Sodium Handling Research Articles

Effect of desmopressin on water and solute circadian rhythms in treatment-naïve children with monosymptomatic enuresis and nocturnal polyuria.

Enuresis has a complex pathophysiology involving nocturnal polyuria, reduced bladder capacity at nighttime, and impaired arousability. Desmopressin has long been used as a treatment. However, approximately 30% of children do not fully respond to it, suggesting the involvement of other factors. Solute handling and osmotic excretion have been studied in refractory patients. Nevertheless, data on the effect of desmopressin on these factors are sparse. We conducted a post hoc analysis of the SLEEP study. We analyzed the circadian rhythm of solute and water excretion before and after desmopressin in 30 children with monosymptomatic enuresis and nocturnal diuresis > 100% of expected bladder capacity by means of a 24-h urine concentration profile (four daytime and four nighttime urine portions at equivalent time intervals). Under desmopressin, nocturnal diuresis (rate) and Na/creatinine ratio were significantly lower compared to day values (p = 0.009, p = 0.021, respectively). Osmolality, Na/creatinine, and osmotic excretion showed a significant day vs. night variance only after desmopressin. Nighttime osmotic and sodium excretion were significantly lower (p = 0.004, p = 0.019, respectively) under treatment, indicating the impact of desmopressin on kidney sodium handling. During desmopressin treatment, nocturnal diuresis (rate) showed strong positive correlation with nighttime Na/creatinine (r = 0.436, p < 0.05) and very strongly with nighttime osmotic excretion (r = 0.875, p < 0.0001). However, no correlation was observed with osmolality under desmopressin treatment. The anti-enuretic and antidiuretic effects of desmopressin therapy are not only related to urinary concentration and nocturnal diuresis but also to the amelioration of circadian rhythms of sodium and solute handling.

Psidium guajava leaves extract alters colonic microbiome composition and reduces intestinal sodium absorption in rats exposed to a high-sodium diet.

High sodium intake is a major risk factor for hypertension and renal diseases. Previous studies have shown that a suspension of ethanolic extract of Psidium guajava (guava) leaves (PsE) has antihypertensive effects in rats on a high-sodium diet (HSD), but some mechanisms to that remain unexplored. This study explored whether oral PsE treatment affects sodium handling by the intestine and alters the gut microbiome in HSD-fed rats. Male Wistar rats were divided into two groups: standard salt diet (SSD) and HSD (0.9% Na+), from weaning. After 12 weeks, both groups received PsE (200mg/kg) or a vehicle for an additional 4 weeks. Sodium excretion was measured using flame photometry, and sodium absorption was assessed by intestinal perfusion technique. The gut microbiome was analysed through 16S ribosomal gene sequencing. HSD increased faecal sodium, further elevated by PsE, which inhibited intestinal sodium absorption in HSD rats. HSD altered the abundance of specific bacterial families, which PsE partially reversed. No changes in alpha diversity were noted among groups. These findings suggest that PsE inhibited intestinal sodium handling and that PsE, combined with increased faecal sodium, may reshape the gut microbiome of HSD rats to resemble that of SSD rats.

5/6 Nephrectomy Impairs Acute Kaliuretic Responses and Predisposes to Postprandial Hyperkalemia.

The susceptibility of patients with chronic kidney disease (CKD) to develop postprandial hyperkalemia suggests alterations in normal kidney sodium (Na+) and potassium (K+) handling, but the exact nature of these changes is largely unknown. To address this, we analyzed the natriuretic and kaliuretic responses to diuretics and acute K+ loading in rats who underwent 5/6 nephrectomy (5/6Nx) and compared this to the response in sham-operated rats. The natriuretic and kaliuretic responses to furosemide, hydrochlorothiazide, and amiloride were largely similar between 5/6Nx and sham rats except for a significantly reduced kaliuretic response to hydrochlorothiazide in 5/6Nx rats. Acute dietary K+ loading with either 2.5% potassium chloride or 2.5% potassium citrate caused lower natriuretic and kaliuretic responses in 5/6Nx rats compared with sham rats. This resulted in significantly higher plasma K+ concentrations in 5/6Nx rats which were accompanied by corresponding increases in plasma aldosterone. Acute K+ loading caused dephosphorylation of Ste20-related proline/alanine-rich kinase (SPAK) and the sodium-chloride cotransporter (NCC) both in sham and 5/6Nx rats. In contrast, the acute K+ load decreased the Na+/hydrogen exchanger 3 (NHE3) and increased serum- and glucocorticoid-regulated kinase 1 (SGK1) and the α-subunit of the epithelial sodium channel (ENaC) only in sham rats. Together, our data show that 5/6Nx impairs the natriuretic and kaliuretic response to an acute dietary K+ load which is further characterized by a loss of ENaC adaptation and the development of postprandial hyperkalemia.

Sodium-Glucose Cotransporter 2 (SGLT2) Inhibitors: Guardians against Mitochondrial Dysfunction and Endoplasmic Reticulum Stress in Heart Diseases.

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are an innovative class of antidiabetic drugs that provide cardiovascular benefits to both diabetic and nondiabetic patients, surpassing those of other antidiabetic drugs. Although the roles of mitochondria and endoplasmic reticulum (ER) in cardiovascular research are increasingly recognized as promising therapeutic targets, the exact molecular mechanisms by which SGLT2 inhibitors influence mitochondrial and ER homeostasis in the heart remain incompletely elucidated. This review comprehensively summarizes and discusses the impacts of SGLT2 inhibitors on mitochondrial dysfunction and ER stress in heart diseases including heart failure, ischemic heart disease/myocardial infarction, and arrhythmia from preclinical and clinical studies. Based on the existing evidence, the effects of SGLT2 inhibitors may potentially involve the restoration of mitochondrial biogenesis and alleviation of ER stress. Such consequences are achieved by enhancing adenosine triphosphate (ATP) production, preserving mitochondrial membrane potential, improving the activity of electron transport chain complexes, maintaining mitochondrial dynamics, mitigating oxidative stress and apoptosis, influencing cellular calcium and sodium handling, and targeting the unfolded protein response (UPR) through three signaling pathways including inositol requiring enzyme 1α (IRE1α), protein kinase R like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6). Therefore, SGLT2 inhibitors have emerged as a promising target for treating heart diseases due to their potential to improve mitochondrial functions and ER stress.

6849 Insulin Edema in newly diagnosed T1DM Pediatric Patient

Abstract Disclosure: A. Ansar: None. K. McNerney: None. Background: Insulin edema is a rare complication of insulin therapy, especially in the pediatric populations. The pathogenesis is not fully understood but has been linked to Insulin’s role in renal sodium handling and vascular permeability. It has been seen with the initiation of insulin in newly diagnosed patients or the intensification of insulin therapy in those with poor glycemic control.Clinical Case: A previously healthy 12 year old girl presented to the ED with polyuria, polydipsia and fatigue. She was alert and oriented but had kussmaul breathing. She was tachycardic but all other vitals were appropriate. Lab work up showed that she was in DKA with pH 7.07 and bicarbonate 7 mmol/L. Her corrected sodium and electrolytes were normal. Her HbA1C was elevated at 11.7% (4.0-5.6%). Initial fluid resuscitation was performed with 20 mL/kg NS fluids. She was transferred to our Pediatric ICU and was started on the DKA protocol consisting of intravenous insulin infusion at 0.1 unit/kg per hour and 2-bags of dextrose and non-dextrose containing intravenous fluids. She was given a new diagnosis of Type 1 Diabetes. She was transitioned to subcutaneous insulin 22 hours later with multiple daily injections with insulin lispro and glargine, with total dose of insulin at 0.7 unit/kg per day. She was transferred to the general care floor and received diabetes education while in the hospital. On the fifth day after discharge, patient started complaining of leg tightness, puffiness around her eyes and generalized swelling of both feet. She returned to the ED, where she was found to be hemodynamically stable and normotensive with a blood pressure of 113/54 mmHg. Her weight had increased 8.8 kg from the weight at discharge. Her physical exam was notable facial and bilateral periorbital edema, abdominal distension, and 2+ bilateral non-pitting non-tender edema of both legs extending to her medial malleolus. Neurologic exam was performed which was unremarkable. Work up was performed to rule out other causes of edema, including a complete blood count, electrolytes, kidney and liver function tests, all of which were normal. She received 20 mg of furosemide and was instructed to perform fluid restriction to 1 L/m2/day and sodium restriction to &amp;lt;2 grams per day at home. She followed up in clinic 3 days after her ED visit where her weight had decreased by 4.2 kg and her edema had mostly resolved with only 1+ bilateral non-pitting edema. Her total dose of insulin remained at 0.7 unit/kg per day, with acceptable blood glucose levels at home. Her fluid restriction was discontinued and patient was instructed to follow up as usual, and she had no further edema in follow-up. Conclusion: This was a rare case of a newly diagnosed pediatric patient presenting with Insulin edema, which is essential for clinicians to recognize, so they can identify patients presenting with this uncommon side effect to rule out conditions that may present in a similar manner. Presentation: 6/2/2024

Rho-associated, coiled-coil-containing protein kinase 2 regulates expression of mineralocorticoid receptor to mediate sodium reabsorption in mice

The mineralocorticoid receptor (MR) is a member of the nuclear receptor family that was initially identified to regulate blood pressure through its ability to modulate kidney sodium handling in response to aldosterone. MR can be regulated by signals other than aldosterone; however, the detailed mechanisms remain to be elucidated. We found that MR is controlled in a Rho-associated coiled-coil-containing protein kinase 2 (ROCK2)-dependent manner. Mice with a specific deletion of ROCK2 in the kidney tubules showed decreased MR expression levels and increased urinary excretion of sodium. Mechanistically, signal transducer and activator of transcription 3 (STAT3) is a key molecule that mediates MR expression in these mice. This study highlights an important role of tubular ROCK2 in electrolyte homeostasis.

Left ventricular structure and function in relation to sodium dietary intake and renal handling in untreated Chinese patients.

Whether left ventricular structure and function is associated with sodium dietary intake and renal handling while considering blood pressure (BP) remains unclear. Consecutive untreated patients referred for ambulatory BP monitoring were recruited. Standard echocardiography was performed to measure left ventricular structure and function. Fractional excretion of lithium (FELi) and fractional distal reabsorption rate of sodium (FDRNa) were calculated as markers of proximal and distal tubular sodium handling, respectively. The 952 participants (51.0% women; mean age, 50.8 years) included 614 (64.5%) ambulatory hypertension and 103 (10.8%) left ventricular hypertrophy. There were significant interactions of urinary sodium excretion with FELi (P ≤ 0.045), but not FDRNa (P ≥ 0.36), in relation to left ventricular posterior wall thickness (LVPW), mass (LVM) and mass index (LVMI), but not functional measurements. Only in tertile 1 of FELi, the multivariate-adjusted regression coefficients for urinary sodium excretion reached statistical significance (P ≤ 0.049), being 0.16 ± 0.05 mm, 4.32 ± 1.48 g, and 1.64 ± 0.83 g/m2 for LVPW, LVM and LVMI, respectively. In mutually adjusted analyses, the regression coefficient for LVMI was statistically significant for FELi, FDRNa and 24-h systolic BP, being -2.17 ± 0.49, -1.95 ± 0.54, and 2.99 ± 0.51 g/m2, respectively (P < 0.001). Multivariable analysis of variance showed that sodium renal handling indexes (P ≥ 0.14), but not sodium urinary excretion (P = 0.007), were similarly as 24-h BP associated with LVMI. Heat maps on left ventricular hypertrophy provided a graphical confirmation of the findings. Sodium dietary intake and renal handling interact to be associated with left ventricular structure. Renal handling indexes were similarly in size as, jointly in action with and independently of 24-h BP.

Abstract P378: Impaired Diurnal Control of Blood Pressure and Sodium Excretion in Aged Hypertensive Male Sprague Dawley Rats

Hypothesis: The diurnal rhythmicity of blood pressure (BP) and sodium excretion is important to blood pressure regulation and is strongly influenced by the circadian clock genes. We hypothesized that the diurnal control of BP and natriuresis is impaired in aged male Sprague Dawley (SD) rats and may be associated with altered kidney expression of circadian clock gene proteins. Methods: Radiotelemetry (to record mean arterial BP (MAP)) and metabolic balance (to assess sodium excretion) was conducted in 3-month-old (3M) and 16-month-old (16M) male SD rats. On a separate day, 3M and 16M rats received an acute 900 μEq NaCl load by oral gavage at ZT0 and sodium excretion was assessed. Total renal cortex expression of Per1 and Bmal1 was assessed by immunoblotting (N=4-6/group ± SD). Results: 16M rats exhibit significantly increased MAP and 24-h sodium retention vs. 3M rats [MAP (mmHg) 3M 102±4 vs. 16M 127±5, P&lt;0.05; 24h Na retention (mEq/24h) 3M 0.3±0.1 vs. 16M 0.8±0.2, P&lt;0.05). 16M rats exhibit an attenuation of the circadian MAP pattern compared to 3M rats. Aged rats have a significant decrease in the blood pressure rise during the dark (active) vs. 3M rats (Dark phase increase in MAP (mmHg) 3M +13.6±2.1 vs. 16M +4.8±1.9, P&lt;0.05). 3M rats exhibit a classical diurnal pattern of 24-h sodium excretion with increased natriuresis during the dark (active) phase – a response that is attenuated in 16M rats that exhibit a significant reduction in the increase in natriuresis in the dark phase (Light phase UNaV (μEq/12h) 3M 380±48 vs. 16M 410±36, Dark phase natriuresis 3M 620±31 vs 16M 502±27, P&lt;0.05). 16M rats had an impaired natriuretic response to an acute oral NaCl load in the first 12h post-gavage (UNaV 12h (μEq/12h) 3M 681±42 vs. 16M 243±39, P&lt;0.05). In 16M old rats there was no change in renal Per1 and decreased renal Bmal1 protein (Bmal1 fold change 16M vs. 3M, 0.65±0.7, P&lt;0.05). Conclusions: We observed impaired circadian control of blood pressure and renal sodium excretion in aged male SD rats. These changes in renal sodium handling may reflect endogenous decreases in renal Bmal1 levels with age and contribute to the observed hypertensive phenotype in aged rats.

Abstract P200: Immune memory contributes to chronic hypertension recurrence

Keeping blood pressure under control is a challenge in hypertension treatment because high blood pressure quickly returns with a momentary lapse in treatment or a high-salt diet. We have previously reported the CD8+ T cells (CD8Ts) in the kidney can drive aberrant sodium handling to aggravate blood pressure. Recently, our new findings suggest that these CD8Ts remain long-term within the kidney. Here, we propose these CD8Ts have developed into a resident memory (Trm) population with the aid of TGFβ signaling, and this residency continually aggravates and leads to the recurrence of hypertension . To explore this hypothesis, we utilized two mouse models of hypertension, including a classic DOCA-salt model and a novel Angiotensin II (Ang II) induced salt memory model, with continuous blood pressure monitored by radiotelemetry. In the Ang II-induced salt memory model, the mice were administered Ang II and high salt for a week before a resting period to restore normal blood pressure. Thereafter, the mice were given a second high salt challenge to model the high salt-driven recurrence of hypertension. Mouse strains include both wild-type (WT) and a T-cell specific TGFβRII KO (Tsp-TGFβR KO), which has T cells unable to develop into Trm due to the reliance of Trm on TGFβ signaling. T cells were analyzed with flow cytometry. In the DOCA-salt model, WT mice developed a significant CD8Trm population within the kidney. In contrast, TSP-TGFβR KO mice, which lack the ability to develop Trm, had an attenuated development of hypertension with DOCA-salt treatment. Testing the capability for hypertension to recur, both WT and Tsp-TGFβR KO mice experienced a similar degree of hypertension with Ang II-salt treatment. However, only the WT had a significant expansion of Trm and demonstrated the clinical manifestation of recurring hypertension with the rapid increase of blood pressure with a high salt challenge. Isolating the T cells from the kidneys confirmed that the significant CD8Trm population development in the WT was not present in the Tsp-TGFβR KO. In summary, our findings suggest that the memory T cell population developed in the kidney during hypertension instills a perpetual memory for salt sensitivity in hypertension. Without the ability to develop this memory population, mice are protected against this recurrence of high-salt-induced hypertension.

P097 SEXUAL DIMORPHISM IN A HYPERTENSIVE MODEL OF FRUCTOSE PLUS HIGH SALT DIET

High salt diet (HSD) and fructose are both consumed in excess and contributes to hypertension (HTN). Fructose is commonly used to sweeten soft drinks, and studies have linked soft drink consumption to salt-sensitive HTN. However, full mechanisms aren’t understood. Previous data indicates that an acute fructose-enriched diet (FED) increases Na/K/2Cl cotransporter (NKCC2) activity, promoting salt-sensitive HTN in rats; however, there is no research on long-term consumption. Here, our goal was to evaluate whether a FED, coupled to HSD, can induce HTN. Given the known sex-dependent differences in salt-sensitive HTN, we also hypothesized differences between male and female mice. Male and female C57BI/6 mice (10 weeks old, n=4-6) were treated with vehicle or fructose (10% in drinking water) plus HSD (4% in food) for 28 days. Systolic blood pressure (SBP) was measured by tail-cuff plethysmography, and cardiac hypertrophy (morphometry). We performed an acute diuresis test using furosemide to inhibit NKCC2 (20 mg/kg bw, ip) at day 26, and then measured natriuresis (metabolic cages) for 2-hrs. All data are presented by mean standard deviation. Fructose+HSD increased SBP in male mice after 28 days (Veh=110.5±4.6 vs. Frucose+HSD=130.2±5.6 mmHg; p&lt;0.01); in contrast, HTN was completely prevented in female mice (Veh=109.8±6.8 vs. Fructose+HSD=114.0±11.0 mmHg; ns). We did not observe changes in cardiac hypertrophy in either sex. We observed a significant decrease in natriuresis (∼20%) after furosemide injection in male mice (Veh=5.9±1.1 vs. Fructose+HSD=4.7±0.8 μEq/2 h/g bw; ns). Surprisingly, we observed an increase in natriuresis following furosemide injection in female mice (Veh=3.8±5.0 vs. Fructose+HSD= 7.7±2.7 μEq/2 h/g bw; p&lt;0.01). We observed HTN in males following a FED combined with HSD, which was not associated with increased NKCC2 activation. In contrast, female mice showed a resistance to HTN, and yet an apparent increase in NKCC2 activity. This probably suggests a dysregulation of other transporters not evaluated in this work. Finally, we demonstrate that long-term FED, with HSD, induces HTN with a sexual dimorphic effect, apparently through differential renal sodium handling.

Physical Activity and Urinary Sodium Excretion Circadian Rhythm: A Population-Based Cross-Sectional Pilot Study.

Background/Objectives: Blood pressure (BP) is characterized by a circadian rhythm (Circr) with lower nighttime values, called dipping. Non-dipping is associated with higher CVD risk. The Circr of urinary sodium excretion (NaCle), peaking during the day, is linked to BP patterns. Physical activity (PA) is known to improve BP control and enhance the dipping phenomenon, but its possible effect on NaCle remains unclarified. This study aimed to investigate the correlation between PA and the Circr of NaCle and to determine if the relationship is independent of age, sex, BP values, dipping pattern, and salt intake. Methods: A pilot cross-sectional analysis was conducted using data from the Ticino Epidemiological Stiffness Study, involving 953 participants in Switzerland. Data collection included standardized questionnaires, blood samples, 24 h urine collections, and ambulatory BP monitoring. Participants were categorized into sedentary, partially active, and active. The effect of PA, NaCl intake, and dipping on the day/night NaCle ratio was assessed with multivariable linear regressions. Results: Participants' median age was 49 years, with 78% having normal BP values and 47% exhibiting a dipping pattern; 51% were classified as sedentary and 22% as partially active. The median NaCl intake was 7.9 g/day. The youngest subjects had a higher hourly NaCle ratio compared to older subjects. Higher NaCl intake correlated with increased BP, a phenomenon more pronounced in men and younger subjects. The hourly day/night NaCle ratio positively correlates with dipping; however, PA did not show a significant correlation with the NaCle ratio. Conclusions: This study indicates that while the day/night NaCle ratio correlates with the dipping pattern, PA is unrelated to the circadian rhythm of renal sodium handling. The beneficial effects of PA on BP and cardiovascular health thus appear to be mediated through mechanisms other than NaCle. These are explorative findings only but relativize the need for further investigations on the topic.

Integrated renal and sympathetic mechanisms underlying the development of sex- and age-dependent hypertension and the salt sensitivity of blood pressure

Aging is a non-modifiable understudied risk factor for hypertension. We hypothesized that sympathetically mediated activation of renal sodium reabsorption drives age-dependent hypertension and the salt sensitivity of blood pressure (BP). Using 3-, 8-, and 16-month-old male and female Sprague–Dawley rats as a model of normal aging, we assessed BP, indices of sympathetic tone, and the physiological responses to acute and chronic sodium challenge including sodium chloride cotransporter (NCC) regulation. The effects of renal nerve ablation and NCC antagonism were assessed in hypertensive male rats. We observed sex-dependent impaired renal sodium handling (24 h sodium balance (meq), male 3-month 0.36 ± 0.1 vs. 16-month 0.84 ± 0.2; sodium load excreted during 5% bodyweight isotonic saline volume expansion (%) male 3-month 77 ± 5 vs. 16-month 22 ± 8), hypertension (MAP (mmHg) male 3-month 123 ± 4 vs. 16-month 148 ± 6), and the salt sensitivity of BP in aged male, but not female, rats. Attenuated sympathoinhibitory afferent renal nerve (ARN) responses contributed to increased sympathetic tone and hypertension in male rats. Increased sympathetic tone contributes to renal sodium retention, in part through increased NCC activity via a dysfunctional with-no-lysine kinase-(WNK) STE20/SPS1-related proline/alanine-rich kinase signaling pathway, to drive hypertension and the salt sensitivity of BP in aged male rats. NCC antagonism and renal nerve ablation, which reduced WNK dysfunction and decreased NCC activity, attenuated age-dependent hypertension in male Sprague–Dawley rats. The contribution of an impaired sympathoinhibitory ARN reflex to sex- and age-dependent hypertension in an NCC-dependent manner, via an impaired WNK1/WNK4 dynamic, suggests this pathway as a mechanism-based target for the treatment of age-dependent hypertension.

LEFT VENTRICULAR REMODELING IN RELATION TO INTERACTION BETWEEN BLOOD PRESSURE AND SODIUM RENAL HANDLING AND INTAKE IN UNTREATED CHINESE PATIENTS

Objective: Whether or not renal sodium handling was associated with left ventricular remodeling independent of blood pressure (BP) is uncertain. Design and method: Consecutive untreated patients referred for ambulatory BP monitoring were recruited. Two-dimensional echocardiography was performed to measure left ventricular properties. Fractional excretion of lithium (FELi) and fractional distal reabsorption rate of sodium (FDRNa) were calculated as markers of proximal and distal sodium handling, respectively. Results: The 952 untreated patients (51.0% women; mean age, 50.8 years) included 614 (64.5%) ambulatory hypertension and 138 (14.5%) with left ventricular hypertrophy. FELi and FDRNa averaged 21.5% and 95.9%, respectively. In multivariable-adjusted analyses, per 1-SD increment in systolic/diastolic BP (+12.4/9.0 mm Hg) and reduction in FELi (-11.3%) and FDRNa (-2.4%) were associated with 0.19/0.19 and 0.19/0.20 mm higher interventricular septal wall thickness (IVS), respectively, 0.10/0.12 and 0.18/0.22 mm higher left ventricular posterior wall thickness (LVPW), respectively, and 2.99/2.68 and 2.17/1.95 g/m2 higher left ventricular mass index (LVMI), respectively. Associations of IVS and LVPW with FELi and FDRNa were tighter than with BP (P&lt;0.001), whereas the opposite trend was observed for LVMI (P&lt;0.001). There was significant (P&lt;0.045) interaction between urinary sodium excretion and FELi in relation to LVPW and LVMI. Only in tertile 1 of FELi, LVPW and LVMI were positively associated with urinary sodium excretion (P&lt;0.040). The interaction between urinary sodium excretion and FDRNa in relation to left ventricular structure was nonsignificant (P&gt;0.25). Conclusions: Renal sodium handling as assessed by FELi and FDRNa, were independently associated with left ventricular remodeling, particularly with ventricular wall thickening.

Humanized Diets Define Optimal Pressure Lowering Response to Dietary Potassium in Mice

High potassium (K) diets are known to lower blood pressure (BP) in rodents and humans but can also raise BP when consumed in extreme. Interestingly, this response also appears to be influenced by dietary sodium (Na) such that when Na intake is high, high K lowers BP, whereas when sodium intake is lower, high K increases BP (Little et al, Hypertension, 2023). We recently reported (Little et al, JCI Insight, 2023) that the K-mediated BP lowering response, driven by the inactivation of the thiazide-sensitive sodium chloride cotransporter (NCC), is offset by an increase in ENaC (epithelial sodium channel) when an extremely high K diet is chronically consumed. Here, we define the optimal dietary K level needed to inactivate NCC without activating ENaC in the high Na setting and show this K level approximates the recommended level for humans by the DASH (Dietary Approaches to Stop Hypertension) trials. Mice were fed diets containing 6 different K contents, all with high Na (1.7%), so the effects of the control diet (1% K, 1.7% Na) could be compared to traditional extremes (0.1% and 5% K) and others (0.35%, 0.7%, 1.7%) that mimic typical variation in human diets (30-120 mEq/d) when mouse consumption is normalized for caloric intake relative to body mass. Metabolic cage and renal clearance studies were used to assess electrolyte and aldosterone (aldo) excretion as well as NCC- (hydrochlorothiazide (HCTZ) sensitive) and ENaC- (benzamil sensitive) dependent sodium handling. Blood potassium (PK) was measured using iSTAT. BP was measured hourly for 10 days using DSI telemetry probes in male mice (C57Bl6J). The BP response to the diuretics was also measured. PK levels changed significantly with each diet relative to the control diet from 3.2mM to 4.8mM. Systolic blood pressure (SBP; 12-hour active period average) also changed significantly with the different K diets. Extreme high or low K diets (0.1% and 5%) increased SBP by 7mmHg, 0.35% and 0.7% K diets increased SBP by 6 and 3mmHg, while the 1.7% K diet lowered SBP by 4mmHg relative to control (1% K, 132 mmHg). Thus, the relationship between SBP and PK is ‘U-shaped’. Diuretic studies revealed that HCTZ reduces SBP in the 0.1%, 0.35%, 0.7% K groups but had minimal effect in the 1.7% and 5% K groups. Conversely, inhibiting ENaC activity with benzamil normalized SBP in the 5% K group but had a minimal effect in the 1.7% group and no BP effect in the other groups. The BP-lowering effect of each diuretic correlated with increased natriuresis suggesting dietary K influences blood pressure by affecting distal nephron sodium transport. Lastly, urinary aldo levels increased with increasing dietary K, but compared to the control group, aldo levels were significantly lower in the 0.1%, 0.35%, and 0.7% groups, significantly higher in the 5% group, and not different in the 1.7% group. As previously reported, our results demonstrate that extremes in dietary intake can elevate blood pressure by stimulating distal nephron sodium transport proteins with low K inducing NCC activation and high K stimulating ENaC with elevated aldosterone. An optimal dietary K level (1.7%) that maximally reduces BP in mice was identified, suppressing NCC activity while limiting aldosterone production and ENaC activity. Remarkably, this diet mimics the human DASH diet in K content and further supports its effcacy as a blood pressure-lowering modality. DE (DK054231, DK51496); PW (DK054231, DK093501, DK110375): Leducq Foundation U54 DK137331-01. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Evaluation of renal sodium handling in heart failure with preserved ejection fraction: A pilot study.

The pathophysiology behind sodium retention in heart failure with preserved ejection fraction (HFpEF) remains poorly understood. We hypothesized that patients with HFpEF have impaired natriuresis and diuresis in response to volume expansion and diuretic challenge, which is associated with renal hypo-responsiveness to endogenous natriuretic peptides. Nine HFpEF patients and five controls received saline infusion (0.25 mL/kg/min for 60 min) followed by intravenous furosemide (20 mg or home dose) 2 h after the infusion. Blood and urine samples were collected at baseline, 2 h after saline infusion, and 2 h after furosemide administration; urinary volumes were recorded. The urinary cyclic guanosine monophosphate (ucGMP)/plasma B-type NP (BNP) ratio was calculated as a measure of renal response to endogenous BNP. Wilcoxon rank-sum test was used to compare the groups. Compared to controls, HFpEF patients had reduced urine output (2480 vs.3541 mL; p = 0.028), lower urinary sodium excretion over 2 h after saline infusion (the percentage of infused sodium excreted 12% vs. 47%; p = 0.003), and a lower baseline ucGMP/plasma BNP ratio (0.7 vs. 7.3 (pmol/mL)/(mg/dL)/(pg/mL); p = 0.014). Patients with HFpEF had impaired natriuretic response to intravenous saline and furosemide administration and lower baseline ucGMP/plasma BNP ratios indicating renal hypo-responsiveness to NPs.

Deletion of dipeptidyl peptidase 4 attenuates angiotensin II-induced blood pressure rise and enhances NHE3 phosphorylation at serine 552 in the kidneys of male and female mice

Dipeptidyl peptidase 4 (DPP4) physically associates with the Na+/H+ exchanger isoform3 (NHE3), and DPP4 inhibitors reduce NHE3-dependent sodium reabsorption in the renal proximal tubule. Angiotensin II (Ang II) is a key mediator of sodium and water retention by the kidneys, partly through the activation of proximal tubule NHE3. Recent studies from our group reveled that Ang II activates DPP4 by, both in vivo and in vitro, and that inhibition of several canonical and non-canonical pathways can suppress this activation. However, the impact of this interaction on renal sodium handling and blood pressure remains unclear. This study aimed to test the hypothesis that DPP4 deletion mitigates the blood pressure elevation induced by Ang II in male and female mice, at least partly due to the downregulation of NHE3 in the renal proximal tubule. Male and female mice with global DPP4 deletion or wild-type controls were acutely administered either a pressor dose of Ang II (1000 ng/kg/minute) or saline. Blood pressure was measured before and one hour after the administration of Ang II or saline by tail-cuff plethysmography. Kidneys were subsequently collected for protein homogenate preparation. Increased DPP4 activity was observed in response to acute Ang II stimulation in both male and female wild-type mice, with female mice exhibiting higher basal DPP4 activity. As expected, DPP4 knockout mice exhibited minimal DPP4 activity. Baseline blood pressure did not differ significantly between male wild-type and DPP4 knockout mice or between females. In line with our hypothesis, both male and female DPP4 knockout mice displayed a reduced increase in blood pressure in response to acute Ang II administration compared to their wild-type counterparts. Furthermore, the phosphorylation of NHE3 at serine 552 (pS552-NHE3), a surrogate marker of NHE3 inhibition, was higher in wild-type females than males. Interestingly, pS552-NHE3 was fivefold higher in male DPP4 knockout mice and threefold higher in female DPP4 knockout mice compared to their wild-type counterparts. Additionally, the increase in pS552-NHE3 one hour after Ang II administration was higher in males (1208 ± 119 vs. 544 ± 54 %, P &lt; 0.01) and females (385 ± 18 vs. 271 ± 27%, P &lt; 0.01) DPP4 knockout mice compared to wild-type animals. Moreover, ERK, a well-known effector of the AT1R signaling cascade, was phosphorylated in a similar manner as NHE3 in response to Ang II in males but not in females. In conclusion, our data demonstrate that the absence of DPP4 reduces the rise in blood pressure induced by acute Ang II stimulation, possibly through Ang II/AT1R signaling pathways influencing phosphorylation of downstream effectors such as NHE3. Furthermore, we observe significant sex differences in Ang II effects on DPP4 activity, and AT1R signaling cascades. FAPESP 2021/14524-3 NIDDKD - K08DK115886. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

P2X7 receptor knockout does not alter renal function or prevent angiotensin II-induced kidney injury in F344 rats

P2X7 receptors (P2X7) mediate immune and endothelial cell responses to extracellular ATP. Acute pharmacological blockade increases renal blood flow (RBF) and glomerular filtration rate (GFR), suggesting that P2X7 receptor activation promotes tonic vasoconstriction. P2X7 expression is increased in kidney disease and blockade/knockout is renoprotective. Here, we generated a novel P2X7 global knockout (KO) rat on the F344 background, hypothesising enhanced RBF and protection from chronic angiotensin II (ANG II)-induced injury. CRISPR/Cas9 technology introduced an early stop codon into exon 2 of P2rx7. In male and female KO and WT rats, renal P2X7 expression was measured by RTqPCR (n=4-5/group) and western blotting (n=3/group). Bone marrow-derived macrophages (BMDM) were used to assess P2X7 function by measuring interleukin (IL)-1β release (ELISA) after stimulation with lipopolysaccharide (LPS) (1μg/mL, 4h) and ATP (3mM, 1h) (n=5-6/group). In vivo kidney function was assessed in anesthetized rats (thiopental, 50mg/kg, i.p.) at baseline and following serial arterial ligation to induce acute pressure natriuresis (n=9-10/group). Arterial blood pressure (BP) was measured directly, and urine was collected via tube cystotomy. RBF was measured using a Transonic Doppler flow probe placed around the main renal artery, and cortical and medullary flux by laser Doppler needle probes. GFR was determined by FITC-inulin clearance. Urinary sodium was measured by sodium-selective electrode analysis. In a separate experiment, BP was recorded over five consecutive days in conscious male KO and WT rats via implanted radiotelemetry devices (n=7-8/group). Finally, male KO and WT rats (n=9-10/group) were infused with ANG II (250ng/kg/min, s.c.) for 6 weeks. At end, one renal artery was isolated and vascular reactivity to phenylephrine, acetylcholine and sodium nitroprusside determined by wire myography. Bladder urine was collected to measure albumin/creatinine ratio (n=4-7/group), and kidneys were harvested for histological analyses (n=6/group). Data were analysed with unpaired t-test (two groups compared) or two-way ANOVA (two variables), with p&lt;0.05 statistically significant. P2rx7 mutation was confirmed by genome sequencing (Sanger). P2rx7 mRNA abundance was partially decreased in kidney from male (-54%) and female (-25%) KO vs WT. P2X7 protein was detected in kidneys from WT but not from KO rats. In BMDM from WT rats, LPS+ATP stimulation induced IL-1β release; this response was markedly suppressed in KO BMDM (males: 2577±140 vs 413±175pg/mL, p&lt;0.0001; females: 1889±394 vs 265±121pg/mL, p&lt;0.0001). In vivo BP, renal haemodynamics and tubular sodium handling were not different between genotypes for either sex (P&gt;0.05). Radiotelemetry confirmed no difference in BP between KO and WT rats. Following chronic ANG II infusion, KO and WT rats had no renal artery dysfunction but showed similar increases in albuminuria (P=0.3587), renal perivascular fibrosis (Picrosirius Red, P=0.5393), cortical interstitium CD68-positive area (p=0.6546) and tubular casts (Periodic acid-Schiff, P=0.8803), compared with naïve controls. Contrary to our hypothesis, global genetic deletion of P2X7 did not affect renal hemodynamics and we found no significant role for P2X7 in the modulation of tubular sodium reabsorption. Our data do not support a major role of P2X7 in causing renal vascular and tubular injury. This work was supported by Diabetes UK grant 17/0005685, The British Heart Foundation(FS/15/60/31510; RE/18/5/34216), the Medical Research Council (MR/S01053X), and the University of Edinburgh College of Medicine &amp; Veterinary Medicine PhD Studentship. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Dietary sodium and fluid intake in heart failure. A clinical consensus statement of the Heart Failure Association of the ESC.

Sodium and fluid restriction has traditionally been advocated in patients with heart failure (HF) due to their sodium and water avid state. However, most evidence regarding the altered sodium handling, fluid homeostasis and congestion-related signs and symptoms in patients with HF originates from untreated patient cohorts and physiological investigations. Recent data challenge the beneficial role of dietary sodium and fluid restriction in HF. Consequently, the European Society of Cardiology HF guidelines have gradually downgraded these recommendations over time, now advising for the limitation of salt intake to no more than 5 g/day in patients with HF, while contemplating fluid restriction of 1.5-2 L/day only in selected patients. Therefore, the objective of this clinical consensus statement is to provide advice on fluid and sodium intake in patients with acute and chronic HF, based on contemporary evidence and expert opinion.

Salt-Sensitive Hypertension and the Kidney.

Salt-sensitive hypertension (SS-HT) is characterized by blood pressure elevation in response to high dietary salt intake and is considered to increase the risk of cardiovascular and renal morbidity. Although the mechanisms responsible for SS-HT are complex, the kidneys are known to play a central role in the development of SS-HT and the salt sensitivity of blood pressure (SSBP). Moreover, several factors influence renal function and SSBP, including the renin-angiotensin-aldosterone system, sympathetic nervous system, obesity, and aging. A phenotypic characteristic of SSBP is aberrant activation of the renin-angiotensin system and sympathetic nervous system in response to excessive salt intake. SSBP is also accompanied by a blunted increase in renal blood flow after salt loading, resulting in sodium retention and SS-HT. Obesity is associated with inappropriate activation of the aldosterone mineralocorticoid receptor pathway and renal sympathetic nervous system in response to excessive salt, and mineralocorticoid receptor antagonists and renal denervation attenuate sodium retention and inhibit salt-induced blood pressure elevation in obese dogs and humans. SSBP increases with age, which has been attributed to impaired renal sodium handling and a decline in renal function, even in the absence of kidney disease. Aging-associated changes in renal hemodynamics are accompanied by significant alterations in renal hormone levels and renal sodium handling, resulting in SS-HT. In this review, we focus mainly on the contribution of renal function to the development of SS-HT.

SiRNA as potential therapeutic strategy for hypertension

Hypertension, a well-known cardiovascular disorder noticed by rise in blood pressure, poses a significant global health challenge. The development RNA interfering (RNAi)-based therapies offers a ground-breaking molecular tool, holds promise for addressing hypertension's intricate molecular mechanisms. Harnessing the power of small interfering RNA (siRNA), researchers aim to selectively target and modulate genes associated with hypertension. Furthermore, they aim to downregulate the levels of mRNA by activating cellular nucleases in response to sequence homology between the siRNA and the corresponding mRNA molecule. As a result, genes involved in the cause of disorders linked to a known genetic background can be silenced using siRNA strategy. In the realm of hypertension, siRNA therapy emerges as a potential therapy for prognostics, diagnostics and treatments. It plays an important role in execution of targeting suppression of genes involved in vascular tone regulation, sodium handling, and pathways contributing to high blood pressure. A clinical trial involving intervention like angiotensinogen siRNA (AGT siRNA) is currently being carried out to treat hypertension. Genetic correlations between uromodulin (UMOD) and hypertension are investigated as emerging Non AGT siRNA target. Furthermore, expression of UMOD is responsible for regulation of sodium by modulating the tumor necrosis factor-α and regulating the Na + -K + -2Cl-cotransporter (NKCC2) in the thick ascending limb, which makes it an important target for blood pressure regulation.