Sodium Balance Research Articles

Correlation with renin-angiotensin-aldosterone and glomerular filtration rate in chronic renal failure patients

Background: One of the more significant hormonal systems, the renin-angiotensin-aldosterone system, controls the kidney function, adrenal gland through its effect on the balance of sodium and potassium, blood pressure, fluid volume, and also manages the functions of cardiovascular.
 Objective: To clarify the interrelationship between renal dysfunction and renin-angiotensin-aldosterone system.
 Patients and Methods: One hundred samples were collected from December 1, 2022, to February 18, 2023, from Al Shams Medical Laboratories (56 male, and 44) female, age range (of 45-60 years), all of them were volunteers suffering from chronic renal failure in the third stage the average glomerular filtration rate was 35. 70 ± 0.37 125 mL/min/1.73m2. and under conservative treatment. Kidney function test, active renin, angiotensin II, and aldosterone were assessed in the serum of all subjects. The p - value of differences less than 0.05 is measured significant, and uses the statistical package for the social sciences (23) software to calculate the correlation coefficient between various parameters.
 Results: The result shows relationship between the changes in GFR with creatinine, urea and active renin, the mean GFR showed significant negative correlated with mean creatinine (R = -0.76, p < 0.01. As well as the mean GFR with mean urea (R = -0.64, p < 0.01). The mean GFR also showed significant negative correlated with mean active renin in (R = -0.41, p < 0.01). Also, the mean serum active renin level was significantly positive correlated with mean aldosterone (R =0.33, p < 0.05).
 Conclusion: Renin enzyme is inversely related to renal dysfunction, so when the glomerular filtration rate decrease, the higher the renin increased, and as a result, the increase in blood pressure in chronic renal failure patients.

A2AR-mediated lymphangiogenesis via VEGFR2 signaling prevents salt-sensitive hypertension.

Excess dietary sodium intake and retention lead to hypertension. Impaired dermal lymphangiogenesis and lymphatic dysfunction-mediated sodium and fluid imbalance are pathological mechanisms. The adenosine A2A receptor (A2AR) is expressed in lymphatic endothelial cells (LECs), while the roles and mechanisms of LEC-A2AR in skin lymphangiogenesis during salt-induced hypertension are not clear. The expression of LEC-A2AR correlated with lymphatic vessel density in both high-salt diet (HSD)-induced hypertensive mice and hypertensive patients. Lymphatic endothelial cell-specific A2AR knockout mice fed HSD exhibited 17 ± 2% increase in blood pressure and 17 ± 3% increase in Na+ content associated with decreased lymphatic density (-19 ± 2%) compared with HSD-WT mice. A2AR activation by agonist CGS21680 increased lymphatic capillary density and decreased blood pressure in HSD-WT mice. Furthermore, this A2AR agonist activated MSK1 directly to promote VEGFR2 activation and endocytosis independently of VEGF as assessed by phosphoprotein profiling and immunoprecipitation assays in LECs. VEGFR2 kinase activity inhibitor fruquintinib or VEGFR2 knockout in LECs but not VEGF-neutralizing antibody bevacizumab suppressed A2AR activation-mediated decrease in blood pressure. Immunostaining revealed phosphorylated VEGFR2 and MSK1 expression in the LECs were positively correlated with skin lymphatic vessel density and A2AR level in hypertensive patients. The study highlights a novel A2AR-mediated VEGF-independent activation of VEGFR2 signaling in dermal lymphangiogenesis and sodium balance, which might be a potential therapeutic target in salt-sensitive hypertension.

#4196 MAGNETIC RESONANCE IMAGING ASSESSMENT OF SKIN AND MUSCLE SODIUM IN HAEMODIALYSIS

Abstract Background and Aims Haemodialysis (HD) is life sustaining for patients with end-stage kidney disease (ESKD) but is associated with a marked increase in incidence of cardiovascular disease (CVD) and high annual mortality rates. Sodium balance is regulated by the kidneys in health but has to be achieved by sodium removal during HD for those with ESKD. Recent evidence suggests that non-osmotically stored sodium in the muscle and/or skin may be a critical factor impacting the development of hypertension and CVD. Sodium magnetic resonance imaging (23Na MRI) allows assessment of skin and muscle sodium storage and may provide a valuable tool in evaluating sodium storage in dialysis patients. In this study, we used 23Na MRI to measure muscle and skin sodium content in younger and older healthy individuals and people receiving HD, and investigated the effect of a single dialysis session on muscle and skin sodium content. Method 23Na MRI was acquired on a 3T Philips Ingenia scanner using a custom-made 23Na RF coil. 3D GRE 23Na scans (3 × 3 × 30mm3, 10 slices) were acquired in a 15-minute scan. Four reference bottles of increasing sodium concentration were placed in the RF coil above the leg to calibrate sodium concentration. In the same imaging session, 1H MR images were acquired to delineate muscle groups, skin structures and tissue water content. 23Na concentration maps were generated using custom software and regions of interest of each muscle and the skin were manually segmented. Data was collected on 14 younger (23-38yrs,7M:7F) and three older (66-77yrs,3M:1F) healthy volunteers (HVs), and 5 male HD patients (55-68 yrs) who had been on HD for more than 3-months. HD patients underwent a pre-dialysis 23Na MRI calf scan, then had their usual dialysis session with a dialysate Na prescription of 137 mmol/L, followed by a repeat 23Na MRI calf scan post dialysis. Patient demographics, dialysis vintage, residual renal function, and ultrafiltration volume were collected, along with blood samples at the start and end of the dialysis session, including serum sodium. Results Figure 1 shows 23Na images in the younger and older HV group and HD patients pre-dialysis. Muscle and skin sodium was increased in older HVs compared to younger, with HD patients pre-dialysis tending to be lower than older HVs (Fig. 2). HD patients’ demographics and clinical measures pre- and post-dialysis are shown in Table 1. HD treatment reduced muscle sodium whilst skin sodium showed little change (Fig. 3). Conclusion We have optimised methods for measuring muscle and skin sodium. 23Na concentration in muscle and skin is higher in older subjects. HD patients’ 23Na values fall between those observed in the older and younger HV groups. These values are consistent with published data from patients dialysed against 137mmol/l sodium dialysate, but lower than other studies in which dialysate sodium levels were higher. Further studies are planned to study the effect of dialysate sodium on skin and muscle sodium concentrations and mechanistic links to cardiovascular disease.

#3642 SERUM APELIN AND RENAL PROGNOSIS IN PATIENTS WITH NON-DIALYSIS DEPENDENT CHRONIC KIDNEY DISEASE

Abstract Background and Aims The apelin/APJ system is a novel pleiotropic system with an essential role in renal and cardiovascular physiology and disease. A role for the apelin/APJ system in diverse pathological states, including disorders of sodium and water balance, hypertension, heart failure, pre-eclampsia, acute kidney injury, sepsis and diabetic nephropathy, has recently been reported. Especially, the impact of apelin/APJ system on cardiovascular system has been attracting attention, but scarce data is available in chronic kidney disease (CKD). Method We measured serum apelin-36 by ELISA in 411 outpatients with non-dialysis dependent (NDD) CKD and analyzed factors associated with serum apelin. Furthermore, we examined the association of serum apelin with renal outcome (renal replacement therapy, RRT) using multivariate Cox proportional hazards model. Results Median age and eGFR were 71 years and 21.7 ml/min/1.73 m2, respectively and the prevalence of male gender and diabetes was 26.8% and 50.8%, respectively. Median serum apelin was 0.81pg/ml. There was no significant difference in serum apelin level between male and female patients, or those with and without diabetes. Moreover, serum apelin level had no significant association with age and eGFR; however, there was a significant relationship between serum apelin and brain natriutetic peptide. During the follow-up period of 38 months, 126 patients started RRT. eGFR and age were associated with the time to RRT induction. Serum apelin was not associated with renal outcome (HR, 1.05; 95%CI, 0.64-1.71; P,0.86); however, this association was interacted by diabetes and gender (P for interaction, 0.073 and 0.070, respectively). Conclusion Serum apelin could be a predictive marker of renal prognosis in male and non-diabetic CKD patients.

#4412 URINARY SODIUM-TO-POTASSIUM RATIO DOES NOT ACCURATELY REFLECT DIETARY SODIUM-TO-POTASSIUM RATIO

Abstract Background and Aims Low sodium intake is associated with a lower blood pressure and less proteinuria, which are important therapeutic targets in chronic kidney disease. In contrast, a low potassium intake has been associated with higher blood pressure and a higher incidence of chronic kidney disease and cardiovascular events. Counselling of patients regarding their sodium and potassium intake requires accurate estimation of their intake, but 24-hour urinary sodium and potassium excretion can deviate substantially from actual intake. Urinary sodium-to-potassium (Na/K) ratio is a promising alternative as it is less affected by incomplete urine collections and additionally captures both the effect of sodium and potassium. Our study aimed to assess whether the Na/K ratio in 24-hour urine reflects dietary intake more accurately than separate measurement of sodium or potassium in 24-hour urine. Method We performed a post-hoc analysis on data from the long-term sodium balance studies Mars105 and Mars520. Ten healthy participants consumed a diet with a known sodium and potassium content and collected 24-hour urine samples for 105 or 205 days. We calculated the log fold difference between dietary intake and urinary excretion of sodium, potassium and Na/K ratio. A mixed-effects model with a random intercept per subject was used to compare these estimates of accuracy. Subsequently, we performed a subgroup analysis per salt intake level (i.e. 6, 9 or 12 grams per day) and assessed the effect of increasing the number of 24-hour urine collections. Results Overall, the urinary Na/K ratio underestimated dietary Na/K ratio with a median difference of -0.21 (IQR -0.47 to 0.09). Estimation of dietary Na/K ratio intake using the urinary Na/K ratio was significantly less accurate compared to using urinary sodium or potassium measurement for estimation of sodium or potassium intake (Figure 1A). Only during a salt intake of 6 grams per day, the urinary Na/K ratio did not perform significantly worse than sodium measurements. Although increasing the number of 24-hour urine measurements to three or seven improved the accuracy of the urinary Na/K ratio, it remained inferior to separate assessment of urinary sodium and potassium excretion (Figure 1B). Conclusion The 24-hour urinary Na/K ratio is less accurate than 24-hour urinary sodium or potassium excretion for estimation of dietary intake in a controlled setting in healthy volunteers.

#4470 THE IMPACT OF RESIDUAL NATRIURESIS ON INTRADIALYTIC HYPERTENSION IN PATIENTS ON ISONATRIC DIALYSIS: A MONOCENTRIC STUDY AT THE FRANCK JOLY HOSPITAL CENTER

Abstract Background and Aims Intradialytic hypertension (IDH) is an elevation of blood pressure recorded during dialysis monitoring and at the end of the session relative to the values recorded at the connection. Hypervolemia and positive sodium balance are the main mechanisms. Isonatric dialysis allows a restoration of natremia corresponding to an optimal state of cellular hydration at the end of the session, and residual natriuresis is related to the state of extracellular hydration. Hence, their potential role in the appearance of IDH. The objective of this study is to measure the impact of residual natriuresis on IDH in patients on chronic isonatric hemodialysis. Method Transversal, descriptive and analytical study, having examined 12 last dialysis sessions of December 2023 of 65 patients in chronic hemodialysis (780 dialysis sessions) at the FRANCK JOLY Hospital Center in French Guiana. The primary outcome was the presence of intradialytic hypertension (IDH), defined as a difference in mean blood pressure ≥ 15 mmHg at disconnection from branching, or the need for antihypertensive treatment during the session with as main explanatory variables: residual natriuresis and sodium perdialytic concentration. Welche, Mann Whitney, Fisher and chi2 tests were used in univariate analysis and logistic regression in multivariate analysis to determine factors associated with IDH. The significance threshold was set at: p < 0.005. Results The 65 files analyzed had a predominance of women at 55%. 780 dialysis sessions were reviewed, including 206 with IDH, or nearly 1/4 of the sessions. 37% of patients were affected by IDH with a sex ratio of 1. 94% of patients had a history of hypertension and 22% were diabetic. 57% of patients had zero residual diuresis. The average interdialytic weight gain was 2.3 kg. 48% had at least triple antihypertensive therapy. The average duration of a dialysis session was 4 hours, the mean KT/V was 1.2; The mean natremia was 138 mEq/L and the mean perdialytic sodium concentration was 140 mEq/L. The median residual natriuresis was 8.55[0; 26.2] mEq/L. The mean NT-proBNP level was 2407 pg/ml. In univariate analysis, residual natriuresis and perdialytic natremia were not statistically associated with HID. Factors significantly associated with IDH were a number of antihypertensive treatments, NT-proBNP level and duration of dialysis session. In multivariate analysis: the high number of antihypertensive treatments and the increased duration of the dialysis session emerged as risk factors for IDH. Indeed, when the number of antihypertensives increased by 1 unit, the IDH score was multiplied on average by 2.74 (p<0.001), and when the session duration (h) increased by 0.1 units, the IDH score was multiplied by an average of 1.39 (p = 0.019). Residual natriuresis appeared as a protective factor against interdialytic weight gain, because when urinary sodium (mEq/l) increased by 10 units, mean interdialytic weight gain (kg) decreased by an average of -0.116 (p = 0.043). Conclusion Intradialytic hypertension is common and multifactorial. Antihypertensive combination therapy, usually reflecting resistant high blood pressure, is a major risk factor. The present study, at the expense of the definition criteria used, did not find significant associations with perdialytic natremia and residual natriuresis. However, the latter remains protective against interdialytic hypervolemia. Hence, the need for its preservation.

#5527 ALDOSTERONE, CORTISOL AND URINE VOLUME CAN EXPLAIN DISCREPANCIES BETWEEN DIETARY AND URINARY NA/K RATIO

Abstract Background and Aims Increased urinary sodium-to-potassium (Na/K) ratio has been associated with chronic kidney disease. However, we demonstrated that urinary Na/K ratio does not accurately reflect dietary Na/K ratio. Rhythmic patterns of sodium storage and release from the skin interstitium are associated with aldosterone and cortisol levels and previous studies linked tissue sodium accumulation to water conservation. Therefore, we investigated whether the discrepancy between urinary and dietary Na/K ratio could be explained by these factors. Method For this post-hoc analysis, we used data from the long-term sodium balance studies Mars105 and Mars520. These studies collected 24-hour urine samples and controlled dietary salt intake for 105 (4 men) and 205 days (6 men) at levels of 6, 9 and 12 grams per day. We calculated the difference between urinary and dietary Na/K ratio. We tested whether this difference varied across salt intake levels in a linear mixed-effects model. Furthermore, we fitted two linear mixed-effect models to explain discrepancies between urinary and dietary Na/K ratio. In the first model, sodium intake, potassium intake, urinary aldosterone and urinary cortisol were fixed effects and for each factor random slopes per participant were allowed. In the second model, sodium intake, potassium intake and urine volume were fixed effects and for each factor random slopes per participant were allowed. Each salt intake level was assessed separately. Results The median difference between 24-hour urinary and dietary Na/K ratio was −0.21 (IQR −0.47 to 0.09). At higher salt intake levels the underestimation was significantly larger (mean difference −0.11, −0.22 and −0.36 for 6, 9 and 12 grams salt intake, respectively; P<0.001). At each salt intake level, higher urinary aldosterone was associated with underestimation of the dietary Na/K ratio (Figure 1A). In contrast, higher urinary cortisol and higher urine volume were associated with relative overestimation of the dietary Na/K ratio (Figure 1B and C, respectively). Conclusion The discrepancy between dietary and urinary Na/K ratio can be explained by sodium intake, aldosterone, cortisol and urine volume. This suggests that tissue sodium accumulation contributes to the inaccuracy of a single 24-hour urine collection for estimation of dietary sodium and potassium intake.

WATER LOAD EFFECT ON URINARY HYALURONIDASE ACTIVITY IN NORMOTENSIVE OFFSPRING OF NORMOTENSIVE AND HYPERTENSIVE SUBJECTS: A POSSIBLE LINK TO HYPERTENSION DEVELOPMENT

Objective: Alterations in sodium and water intake-excretion balance are currently admitted as a relevant factor in arterial hypertension development. Hyaluronic acid metabolism in renal medullary has been proved to play a relevant role in the regulation of water resorption by the collecting duct, and hyaluronidase excretion in urine has been found to be inversely related to hydration status. Thus, the aim of our study was to assess urinary hyaluronidase activity in response to water loading in hypertensive and normotensive subjects with and without familial predisposition to hypertension. Design and method: Eighty-six adult Caucasian men underwent a water loading test consisting of oral administration of 15-20 ml of water/kg body weight over 40-45 min. Urinary hyaluronidase activity was assessed by turbidimetric assay at baseline and every 60 min for 4 hours. The study cohort included 21 hypertensive patients (HT) and 65 normotensive offsprings of normotensive (NT neg, n = 29) and hypertensive subjects (NT pos, n = 36). Results: Urinary hyaluronidase activity decreased in response to water loading in all groups, attaining the lowest levels at 60 and 120 min. However, while at baseline and after 240 min hyaluronidase activity was similar for all subjects, between 60 and 180 min NT pos subjects maintained significantly highest levels than both NT neg and HT patients (p<0.0001 and p<0.001 at 120 min, respectively). Conclusions: Consistent with previous findings, our results show that hyaluronidase activity in urine is inversely correlated with hydration status as we observed in all studied groups in response to water loading. However, while baseline levels did not differ between groups, the decrease in hyaluronidase activity was significantly lower in the subgroup of subjects having a family history of hypertension. Since hyaluronidase activity in the renal medullary has been postulated to be associated with ADH metabolism, individuals genetically predisposed to hypertension might exhibit increased renal sensitivity to ADH action resulting in alterations in the management of water loading by the vasopressinergic system that could precede and contribute to hypertension development.

DISCREPANCIES BETWEEN DIETARY AND URINE NA/K RATIO CAN BE EXPLAINED BY ALDOSTERONE, CORTISOL AND URINE VOLUME

Objective: Increased urine sodium-to-potassium (Na/K) ratio is associated with hypertension and cardiovascular disease. However, we demonstrated that urine Na/K ratio does not accurately reflect dietary Na/K ratio. As rhythmic patterns of sodium storage and release are associated with aldosterone and cortisol levels and previous studies linked tissue sodium accumulation to water conservation, we investigated whether the discrepancy between urine and dietary Na/K ratio could be explained by these factors. Design and method: We performed a post-hoc analysis of the long-term sodium balance studies Mars105 and Mars520. Ten healthy participants consumed a diet with known sodium and potassium content. For 105 or 205 days 24-hour urine samples were collected. We calculated the difference between urine and dietary Na/K ratio. A linear mixed-effect model was used to determine whether this difference varied across salt intake levels. Furthermore, we fitted two linear mixed-effect models to explain discrepancies between urine and dietary Na/K ratio. In the first, sodium intake, potassium intake, urine aldosterone and urine cortisol were fixed effects and for each factor random slopes per participant were allowed. In the second, sodium intake, potassium intake and urine volume were fixed effects and for each factor random slopes per participant were allowed. We analysed the salt intake levels 6, 9 and 12 grams separately. Results: Urine Na/K ratio underestimated dietary Na/K ratio (median difference -0.21, IQR -0.47 to 0.09). The discrepancy was significantly larger at higher salt intake levels (mean difference -0.11, -0.22 and -0.36 for 6, 9 and 12 grams salt intake, respectively, P < 0.001). At all salt intake levels, higher aldosterone levels were associated with underestimation of the dietary Na/K ratio (Figure 1A). In contrast, higher urine cortisol and higher urine volume were associated with overestimation of the dietary Na/K ratio (Figure 1B and C respectively). Conclusions: Sodium intake, aldosterone, cortisol and urine volume can explain the discrepancy between dietary and urine Na/K ratio. These data suggest that tissue sodium accumulation contributes to the inability to estimate dietary intake using the Na/K ratio in a single 24-hour urine collection.

EPS5.10 Normonatremic salt depletion is not corrected in patients with cystic fibrosis treated with CFTR modulators

Objectives: Patients with cystic fibrosis are at increased risk for electrolyte abnormalities and this problem extends beyond early age. The aim of this study is to evaluate the incidence of sodium depletion in children treated with ivacafor/tezacaftor/elexaftor (IVA/TEZ/ELEX) and establish if there is a change in sodium balance compared to pre-modulator state.

URINE SODIUM-TO-POTASSIUM RATIO DOES NOT ACCURATELY REFLECT DIETARY SODIUM-TO-POTASSIUM RATIO

Objective: High sodium intake is associated with an increased risk of cardiovascular disease, whereas a high potassium intake is associated with a reduced risk. Dietary counselling requires accurate estimation of sodium and potassium intake, but 24-hour urine sodium and potassium excretion demonstrated not to reflect actual intake. Urine sodium-to-potassium (Na/K) ratio is a promising alternative as it may be less affected by aldosterone-induced rhythmic changes in total body sodium and potassium content, is less influenced by incomplete urine collections, and incorporates both the effect of sodium and potassium. Our study assesses whether 24-hour urine Na/K ratio is superior in predicting dietary intake compared to 24-hour urine sodium or potassium excretion. Design and method: A post-hoc analysis was performed on data from the long-term sodium balance studies Mars105 and Mars520. Ten healthy participants received a diet with a known sodium and potassium content and collected 24-hour urine samples for 105 or 205 days. We calculated the log fold difference between dietary intake and urine content of sodium, potassium and Na/K ratio. We compared these estimates of accuracy using a mixed-effects model with a random intercept per subject. We analysed whether the accuracy differed among 6, 9 and 12 grams salt intake or was affected by the number of 24-hour urine collections. Results: Urine Na/K ratio underestimated dietary Na/K ratio with a median difference of -0.21 (IQR -0.47 to 0.09). Compared to sodium and potassium assessment, the Na/K ratio was significantly less accurate in predicting intake (Figure 1A). Only for the 6 gram salt phase the Na/K ratio did not perform significantly worse than sodium measurements. Increasing the number of 24-hour urine measurements to three or seven improved accuracy of the Na/K ratio, although it remained inferior to separate assessment of sodium and potassium excretion (Figure 1B). Conclusions: The 24-hour urine Na/K ratio is less accurate than 24-hour urine sodium excretion for estimation of dietary intake in a controlled setting.

Mineralocorticoid receptor blockade protects the kidneys but does not affect inverted blood pressure rhythm in hypertensive transgenic (mRen-2)27 rats

Aldosterone regulates blood pressure (BP) through water and sodium balance. In our study, we studied if continuous treatment with a mineralocorticoid receptor antagonist, spironolactone (30 mg/kg/day) for 20 days can: 1) attenuate hypertension development and restore inverted 24-h BP rhythm in hypertensive transgenic (mRen-2)27 rats (TGR) measured by telemetry; 2) improve function of the kidneys and heart; 3) be protective against high salt load (1% in water) by mitigating oxidative injury and improving kidney function. Spironolactone decreased albuminuria and 8-isoprostane in normal and salt load conditions in BP-independent effects. Salt load increased BP, impaired autonomic balance, suppressed plasma aldosterone level and increased natriuresis, albuminuria and oxidative injury in TGR. Spironolactone did not restore the inverted 24-h rhythm of BP in TGR, therefore, mineralocorticoids are not crucial in regulation of BP daily profile. Spironolactone improved kidney function, decreased oxidative stress and was protective against high salt load in the BP-independent manner.

Renal Medullary Overexpression of Sphingosine-1-Phosphate Receptor 1 Transgene Attenuates Deoxycorticosterone Acetate (DOCA)-Salt Hypertension.

Our previous studies showed that renal medullary sphingosine-1-phosphate receptor 1 (S1PR1) mediated sodium excretion, high salt intake increased S1PR1 level, deoxycorticosterone acetate (DOCA) blocked high salt-induced S1PR1 in the renal medulla, and that conditional knockout of S1PR1 in the collecting duct aggravated DOCA-salt hypertension. The present study tested the hypothesis that overexpression of S1PR1 transgene in the renal medulla attenuates the sodium retention and hypertension in DOCA-salt mouse model. Male C57BL/6J mice received renal medullary transfection of control or S1PR1-expressing plasmids and then DOCA-salt treatment. Renal sodium excretion and arterial pressure were compared between control and S1PR1-overexpressed mice in response to high salt loading or pressure natriuresis. S1PR1-transfected mice showed significantly enhanced urinary sodium excretion in response to acute sodium loading (0.93 ± 0.27 in control vs. 4.72 ± 1.12 µmol/min/gKW in S1PR1-overexpressed mice, P < 0.05) and the pressure natriuresis (3.58 ± 1.77 vs. 9.52 ± 1.38, P < 0.05), less positive sodium balance in response to chronic high-salt intake (3.05 ± 0.39 vs. 1.65 ± 0.39 mmol/72 hr, P < 0.05), and consequently, the attenuation of DOCA-salt hypertension (134.2 ± 6.79 vs. 109.8 ± 3.54 mm Hg, P < 0.05). The αENaC protein amount in the renal medulla was not changed, however, the βENaC was significantly decreased and the γENaC was significantly increased in S1PR1-overexpressed mice. The immunostaining showed apical membrane translocation of γENaC, while no change of αENaC and βENaC in control mice, and that the apical membrane translocation of γENaC was blocked in S1PR1-treasffected mice. These results suggested that activation of S1PR1 in the renal medulla attenuates DOCA-induced sodium retention and salt-sensitive hypertension associated with inhibition of ENaC.

Structural Organization of GABA- and Nitroxidergic Systems of Subfornical Organ in Wistar Rats Postnatal Development

The subfornical organ (SFO) is one of the circumventricular organs (CVOs) of the mammalian nervous system responsible for maintaining the energy and water and sodium balance. Despite notable interest in the SFO and its physiological functions, the organization of individual populations of SFO cells, as well as their interactions remain to be clearly established. In this study we examined GABA and nitroxidergic systems of SFO using immunohistochemical (IHC) methods. The brain of male Wistar rats at different stages of postnatal development: postnatal day 7 (P7), 14 (P14) and adult (4–6 months), was examined. The data obtained allowed us to characterize changes in the activity of the GABA- and nitroxidergic systems of the SFO during development. In adult rats, three subpopulations of nitroxidergic cells, differing in the intensity of the reaction and tissue localization, can be distinguished. The revealed morphological heterogeneity of nitroxidergic cells in SFO may reflect their diverse functional status.

Signaling crosstalk between Dipeptidyl Peptidase 4 and Angiotensin II-AT1R plays a role in proximal tubule NHE3 regulation and salt sensitive hypertension

Background: Salt sensitivity to hypertension occurs in 50-60% of all hypertensive patients and is more common in overweight/obese, females and aging population. In salt sensitive hypertension, the renin-angiotensin system (RAS) is known to play a major role and in particular, Angiotensin II (Ang II) regulation of the sodium hydrogen exchanger (NHE3) in the proximal tubule may mediate the pathophysiology. Dipeptidyl peptidase 4 (DPP4), an exopeptidase expressed abundantly on the brush border, binds to NHE3 and DPP4 inhibition reduces NHE3-mediated sodium reabsorption in proximal tubule cells. Interestingly, we observed both in vitro and in vivo that Ang II stimulates DPP4 activity. However, the mechanisms mediating the interplay between Ang II and DPP4 and its role in NHE3 regulation remain unknown. Therefore, we hypothesized that Ang II stimulation of DPP4 activity via crosstalk between AT1R and DPP4 may account for NHE3 modulation and, consequently, salt-sensitive hypertension. Methods: To address this hypothesis, we stimulated OK-AT1R (stable expressing rat AT1R) proximal tubule cells with Ang II (10 -8 to 10 -10 M), OKP cells with Ang II 10 -8 M and microperfused rat nephrons (Ang II 10 -10 M). In addition, sodium balance studies were conducted on DPP4-/- mice with high salt (1% sodium choride in drinking water) and low salt (0.02% in diet) Results: In OK-AT1R cells, we observed a dose-dependent increase in DPP4 activity, which was inhibited with AT1R blockade, and a battery of kinase inhibitors, including those for Src, PI3K, mTOR, S6K, ERK, and EGFR. Blockade with the DPP4 inhibitor MK-0626 not only suppressed DPP4 activity but partially suppressed Ang II-mediated signaling via EGFR, src, PI3K, mTOR and S6K. Further dissection of the pathways revealed that the blockade of src, which binds to both AT1R and DPP4, mimicked many of the effects of AT1R and DPP4 blockade. Mechanistically, blockade of motor proteins myosin II and myosin VI, which have been shown to redistribute with DPP4 and NHE3 along the microvilli microdomains, did not inhibit Ang II-induced DPP4 activity suggesting other mechanisms (phosphorylation) may underlie Ang II-DPP4 crosstalk in proximal tubule cells. Importantly, we found that DPP4 inhibition blocked Ang II-mediated stimulation of NHE3 activity (pHi) in vitro (OKP cells) and JHCO 3 - in vivo (rat nephrons). In addition, we observed that DPP4 gene-deleted mice lose more salt under both high and low salt ingestion and that DPP4 deficiency lowers BP under conditions of high salt, suggesting that DPP4 may regulate salt-sensitive hypertension. In conclusion, Ang II-AT1R and DPP4 likely crosstalk via binding to src and/or PI3-K, and inhibition of DPP4 suppresses Ang II-AT1R signaling and downstream effectors, including NHE3. Moreover, inhibition of signaling downstream of AT1R can suppress DPP4 activity, suggesting that AT1R and DPP4 act in concert but not via subcellular redistribution via motor proteins. The Sao Paulo Research Foundation - FAPESP (2021/14534-3), Sao Paulo, SP, Brazil to Flavia Martins and Dr. Adriana Girardi; NIH/NIDDK - K08 DK115886 to Dr. Ravi Nistala This is the full abstract presented at the American Physiology Summit 2023 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.

Post-exercise rehydration: Comparing the efficacy of three commercial oral rehydration solutions.

This study compared the efficacy of three commercial oral rehydration solutions (ORS) for restoring fluid and electrolyte balance, after exercise-induced dehydration. Healthy, active participants (N = 20; ♀ = 3; age ∼27 y, O2peak ∼52 ml/kg/min) completed three randomised, counterbalanced trials whereby intermittent exercise in the heat (∼36°C, ∼50% humidity) induced ∼2.5% dehydration. Subsequently, participants rehydrated (125% fluid loss in four equal aliquots at 0, 1, 2, 3 h) with a glucose-based (G-ORS), sugar-free (Z-ORS) or amino acid-based sugar-free (AA-ORS) ORS of varying electrolyte composition. Urine output was measured hourly and capillary blood samples collected pre-exercise, 0, 2 and 5 h post-exercise. Sodium, potassium, and chloride concentrations in urine, sweat, and blood were determined. Net fluid balance peaked at 4 h and was greater in AA-ORS (141 ± 155 ml) and G-ORS (101 ± 195 ml) than Z-ORS (-47 ± 208 ml; P ≤ 0.010). Only AA-ORS achieved positive sodium and chloride balance post-exercise, which were greater for AA-ORS than G-ORS and Z-ORS (P ≤ 0.006), as well as for G-ORS than Z-ORS (P ≤ 0.007) from 1 to 5 h. when provided in a volume equivalent to 125% of exercise-induced fluid loss, AA-ORS produced comparable/superior fluid balance and superior sodium/chloride balance responses to popular glucose-based and sugar-free ORS.

Marinobufagenin, Left Ventricular Hypertrophy and Residual Renal Function in Kidney Transplant Recipients.

Left ventricular hypertrophy (LVH), which is a pervasive complication of end-stage kidney disease (ESKD), persists in some uremic individuals even after kidney transplantation (Ktx), contributing to worsening CV outcomes. Marinobufagenin (MBG), an endogenous steroid cardiotonic hormone endowed with natriuretic and vasoconstrictive properties, is an acknowledged trigger of uremic cardiomyopathy. However, its clinical significance in the setting of Ktx remains undefined. In a cohort of chronic Ktx recipients (n = 40), we assessed circulating MBG together with a thorough clinical and echocardiographic examination. Forty matched haemodialysis (HD) patients and thirty healthy subjects served as controls for MBG measurements. Patients were then prospectively followed up to 12 months and the occurrence of an established cardio-renal endpoint (death, CV events, renal events, graft rejection) was recorded. Median MBG plasma levels were lower in Ktx as compared with HD patients (p = 0.02), but higher as compared with healthy controls (p = 0.0005). Urinary sodium (β = 0.423; p = 0.01) and eGFR (β = -0.324; p = 0.02) were the sole independent predictors of MBG in this cohort, while a strong correlation with left ventricular mass index (LVMi), found in univariate analyses (R = 0.543; p = 0.0007), gained significance only in multivariate models not including eGFR. Logistic regression analyses indicated MBG as a significant predictor of the combined endpoint (OR 2.38 [1.10-5.12] per each 1 nmoL/L increase; p = 0.01), as well as eGFR, LVMi, serum phosphate and proteinuria. Ktx recipients display altered MBG levels which are influenced by sodium balance, renal impairment and the severity of LVH. Thus, MBG might represent an important missing link between reduced graft function and pathological cardiac remodelling and may hold important prognostic value for improving cardio-renal risk assessment.

Computational investigation of the impact of potential AT2R polymorphism on small molecule binding

For more than a century, the renin-angiotensin system (RAS) has been acknowledged for playing a crucial part in the physiological control of arterial pressure, as well as sodium and fluid balance. It is now generally acknowledged that one of the receptor of RAS system i.e. angiotensin type 2 receptor (AT2R) functions as a repair system during pathophysiologic circumstances and performs a significant protective role. Efforts have been made previously to design suitable agonist and antagonist molecules to potentially modulate AT2R. One of the agonists and antagonists, named C21 and EMA401, has been studied in a number of pathological conditions. Additionally, a wide panel of single nucleotide polymorphisms (SNPs) has been reported for AT2R, which might potentially affect the efficacy of these molecules. Therefore, computational investigations have been carried out to analyze all the SNPs (1151) reported in NCBI to find potential SNPs affecting the active site of AT2R, as this domain is still unexplored. Structures of these polymorphic forms were modeled, and in silico drug interaction studies with C21 and EMA401 were carried out. The two mutants (rs868939201 and rs1042852794) that significantly affect the binding affinity as that of the wild type were subjected to molecular dynamics simulations. Our analysis of native and mutant AT2R and their complexes with C21 and EMA401 indicated that the occurrence of these mutations affects the conformation of the protein and has affected the binding of these ligand molecules. The study’s findings will aid in the development of better, more versatile medications in the near future, and also in vitro and in vivo studies might be planned in accordance with recent findings. Communicated by Ramaswamy H. Sarma

CYP11B2 inhibitor dexfadrostat phosphate suppresses the aldosterone-to-renin ratio, an indicator of sodium retention, in healthy volunteers.

High aldosterone is a key driver of hypertension and long-term negative sequelae. We evaluated the safety and efficacy of dexfadrostat phosphate (DP13), a novel aldosterone synthase (CYP11B2) inhibitor, in healthy participants. This randomized, double-blind, placebo-controlled study was conducted in two parts. In part A, a single-ascending dose escalation, 16 participants received oral DP13 1-16 mg. Part B was a multiple-ascending dose, sequential group study in which 32 participants received oral DP13 4, 8 or 16 mg once daily for 8 days. Safety and tolerability were monitored throughout. An adrenocorticotropic hormone (ACTH) stimulation test at maximal blood drug concentrations defined the dose range for multiple dosing. DP13 was well tolerated at all doses, with no serious adverse events. In part B, all DP13 doses (4, 8 and 16 mg) over 8 days effectively suppressed aldosterone production, increased the urinary sodium/potassium ratio, decreased plasma sodium and increased plasma potassium and renin levels compared with placebo, resulting in potent suppression of the aldosterone-to-renin ratio (ARR). Endocrine counter-regulation resulted in the 4 mg dose no longer sustaining 24-h aldosterone suppression after 8 days of treatment, unlike the 8- and 16 mg doses. There was no evidence of drug-induced adrenal insufficiency (ACTH stress challenge). In patients with excess aldosterone and ensuing sodium retention driving hypertension, managing sodium balance is critical. A CYP11B2 inhibitor like DP13, whose effectiveness can be monitored by a reduction in ARR, may prove valuable in managing aldosterone-dependent hypertension and primary aldosteronism.

Post-obstructive polyuria. Pathophysiological analysis of a case

The relief of the impediment to urinary flow is the treatment of acute kidney failure due to urinary tract obstruction. However, there is a risk of inducing massive polyuria, which can be self-limited or produce severe contraction of the intravascular volume with pre-renal acute kidney failure and alterations in the internal environment. Polyuria, urine output > 3 L/d or > 200 mL/min for more than 2 hours, can have multiple causes, and can be classified as osmotic, aqueous or mixed. Post-obstructive polyuria obeys different pathogenic mechanisms, which overlap and vary during a patient's evolution. Initially, there is a decrease in vasoconstrictor factors and an increase in renal blood flow, which, added to the excess of urea accumulated, will cause intense osmotic diuresis (osmotic polyuria due to urea). Added to these factors are the positive sodium and water balance during acute renal failure, plus the contributions of crystalloid solutions to replace diuresis (ionic osmotic polyuria). Finally, there may be tubular dysfunction and decreased solutes in the renal medullary interstitium, adding resistance to the action of vasopressin. The latter causes a loss of free water (mixed polyuria). We present the case of a patient with post-obstructive polyuria where, by analyzing the clinical symptoms and laboratory alterations, it was possible to interpret the mechanisms of polyuria and administer appropriate treatment for the pathogenic mechanism.