Evidence That Binding of Cyclic GMP to the Extracellular Domain of NKA (Sodium-Potassium ATPase) Mediates Natriuresis.

BACKGROUND: Extracellular renal interstitial guanosine cyclic 3',5'-monophosphate (cGMP) inhibits renal proximal tubule (RPT) sodium (Na+) reabsorption via Src (Src family kinase) activation. Through which target extracellular cGMP acts to induce natriuresis is unknown. We hypothesized that cGMP binds to the extracellular α1-subunit of NKA (sodium-potassium ATPase) on RPT basolateral membranes to inhibit Na+ transport similar to ouabain-a cardiotonic steroid. METHODS: Urine Na+ excretion was measured in uninephrectomized 12-week-old female Sprague-Dawley rats that received renal interstitial infusions of vehicle (5% dextrose in water), cGMP (18, 36, and 72 µg/kg per minute; 30 minutes each), or cGMP+rostafuroxin (12 ng/kg per minute) or were subjected to pressure-natriuresis±rostafuroxin infusion. Rostafuroxin is a digitoxigenin derivative that displaces ouabain from NKA. RESULTS: Renal interstitial cGMP and raised renal perfusion pressure induced natriuresis and increased phosphorylated SrcTyr416 and Erk 1/2 (extracellular signal-regulated protein kinase 1/2)Thr202/Tyr204; these responses were abolished with rostafuroxin coinfusion. To assess cGMP binding to NKA, we performed competitive binding studies with isolated rat RPTs using bodipy-ouabain (2 µM)+cGMP (10 µM) or rostafuroxin (10 µM) and 8-biotin-11-cGMP (2 µM)+ouabain (10 µM) or rostafuroxin (10 µM). cGMP or rostafuroxin reduced bodipy-ouabain fluorescence intensity, and ouabain or rostafuroxin reduced 8-biotin-11-cGMP staining. We cross-linked isolated rat RPTs with 4-N3-PET-8-biotin-11-cGMP (2 µM); 8-N3-6-biotin-10-cAMP served as negative control. Precipitation with streptavidin beads followed by immunoblot analysis showed that RPTs after cross-linking with 4-N3-PET-8-biotin-11-cGMP exhibited a significantly stronger signal for NKA than non-cross-linked samples and cross-linked or non-cross-linked 8-N3-6-biotin-10-cAMP RPTs. Ouabain (10 µM) reduced NKA in cross-linked 4-N3-PET-8-biotin-11-cGMP RPTs confirming fluorescence staining. 4-N3-PET-8-biotin-11-cGMP cross-linked samples were separated by SDS gel electrophoresis and slices corresponding to NKA molecular weight excised and processed for mass spectrometry. NKA was the second most abundant protein with 50 unique NKA peptides covering 47% of amino acids in NKA. Molecular modeling demonstrated a potential cGMP docking site in the ouabain-binding pocket of NKA. CONCLUSIONS: cGMP can bind to NKA and thereby mediate natriuresis.

Decongestion With Acetazolamide in Acute Decompensated Heart Failure Across the Spectrum of Left Ventricular Ejection Fraction: A Prespecified Analysis From the ADVOR Trial.

BACKGROUND: Acetazolamide inhibits proximal tubular sodium reabsorption and improved decongestion in the ADVOR (Acetazolamide in Decompensated Heart Failure with Volume Overload) trial. It remains unclear whether the decongestive effects of acetazolamide differ across the spectrum of left ventricular ejection fraction (LVEF). METHODS: This is a prespecified analysis of the randomized, double-blind, placebo-controlled ADVOR trial that enrolled 519 patients with acute heart failure (HF), clinical signs of volume overload (eg, edema, pleural effusion, or ascites), NTproBNP (N-terminal pro-B-type natriuretic peptide) >1000 ng/L, or BNP (B-type natriuretic peptide) >250 ng/mL to receive intravenous acetazolamide (500 mg once daily) or placebo in addition to standardized intravenous loop diuretics (twice that of the oral home maintenance dose). Randomization was stratified according to LVEF (≤40% or >40%). The primary end point was successful decongestion, defined as the absence of signs of volume overload within 3 days from randomization without the need for mandatory escalation of decongestive therapy because of poor urine output. RESULTS: Median LVEF was 45% (25th to 75th percentile; 30% to 55%), and 43% had an LVEF ≤40%. Patients with lower LVEF were younger and more likely to be male with a higher prevalence of ischemic heart disease, higher NTproBNP, less atrial fibrillation, and lower estimated glomerular filtration rate. No interaction on the overall beneficial treatment effect of acetazolamide to the primary end point of successful decongestion (OR, 1.77 [95% CI, 1.18-2.63]; P=0.005; all P values for interaction >0.401) was found when LVEF was assessed per randomization stratum (≤40% or >40%), or as HF with reduced ejection fraction, HF with mildly reduced ejection fraction, and HF with preserved ejection fraction, or on a continuous scale. Acetazolamide resulted in improved diuretic response measured by higher cumulative diuresis and natriuresis and shortened length of stay without treatment effect modification by baseline LVEF (all P values for interaction >0.160). CONCLUSIONS: When added to treatment with loop diuretics in patients with acute decompensated HF, acetazolamide improves the incidence of successful decongestion and diuretic response, and shortens length of stay without treatment effect modification by baseline LVEF. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: NCT03505788.

Critical Analysis of the Effects of SGLT2 Inhibitors on Renal Tubular Sodium, Water and Chloride Homeostasis and Their Role in Influencing Heart Failure Outcomes.

SGLT2 (sodium-glucose cotransporter 2) inhibitors interfere with the reabsorption of glucose and sodium in the early proximal renal tubule, but the magnitude and duration of any ensuing natriuretic or diuretic effect are the result of an interplay between the degree of upregulation of SGLT2 and sodium-hydrogen exchanger 3, the extent to which downstream compensatory tubular mechanisms are activated, and (potentially) the volume set point in individual patients. A comprehensive review and synthesis of available studies reveals several renal response patterns with substantial variation across studies and clinical settings. However, the common observation is an absence of a large acute or chronic diuresis or natriuresis with these agents, either when given alone or combined with other diuretics. This limited response results from the fact that renal compensation to these drugs is rapid and nearly complete within a few days or weeks, preventing progressive volume losses. Nevertheless, the finding that fractional excretion of glucose and lithium (the latter being a marker of proximal sodium reabsorption) persists during long-term treatment with SGLT2 inhibitors indicates that pharmacological tolerance to the effects of these drugs at the level of the proximal tubule does not meaningfully occur. This persistent proximal tubular effect of SGLT2 inhibitors can be hypothesized to produce a durable improvement in the internal set point for volume homeostasis, which may become clinically important during times of fluid expansion. However, it is difficult to know whether a treatment-related change in the volume set point actually occurs or contributes to the effect of these drugs to reduce the risk of major heart failure events. SGLT2 inhibitors exert cardioprotective effects by a direct effect on cardiomyocytes that is independent of the presence of or binding to SGLT2 or the actions of these drugs on the proximal renal tubule. Nevertheless, changes in the volume set point mediated by SGLT2 inhibitors might potentially act cooperatively with the direct favorable molecular and cellular effects of these drugs on cardiomyocytes to mediate their benefits on the development and clinical course of heart failure.

Inhibition of mTORC2 promotes natriuresis in Dahl salt-sensitive rats via the decrease of NCC and ENaC activity.

We have previously observed that prolonged administration of rapamycin, an inhibitor targeting the mammalian target of rapamycin complex (mTORC)1, partially reduced hypertension and alleviated kidney inflammation in Dahl salt-sensitive (SS) rats. In contrast, treatment with PP242, an inhibitor affecting both mTORC1/mTORC2, not only completely prevented hypertension but also provided substantial protection against kidney injury. Notably, PP242 exhibited potent natriuretic effects that were not evident with rapamycin. The primary objective of this study was to pinpoint the specific tubular sites responsible for the natriuretic effect of PP242 in SS rats subjected to either 0.4% NaCl (normal salt) or 4.0% NaCl (high salt) diet. Acute effects of PP242 on natriuretic, diuretic, and kaliuretic responses were determined in unanesthetized SS rats utilizing benzamil, furosemide, or hydrochlorothiazide [inhibitors of epithelial Na+ channel (ENaC), Na-K-2Cl cotransporter (NKCC2), or Na-Cl cotransporter (NCC), respectively] either administered alone or in combination. The findings indicate that the natriuretic effects of PP242 in SS rats stem predominantly from the inhibition of NCC and a reduction of ENaC open probability. Molecular analysis revealed that mTORC2 regulates NCC activity through protein phosphorylation and ENaC activity through proteolytic cleavage in vivo. Evidence also indicated that PP242 also prevents the loss of K+ associated with the inhibition of NCC. These findings suggest that PP242 may represent an improved therapeutic approach for antihypertensive intervention, potentially controlling blood pressure and mitigating kidney injury in salt-sensitive human subjects.NEW & NOTEWORTHY This study explored mechanisms underlying the natriuretic effects of mammalian target of rapamycin protein complex 2 inhibition using PP242 and revealed both epithelial Na+ channel and Na-Cl cotransporter in the distal tubular segments were potentially inhibited. These observations, with prior lab evidence, indicate that PP242 prevents hypertension via its potent inhibitory effects on these specific sodium transporters and by reducing renal immune responses. This dual action, coupled with potassium sparing effects, suggests an improved approach for managing hypertension and associated kidney damage.

Rationale and Design of the DECONGEST (Diuretic Treatment in Acute Heart Failure With Volume Overload Guided by Serial Spot Urine Sodium Assessment) Study.

AIMS: To evaluate whether early-combination diuretic therapy guided by serial post-diuretic urine sodium concentration (UNa+) assessments in acute heart failure (AHF) facilitates safe and effective decongestion. METHODS: The Diuretic Treatment in Acute Heart Failure with Volume Overload Guided by Serial Spot Urine Sodium Assessment (DECONGEST) study is a pragmatic, 2-center, randomized, parallel-arm, open-label study aiming to enroll 104 patients with AHF and clinically evident fluid overload requiring treatment with intravenous loop diuretics. Patients are randomized to receive standard of care or a bundled approach comprising: (1) systematic post-diuretic UNa+ assessments until successful decongestion, defined as no remaining clinical signs of fluid overload with a post-diuretic UNa+ ≤ 80 mmol/L; (2) thrice-daily intravenous loop diuretic bolus therapy, with dosing according to estimated glomerular filtration rate; (3) upfront use of intravenous acetazolamide (500 mg once daily [OD]); and (4) full nephron blockade with high-dose oral chlorthalidone (100 mg OD) and intravenous canreonate (200 mg OD) for diuretic resistance, defined as persisting signs of fluid overload with a post-diuretic UNa+ ≤ 80 mmol/L. The primary endpoint of the DECONGEST study is a hierarchical composite of (1) survival at 30 days; (2) days alive and out of hospital or care facility up to 30 days; and (3) greater relative decrease in natriuretic peptide levels from baseline to day 30. CONCLUSION: The DECONGEST study aims to determine whether an intensive diuretic regimen focused on early combination therapy, guided by serial post-diuretic UNa+ assessments, safely enhances decongestion, warranting further evaluation in a larger trial powered for clinical events.

Acetazolamide therapy in patients with acute heart failure: a systematic review and meta-analysis of randomized controlled trials.

Acute heart failure (AHF) often leads to unfavorable outcomes due to fluid overload. While diuretics are the cornerstone treatment, acetazolamide may enhance diuretic efficiency by reducing sodium reabsorption. We performed a systematic review and meta-analysis on the effects of acetazolamide as an add-on therapy in patients with AHF compared to diuretic therapy. PubMed, Embase, and Cochrane databases were searched for randomized controlled trials (RCT). A random-effects model was employed to compute mean differences and risk ratios. Statistical analysis was performed using R software. The GRADE approach was used to rate the certainty of the evidence. We included 4 RCTs with 634 patients aged 68 to 81 years. Over a mean follow-up of 3 days to 34 months, acetazolamide significantly increased diuresis (MD 899.2 mL; 95% CI 249.5 to 1549; p < 0.01) and natriuresis (MD 72.44 mmol/L; 95% CI 39.4 to 105.4; p < 0.01) after 48 h of its administration. No association was found between acetazolamide use and WRF (RR 2.4; 95% CI 0.4 to 14.2; p = 0.3) or all-cause mortality (RR 1.2; 95% CI 0.8 to 1.9; p = 0.3). Clinical decongestion was significantly higher in the intervention group (RR 1.35; 95% CI 1.09 to 1.68; p = 0.01). Acetazolamide is an effective add-on therapy in patients with AHF, increasing diuresis, natriuresis, and clinical decongestion, but it was not associated with differences in mortality.

Renal function in PUSH-AHF: a summary of newly released data from the 2024 Annual Congress of the Heart Failure Association of the ESC.

The Pragmatic Urinary Sodium-based algoritHm in Acute Heart Failure (PUSH-AHF) study, published in August of 2023, was the first randomized clinical trial to compare natriuresis-guided decongestion (based on spot urinary sodium measurement) to standard of care in patients with acute heart failure with congestion receiving loop diuretic therapy. Based on results from their trial, the authors concluded that natriuresis-guided loop diuretic treatment was safe and improved natriuresis and diuresis without impacting long-term clinical outcomes. The original PUSH-AHF trial included limited information about renal outcomes and left clinicians with important questions about how natriuresis-guided decongestion might affect their patients' renal function. On May 12, 2024, however, at the 2024 Annual Congress of the HFA-ESC, Dr. Kevin Damman provided an in-depth exploration of renal outcomes from the trial when he presented a pre-specified, secondary analysis, renal function in the PUSH-AHF trial. This review puts the sub-study findings into context by considering the history of the original trial from which they came from and explaining the need for a close study of its renal outcomes particularly. It highlights the potential impact of renal function in PUSH-AHF on clinical practice and future directions that should be considered by the cardiology research community.

The utility of urine sodium-guided diuresis during acute decompensated heart failure.

Diuresis to achieve decongestion is a central aim of therapy in patients hospitalized for acute decompensated heart failure (ADHF). While multiple approaches have been tried to achieve adequate decongestion rapidly while minimizing adverse effects, no single diuretic strategy has shown superiority, and there is a paucity of data and guidelines to utilize in making these decisions. Observational cohort studies have shown associations between urine sodium excretion and outcomes after hospitalization for ADHF. Urine chemistries (urine sodium ± urine creatinine) may guide diuretic titration during ADHF, and multiple randomized clinical trials have been designed to compare a strategy of urine chemistry-guided diuresis to usual care. This review will summarize current literature for diuretic monitoring and titration strategies, outline evidence gaps, and describe the recently completed and ongoing clinical trials to address these gaps in patients with ADHF with a particular focus on the utility of urine sodium-guided strategies.

Sodium-glucose linked transporter 2 inhibitors in liver cirrhosis: Beyond their antidiabetic use.

Type 2 diabetes mellitus (T2DM) and liver cirrhosis are clinical entities that frequently coexist, but glucose-lowering medication options are limited in cirrhotic patients. Sodium-glucose linked transporter 2 (SGLT2) inhibitors are a class of glucose-lowering medication that act independently of insulin, by causing glycosuria in the proximal convoluted tubule. In this review, we aimed to briefly present the main data and to provide insight into the pathophysiology and potential usefulness of SGLT2 inhibitors in cirrhotic patients with or without T2DM. SGLT2 inhibitors have been proven useful as antidiabetic treatment in patients with metabolic liver disease, with most robust data from patients with metabolic dysfunction-associated steatotic liver disease (MASLD), where they also showed improvement in liver function parameters. Moreover, it has been suggested that SGLT2 inhibitors may have effects beyond their antidiabetic action. Accordingly, they have exhibited cardioprotective effects, expanding their indication in patients with heart failure without T2DM. Since decompensated liver cirrhosis and congestive heart failure share common pathophysiological features, namely renin-angiotensin-aldosterone axis and sympathetic nervous system activation as well as vasopressin secretion, SGLT2 inhibitors could also be beneficial in patients with decompensated cirrhosis, even in the absence of T2DM.

Renal AT2 Receptors Mediate Natriuresis via Protein Phosphatase PP2A.

BACKGROUND: How signals from activated angiotensin type-2 receptors (AT2R) mediate inhibition of sodium ion (Na+) reabsorption in renal proximal tubule cells is currently unknown. Protein phosphatases including PP2A (protein phosphatase 2A) have been implicated in AT2R signaling in tissues other than kidney. We investigated whether inhibition of protein phosphatase PP2A reduced AT2R-mediated natriuresis and evaluated changes in PP2A activity and localization after renal AT2R activation in normal 4- and 10-week-old control Wistar-Kyoto rats and 4-week-old prehypertensive and 10-week-old hypertensive spontaneously hypertensive rats. METHODS AND RESULTS: In Wistar-Kyoto rats, direct renal interstitial administration of selective AT2R nonpeptide agonist Compound-21 (C-21) increased renal interstitial cyclic GMP (cGMP) levels, urine Na+ excretion, and simultaneously increased PP2A activity ≈2-fold in homogenates of renal cortical tubules. The cyclic GMP and natriuretic responses were abolished by concurrent renal interstitial administration of protein phosphatase inhibitor calyculin A. In renal proximal tubule cells in response to C-21, PP2A subunits A, B55α and C, but not B56γ, were recruited to apical plasma membranes together with AT2Rs. Calyculin A treatment abolished C-21-induced translocation of both AT2R and PP2A regulatory subunit B55α to apical plasma membranes. Immunoprecipitation of AT2R solubilized from renal cortical homogenates demonstrated physical association of AT2R with PP2A A, B55α, and C but not B56γ subunits. In contrast, in spontaneously hypertensive rats, administration of C-21 did not alter urine Na+ excretion or PP2A activity and failed to translocate AT2Rs and PP2A subunits to apical plasma membranes. CONCLUSIONS: In renal proximal tubule cells of Wistar-Kyoto rats, PP2A is activated and PP2A subunits AB55αC are recruited to C-21-activated AT2Rs during induction of natriuresis. This response is defective in prehypertensive and hypertensive spontaneously hypertensive rats, presenting a potential novel therapeutic target for treating renal Na+ retention and hypertension.

How can inhibition of glucose and sodium transport in the early proximal tubule protect the cardiorenal system?

What mechanisms can link the inhibition of sodium-glucose cotransporter 2 (SGLT2) in the early proximal tubule to kidney and heart protection in patients with and without type 2 diabetes? Due to physical and functional coupling of SGLT2 to other sodium and metabolite transporters in the early proximal tubule (including NHE3, URAT1), inhibitors of SGLT2 (SGLT2i) reduce reabsorption not only of glucose, inducing osmotic diuresis, but of other metabolites plus of a larger amount of sodium than expected based on SGLT2 inhibition alone, thereby reducing volume retention, hypertension and hyperuricemia. Metabolic adaptations to SGLT2i include a fasting-like response, with enhanced lipolysis and formation of ketone bodies that serve as additional fuel for kidneys and heart. Making use of the physiology of tubulo-glomerular communication, SGLT2i functionally lower glomerular capillary pressure and filtration rate, thereby reducing physical stress on the glomerular filtration barrier, tubular exposure to albumin and nephrotoxic compounds, and the oxygen demand for reabsorbing the filtered load. Together with reduced gluco-toxicity in the early proximal tubule and better distribution of transport work along the nephron, SGLT2i can preserve tubular integrity and transport function and, thereby, glomerular filtration rate in the long-term. By shifting transport downstream, SGLT2i may simulate systemic hypoxia at the oxygen sensors in the deep cortex/outer medulla, which stimulates erythropoiesis and, together with osmotic diuresis, enhances hematocrit and thereby improves oxygen delivery to all organs. The described SGLT2-dependent effects may be complemented by off-target effects of SGLT2i on the heart itself and on the microbiome formation of cardiovascular-effective uremic toxins.

Safety and Efficacy of Dapagliflozin in Recurrent Ascites: A Pilot Study.

BACKGROUND: In cirrhosis, activation of renin-angiotensin-aldosterone system leads to sodium and water retention causing ascites. Dapagliflozin, a sodium glucose linked transporter-2 inhibitor, induces natriuresis in patients with heart failure. A similar natriuretic effect may improve ascites in patients with cirrhosis. In this pilot study, we evaluated the safety and efficacy of dapagliflozin in patients with cirrhosis and recurrent ascites. METHODS: Forty patients with recurrent ascites and cirrhosis were randomized to 1:1 in a double blinded fashion to receive either dapagliflozin (10 mg/day) with standard medical therapy (Group A) or placebo with standard medical therapy (Group B). The primary outcome was control of ascites at 6 months. Secondary outcomes were urine output, 24-h urinary sodium, Child Turcotte Pugh (CTP), model for end-stage liver disease (MELD) scores, survival at 6 months, incidence of acute kidney injury (AKI) and infections. RESULTS: The 2 groups were comparable at baseline. Control of ascites at 6 months was significantly better in group A than that in Group B (p = 0.04). Change in urinary sodium was significantly higher in Group A (p < 0.001]. However, there was no difference in change in urine output, CTP or MELD scores and survival (65% vs 72.2%, p = 0.75) between the groups at 6 months. Incidence of AKI (50% vs 15%, p = 0.04) and infections (55% vs 20%, p = 0.04) were significantly higher in Group A. CONCLUSION: Significantly better control of ascites and higher natriuresis are observed with dapagliflozin. However, it does not improve disease severity scores or survival, and is associated with increased AKI and infections (NCT05014594).

GLP-1 receptor agonists may enhance the effects of desmopressin in individuals with AVP deficiency: a case series and proposed mechanism.

BACKGROUND: Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have diverse effects on sodium and water homeostasis. They decrease thirst perception, potentially inhibit arginine vasopressin (AVP) production, and induce natriuresis. We present three cases of AVP deficiency (AVP-D) where GLP-1 RA initiation led to desmopressin dose reduction. CASES: Three patients with AVP-D on stable desmopressin therapy started GLP-1 RAs for type 2 diabetes mellitus or obesity. Following weight loss and decreased thirst, all patients reduced their desmopressin dose while maintaining normal thirst and urine output. DISCUSSION: GLP-1 RAs influence sodium and water homeostasis through various mechanisms. In individuals with intact AVP systems, GLP-1 RAs may directly suppress AVP production and induce natriuresis in the kidney leading to increased water excretion. In AVP-D, with exogenous desmopressin replacing endogenous AVP, the osmotic permeability of collecting ducts is primarily influenced by desmopressin dose. Thus, increased distal fluid delivery may allow for lower desmopressin doses to maintain water balance. CONCLUSION: Our findings indicate a potential interaction between GLP-1 RAs and desmopressin in AVP-D. Clinicians should reassess desmopressin dosage upon initiating GLP-1 RA therapy.

Pre-treatment bicarbonate levels and decongestion by acetazolamide: the ADVOR trial.

AIMS: Acetazolamide inhibits proximal tubular sodium and bicarbonate re-absorption and improved decongestive response in acute heart failure in the ADVOR trial. It is unknown whether bicarbonate levels alter the decongestive response to acetazolamide. METHODS AND RESULTS: This is a sub-analysis of the randomized, double-blind, placebo-controlled ADVOR trial that randomized 519 patients with acute heart failure and volume overload in a 1:1 ratio to intravenous acetazolamide (500 mg/day) or matching placebo on top of standardized intravenous loop diuretics (dose equivalent of twice oral maintenance dose). The primary endpoint was complete decongestion after 3 days of treatment (morning of day 4). Impact of baseline HCO3 levels on the treatment effect of acetazolamide was assessed. : Of the 519 enrolled patients, 516 (99.4%) had a baseline HCO3 measurement. Continuous HCO3 modelling illustrated a higher proportional treatment effect for acetazolamide if baseline HCO3 ≥ 27 mmol/l. A total of 234 (45%) had a baseline HCO3 ≥ 27 mmol/l. Randomization towards acetazolamide improved decongestive response over the entire range of baseline HCO3- levels (P = 0.004); however, patients with elevated baseline HCO3 exhibited a significant higher response to acetazolamide [primary endpoint: no vs. elevated HCO3; OR 1.37 (0.79-2.37) vs. OR 2.39 (1.35-4.22), P-interaction = 0.065), with higher proportional diuretic and natriuretic response (both P-interaction < 0.001), greater reduction in congestion score on consecutive days (treatment × time by HCO3-interaction <0.001) and length of stay (P-interaction = 0.019). The larger proportional treatment effect was mainly explained by the development of diminished decongestive response in the placebo arm (loop diuretics only), both with regard to reaching the primary endpoint of decongestion as well as reduction in congestion score. Development of elevated HCO3 further worsened decongestive response in the placebo arm (P-interaction = 0.041). A loop diuretic only strategy was associated with an increase in the HCO3 during the treatment phase which was prevented by acetazolamide (day 3: placebo 74.8% vs. acetazolamide 41.3%, P < 0.001). CONCLUSION: Acetazolamide improves decongestive response over the entire range of HCO3- levels; however, the treatment response is magnified in patients with baseline or loop diuretic-induced elevated HCO3 (marker of proximal nephron NaHCO3 retention) by specifically counteracting this component of diuretic resistance.

Naringen's Effects on Diuresis and Prevention of Urolithiasis in Hypertensive Rats.

This research demonstrates the diuretic effect of naringenin, a flavanone aglycone found in citrus, on spontaneously hypertensive female and male rats (SHR). The data reinforces existing literature findings that male SHR exhibits higher systolic blood pressure than age-matched females. Urine volume assessed over 8 hours was lower when obtained from SHR males than females. When these animals were orally treated with different doses of naringenin (0.1-1 mg/kg), this increased urinary volume in both genders at the highest dose tested. In contrast, the lowest dose promoted a significant natriuretic effect. The other electrolytes analyzed in urine were not significantly altered, except potassium excretion, which was shown to be increased in the urine of SHR males. Furthermore, naringenin showed promise in reducing calcium oxalate (CaOx) crystal formation in an in vitro model, presenting potential advantages in lithiasis prevention.

Angiotensin II hypertension along the female rat tubule: predicted impact on coupled transport of Na+ and K.

Chronic infusion of subpressor level of angiotensin II (ANG II) increases the abundance of Na+ transporters along the distal nephron, balanced by suppression of Na+ transporters along the proximal tubule and medullary thick ascending limb (defined as "proximal nephron"), which impacts K+ handling along the entire renal tubule. The objective of this study was to quantitatively assess the impact of chronic ANG II on the renal handling of Na+ and K+ in female rats, using a computational model of the female rat renal tubule. Our results indicate that the downregulation of proximal nephron Na+ reabsorption (TNa), which occurs in response to ANG II-triggered hypertension, involves changes in both transporter abundance and trafficking. Our model suggests that substantial (∼30%) downregulation of active NHE3 in proximal tubule (PT) microvilli is needed to reestablish the Na+ balance at 2 wk of ANG II infusion. The 35% decrease in SGLT2, a known NHE3 regulator, may contribute to this downregulation. Both depression of proximal nephron TNa and stimulation of distal ENaC raise urinary K+ excretion in ANG II-treated females, while K+ loss is slightly mitigated by cortical NKCC2 and NCC upregulation. Our model predicts that K+ excretion may be more significantly limited during ANG II infusion by ROMK inhibition in the distal nephron and/or KCC3 upregulation in the PT, which remain open questions for experimental validation. In summary, our analysis indicates that ANG II hypertension triggers a series of events from distal TNa stimulation followed by compensatory reduction in proximal nephron TNa and accompanying adjustments to limit excessive K+ secretion.NEW & NOTEWORTHY We used a computational model of the renal tubule to assess the impact of 2-wk angiotensin II (ANG II) infusion on the handling of Na+ and K+ in female rats. ANG II strongly stimulates distal Na+ reabsorption and K+ secretion. Simulations indicate that substantial downregulation of proximal tubule NHE3 is needed to reestablish Na+ balance at 2 wk. Proximal adaptations challenge K+ homeostasis, and regulation of distal NCC and specific K+ channels likely limit urinary K+ losses.

Oral Sodium to Preserve Renal Efficiency in Acute Heart Failure: A Randomized, Placebo-Controlled, Double-Blind Study.

BACKGROUND: Evidence for modulating the sodium chloride (NaCl) intake of patients hospitalized with acute heart failure (AHF) is inconclusive. Salt restriction may not benefit; hypertonic saline may aid diuresis. OBJECTIVE: To compare the safety and efficacy of oral NaCl during intravenous (IV) diuretic therapy in renal function and weight. METHODS: Seventy hospitalized patients with AHF who were being treated with IV furosemide infusion consented to receive, randomly, 2 grams of oral NaCl or placebo 3 times a day in a double-blind manner during diuresis. Treatment efficacy (bivariate primary endpoints of change in serum creatinine levels and change in weight) was measured at 96 hours, and adverse safety events were tracked for 90 days. RESULTS: Sixty-five patients (34 NaCl, 31 placebo) were included for analysis after 5 withdrew. A median of 13 grams of NaCl was given compared to placebo. At 96 hours, there was no significant difference between treatment groups with respect to the primary endpoint (P = 0.33); however, the trial was underpowered, and there was greater than expected standard deviation in weight change. The mean change in creatinine levels and weight was 0.15 ± 0.44 mg/dL and 4.6 ± 4.2 kg in the placebo group compared with 0.04 ± 0.40 mg/dL and 4.0 ± 4.3 kg in the NaCl group (P = 0.30 and 0.57, respectively). Across efficacy and safety endpoints, we observed no significant difference between the 2 groups other than changes in serum sodium levels (-2.6 ± 2.7 in the placebo group and -0.3 ± 3.3 mEq/L in the NaCl group; P < 0.001) and in serum blood urea nitrogen levels (11 ± 15 in the placebo group; 3.1 ± 13 mEq/L in the NaCl group; P = 0.025). CONCLUSIONS: In this single-center study, liberal vs restrictive oral sodium chloride intake strategies did not impact the safety and efficacy of intravenous diuretic therapy in patients with AHF. (ClinicalTrials.gov registration NCT04334668.).

Sodium-glucose cotransporter 2 inhibition does not improve the acute pressure natriuresis response in rats with type 1 diabetes.

NEW FINDINGS: What is the central question of this study? Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce cardiovascular risk in patients with both diabetic and non-diabetic kidney disease: can SGLT2 inhibition improve renal pressure natriuresis (PN), an important mechanism for long-term blood pressure control, which is impaired in type 1 diabetes mellitus (T1DM)? What is the main finding and its importance? The SGLT2 inhibitor dapagliflozin did not enhance the acute in vivo PN response in either healthy or T1DM Sprague-Dawley rats. The data suggest that the mechanism underpinning the clinical benefits of SGLT2 inhibitors on health is unlikely to be due to an enhanced natriuretic response to increased blood pressure. ABSTRACT: Type 1 diabetes mellitus (T1DM) leads to serious complications including premature cardiovascular and kidney disease. Hypertension contributes importantly to these adverse outcomes. The renal pressure natriuresis (PN) response, a key regulator of blood pressure (BP), is impaired in rats with T1DM as tubular sodium reabsorption fails to down-regulate with increasing BP. We hypothesised that sodium-glucose cotransporter 2 (SGLT2) inhibitors, which reduce cardiovascular risk in kidney disease, would augment the PN response in T1DM rats. Non-diabetic or T1DM (35-50 mg/kg streptozotocin i.p.) adult male Sprague-Dawley rats were anaesthetised (thiopental 50 mg/kg i.p.) and randomised to receive either dapagliflozin (1 mg/kg i.v.) or vehicle. Baseline sodium excretion was measured and then BP was increased by sequential arterial ligations to induce the PN response. In non-diabetic animals, the natriuretic and diuretic responses to increasing BP were not augmented by dapagliflozin. Dapagliflozin induced glycosuria, but this was not influenced by BP. In T1DM rats the PN response was impaired. Dapagliflozin again increased urinary glucose excretion but did not enhance PN. Inhibition of SGLT2 does not enhance the PN response in rats, either with or without T1DM. SGLT2 makes only a minor contribution to tubular sodium reabsorption and does not contribute to the impaired PN response in T1DM.

Effect of fluid replacement with green tea on body fluid balance and renal responses under mild thermal hypohydration: a randomized crossover study.

PURPOSE: Maintaining an appropriate hydration level by ingesting fluid in a hot environment is a measure to prevent heat-related illness. Caffeine-containing beverages, including green tea (GT), have been avoided as inappropriate rehydration beverages to prevent heat-related illness because caffeine has been assumed to exert diuretic/natriuretic action. However, the influence of caffeine intake on urine output in dehydrated individuals is not well documented. The aim of the present study was to examine the effect of fluid replacement with GT on body fluid balance and renal water and electrolyte handling in mildly dehydrated individuals. METHODS: Subjects were dehydrated by performing three bouts of stepping exercise for 20 min separated by 10 min of rest. They were asked to ingest an amount of water (H2O), GT, or caffeinated H2O (20 mg/100 ml; Caf-H2O) that was equal to the volume of fluid loss during the dehydration protocol; fluid balance was measured for 2 h after fluid ingestion. RESULTS: The dehydration protocol induced hypohydration by ~ 10 g/kg body weight (~ 1% of body weight). Fluid balance 2 h after fluid ingestion was significantly less negative in all trials, and the fluid retention ratio was 52.2 ± 4.2% with H2O, 51.0 ± 5.0% with GT, and 47.9 ± 6.2% with Caf-H2O; those values did not differ among the trials. After rehydration, urine output, urine osmolality, and urinary excretions of osmotically active substances, sodium, potassium and chloride were not different among the trials. CONCLUSION: The data indicate that ingestion of GT or an equivalent caffeine amount does not worsen the hydration level 2 h after ingestion and can be effective in reducing the negative fluid balance for acute recovery from mild hypohydration. TRIAL REGISTRATION: ISRCTN53057185; retrospectively registered.

Spot Urinary Sodium Measurements: the Future Direction of the Treatment and Follow-up of Patients with Heart Failure.

PURPOSE OF REVIEW: Heart failure is characterized by episodes of congestion with need for hospitalization. The current metrics lack the accuracy to predict and prevent episodes of congestion and to guide diuretic titration to reach euvolemia in case of decompensation. This article aims to provide answers to the role of urinary sodium measurements in acute and chronic heart failure. RECENT FINDINGS: In acute heart failure, urinary sodium concentrations at the moment of admission and after diuretic administration are correlated with short- and long-term outcome. As this is a reflection of the degree of sodium retention, it can be used as a guide in the diuretic titration. In chronic heart failure, it might be used to predict and consequently prevent episodes of decompensation. Urinary sodium measurements hold great promises to be a novel diagnostic and therapeutic parameter in patients with acute and chronic heart failure. However, more research is needed.