of HKA2, AQP2 and NKCC2. Collectively, our data unveil a novel role of the serine protease CAP2/Tmprss4 and GR on renal water handling upon dietary K⁺ depletion.

Physiologic changes of urinary proteome by caffeine and excessive water intake

Background:

Diurnal variations and physiologic changes of urinary proteome have been suggested in the urinary proteomics field. However, no clear evidence has been demonstrated. The present study thus aimed to define changes in urinary proteome by physiological stimuli, i.e. caffeine intake and excessive water drinking, both of which cause physiologic diuresis.

Methods:

Urine samples were collected from 30 healthy individuals under three different conditions: (i) morning void as the control; (ii) after drinking a cup of coffee; and (iii) after drinking 1 L of water within 20 min. Thereafter, differentially excreted proteins were analyzed by 2-DE proteomics approach and validated by Western blotting and ELISA.

Results:

Spot matching, quantitative intensity analysis, and ANOVA followed by Tukey’s post-hoc multiple comparisons and the Bonferroni correction revealed significant differences in levels of five protein spots among three different conditions. These proteins were identified by quadrupole time-of-flight mass spectrometry (Q-TOF MS) and/or MS/MS analyses as kininogen 1 isoform 3, β-actin, prostaglandin D synthase (PGDS), fibrinogen α-chain and immunoglobulin light chain. Among these, the decreased level of immunoglobulin was successfully validated by Western blotting and ELISA.

Conclusions:

These data indicated that caffeine intake and excessive water drinking could affect urinary excretion of some proteins and may affect urinary proteome analysis.

A novel therapeutic effect of statins on nephrogenic diabetes insipidus

Statins competitively inhibit hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase, resulting in reduced plasma total and low-density lipoprotein cholesterol levels. Recently, it has been shown that statins exert additional ‘pleiotropic’ effects by increasing expression levels of the membrane water channels aquaporin 2 (AQP2). AQP2 is localized mainly in the kidney and plays a critical role in determining cellular water content. This additional effect is independent of cholesterol homoeostasis, and depends on depletion of mevalonate-derived intermediates of sterol synthetic pathways, i.e. farnesylpyrophosphate and geranylgeranylpyrophosphate. By up-regulating the expression levels of AQP2, statins increase water reabsorption by the kidney, thus opening up a new avenue in treating patients with nephrogenic diabetes insipidus (NDI), a hereditary disease that yet lacks high-powered and limited side effects therapy. Aspects related to water balance determined by AQP2 in the kidney, as well as standard and novel therapeutic strategies of NDI are discussed.

Aldosterone synthase inhibition: cardiorenal protection in animal disease models and translation of hormonal effects to human subjects

Background

Aldosterone synthase inhibition provides the potential to attenuate both the mineralocorticoid receptor-dependent and independent actions of aldosterone. In vitro studies with recombinant human enzymes showed LCI699 to be a potent, reversible, competitive inhibitor of aldosterone synthase (K_i = 1.4 ± 0.2 nmol/L in humans) with relative selectivity over 11β-hydroxylase.

Methods

Hormonal effects of orally administered LCI699 were examined in rat and monkey in vivo models of adrenocorticotropic hormone (ACTH) and angiotensin-II-stimulated aldosterone release, and were compared with the mineralocorticoid receptor antagonist eplerenone in a randomized, placebo-controlled study conducted in 99 healthy human subjects. The effects of LCI699 and eplerenone on cardiac and renal sequelae of aldosterone excess were investigated in a double-transgenic rat (dTG rat) model overexpressing human renin and angiotensinogen.

Results

Rat and monkey in vivo models of stimulated aldosterone release predicted human dose– and exposure–response relationships, but overestimated the selectivity of LCI699 in humans. In the dTG rat model, LCI699 dose-dependently blocked increases in aldosterone, prevented development of cardiac and renal functional abnormalities independent of blood pressure changes, and prolonged survival. Eplerenone prolonged survival to a similar extent, but was less effective in preventing cardiac and renal damage. In healthy human subjects, LCI699 0.5 mg selectively reduced plasma and 24 h urinary aldosterone by 49 ± 3% and 39 ± 6% respectively (Day 1, mean ± SEM; P < 0.001 vs placebo), which was associated with natriuresis and an increase in plasma renin activity. Doses of LCI699 greater than 1 mg inhibited basal and ACTH-stimulated cortisol. Eplerenone 100 mg increased plasma and 24 h urinary aldosterone while stimulating natriuresis and increasing renin activity. In contrast to eplerenone, LCI699 increased the aldosterone precursor 11-deoxycorticosterone and urinary potassium excretion.

Conclusions

These results provide new insights into the cardiac and renal effects of inhibiting aldosterone synthase in experimental models and translation of the hormonal effects to humans. Selective inhibition of aldosterone synthase appears to be a promising approach to treat diseases associated with aldosterone excess.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0340-9) contains supplementary material, which is available to authorized users.

Fanconi syndrome and severe polyuria: an uncommon clinicobiological presentation of a Gitelman syndrome

BACKGROUND

Gitelman syndrome is an autosomal recessive tubulopathy characterized by hypokalemia, hypomagnesemia, metabolic alkalosis and hypocalciuria. The majority of patients do not present with symptoms until late childhood or adulthood, and the symptoms are generally mild. We report here the first case of Gitelman syndrome presenting with the biological features of Fanconi syndrome and an early polyuria since the neonatal period. We discuss in this article the atypical electrolytes losses found in our patient, as well as the possible mechanisms of severe polyuria.

CASE PRESENTATION

A 6-year-old Caucasian girl was admitted via the Emergency department for vomiting, and initial laboratory investigations found hyponatremia, hypokalemia, metabolic acidosis with normal anion gap, hypophosphatemia, and hypouricemia. Urinalysis revealed Na, K, Ph and uric acid losses. Thus, the initial biological profile was in favor of a proximal tubular defect. However, etiological investigations were inconclusive and the patient was discharged with potassium chloride and phosphorus supplementation. Three weeks later, further laboratory analysis indicated persistent hypokalemia, a metabolic alkalosis, hypomagnesemia, and hypocalciuria. We therefore sequenced the SLC12A3 gene and found a compound heterozygosity for 2 known missense mutations.

CONCLUSIONS

Gitelman syndrome can have varying and sometimes atypical presentations, and should be suspected in case of hypokalemic tubular disorders that do not belong to any obvious syndromic entity. In this case, the proximal tubular dysfunction could be secondary to the severe hypokalemia. This report emphasizes the need for clinicians to repeat laboratory tests in undiagnosed tubular disorders, especially not during decompensation episodes.

Aquaporin-2 regulation in health and disease

Aquaporin-2 (AQP2), the vasopressin-regulated water channel of the renal collecting duct, is dysregulated in numerous disorders of water balance in people and animals, including those associated with polyuria (urinary tract obstruction, hypokalemia, inflammation, and lithium toxicity) and with dilutional hyponatremia (syndrome of inappropriate antidiuresis, congestive heart failure, cirrhosis). Normal regulation of AQP2 by vasopressin involves 2 independent regulatory mechanisms: (1) short-term regulation of AQP2 trafficking to and from the apical plasma membrane, and (2) long-term regulation of the total abundance of the AQP2 protein in the cells. Most disorders of water balance are the result of dysregulation of processes that regulate the total abundance of AQP2 in collecting duct cells. In general, the level of AQP2 in a collecting duct cell is determined by a balance between production via translation of AQP2 mRNA and removal via degradation or secretion into the urine in exosomes. AQP2 abundance increases in response to vasopressin chiefly due to increased translation subsequent to increases in AQP2 mRNA. Vasopressin-mediated regulation of AQP2 gene transcription is poorly understood, although several transcription factor-binding elements in the 5' flanking region of the AQP2 gene have been identified, and candidate transcription factors corresponding to these elements have been discovered in proteomics studies. Here, we review progress in this area and discuss elements of vasopressin signaling in the collecting duct that may impinge on regulation of AQP2 in health and in the context of examples of polyuric diseases.

Bicarbonate promotes BK-α/β4-mediated K excretion in the renal distal nephron

Ca-activated K channels (BK), which are stimulated by high distal nephron flow, are utilized during high-K conditions to remove excess K. Because BK predominantly reside with BK-β4 in acid/base-transporting intercalated cells (IC), we determined whether BK-β4 knockout mice (β4KO) exhibit deficient K excretion when consuming a high-K alkaline diet (HK-alk) vs. high-K chloride diet (HK-Cl). When wild type (WT) were placed on HK-alk, but not HK-Cl, renal BK-β4 expression increased (Western blot). When WT and β4KO were placed on HK-Cl, plasma K concentration ([K]) was elevated compared with control K diets; however, K excretion was not different between WT and β4KO. When HK-alk was consumed, the plasma [K] was lower and K clearance was greater in WT compared with β4KO. The urine was alkaline in mice on HK-alk; however, urinary pH was not different between WT and β4KO. Immunohistochemical analysis of pendrin and V-ATPase revealed the same increases in β-IC, comparing WT and β4KO on HK-alk. We found an amiloride-sensitive reduction in Na excretion in β4KO, compared with WT, on HK-alk, indicating enhanced Na reabsorption as a compensatory mechanism to secrete K. Treating mice with an alkaline, Na-deficient, high-K diet (LNaHK) to minimize Na reabsorption exaggerated the defective K handling of β4KO. When WT on LNaHK were given NH(4)Cl in the drinking water, K excretion was reduced to the magnitude of β4KO on LNaHK. These results show that WT, but not β4KO, efficiently excretes K on HK-alk but not on HK-Cl and suggest that BK-α/β4-mediated K secretion is promoted by bicarbonaturia.

Primary polydipsia, but not accumulated ceramide, causes lethal renal damage in saposin D-deficient mice

Saposin D-deficient (Sap-D(-/-)) mice develop polydipsia/polyuria and die prematurely due to renal failure with robust hydronephrosis. Such symptoms emerged when they were around 3 mo of age. To investigate the pathogenesis of their water mishandling, we attempted to limit water supply and followed sequential changes of physiological and biochemical parameters. We also analyzed renal histological changes at several time points. At 3 mo old just before water restriction challenge was started, their baseline arginine vasopressin level was comparable to the wild-type (WT) level. Twenty-four-hour water deprivation and desamino d-arginine vasopressin administration improved polydipsia and polyuria to certain degrees. However, creatinine concentrations in Sap-D(-/-) mice were significantly higher than those in WT mice, suggesting that some renal impairment already emerged in the affected mice at this age. Renal histological analyses revealed that renal tubules and collecting ducts were expanded after 3 mo old. After 6 mo old, vacuolar formation was observed, many inflammatory cells migrated around the ducts, and epithelial monolayer cells of tubular origin were replaced by plentiful cysts of various sizes. At 10∼12 mo old, severe cystic deformity appeared. On the other hand, 8-mo-long water restriction started at 4 mo old dramatically improved tubular damage and restored once-dampened amount of tubular aquaporin2 protein to the WT level. Furthermore, 10-mo-long water restriction ameliorated their renal function. Remarkably, by continuing water restriction thereafter, overall survival period became comparable with that of the WT. Together, polyuria, devastating renal tubular lesions, and renal failure were ameliorated by the mere 10-mo-long water restriction, which would trigger lethal dehydration if the disease were to be caused by any processes other than primary polydipsia. Our study demonstrates that long-term water restriction surely improved renal histopathological changes leading to prevention of premature death in Sap-D(-/-) mice.

Activation of the renal Na+:Cl- cotransporter by angiotensin II is a WNK4-dependent process

Pseudohypoaldosteronism type II is a salt-sensitive form of hypertension with hyperkalemia in humans caused by mutations in the with-no-lysine kinase 4 (WNK4). Several studies have shown that WNK4 modulates the activity of the renal Na(+)Cl(-) cotransporter, NCC. Because the renal consequences of WNK4 carrying pseudoaldosteronism type II mutations resemble the response to intravascular volume depletion (promotion of salt reabsorption without K(+) secretion), a condition that is associated with high angiotensin II (AngII) levels, it has been proposed that AngII signaling might affect WNK4 modulation of the NCC. In Xenopus laevis oocytes, WNK4 is required for modulation of NCC activity by AngII. To demonstrate that WNK4 is required in the AngII-mediated regulation of NCC in vivo, we used a total WNK4-knockout mouse strain (WNK4(-/-)). WNK4 mRNA and protein expression were absent in WNK4(-/-) mice, which exhibited a mild Gitelman-like syndrome, with normal blood pressure, increased plasma renin activity, and reduced NCC expression and phosphorylation at T-58. Immunohistochemistry revealed normal morphology of the distal convoluted tubule with reduced NCC expression. Low-salt diet or infusion of AngII for 4 d induced phosphorylation of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and of NCC at S-383 and T-58, respectively, in WNK4(+/+) but not WNK4(-/-) mice. Thus, the absence of WNK4 in vivo precludes NCC and SPAK phosphorylation promoted by a low-salt diet or AngII infusion, suggesting that AngII action on the NCC occurs via a WNK4-SPAK-dependent signaling pathway. Additionally, stimulation of aldosterone secretion by AngII, but not by a high-K(+) diet, was impaired in WNK4(-/-) mice.

Colonic potassium handling

Homeostatic control of plasma K+ is a necessary physiological function. The daily dietary K+ intake of approximately 100 mmol is excreted predominantly by the distal tubules of the kidney. About 10% of the ingested K+ is excreted via the intestine. K+ handling in both organs is specifically regulated by hormones and adapts readily to changes in dietary K+ intake, aldosterone and multiple local paracrine agonists. In chronic renal insufficiency, colonic K+ secretion is greatly enhanced and becomes an important accessory K+ excretory pathway. During severe diarrheal diseases of different causes, intestinal K+ losses caused by activated ion secretion may become life threatening. This topical review provides an update of the molecular mechanisms and the regulation of mammalian colonic K+ absorption and secretion. It is motivated by recent results, which have identified the K+ secretory ion channel in the apical membrane of distal colonic enterocytes. The directed focus therefore covers the role of the apical Ca2+ and cAMP-activated BK channel (KCa1.1) as the apparently only secretory K+ channel in the distal colon.

Carcinoid tumor of the thymus associated with Cushing's syndrome and dysgeusia: case report and review of the literature

A 30-year-old man was hospitalized with edema, polyuria, and abnormalities in taste. ACTH and cortisol levels at admission were markedly elevated, even after attempted suppression with 8 mg dexamethasone. A thoracic-abdominal CT revealed an anterior mediastinal lesion and hyperplasia of both adrenal glands. After excision of the mediastinal mass, which confirmed the presence of a carcinoid thymic tumor, the patient became totally asymptomatic, with normal ACTH and cortisol levels. A carcinoid thymic tumor has a poor prognosis, especially when it is associated with Cushing's syndrome. Most patients will present recidivism or metastasis within 5 years after surgery. However, the low number of cases available for analysis makes it difficult to establish optimum therapeutic approaches.

Hyponatremia: case vignettes

The diagnosis and management of hyponatremia can be intimidating, for both trainees and clinicians alike. We present five clinical scenarios of patients with hyponatremia. These discussions reinforce concepts reviewed elsewhere in this issue of Seminars in Nephrology and/or emphasize specific causes and management issues.

Licking for taste solutions by potassium-deprived rats: specificity and mechanisms

There has been little work on the specificity and mechanisms underlying the appetite of potassium (K(+)) deprived rats, and there are conflicting results. To investigate the contribution of oral factors to changes in intake induced by K(+) deficiency, we conducted two experiments using 20-s "brief access" tests. In Experiment 1, K(+)-deprived rats licked less for water than did replete rats. After adjusting for this difference, K(+)-deprived rats exhibited increased licking for 100 mM CaCl(2), 100 mM MgCl(2), and 100 mM FeCl(2) compared with K(+)-replete rats. In Experiment 2, which used larger rats, the K(+)-deprived and replete groups licked equally for water, 500 mM Na.Gluconate, 350 mM KCl, 500 mM KHCO(3), and 1 mM quinine.HCl, but the K(+)-deprived rats licked more for 500 mM KCl, 500 mM CsCl, and 500 mM NaCl than did the replete rats. Licking was unaffected by addition to NaCl of 200 muM amiloride, an epithelial Na(+) channel (ENaC) blocker, or 100 muM ruthenium red, a vanilloid receptor 1 (VR-1) antagonist, or by addition to KCl of 50 muM 4-aminopyridine, a K(+) channel blocker. These findings suggest that K(+)-deprivation produces a non-specific appetite that is guided by oral factors. We found no evidence that this response was mediated by ENaC, VR-1, or K(+) channels in taste receptor cells.

Long-term aldosterone treatment induces decreased apical but increased basolateral expression of AQP2 in CCD of rat kidney

The purpose of the present studies was to determine the effects of high-dose aldosterone and dDAVP treatment on renal aquaporin-2 (AQP2) regulation and urinary concentration. Rats were treated for 6 days with either vehicle (CON; n = 8), dDAVP (0.5 ng/h, dDAVP, n = 10), aldosterone (Aldo, 150 μg/day, n = 10) or combined dDAVP and aldosterone treatment (dDAVP+Aldo, n = 10) and had free access to water with a fixed food intake. Aldosterone treatment induced hypokalemia, decreased urine osmolality, and increased the urine volume and water intake in ALDO compared with CON and dDAVP+Aldo compared with dDAVP. Immunohistochemistry and semiquantitative laser confocal microscopy revealed a distinct increase in basolateral domain AQP2 labeling in cortical collecting duct (CCD) principal cells and a reduction in apical domain labeling in Aldo compared with CON rats. Given the presence of hypokalemia in aldosterone-treated rats, we studied dietary-induced hypokalemia in rats, which also reduced apical AQP2 expression in the CCD but did not induce any increase in basolateral AQP2 expression in the CCD as observed with aldosterone treatment. The aldosterone-induced basolateral AQP2 expression in the CCD was thus independent of hypokalemia but was dependent on the presence of sodium and aldosterone. This redistribution was clearly blocked by mineralocorticoid receptor blockade. The increased basolateral expression of AQP2 induced by aldosterone may play a significant role in water metabolism in conditions with increased sodium reabsorption in the CCD.

À propos de deux cas de paralysie périodique hypokaliémique

We report on two cases of hypokaliemic periodic paralysis due to a potassium shift from the extracellular to the intracellular compartment of skeletal muscle cells. The first case occurred in a 15-year-old boy who experienced rapid onset flaccid tetraplegia without neurological abnormalities. Physical exam revealed facial dysmorphy, and EKG a long QT. Biology evidenced shift hypokalemia that was quickly reversible after administration of intravenous potassium. After exclusion of Andersen-Tawil syndrom, hypokalemic familial paralysis (Westphall disease) was diagnosed by molecular genetic testing (disease-causing mutation in CACNA1S) in the proband and in three other family members. The second case occurred in a 24-year-old male who experienced rapid onset flaccid tetraplegia due to intracellular potassium shift that was quickly reversible after administration of intravenous potassium. Biology revealed thyrotoxicosis due to Grave's disease. To the best of our knowledge, this is the first case described in a people from pacific origin. The clinical, biological, and electromyographic findings of the most frequent causes of periodic paralysis are underlined as well as the molecular genetic diagnosis in familial forms.

Proteomic identification of alterations in metabolic enzymes and signaling proteins in hypokalemic nephropathy

Hypokalemic nephropathy caused by prolonged K(+) deficiency is associated with metabolic alkalosis, polydipsia, polyuria, growth retardation, hypertension, and progressive tubulointerstitial injury. Its pathophysiology, however, remains unclear. We performed gel-based, differential proteomics analysis of kidneys from BALB/c mice fed with high-normal-K(+) (HNK), low-normal-K(+) (LNK), or K(+)-depleted diet for 8 wk (n = 6 in each group). Plasma K(+) levels were 4.62 +/- 0.35, 4.46 +/- 0.23, and 1.51 +/- 0.21 mmol/L for HNK, LNK, and KD mice, respectively (p < 0.0001; KD vs. others). With comparable amounts of food intake, the KD mice drank significantly more water than the other two groups and had polyuria. Additionally, the KD mice had growth retardation, metabolic alkalosis, markedly enlarged kidneys, renal tubular dilation, intratubular deposition of amorphous and laminated hyaline materials, and tubular atrophy. A total of 33 renal proteins were differentially expressed between the KD mice and others, whereas only eight proteins were differentially expressed between the HNK and LNK groups, as determined by quantitative intensity analysis and ANOVA with Tukey's post hoc multiple comparisons. Using MALDI-MS and/or quadrupole-TOF MS/MS, 30 altered proteins induced by K(+)-depletion were identified as metabolic enzymes (e.g., carbonic anhydrase II, aldose reductase, glutathione S-transferase GT41A, etc.), signaling proteins (14-3-3 epsilon, 14-3-3 zeta, and cofilin 1), and cytoskeletal proteins (gamma-actin and tropomyosin). Some of these altered proteins, particularly metabolic enzymes and signaling proteins, have been demonstrated to be involved in metabolic alkalosis, polyuria, and renal tubular injury. Our findings may lead to a new road map for research on hypokalemic nephropathy and to better understanding of the pathophysiology of this medical disease when the functional and physiological significances of these altered proteins are defined.

Hypokalemia in a mouse model of Gitelman's syndrome

Hypokalemia is a prominent feature of Gitelman syndrome and a common side effect of thiazide use in the treatment of hypertension. It is widely recognized that genetic or pharmacological inhibition of the renal thiazide-sensitive sodium-chloride cotransporter (NCC) initiates the potentially severe renal potassium loss observed in these settings. Surprisingly, hypokalemia has not been detected in NCC (-/-) mice maintained on normal rodent diets (Schultheis PJ, Lorenz JN, Meneton P, Nieman ML, Riddle TM, Flagella M, Duffy JJ, Doetschman T, Miller ML, and Shull GE. J Biol Chem 273: 29150-29155, 1998). We show that modest reduction of dietary potassium induced a marked reduction in plasma potassium and elevated renal potassium excretion in NCC (-/-) mice that was associated with a pronounced polydipsia and polyuria of central origin. These findings are consistent with the development of potassium depletion in NCC (-/-) mice and were not seen in wild-type mice maintained on the same low-potassium diet. In addition, plasma aldosterone levels were significantly elevated in NCC (-/-) mice even in the presence of a low-potassium diet. Collectively, these findings suggest an early central component to the polyuria of Gitelman syndrome and show that both elevated aldosterone and dietary potassium content contribute to the development of hypokalemia in Gitelman syndrome. Therefore, NCC (-/-) mice are more sensitive to reductions in dietary potassium than wild-type mice and become hypokalemic, thus more faithfully representing the Gitelman phenotype seen in humans.

Intrafamilial phenotype variability in patients with Gitelman syndrome having the same mutations in their thiazide-sensitive sodium/chloride cotransporter

BACKGROUND

Gitelman syndrome (GS) most often results from mutations in the thiazide-sensitive sodium chloride cotransporter (NCC). Although the severity of symptoms may vary in patients who have the same mutations, a markedly different clinical presentation in family members with identical mutations is truly rare.

METHODS

Five patients (3 women and 2 men) belonging to 2 unrelated Chinese families were investigated. All had chronic hypokalemia, renal potassium (K+) wasting, metabolic alkalosis, and normal blood pressure. Direct sequencing of both the NCC and CLCNKB genes were performed.

RESULTS

The probands in each family were men. They had very severe hypokalemia and were symptomatic with episodes of paralysis. They had normal plasma magnesium concentrations, normal calcium excretion rates, and impaired maximal urine concentrating ability. In contrast, female family members were asymptomatic. They had laboratory findings typical of GS--less severe hypokalemia, hypomagnesemia, hypocalciuria, and intact maximal renal concentrating ability. Nevertheless, all patients had the same novel pair of NCC mutations and no mutations detected in CLCNKB.

CONCLUSION

Differences in sex may help explain the different clinical presentations in these 2 Chinese families with novel NCC mutations. Hypomagnesemia and hypocalciuria are not always present in patients with GS.

A simple and rapid approach to hypokalemic paralysis

Hypokalemia with paralysis (HP) is a potentially reversible medical emergency. It is primarily the result of either hypokalemic periodic paralysis (HPP) caused by an enhanced shift of potassium (K(+)) into cells or non-HPP resulting from excessive K(+) loss. Failure to make a distinction between HPP and non-HPP could lead to improper management. The use of spot urine for K(+) excretion rate and evaluation of blood acid-base status could be clinically beneficial in the diagnosis and management. A very low rate of K(+) excretion coupled with the absence of a metabolic acid-base disorder suggests HPP, whereas a high rate of K(+) excretion accompanied by either metabolic alkalosis or metabolic acidosis favors non-HPP. The therapy of HPP requires only small doses of potassium chloride (KCl) to avoid rebound hyperkalemia. In contrast, higher doses of KCl should be administered to replete the large K(+) deficiency in non-HPP.

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.

Systemic diseases associated with disorders of water homeostasis

Disorders of AVP secretion and action sometimes present as the first manifestation of a variety of different systemic diseases. It is prudent for the clinician to consider these causes in the differential diagnosis of hypoosmolar hyponatremia, polyuria and polydipsia, since recognizing the underlying disorder may affect treatment decisions, and intervention directed at the primary disorder often can reverse the abnormal water metabolism in these patients. Although much of the pathophysiology of these disorders is not understood completely, great progress has been made toward appreciating the complex and precise system involving thirst, AVP secretion, and renal responsiveness to AVP. Further investigation in this field likely will allow physicians to offer more effective and potent treatments in the future, such as the development of AVP V2 receptor antagonists for the treatment of SIADH [81] and edema-forming states [18, 109].

Hypertension in mice lacking 11beta-hydroxysteroid dehydrogenase type 2

Deficiency of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) in humans leads to the syndrome of apparent mineralocorticoid excess (SAME), in which cortisol illicitly occupies mineralocorticoid receptors, causing sodium retention, hypokalemia, and hypertension. However, the disorder is usually incompletely corrected by suppression of cortisol, suggesting additional and irreversible changes, perhaps in the kidney. To examine this further, we produced mice with targeted disruption of the 11beta-HSD2 gene. Homozygous mutant mice (11beta-HSD2(-/-)) appear normal at birth, but approximately 50% show motor weakness and die within 48 hours. Both male and female survivors are fertile but exhibit hypokalemia, hypotonic polyuria, and apparent mineralocorticoid activity of corticosterone. Young adult 11beta-HSD2(-/-) mice are markedly hypertensive, with a mean arterial blood pressure of 146 +/- 2 mmHg, compared with 121 +/- 2 mmHg in wild-type controls and 114 +/- 4 mmHg in heterozygotes. The epithelium of the distal tubule of the nephron shows striking hypertrophy and hyperplasia. These histological changes do not readily reverse with mineralocorticoid receptor antagonism in adulthood. Thus, 11beta-HSD2(-/-) mice demonstrate the major features of SAME, providing a unique rodent model to study the molecular mechanisms of kidney resetting leading to hypertension.

Angiotensin, thirst, and sodium appetite

Angiotensin (ANG) II is a powerful and phylogenetically widespread stimulus to thirst and sodium appetite. When it is injected directly into sensitive areas of the brain, it causes an immediate increase in water intake followed by a slower increase in NaCl intake. Drinking is vigorous, highly motivated, and rapidly completed. The amounts of water taken within 15 min or so of injection can exceed what the animal would spontaneously drink in the course of its normal activities over 24 h. The increase in NaCl intake is slower in onset, more persistent, and affected by experience. Increases in circulating ANG II have similar effects on drinking, although these may be partly obscured by accompanying rises in blood pressure. The circumventricular organs, median preoptic nucleus, and tissue surrounding the anteroventral third ventricle in the lamina terminalis (AV3V region) provide the neuroanatomic focus for thirst, sodium appetite, and cardiovascular control, making extensive connections with the hypothalamus, limbic system, and brain stem. The AV3V region is well provided with angiotensinergic nerve endings and angiotensin AT1 receptors, the receptor type responsible for acute responses to ANG II, and it responds vigorously to the dipsogenic action of ANG II. The nucleus tractus solitarius and other structures in the brain stem form part of a negative-feedback system for blood volume control, responding to baroreceptor and volume receptor information from the circulation and sending ascending noradrenergic and other projections to the AV3V region. The subfornical organ, organum vasculosum of the lamina terminalis and area postrema contain ANG II-sensitive receptors that allow circulating ANG II to interact with central nervous structures involved in hypovolemic thirst and sodium appetite and blood pressure control. Angiotensin peptides generated inside the blood-brain barrier may act as conventional neurotransmitters or, in view of the many instances of anatomic separation between sites of production and receptors, they may act as paracrine agents at a distance from their point of release. An attractive speculation is that some are responsible for long-term changes in neuronal organization, especially of sodium appetite. Anatomic mismatches between sites of production and receptors are less evident in limbic and brain stem structures responsible for body fluid homeostasis and blood pressure control. Limbic structures are rich in other neuroactive peptides, some of which have powerful effects on drinking, and they and many of the classical nonpeptide neurotransmitters may interact with ANG II to augment or inhibit drinking behavior. Because ANG II immunoreactivity and binding are so widely distributed in the central nervous system, brain ANG II is unlikely to have a role as circumscribed as that of circulating ANG II. Angiotensin peptides generated from brain precursors may also be involved in functions that have little immediate effect on body fluid homeostasis and blood pressure control, such as cell differentiation, regeneration and remodeling, or learning and memory. Analysis of the mechanisms of increased drinking caused by drugs and experimental procedures that activate the renal renin-angiotensin system, and clinical conditions in which renal renin secretion is increased, have provided evidence that endogenously released renal renin can generate enough circulating ANG II to stimulate drinking. But it is also certain that other mechanisms of thirst and sodium appetite still operate when the effects of circulating ANG II are blocked or absent, although it is not known whether this is also true for angiotensin peptides formed in the brain. Whether ANG II should be regarded primarily as a hormone released in hypovolemia helping to defend the blood volume, a neurotransmitter or paracrine agent with a privileged role in the neural pathways for thirst and sodium appetite of all kinds, a neural organizer especially in sodium appetit

Adjustment of the osmostat in primary aldosteronism

OBJECTIVE

To analyze osmoregulation in primary aldosteronism.

DESIGN

The physiologic and pathologic factors involved in function of the osmostat and in hypernatremia were reviewed.

RESULTS

Patients with primary aldosteronism commonly have mild hypernatremia, with serum sodium concentrations usually less than 150 meq/L. Hypernatremia has been detected in patients with aldosterone-producing adrenal adenomas and adrenal hyperplasia. The patients seem to ingest normal amounts of water. Adjustment of the osmosta (in the hypothalamus) to a higher than normal level of plasma osmolality seems to be the cause. Resetting of the osmostat to a higher level has rarely been noted in conditions other than primary aldosteronism. The hypernatremia can be corrected by either medical or surgical treatment of the primary aldosteronism.

CONCLUSION

Mild hypernatremia in primary aldosteronism is attributable to shifting of the osmostat to the right.

The renal concentrating defect associated with potassium depletion is independent of prostaglandin E2

Prostaglandin E2 (PGE2) impairs the hydrosmotic effect of vasopressin in toad bladder and mammalian kidney. Because some studies in animals have suggested that potassium depletion enhances renal PGE2 production, the present study examined whether the renal concentrating defect of potassium depletion in humans is mediated by PGE2. Five normal volunteers were studied before and after moderate potassium depletion achieved by 10 days of dietary potassium restriction and administration of a polystyrene sulfonate potassium exchange resin (Kayexalate). Maximal urinary osmolality (Umax) decreased from 1,094 +/- 58 (mean +/- SEM) to 820 +/- 26 mmol/kg (mOsm/kg) (P less than 0.01) following potassium depletion, but urinary PGE2 excretion did not change (496 +/- 145 and 435 +/- 186 ng/d, respectively). Indomethacin suppressed PGE2 excretion significantly, but failed to increase Umax in either the normal or the potassium-depleted state (1,094 +/- 34 and 825 +/- 56 mmol/kg, respectively). It is concluded that the renal concentrating defect produced by moderate potassium restriction in humans is not mediated by PGE2.

Induction of renal growth and injury in the intact rat kidney by dietary deficiency of antioxidants

We report induction of renal growth and injury in the intact rat kidney using a diet deficient in vitamin E and selenium. This diet was imposed in 3-wk-old male weanling rats, and after 9 wk, enhancement of growth, characterized by increased wet weight, dry weight, protein content, and DNA content appeared. Morphometric analyses revealed increased kidney volume, tubular epithelial volume, and mean glomerular volume. There were no differences in nephron number. The animals on the deficient diet displayed increased urinary protein excretion at 9 wk. Renal injury was also characterized by an interstitial cellular infiltrate and diminutions in glomerular filtration rate. Enhanced growth and injury were antedated by increased renal ammoniagenesis. The deficient diet did not induce metabolic acidosis, potassium depletion, glucose intolerance, or elevated plasma amino acid concentration. Enhancement of renal growth and ammoniagenesis by the deficient diet was not suppressible by chronic alkali therapy. Stimulation of renal growth could not be ascribed to increased intrarenal iron, induction of ornithine decarboxylase, or alterations in glomerular hemodynamics. Stimulation of renal ammoniagenesis by dietary deficiency of antioxidants is a novel finding, as is induction of growth and injury. We suggest that increased renal ammoniagenesis contributes to induction of renal growth and injury.

Altered drinking responses in dogs with chronic metabolic alkalosis

Chronic chloride depletion alkalosis in dogs causes a lowered osmotic threshold and increased sensitivity for vasopressin (AVP) release. Since AVP release and drinking behavior normally are closely associated over a narrow range of changes in plasma osmolality (Posm), we investigated whether alkalotic dogs would also show an altered responsiveness to the dipsogenic effects of angiotensin II (ANG II) and osmotic stimuli. Dogs made chronically alkalotic by a combination of chloride-free diet and furosemide injections developed polydipsia in the absence of any increase in solute intake and in the presence of a significant reduction in Posm. The animals were chronically hypochloremic, hyponatremic and hypokalemic, and appeared to be extracellular fluid (ECF) contracted. Plasma renin activity (PRA) was 10-fold higher in alkalotic dogs than controls. When Posm was increased by a slow 2 hr infusion of hypertonic sodium sulfate, alkalotic dogs were found to have a significantly lower osmotic threshold for inducing drinking (289.8 +/- 1.1 mOsm/kg/H2O vs. 305.1 +/- 1.3 mOsm/kg/H2O in controls), but the slope or sensitivity of the water intake/Posm relationship was not significantly different. Finally, compared to normal animals, alkalotic dogs were unresponsive to the dipsogenic effects of IV ANG II. These data indicate that the central mechanisms which mediate drinking in response to cellular and extracellular thirst stimuli are altered in chronic metabolic alkalosis.

Relative density of urine: methods and clinical significance

The physical properties and chemical composition of urine are highly variable and are determined in large measure by the quantity and the type of food consumed. The specific gravity is the ratio of the density to that of water, and it is dependent on the number and weight of solute particles and on the temperature of the sample. The weight of solute particles is constituted mainly of urea (73%), chloride (5.4%), sodium (5.1%), potassium (2.4%), phosphate (2.0%), uric acid (1.7%), and sulfate (1.3%). Nevertheless, urine osmolality depends only on the number of solute particles. The renal production of maximally concentrated urine and formation of dilute urine may be reduced to two basic elements: (1) generation and maintenance of a renal medullary solute concentration hypertonic to plasma and (2) a mechanism for osmotic equilibration between the inner medulla and the collecting duct fluid. The interaction of the renal medullary countercurrent system, circulating levels of antidiuretic hormone, and thirst regulates water metabolism. Renin, aldosterone, prostaglandins, and kinins also play a role. Clinical estimation of the concentrating and diluting capacity can be performed by relatively simple provocative tests. However, urinary specific gravity after taking no fluids for 12 h overnight should be 1.025 or more, so that the second urine in the morning is a useful sample for screening purposes. Many preservation procedures affect specific gravity measurements. The concentration of solids (or water) in urine can be measured by weighing, hydrometer, refractometry, surface tension, osmolality, a reagent strip, or oscillations of a capillary tube. These measurements are interrelated, not identical. Urinary density measurement is useful to assess the disorders of water balance and to discriminate between prerenal azotemia and acute tubular necrosis. The water balance regulates the serum sodium concentration, therefore disorders are revealed by hypo- and hypernatremia. The disturbances are due to renal and nonrenal diseases, mainly liver, cardiovascular, intestinal, endocrine, and iatrogenic. Fluid management is an important topic of intensive care medicine. Moreover, the usefulness of specific gravity measurement of urine lies in interpreting other findings of urinalysis, both chemical and microscopical.

In vivo and in vitro studies of urinary concentrating ability in potassium-depleted rabbits

The factors responsible for the urinary concentrating defect associated with the potassium-depleted (KD) state are uncertain. The present studies were designed to, first, determine whether a urinary concentrating defect exists in potassium-depleted rabbits and, second, to use the technique of in vitro perfusion to evaluate directly the antidiuretic hormone (ADH) responsiveness of cortical collecting tubules (CCT) in this setting. Feeding female New Zealand White rabbits a potassium-deficient diet for 2 wk caused a significant fall in plasma potassium levels in both the ad-libitum and controlled water intake groups (P less than 0.001). Muscle potassium content after 2 wk of potassium restriction fell from 45.6 +/- 0.9 to 29.0 +/- 1.2 meq/100 g fat-free dry solids (P less than 0.001). Renal papillary sodium content fell significantly from a control value of 234.6 +/- 8.0 to 182.46 +/- 10.0 meq/kg H2O after 2 wk of potassium restriction. Maximal urinary osmolality measured after 12 h of dehydration and 1.25 U pitressin IM was significantly decreased in rabbits after 2 wk of potassium restriction in both the ad-libitum and controlled water intake groups (P less than 0.001). The relationship between plasma potassium concentration and maximum urinary osmolality was significantly correlated in both the ad-libitum and controlled water intake groups, r = 0.73 and 0.68 (P less than 0.001), respectively. In addition, refeeding KD rabbits with normal chow for 1 wk resulted in normalization of both plasma potassium levels and urinary concentrating ability. CCT from control and KD rabbits were perfused in vitro at 25 degrees C. The hydraulic conductivity coefficient, Lp, was significantly reduced at all doses of ADH tested in tubules from KD rabbits when compared with control tubules. In addition, the maximal hydraulic conductivity in tubules from KD rabbits when tested with 200 microU/ml ADH at 37.5 degrees C was only 23% of control values (P less than 0.05). Furthermore, this reduced ADH responsiveness persisted when the bath potassium was elevated from 5 to 20 mM. The reflection coefficient for NaCl when compared with raffinose was 0.91 in tubules from KD animals. Thus, these data suggest that the ADH-resistant urinary concentrating defect associated with potassium depletion is due, at least in part, to a diminished responsiveness of the CCT to ADH. Therefore, further studies were designed to investigate the cellular steps involved in this abnormal response. There was no difference in the 8-para-chlorophenylthio cyclic AMP induced hydroosmotic response between CCT from KD and control rabbits. Since the cAMP-induced hydroosmotic response was similar between KD and control CCT, experiments were performed to evaluate the contribution of phosphodiesterase (PDIE) activity by using the potent PDIE inhibitor isobutylmethylxanthine (10(-4) and 10(-3)M) in the presence of ADH (200 U/ml). Although Lp was increased by PDIE inhibition in CCT from both control and KD animals, the overall hydroosmotic response in CCT from KD rabbits was still significantly reduced when compared with controls. The final experiments used forskolin to evaluate further the adenylate cyclase complex. The resulting hydroosmotic response in CCT from KD rabbits was almost identical to that obtained in controls. In conclusion, these data suggest that the decreased responsiveness of CCT from KD rabbits to ADH involves a step at or proximal to the stimulation of the catalytic subunit of adenylate cyclase, and that PDIE activity makes no contribution to this abnormal hydroosmotic response.

Ascites, renal abnormalities, and electrolyte and acid-base disorders associated with liver disease

Ascites and renal dysfunction are often associated with decreased liver function and reflect the complex abnormalities of water, protein, electrolyte, and acid-base metabolism that may complicate severe liver disease. This article discusses the pathophysiology and management of ascites, polydipsia and polyuria, decreased renal function, and acid-base and electrolyte alterations that can complicate liver disease.

The cyclic AMP system in the inner medullary collecting duct of the potassium-depleted rat

The present study was undertaken to investigate the cyclic AMP system in the isolated inner medullary collecting tubule (IMCT) of hypokalemic (HK) rats. In situ incubation of IMCT with 10(-7) M arginine vasopressin (AVP) at 300 mOsm/kg H2O in control normokalemic rats increased cyclic AMP content (fmoles/mm) from 5.68 +/- 1.41 to 30.3 +/- 5.31 (P less than 0.001). In HK rats the increase in cyclic AMP was blunted from 7.18 +/- 2.0 to 14.78 +/- 3.14 fmoles/mm (P less than 0.05 compared to controls). No such blunting was observed in the outer medullary collecting duct of hypokalemic rats, but was seen in the IMCT when studied at 800 (P less than 0.05), 1200 (P less than 0.01), and 2000 mOsm/kg H2O (P less than 0.05). The increase in cyclic AMP was also blunted in IMCT of HK rats not allowed to become polyuric or polydipsic by pair-watering studied at 300, 800, and 1200 mOsm/kg H2O. To define the process responsible for the failure to normally increase cyclic AMP in HK, adenylate cyclase activity (AC) was determined at 800 mOsm/kg H2O. While basal AC was not different, the response to all concentrations of AVP between 10(-10) and 10(-6) M was markedly depressed in tubules from HK rats. In contrast AC response to 10(-2) M NaF was not different in IMCT of normokalemic and HK rats. While the abnormal cyclic AMP content with AVP could be explained by abnormal generation, a contribution of increased metabolism was also sought.(ABSTRACT TRUNCATED AT 250 WORDS)

Time-dependent changes in inner medullary plasma flow rate during potassium-depletion

Renal concentrating ability becomes impaired after approximately 2 weeks of dietary potassium (K) depletion in the rat. Since inner medullary plasma flow (IMPF) has been shown to be reduced after 3 weeks of K-depletion, IMPF was measured after 2 and 3 weeks of dietary K-deprivation to determine if the change in IMPF is present at the time the renal concentrating defect first appears. In the present study, similar reductions in maximal urine concentration were present in rats K-depleted for 2 and 3 weeks. IMPF measured by the 125I albumin accumulation method, however, was normal after 2 weeks of K-depletion (control, 35.1 +/- 1.93 vs. K-depletion 2 weeks, 32.8 +/- 1.52 ml/min/100 g IM), and was reduced after 3 weeks of this dietary regime (K-depletion, 3 weeks: 13.8 +/- 1.84). To determine the mechanism of the decrease in IMPF after 3 weeks of K-depletion, rats were treated acutely with indomethacin. There was no significant change in IMPF in control or 3-week K-depleted rats following treatment with indomethacin. These results suggest that the reduction in medullary solute content after 2 weeks of K-depletion cannot be attributed to a reduction in IMPF. In addition, products of the cyclooxygenase enzyme systems do not appear to contribute in a major way to the reduction in IMPF measured after 3 weeks of dietary K-depletion.

In vivo evidence of impaired solute transport by the thick ascending limb in potassium-depleted rats

The objective of this investigation was to determine if thick ascending limb (TAL) solute removal is impaired in potassium-depleted rats, in vivo. We estimated TAL NaCl concentration by measuring in situ conductivity of tubular fluid presented to the early distal site after stop-flow periods of 10-60 s, during which a proximal equilibrium solution remained in contact with the reabsorbing epithelium. This allowed us to calculate the rate constant of the decrease in tubular fluid NaCl concentration and to determine equilibrium values for control, potassium-depleted, and potassium-repleted rats. After 60 s of stop-flow, NaCl concentration of TAL fluid decreased to 18.3 +/- 2.73 mM in control rats, while potassium-depleted rats had values almost twice as high (36.5 +/- 2.97 mM, P less than 0.01). The amount of NaCl remaining after 60 s of stop-flow in K-depleted rats was highly correlated with the plasma K concentration. Calculated rates of NaCl efflux from the TAL appeared to be normal in K-depleted rats while the concentration of NaCl achieved at equilibrium was nearly twice that measured in control rats. Acute systemic administration of KCl by gavage or infusion in K-depleted rats was associated with a decrease in TAL NaCl concentration to normal values. Addition of K to the perfusate, however, did not repair the defect. Our results can best be explained by assigning a special role to the peritubular K concentration. We suggest that the defect in TAL solute removal in K-depletion can be rapidly reversed, because decreases in peritubular K concentration limit Na efflux across the peritubular membrane by decreasing the activity of the Na-K-ATPase pump. We recognize that factors such as regional renal blood flow, local angiotensin II levels, and products of the cyclo-oxygenase enzyme system may play a role.

A diabetes insipidus-like syndrome in the intact Yucatan miniature boar following implantation of desoxycorticosterone-acetate (DOCA)

A syndrome of polydipsia and polyuria is described in the intact adult Yucatan miniature boar following implantation of silicone rubber strips impregnated with desoxycorticosterone-acetate (DOCA). Water intake was significantly greater than control 5 days post-DOCA. Urine output was significantly greater than control 7 days post-DOCA, and urine osmolality was significantly decreased 8 days post-DOCA. Serum potassium was significantly less than control 24 hr post-DOCA, and serum sodium was consistently and significantly greater than control by 1 week post-DOCA. As suggested in the dog, the increase in water turnover following DOCA administration in the pig is initiated by an increased thirst followed by an increase in urine output.

Role of vasopressin in support of blood pressure in potassium deficient rats

Arginine vasopressin (AVP) has been found to contribute to the maintenance of blood pressure (BP) in the rat. Since potassium deficiency results in alterations in systemic hemodynamics, the role of AVP in the control of BP was studied after 14 to 21 days of dietary potassium deficiency. When potassium deficient and control rats were allowed free access to water, plasma osmolality (301.4 +/- 1 vs. 293.4 +/- 3 mOsm/kg; P less than 0.02) and plasma AVP (3.5 +/- 0.2 vs. 2.4 +/- 0.2 pg/ml; P less than 0.02) were increased in potassium deficient animals. To determine the role of this increase in AVP in the maintenance of BP, BP was determined in rats made polydipsic by adding glucose to the drinking water. In both control and potassium deficient rats, increased fluid intake resulted in increased urine output, decreased urinary and plasma osmolality, and a decrease in plasma AVP. While there was no change in BP in control rats when fluid intake was increased, BP fell from 103.9 +/- 1.8 to 96 +/- 2.6 mm Hg (P less than 0.05) in potassium deficient rats with increased fluid intake. To confirm that the decrease in plasma AVP caused the decrease in BP in potassium deficient rats, an AVP pressor antagonist was employed. Following the administration of the AVP pressor antagonist, there was no change in BP in control animals. In contrast, BP fell from 104.3 +/- 1.9 to 98.3 +/- 2.5 mm Hg; P less than 0.05 in potassium deficient rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic effects of alterations in potassium

Potassium is the major intracellular cation. Despite this fact, the systemic and renal hemodynamic effects of alterations in either serum K or in total body K are only partially understood. In isolated preparations acute K excess causes vasodilation while acute K deficiency results in vasoconstriction. Although chronic K excess may decrease arterial pressure in experimental models of hypertension, no definitive conclusions can be stated on the effect of K excess in hypertensive patients. In normotensive animals, chronic K depletion is associated with decreased systemic vascular resistance and increased renal vascular resistance. Although a number of studies have shown that K depletion ameliorates experimental hypertension, no definitive conclusions can be stated on the effect of K depletion in hypertensive patients. The vasodilatory effect of K depletion appears to be a direct effect on vascular smooth muscle since it is associated with an increase in total body Na as well as an increase in cardiac output and in renin ane arginine vasopressin levels. Although renin levels are increased in K deficient rats to a value comparable to na-depleted rats, angiotensin antagonism results in a substantially smaller decrease in arterial pressure than in Na-depleted rats (11 +/- 1.6 vs 24 +/- 3.4 mm Hg, p less than 0.01). This relative resistance to the pressor effect of angiotensin also results in a blunted pressor sensitivity to exogenous angiotensin II. Since changes in K balance appear to have a major effect on the control of hemodynamics, further studies are warranted to determine whether alterations in K balance would be useful in the treatment of hypertension.

Disorders of urinary concentration and dilution

A new approach to the classification of disorders of urinary concentration and dilution is recommended based on recent studies of how the kidney elaborates a urine of widely varying osmolality. The capacity to concentrate urine depends on ft, the fractional reabsorption of solute delivered to the loop of Henle; fu, the excretion of solute relative to the sum of solute excretion and solute delivery to Henle's loop; fw, the fraction of solute loss by vascular outflow from the medulla relative to that reabsorbed by the loop; and finally, collecting duct response to antidiuretic hormone (ADH). A decrease in ft or in increased fu or fw will diminish urinary concentrating ability, as will resistance of the tubule to ADH. Conversely, urinary dilution depends on the delivery of sodium and water to the ascending limb; NaCl reabsorption by the ascending limb; and the absence of ADH. A decrease in sodium and water delivery to the ascending limb or in NaCl reabsorption by the ascending limb will impair urinary diluting ability, as will the presence of ADH. The consequences of disorders in urinary concentrating and diluting ability vary widely. In an alert patient with an intact thirst center, there may be no consequence; in a patient unable to communicate thirst or whose thirst center is deranged, the results may be catastrophic. Keeping in mind the kidney's few basic requirements for formation of concentrated or dilute urine may help the physician avoid these potentially serious dislocations of water balance.