Sodium Handling by the Blood Vessel Wall

Effects of polygenic risk score and sodium and potassium intake on hypertension in Asians: A nationwide prospective cohort study

Genetic factors, lifestyle, and diet have been shown to play important roles in the development of hypertension. Increased salt intake is an important risk factor for hypertension. However, research on the involvement of genetic factors in the relationship between salt intake and hypertension in Asians is lacking. We aimed to investigate the risk of hypertension in relation to sodium and potassium intake and the effects of genetic factors on their interactions. We used Korean Genome and Epidemiology Study data and calculated the polygenic risk score (PRS) for the effect of systolic and diastolic blood pressure (SBP and DBP). We also conducted multivariable logistic modeling to evaluate associations among incident hypertension, PRSSBP, PRSDBP, and sodium and potassium intake. In total, 41,351 subjects were included in the test set. The top 10% PRSSBP group was the youngest of the three groups (bottom 10%, middle, top 10%), had the highest proportion of women, and had the highest body mass index, baseline BP, red meat intake, and alcohol consumption. The multivariable logistic regression model revealed the risk of hypertension was significantly associated with higher PRSSBP, higher sodium intake, and lower potassium intake. There was significant interaction between sodium intake and PRSSBP for incident hypertension especially in sodium intake ≥2.0 g/day and PRSSBP top 10% group (OR 1.27 (1.07-1.51), P = 0.007). Among patients at a high risk of incident hypertension due to sodium intake, lifestyle modifications and sodium restriction were especially important to prevent hypertension.

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.

Sodium and water dynamics in the progression of chronic kidney disease: mechanisms and clinical significance

AIM

Lifestyle modifications can postpone the progression of chronic kidney disease toward its terminal stage. This mini-review aims to explore the impact of salt and water intake on the progression of chronic kidney disease (CKD) and provide insights into the optimal consumption levels to preserve the glomerular filtration rate.

METHODS

We reviewed relevant literature to examine the association between salt and water consumption and CKD progression. Our analysis includes discussions on the pathophysiology, findings from clinical trials, and recommended intake guidelines.

RESULTS

Sodium intake, often linked to cardiovascular risk and CKD progression, has shown a complex J-shaped association in some studies, leading to uncertainty about the ideal salt intake level. Sodium and fluid retention are key factors contributing to hypertension, a well-established risk factor for CKD progression. Low-sodium diets have demonstrated promise in reducing blood pressure and enhancing the effects of renin-angiotensin-aldosterone system inhibitors in non-dialysis CKD patients. However, a debate persists regarding the independent effect of salt restriction on CKD progression. Despite medical recommendations, salt consumption remains high among CKD patients. Additionally, the role of water consumption in CKD remains controversial despite its established benefits for CKD prevention in the general population.

CONCLUSION

Lifestyle modifications involving salt and water intake can influence the progression of CKD. While low-sodium diets have shown potential for mitigating hypertension and proteinuria in non-dialysis CKD patients, their independent impact on CKD progression warrants further investigation. The role of water consumption in CKD remains uncertain, and there is a need for additional research in this area. Clinicians should consider individualized dietary recommendations for CKD patients to help preserve the glomerular filtration rate and improve overall outcomes.

Tangram of Sodium and Fluid Balance

Homeostasis of fluid and electrolytes is a tightly controlled physiological process. Failure of this process is a hallmark of hypertension, chronic kidney disease, heart failure, and other acute and chronic diseases. While the kidney remains the major player in the control of whole-body fluid and electrolyte homeostasis, recent discoveries point toward more peripheral mechanisms leading to sodium storage in tissues, such as skin and muscle, and a link between this sodium and a range of diseases, including the conditions above. In this review, we describe multiple facets of sodium and fluid balance from traditional concepts to novel discoveries. We examine the differences between acute disruption of sodium balance and the longer term adaptation in chronic disease, highlighting areas that cannot be explained by a kidney-centric model alone. The theoretical and methodological challenges of more recently proposed models are discussed. We acknowledge the different roles of extracellular and intracellular spaces and propose an integrated model that maintains fluid and electrolyte homeostasis and can be distilled into a few elemental players: the microvasculature, the interstitium, and tissue cells. Understanding their interplay will guide a more precise treatment of conditions characterized by sodium excess, for which primary aldosteronism is presented as a prototype.

Lifestyle management of hypertension: International Society of Hypertension position paper endorsed by the World Hypertension League and European Society of Hypertension

Hypertension, defined as persistently elevated systolic blood pressure (SBP) >140 mmHg and/or diastolic blood pressure (DBP) at least 90 mmHg (International Society of Hypertension guidelines), affects over 1.5 billion people worldwide. Hypertension is associated with increased risk of cardiovascular disease (CVD) events (e.g. coronary heart disease, heart failure and stroke) and death. An international panel of experts convened by the International Society of Hypertension College of Experts compiled lifestyle management recommendations as first-line strategy to prevent and control hypertension in adulthood. We also recommend that lifestyle changes be continued even when blood pressure-lowering medications are prescribed. Specific recommendations based on literature evidence are summarized with advice to start these measures early in life, including maintaining a healthy body weight, increased levels of different types of physical activity, healthy eating and drinking, avoidance and cessation of smoking and alcohol use, management of stress and sleep levels. We also discuss the relevance of specific approaches including consumption of sodium, potassium, sugar, fibre, coffee, tea, intermittent fasting as well as integrated strategies to implement these recommendations using, for example, behaviour change-related technologies and digital tools.

The role of glycosaminoglycans in blood pressure regulation

Essential hypertension (HT) is the global health problem and is a major risk factor for the development of cardiovascular and kidney disease. High salt intake has been associated with HT and impaired kidney sodium excretion is considered to be a major mechanism for the development of HT. Although kidney has a very important role in regulation of BP, this traditional view of BP regulation was challenged by recent findings suggesting that nonosmotic tissue sodium deposition is very important for BP regulation. This new paradigm indicates that sodium can be stored and deposited nonosmotically in the interstitium without water retention and without increased BP. One of the major determinants of this deposition is glycosaminoglycans (GAGs). By binding to GAGs found in the endothelial surface layer (ESL) which contains glycocalyx, sodium is osmotically inactivated and not induce concurrent water retention. Thus, GAGs has important function for homeostatic BP and sodium regulation. In the current review, we summarized the role of GAGs in ESL and BP regulation.

Novel mechanisms of salt-sensitive hypertension

A high dietary sodium-consumption level is considered the most important lifestyle factor that can be modified to help prevent an increase in blood pressure and the development of hypertension. Despite numerous studies over the past decades, the pathophysiology explaining why some people show a salt-sensitive blood pressure response and others do not is incompletely understood. Here, a brief overview of the latest mechanistic insights is provided, focusing on the mononuclear phagocytic system and inflammation, the gut-kidney axis, and epigenetics. The article also discusses the effects of 3 types of novel drugs on salt-sensitive hypertension-sodium-glucose cotransporter 2 inhibitors, nonsteroidal mineralocorticoid receptor antagonists, and aldosterone synthase inhibitors. The conclusion is that besides kidney-centered mechanisms, vasoconstrictor mechanisms are also relevant for both the understanding and treatment of this blood pressure phenotype.

Tissue Sodium Accumulation Induces Organ Inflammation and Injury in Chronic Kidney Disease

High salt intake is a primary cause of over-hydration in chronic kidney disease (CKD) patients. Inflammatory markers are predictors of CKD mortality; however, the pathogenesis of inflammation remains unclear. Sodium storage in tissues has recently emerged as an issue of concern. The binding of sodium to tissue glycosaminoglycans and its subsequent release regulates local tonicity. Many cell types express tonicity-responsive enhancer-binding protein (TonEBP), which is activated in a tonicity-dependent or tonicity-independent manner. Macrophage infiltration was observed in the heart, peritoneal wall, and para-aortic tissues in salt-loading subtotal nephrectomized mice, whereas macrophages were not prominent in tap water-loaded subtotal nephrectomized mice. TonEBP was increased in the heart and peritoneal wall, leading to the upregulation of inflammatory mediators associated with cardiac fibrosis and peritoneal membrane dysfunction, respectively. Reducing salt loading by a diuretic treatment or changing to tap water attenuated macrophage infiltration, TonEBP expression, and inflammatory marker expression. The role of TonEBP may be crucial during the cardiac fibrosis and peritoneal deterioration processes induced by sodium overload. Anti-interleukin-6 therapy improved cardiac inflammation and fibrosis and peritoneal membrane dysfunction. Further studies are necessary to establish a strategy to regulate organ dysfunction induced by TonEBP activation in CKD patients.

Mechanisms of sodium-mediated injury in cardiovascular disease: old play, new scripts

There is a strong association between salt intake and cardiovascular diseases, particularly hypertension, on the population level. The mechanisms that explain this association remain incompletely understood and appear to extend beyond blood pressure. In this review, we describe some of the 'novel' roles of Na⁺ in cardiovascular health and disease: energetic implications of sodium handling in the kidneys; local accumulation in tissue; fluid dynamics; and the role of the microvasculature, with particular focus on the lymphatic system. We describe the interplay between these factors that involves body composition, metabolic signatures, inflammation and composition of the extracellular and intracellular milieus.

Epithelial Na+ channel and the glycocalyx: a sweet and salty relationship for arterial shear stress sensing

PURPOSE OF REVIEW

The ability of endothelial cells to sense mechanical force, and shear stress in particular, is crucial for normal vascular function. This relies on an intact endothelial glycocalyx that facilitates the production of nitric oxide (NO). An emerging arterial shear stress sensor is the epithelial Na+ channel (ENaC). This review highlights existing and new evidence for the interdependent activity of the glycocalyx and ENaC and its implications for vascular function.

RECENT FINDINGS

New evidence suggests that the glycocalyx and ENaC are physically connected and that this is important for shear stress sensing. The connection relies on N-glycans attached to glycosylated asparagines of α-ENaC. Removal of specific N-glycans reduced ENaC's shear stress response. Similar effects were observed following degradation of the glycocalyx. Endothelial specific viral transduction of α-ENaC increased blood pressure (∼40 mmHg). This increase was attenuated in animals transduced with an α-ENaC version lacking N-glycans.

SUMMARY

These observations indicate that ENaC is connected to the glycocalyx and their activity is interdependent to facilitate arterial shear stress sensation. Future research focusing on how N-glycans mediate this interaction can provide new insights for the understanding of vascular function in health and disease.

Does Excess Tissue Sodium Storage Regulate Blood Pressure?

Purpose of Review

The regulation of blood pressure is conventionally conceptualised into the product of “circulating blood volume” and “vasoconstriction components”. Over the last few years, however, demonstration of tissue sodium storage challenged this dichotomous view.

Recent Findings

We review the available evidence pertaining to this phenomenon and the early association made with blood pressure; we discuss open questions regarding its originally proposed hypertonic nature, recently challenged by the suggestion of a systemic, isotonic, water paralleled accumulation that mirrors absolute or relative extracellular volume expansion; we present the established and speculate on the putative implications of this extravascular sodium excess, in either volume-associated or -independent form, on blood pressure regulation; finally, we highlight the prevalence of high tissue sodium in cardiovascular, metabolic and inflammatory conditions other than hypertension.

Summary

We conclude on approaches to reduce sodium excess and on the potential of emerging imaging technologies in hypertension and other conditions.

From salt to hypertension, what is missed?

Excess salt intake is viewed as a major contributor to hypertension and cardiovascular disease, and dietary salt restriction is broadly recommended by public health guidelines. However, individuals can have widely varying physiological responses to salt intake, and a tailored approach to evaluation and intervention may be needed. The traditional sodium related concepts are challenging to assess clinically for two reasons: (1) spot and 24-hour urine sodium are frequently used to evaluate salt intake, but are more suitable for population study, and (2) some adverse effects of salt may be blood pressure-independent. In recent years, previously unknown mechanisms of sodium absorption and storage have been discovered. This review will outline the limitations of current methods to assess sodium balance and discuss new potential evaluation methods and treatment targets.

Perturbed body fluid distribution and osmoregulation in response to high salt intake in patients with hereditary multiple exostoses

Background

Hereditary Multiple Exostoses (HME) is a rare autosomal disorder characterized by the presence of multiple exostoses (osteochondromas) caused by a heterozygous loss of function mutation in EXT1 or EXT2; genes involved in heparan sulfate (HS) chain elongation. Considering that HS and other glycosaminoglycans play an important role in sodium and water homeostasis, we hypothesized that HME patients have perturbed whole body volume regulation and osmolality in response to high sodium conditions.

Methods

We performed a randomized cross-over study in 7 male HME patients and 12 healthy controls, matched for age, BMI, blood pressure and renal function. All subjects followed both an 8-day low sodium diet (LSD, <50 mmol/d) and high sodium diet (HSD, >200 mmol/d) in randomized order. After each diet, blood and urine samples were collected. Body fluid compartment measurements were performed by using the distribution curve of iohexol and ¹²⁵I-albumin.

Results

In HME patients, HSD resulted in significant increase of intracellular fluid volume (ICFV) (1.2 L, p = 0.01). In this group, solute-mediated water clearance was significantly lower after HSD, and no changes in interstitial fluid volume (IFV), plasma sodium, and effective osmolality were observed. In healthy controls, HSD did not influence ICFV, but expanded IFV (1.8 L, p = 0.058) and increased plasma sodium and effective osmolality.

Conclusion

HME patients show altered body fluid distribution and osmoregulation after HSD compared to controls. Our results might indicate reduced interstitial sodium accumulation capacity in HME, leading to ICFV increase. Therefore, this study provides additional support that HS is crucial for maintaining constancy of the internal environment.

Compensatory depression of arterial pressure and reversal of ECG abnormalities by Annona muricata and Curcuma longa in hypertensive Wistar rats

OBJECTIVES

Increasing hypertension incidence in Sub-Sahara Africa and the current cost of management of the metabolic disorder has necessitated research on medicinal plants employed in African Traditional Medicine for hypertension. Thus, this study evaluated antihypertensive effect of Annona muricata leaves or Curcuma longa rhizomes in experimentally-induced hypertensive male Wistar rats (n=70) which were unilaterally nephrectomized and daily loaded with 1% salt. Cardiovascular and haematological changes, as well as urinalysis were determined.

METHODS

Rats were uninephrectomized and NaCl (1%) included in drinking water for 42 days. Extract-treated hypertensive rats were compared to normotensive, untreated hypertensive and hypertensive rats treated with lisinopril (5 mg/70 kg) or hydrochlorothiazide (12.5 mg/70 kg). A. muricata extract or C. longa extract were administered at 100, 200 or 400 mg/kg. Blood pressure (systolic, diastolic and mean arterial) and electrocardiogram was measured on day 41. Twenty-four-hour urine samples were collected from day 42. Blood samples were collected on day 43 for haematology (PCV, red cell indices, WBC and its differentials, and platelets).

RESULTS AND CONCULSIONS

A. muricata or C. longa extracts caused a decline in elevated blood pressure of hypertensive rats. Heart rate and QT segment reduction coupled with prolonged QRS duration were reversed in extract-treated rats, with significant increases in hemogram parameters indicating increased blood viscosity. Also, leukocyturia, proteinuria and ketonuria with increased urine alkalinity, urobilinogen and specific gravity which are classical indicators of poor prognostic outcomes in hypertension were reversed in extract-treated rats. In conclusion, A. muricata and C. longa have cardioprotective effect with reversal of derangements in haemogram and urinalysis associated with hypertension.

Association of overhydration and serum pigment epithelium-derived factor with CKD progression in diabetic kidney disease: A prospective cohort study

AIM

Little is known about whether overhydration (OH), measured using bioimpedance assay (BIA), is associated with CKD progression in patients with type 2 diabetes mellitus (T2DM). We hypothesised that OH was a predictor, and pigment epithelium-derived factor (PEDF) was a modifiable risk factor of CKD progression.

METHODS

We conducted a prospective cohort study of 1,065 patients with clinically euvolemic T2DM who attended the diabetes centre in a tertiary hospital or primary care clinic. CKD progression was defined as a combination of the worsening of the KDIGO defined CKD category by eGFR and a ≥25% decline in eGFR compared to baseline.

RESULTS

Patients with T2DM in the highest tertile of OH and relative OH (OH/ extracellular water > 7%) were positively associated with CKD progression (hazard ratio [HR] 1.45 [95% confidence interval (CI) 1.14-1.85; p = 0.003 and HR 1.29 [95%CI 1.05-1.59; p = 0.017]). There were positive associations between PEDF and CKD progression (β = 1.10; p = 0.001) and between OH and CKD progression (β = 0.21; p = 0.036). OH remained positively associated with CKD progression mediated by PEDF.

CONCLUSIONS

OH is an independent risk factor for CKD progression in patients with T2DM. Our study supports the novel definition of PEDF as a positive mediator between OH and CKD progression.

Distinct osmoregulatory responses to sodium loading in patients with altered glycosaminoglycan structure: a randomized cross-over trial

Background

By binding to negatively charged polysaccharides called glycosaminoglycans, sodium can be stored in the body—particularly in the skin—without concurrent water retention. Concordantly, individuals with changed glycosaminoglycan structure (e.g. type 1 diabetes (DM1) and hereditary multiple exostosis (HME) patients) may have altered sodium and water homeostasis.

Methods

We investigated responses to acute (30-min infusion) and chronic (1-week diet) sodium loading in 8 DM1 patients and 7 HME patients in comparison to 12 healthy controls. Blood samples, urine samples, and skin biopsies were taken to investigate glycosaminoglycan sulfation patterns and both systemic and cellular osmoregulatory responses.

Results

Hypertonic sodium infusion increased plasma sodium in all groups, but more in DM1 patients than in controls. High sodium diet increased expression of nuclear factor of activated t-cells 5 (NFAT5)—a transcription factor responsive to changes in osmolarity—and moderately sulfated heparan sulfate in skin of healthy controls. In HME patients, skin dermatan sulfate, rather than heparan sulfate, increased in response to high sodium diet, while in DM1 patients, no changes were observed.

Conclusion

DM1 and HME patients show distinct osmoregulatory responses to sodium loading when comparing to controls with indications for reduced sodium storage capacity in DM1 patients, suggesting that intact glycosaminoglycan biosynthesis is important in sodium and water homeostasis.

Trial registration These trials were registered with the Netherlands trial register with registration numbers: NTR4095 (https://www.trialregister.nl/trial/3933 at 2013-07-29) and NTR4788 (https://www.trialregister.nl/trial/4645 at 2014-09-12).

High-salt intake affects retinal vascular tortuosity in healthy males: an exploratory randomized cross-over trial

The retinal microcirculation is increasingly receiving credit as a relatively easily accessible microcirculatory bed that correlates closely with clinical cardiovascular outcomes. The effect of high salt (NaCl) intake on the retinal microcirculation is currently unknown. Therefore, we performed an exploratory randomized cross-over dietary intervention study in 18 healthy males. All subjects adhered to a two-week high-salt diet and low-salt diet, in randomized order, after which fundus photographs were taken and assessed using a semi-automated computer-assisted program (SIVA, version 4.0). Outcome parameters involved retinal venular and arteriolar tortuosity, vessel diameter, branching angle and fractal dimension. At baseline, participants had a mean (SD) age of 29.8 (4.4) years and blood pressure of 117 (9)/73 (5) mmHg. Overall, high-salt diet significantly increased venular tortuosity (12.2%, p = 0.001). Other retinal parameters were not significantly different between diets. Changes in arteriolar tortuosity correlated with changes in ambulatory systolic blood pressure (r = - 0.513; p = 0.04). In conclusion, high-salt diet increases retinal venular tortuosity, and salt-induced increases in ambulatory systolic blood pressure associate with decreases in retinal arteriolar tortuosity. Besides potential eye-specific consequences, both phenomena have previously been associated with hypertension and other cardiovascular risk factors, underlining the deleterious microcirculatory effects of high salt intake.

Effect of high-salt diet on blood pressure and body fluid composition in patients with type 1 diabetes: randomized controlled intervention trial

INTRODUCTION

Patients with type 1 diabetes are susceptible to hypertension, possibly resulting from increased salt sensitivity and accompanied changes in body fluid composition. We examined the effect of a high-salt diet (HSD) in type 1 diabetes on hemodynamics, including blood pressure (BP) and body fluid composition.

RESEARCH DESIGN AND METHODS

We studied eight male patients with type 1 diabetes and 12 matched healthy controls with normal BP, body mass index, and renal function. All subjects adhered to a low-salt diet and HSD for eight days in randomized order. On day 8 of each diet, extracellular fluid volume (ECFV) and plasma volume were calculated with the use of iohexol and 125I-albumin distribution. Hemodynamic measurements included BP, cardiac output (CO), and systemic vascular resistance.

RESULTS

After HSD, patients with type 1 diabetes showed a BP increase (mean arterial pressure: 85 (5) mm Hg vs 80 (3) mm Hg; p<0.05), while BP in controls did not rise (78 (5) mm Hg vs 78 (5) mm Hg). Plasma volume increased after HSD in patients with type 1 diabetes (p<0.05) and not in controls (p=0.23). There was no significant difference in ECFV between diets, while HSD significantly increased CO, heart rate (HR) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in type 1 diabetes but not in controls. There were no significant differences in systemic vascular resistance, although there was a trend towards an HSD-induced decrease in controls (p=0.09).

CONCLUSIONS

In the present study, patients with type 1 diabetes show a salt-sensitive BP rise to HSD, which is accompanied by significant increases in plasma volume, CO, HR, and NT-proBNP. Underlying mechanisms for these responses need further research in order to unravel the increased susceptibility to hypertension and cardiovascular disease in diabetes.

TRIAL REGISTRATION NUMBERS

NTR4095 and NTR4788.

Clinical impact of tissue sodium storage

In recent times, the traditional nephrocentric, two-compartment model of body sodium has been challenged by long-term sodium balance studies and experimental work on the dermal interstitium and endothelial surface layer. In the new paradigm, sodium can be stored without commensurate water retention in the interstitium and endothelial surface layer, forming a dynamic third compartment for sodium. This has important implications for sodium homeostasis, osmoregulation and the hemodynamic response to salt intake. Sodium storage in the skin and endothelial surface layer may function as a buffer during periods of dietary depletion and excess, representing an extra-renal mechanism regulating body sodium and water. Interstitial sodium storage may also serve as a biomarker for sodium sensitivity and cardiovascular risk, as well as a target for hypertension treatment. Furthermore, sodium storage may explain the limitations of traditional techniques used to quantify sodium intake and determine infusion strategies for dysnatraemias. This review is aimed at outlining these new insights into sodium homeostasis, exploring their implications for clinical practice and potential areas for further research for paediatric and adult populations.

Renal and Lumbar Sympathetic Nerve Activity During Development of Hypertension in Dahl Salt-Sensitive Rats

To study the contribution of sympathetic nerve activity (SNA) to the development of hypertension, experiments were designed to continuously and simultaneously measure renal (RSNA) and lumbar SNA (LSNA) during the development of hypertension induced by 8% salt loading in Dahl salt-sensitive (DS) rats. Male DS and salt-resistant rats were instrumented with bipolar electrodes to record RSNA and LSNA and a telemeter to record arterial pressure (AP). AP increased during the first 3 days after the onset of salt loading by ≈10 mm Hg in both DS and Dahl salt-resistant rats. AP continued to increase progressively from day 4 to day 14 of salt loading by 33±1 mm Hg in DS rats, while it remained the same in Dahl salt-resistant rats. RSNA and LSNA increased in the initial few days by 6% to 8%, and decreased gradually thereafter, suggesting that increases in neither RSNA nor LSNA are directly linked with the progressive increase in AP induced by salt loading in DS rats. After the cessation of salt loading, AP pressure returned to the presalt loading level in both DS and Dahl salt-resistant rats. RSNA increased significantly by 32±3% after the cessation of salt loading, while LSNA remained the same in DS rats, suggesting that salt-sensitive mechanisms respond to a loss of sodium, not a gain, and selectively activate RSNA in DS rats. In summary, RSNA and LSNA are not likely to be a primary trigger to initiate the progressive increase in AP induced by 8% salt loading in DS rats.

Insulin Resistance and Renal Sodium Handling Influence Arterial Stiffness in Hypertensive Patients with Prevailing Sodium Intake

BACKGROUND

Insulin resistance and renal tubular sodium handling influence arterial structure and function and play an essential role in salt-sensitive forms of hypertension.

METHODS

In a population with prevailing sodium consumption, we assessed the relationship between cardiovascular phenotypes (peripheral and central blood pressures, elastic properties of large arteries, the left ventricular structure) and sodium handling parameters (daily urinary sodium excretion, fractional urinary lithium excretion in proximal-FELi and distal tubules), as a function of insulin sensitivity-measured by homeostasis model assessment-insulin resistance (HOMA-IR), leptin-to-adiponectin (L/A) ratio, and homeostasis model assessment-adiponectin (HOMA-AD).

RESULTS

In patients with FELi below the median value (corresponding to the group with increased proximal sodium reabsorption) and higher insulin resistance as measured by HOMA-IR, pulse wave augmentation indexes were significantly higher-AIxP (99.4% vs. 86.2%; P = 0.007), AIxC1 (159.4% vs. 144.2%; P = 0.04), and AIxC2 (36.1% vs. 28.3%; P = 0.02), than in patients with lower insulin resistance. The same trend was observed in relation to L/A ratio-AIxP (98.7% vs. 87.1%; P = 0.005), AIxC1 (158.6% vs. 144.5%; P = 0.02), and AIxC2 (35.6% vs. 28.5%; P = 0.01) and HOMA-AD-AIxP (99.7% vs. 83.8%; P = 0.001), AIxC1 (160.5% vs. 140.3%; P = 0.007), and AIxC2 (36.6% vs. 26.3%; P = 0.003). Such relationships were not observed in patients with FELi above the median value.

CONCLUSIONS

In the hypertensive population with prevailing sodium intake, insulin resistance and increased sodium reabsorption in proximal tubules may affect arterial wall function.

Abnormal sodium and water homeostasis in mice with defective heparan sulfate polymerization

Glycosaminoglycans in the skin interstitium and endothelial surface layer have been shown to be involved in local sodium accumulation without commensurate water retention. Dysfunction of heparan sulfate glycosaminoglycans may therefore disrupt sodium and water homeostasis. In this study, we investigated the effects of combined heterozygous loss of heparan sulfate polymerization genes (exostosin glycosyltransferase 1 and 2; Ext1^+/-Ext2^+/-) on sodium and water homeostasis. Sodium storage capacity was decreased in Ext1^+/-Ext2^+/- mice as reflected by a 77% reduction in endothelial surface layer thickness and a lower skin sodium-to-glycosaminoglycan ratio. Also, these mice were characterized by a higher heart rate, increased fluid intake, increased plasma osmolality and a decreased skin water and sodium content, suggesting volume depletion. Upon chronic high sodium intake, the initial volume depletion was restored but no blood pressure increase was observed. Acute hypertonic saline infusion resulted in a distinct blood pressure response: we observed a significant 15% decrease in control mice whereas blood pressure did not change in Ext1^+/-Ext2^+/- mice. This differential blood pressure response may be explained by the reduced capacity for sodium storage and/or the impaired vasodilation response, as measured by wire myography, which was observed in Ext1^+/-Ext2^+/- mice. Together, these data demonstrate that defective heparan sulfate glycosaminoglycan synthesis leads to abnormal sodium and water homeostasis and an abnormal response to sodium loading, most likely caused by inadequate capacity for local sodium storage.

Body Fluids in End-Stage Renal Disease: Statics and Dynamics

BACKGROUND

Abnormalities in fluid status in hemodialysis (HD) patients are highly prevalent and are related to adverse outcomes.

SUMMARY

The inherent discontinuity of the HD procedure in combination with an often compromised cardiovascular response is a major contributor to this phenomenon. In addition, systemic inflammation and endothelial dysfunction are related to extracellular fluid overload (FO). Underlying this relation may be factors such as hypoalbuminemia and an increased capillary permeability, leading to an altered fluid distribution between the blood volume (BV) and the interstitial fluid compartments, compromising fluid removal during dialysis. Indeed, whereas estimates of extracellular volume by bioimpedance spectroscopy are highly predictive of mortality, absolute BV assessed by the saline dilution technique was predictive of intra-dialytic morbidity. Changes in relative BV during HD are positively related to ultrafiltration rate (UFR) and, at least in some studies, negatively to FO. High UFR is also related to changes in central venous oxygen saturation (ScvO2), a marker for tissue perfusion. On the one hand, high UFR and more pronounced declines in ScvO2, but on the other hand, flat relative BV curves are also predictive of mortality; the relation between outcome which statics and dynamics of fluid status appears to be complex. Key Message: While technological developments enable the clinician to monitor statics and dynamics of fluid status and hemodynamics during HD in an accessible way, the role of technology-based interventions needs further study.