Salt inactivates endothelial nitric oxide synthase in endothelial cells

Spontaneous vascular dysfunction in Dahl salt-sensitive male rats raised without a high-salt diet

Dahl salt-sensitive (SS) rats fed a high-salt diet, but not low-salt, exhibit vascular dysfunction. Several substrains of SS rats exist that differ in their blood pressure phenotypes and salt sensitivity. The goal of this study was to investigate whether the John-Rapp-derived SS rat (SS/Jr), which exhibits spontaneous hypertension on a low-salt diet, presents with hallmarks of vascular dysfunction observed in another experimental model of hypertension independent of dietary salt, the spontaneously hypertensive rat (SHR). Endothelium-intact aortic rings and mesenteric resistance arteries were isolated from low-salt fed adult male SS/Jr rats and SHRs, or their respective controls, for isometric wire myography. Vessels were challenged with cumulative concentrations of various vasoactive substances, in the absence or presence of nitric oxide synthase or cyclooxygenase inhibitors. Despite showing some differences in their responses to various vasoactive substances, both SS/Jr rats and SHRs exhibited key features of vascular dysfunction, including endothelial dysfunction and hyperresponsiveness to vasocontractile agonists. In conclusion, this study provides evidence to support the utility of the SS/Jr rat strain maintained on a low-salt diet as a valid experimental model for vascular dysfunction, a key feature of human hypertension.

High-salt diet augments systolic blood pressure and induces arterial dysfunction in outbred, genetically diverse mice

Excess salt consumption contributes to hypertension and arterial dysfunction in humans living in industrialized societies. However, this arterial phenotype is not typically observed in inbred, genetically identical mouse strains that consume a high-salt (HS) diet. Therefore, we sought to determine the effects of HS diet consumption on systolic blood pressure (BP) and arterial function in UM-HET3 mice, an outbred, genetically diverse strain of mice. Male and female UM-HET3 mice underwent a low-salt [LS (1% NaCl)] or HS (4% NaCl) diet for 12 wk. Systolic BP and aortic stiffness, determined by pulse wave velocity (PWV), were increased in HS after 2 and 4 wk, respectively, compared with baseline and continued to increase through week 12 (P < 0.05). Systolic BP was higher from weeks 2-12 and PWV was higher from weeks 4-12 in HS compared with LS mice (P < 0.05). Aortic collagen content was ∼81% higher in HS compared with LS (P < 0.05), whereas aortic elastin content was similar between groups (P > 0.05). Carotid artery endothelium-dependent dilation (EDD) was ∼10% lower in HS compared with LS (P < 0.05), endothelium-independent dilation was similar between groups (P > 0.05). Finally, there was a strong relationship between systolic BP and PWV (r2 = 0.40, P < 0.05), as well as inverse relationship between EDD and systolic BP (r2 = 0.21, P < 0.05) or PWV (r2 = 0.20, P < 0.05). In summary, HS diet consumption in UM-HET3 mice increases systolic BP, which is accompanied by aortic stiffening and impaired EDD. These data suggest that outbred, genetically diverse mice may provide unique translational insight into arterial adaptations of humans that consume an HS diet.NEW & NOTEWORTHY Excess salt consumption is a contributor to hypertension and arterial dysfunction in humans living in industrialized societies, but this phenotype is not observed in inbred, genetically identical mice that consume a high-salt (HS) diet. This study reveals that a HS diet in outbred, genetically diverse mice progressively increases systolic blood pressure and induce arterial dysfunction. These data suggest that genetically diverse mice may provide translational insight into arterial adaptations in humans that consume an HS diet.

Endothelial dysfunction: developmental mechanisms and therapeutic strategies

Introduction: Every year the importance of the normal functioning of the endothelial layer of the vascular wall in maintaining the health of the body becomes more and more obvious.

The physiological role of the endothelium: The endothelium is a metabolically active organ actively involved in the regulation of hemostasis, modulation of inflammation, maintenance of hemovascular homeostasis, regulation of angiogenesis, vascular tone, and permeability.

Risk factors for the development of endothelial dysfunction: Currently, insufficient bioavailability of nitric oxide is considered the most significant risk factor for endothelial dysfunction.

Mechanisms of development of endothelial dysfunction: The genesis of endothelial dysfunction is a multifactorial process. Among various complex mechanisms, this review examines oxidative stress, inflammation, hyperglycemia, vitamin D deficiency, dyslipidemia, excess visceral fat, hyperhomocysteinemia, hyperuricemia, as well as primary genetic defect of endotheliocytes, as the most common causes in the population underlying the development of endothelial dysfunction.

Markers of endothelial dysfunction in various diseases: This article discusses the main biomarkers of endothelial dysfunction currently used, as well as promising biomarkers in the future for laboratory diagnosis of this pathology.

Therapeutic strategies: Therapeutic approaches to the endothelium in order to prevent or reduce a degree of damage to the vascular wall are briefly described.

Conclusion: Endothelial dysfunction is a typical pathological process involved in the pathogenesis of many diseases. Thus, pharmacological agents with endothelioprotective properties can provide more therapeutic benefits than a drug without such an effect.

Endothelial sodium channel activation mediates DOCA-salt-induced endothelial cell and arterial stiffening

INTRODUCTION

High salt intake and aldosterone are both associated with vascular stiffening in humans. However, our preliminary work showed that high dietary salt alone did not increase endothelial cell (EC) or vascular stiffness or endothelial sodium channel (EnNaC) activation in mice, presumably because aldosterone production was significantly suppressed as a result of the high salt diet. We thus hypothesized that high salt consumption along with an exogenous mineralocorticoid would substantially increase EC and vascular stiffness via activation of the EnNaC.

METHODS AND RESULTS

Mice were implanted with slow-release DOCA pellets and given salt in their drinking water for 21 days. Mice with either specific deletion of the alpha subunit of EnNaC or treated with a pharmacological inhibitor of mTOR, a downstream signaling molecule involved in mineralocorticoid receptor activation of EnNaC, were studied. DOCA-salt treated control mice had increased blood pressure, EC Na⁺ transport activity, EC and arterial stiffness, which were attenuated in both the αEnNaC^-/- and mTOR inhibitor treated groups. Further, depletion of αEnNaC prevented DOCA-salt-induced impairment in EC-dependent vascular relaxation.

CONCLUSION

While high salt consumption alone does not cause EC or vascular stiffening, the combination of EC MR activation and high salt causes activation of EnNaC which increases EC and arterial stiffness and impairs vascular relaxation. Underlying mechanisms appear to include mTOR signaling.

Sodium Intake as a Cardiovascular Risk Factor: A Narrative Review

While sodium is essential for human homeostasis, current salt consumption far exceeds physiological needs. Strong evidence suggests a direct causal relationship between sodium intake and blood pressure (BP) and a modest reduction in salt consumption is associated with a meaningful reduction in BP in hypertensive as well as normotensive individuals. Moreover, while long-term randomized controlled trials are still lacking, it is reasonable to assume a direct relationship between sodium intake and cardiovascular outcomes. However, a consensus has yet to be reached on the effectiveness, safety and feasibility of sodium intake reduction on an individual level. Beyond indirect BP-mediated effects, detrimental consequences of high sodium intake are manifold and pathways involving vascular damage, oxidative stress, hormonal alterations, the immune system and the gut microbiome have been described. Globally, while individual response to salt intake is variable, sodium should be perceived as a cardiovascular risk factor when consumed in excess. Reduction of sodium intake on a population level thus presents a potential strategy to reduce the burden of cardiovascular disease worldwide. In this review, we provide an update on the consequences of salt intake on human health, focusing on BP and cardiovascular outcomes as well as underlying pathophysiological hypotheses.

Endogenous Taurine Downregulation Is Required for Renal Injury in Salt-Sensitive Hypertensive Rats via CBS/H2S Inhibition

Although taurine is known to exert an antihypertensive effect, it is unclear whether it is involved in the mechanism for hypertension-related target organ injury. To reveal the role of endogenous taurine in renal injury formation during salt-sensitive hypertension and clarify its mechanisms, both salt-sensitive Dahl rats and salt-resistant SS-13BN rats were fed a high-salt diet (8% NaCl) and given 2% taurine for 6 weeks. Rat systolic blood pressure (SBP) was measured by the tail-cuff method and artery catheterization. Kidney ultrastructure was observed under an electron microscope. Taurine content and mRNA and protein levels of taurine synthases, cysteine dioxygenase type 1 (CDO1) and cysteine sulfinic acid decarboxylase (CSAD), were decreased in Dahl rats fed a high-salt diet. However, taurine supplementation and the resulting increase in renal taurine content reduced the increased SBP and improved renal function and structural damage in high-salt diet-fed Dahl rats. In contrast, taurine did not affect SS-13BN SBP and renal function and structure. Taurine intervention increased the renal H₂S content and enhanced cystathionine-β-synthase (CBS) expression and activity in Dahl rats fed a high-salt diet. Taurine reduced the renin, angiotensin II, and aldosterone contents and the levels of oxidative stress indices in Dahl rat renal tissues but increased antioxidant capacity, antioxidant enzyme activity, and protein expression. However, taurine failed to achieve this effect in the renal tissue of SS-13BN rats fed a high-salt diet. Pretreatment with the CBS inhibitor HA or renal CBS knockdown inhibited H₂S generation and subsequently blocked the effect of taurine on renin, superoxide dismutase 1 (SOD1), and superoxide dismutase 2 (SOD2) levels in high-salt-stimulated Dahl renal slices. In conclusion, the downregulation of endogenous taurine production resulted in a decrease in the renal CBS/H₂S pathway. This decrease subsequently promoted renin-angiotensin-aldosterone system (RAAS) activation and oxidative stress in the kidney, ultimately contributing to renal injury in salt-sensitive Dahl rats.

High Na+ Salt Diet and Remodeling of Vascular Smooth Muscle and Endothelial Cells

Our knowledge on essential hypertension is vast, and its treatment is well known. Not all hypertensives are salt-sensitive. The available evidence suggests that even normotensive individuals are at high cardiovascular risk and lower survival rate, as blood pressure eventually rises later in life with a high salt diet. In addition, little is known about high sodium (Na⁺) salt diet-sensitive hypertension. There is no doubt that direct and indirect Na⁺ transporters, such as the Na/Ca exchanger and the Na/H exchanger, and the Na/K pump could be implicated in the development of high salt-induced hypertension in humans. These mechanisms could be involved following the destruction of the cell membrane glycocalyx and changes in vascular endothelial and smooth muscle cells membranes’ permeability and osmolarity. Thus, it is vital to determine the membrane and intracellular mechanisms implicated in this type of hypertension and its treatment.

Detrimental or beneficial: Role of endothelial ENaC in vascular function

In the past, it was believed that the expression of the epithelial sodium channel (ENaC) was restricted to epithelial tissues, such as the distal nephron, airway, sweat glands, and colon, where it is critical for sodium homeostasis. Over the past two decades, this paradigm has shifted due to the finding that ENaC is also expressed in various nonepithelial tissues, notably in vascular endothelial cells. In this review, the recent findings of the expression, regulation, and function of the endothelial ENaC (EnNaC) are discussed. The expression of EnNaC subunits is reported in a variety of endothelial cell lines and vasculatures, but this is controversial across different species and vessels and is not a universal finding in all vascular beds. The expression density of EnNaC is very faint compared to ENaC in the epithelium. To date, little is known about the regulatory mechanism of EnNaC. Through it can be regulated by aldosterone, the detailed downstream signaling remains elusive. EnNaC responds to increased extracellular sodium with the feedforward activation mechanism, which is quite different from the Na⁺ self-inhibition mechanism of ENaC. Functionally, EnNaC was shown to be a determinant of cellular mechanics and vascular tone as it can sense shear stress, and its activation or insertion into plasma membrane causes endothelial stiffness and reduced nitric oxide production. However, in some blood vessels, EnNaC is essential for maintaining the integrity of endothelial barrier function. In this context, we discuss the possible reasons for the distinct role of EnNaC in vasculatures.

A Low-Sodium Diet Boosts Ang (1-7) Production and NO-cGMP Bioavailability to Reduce Edema and Enhance Survival in Experimental Heart Failure

Sodium restriction is often recommended in heart failure (HF) to block symptomatic edema, despite limited evidence for benefit. However, a low-sodium diet (LSD) activates the classical renin-angiotensin-aldosterone system (RAAS), which may adversely affect HF progression and mortality in patients with dilated cardiomyopathy (DCM). We performed a randomized, blinded pre-clinical trial to compare the effects of a normal (human-equivalent) sodium diet and a LSD on HF progression in a normotensive model of DCM in mice that has translational relevance to human HF. The LSD reduced HF progression by suppressing the development of pleural effusions (p < 0.01), blocking pathological increases in systemic extracellular water (p < 0.001) and prolonging median survival (15%, p < 0.01). The LSD activated the classical RAAS by increasing plasma renin activity, angiotensin II and aldosterone levels. However, the LSD also significantly up-elevated the counter-regulatory RAAS by boosting plasma angiotensin converting enzyme 2 (ACE2) and angiotensin (1-7) levels, promoting nitric oxide bioavailability and stimulating 3'-5'-cyclic guanosine monophosphate (cGMP) production. Plasma HF biomarkers associated with poor outcomes, such as B-type natriuretic peptide and neprilysin were decreased by a LSD. Cardiac systolic function, blood pressure and renal function were not affected. Although a LSD activates the classical RAAS system, we conclude that the LSD delayed HF progression and mortality in experimental DCM, in part through protective stimulation of the counter-regulatory RAAS to increase plasma ACE2 and angiotensin (1-7) levels, nitric oxide bioavailability and cGMP production.

Non-pharmacologic management of orthostatic hypotension

Orthostatic hypotension (OH), a debilitating disorder characterized by a drop in blood pressure when in the upright position, may be treated through several pharmacologic and lifestyle modifications. The treatment is aimed at decreasing the symptoms, mainly the falls, increase the standing time, and improve the activities of daily life. A recent expert consensus outlined the management of orthostatic hypotension and included 4 sequential steps: 1) review medications and modify or remove those that may aggravate or cause OH; 2) non-pharmacologic measures; 3) pharmacologic measures and 4) treatment combinations. The aim of this manuscript is to review the non-pharmacological approach. In milder cases, this approach may suffice, but with more severe symptoms, such as falls, syncope or near-syncope, a pharmacological strategy is simultaneously employed. Furthermore, most non-pharmacological measures are combined. The non-pharmacological approach is aimed at optimizing blood volume, decreasing postural venous pooling, reducing heat and post-prandial induced vasodilation, emphasizing physical conditioning, and minimizing nocturnal diuresis.

An acute rise of plasma Na+ concentration associates with syndecan-1 shedding during hemodialysis

Endothelial dysfunction (ED) contributes to the high incidence of cardiovascular events in patients undergoing hemodialysis. Syndecan-1 in the endothelial glycocalyx can be shed into the circulation, serving as a biomarker for ED. As Na+ is a trigger for glycocalyx shedding, we now tested whether hemodialysis, with higher dialysate Na+ concentrations, is associated with more syndecan-1 shedding compared with standard hemodialysis (SHD). In this crossover study in 29 patients, plasma syndecan-1 was repeatedly measured during SHD and during Hemocontrol hemodialysis (HHD), which is characterized by initially higher dialysate and plasma Na+ levels. Courses of syndecan-1 were compared with linear mixed models. Syndecan-1 shedding was assessed by area under the curve analysis. Plasma Na+ increased early after the start of SHD and HHD, with higher values during HHD (30 min: 142.3 vs. 139.9 mM, P < 0.001). Syndecan-1 increased significantly during both conditions, but the percent change was higher (42.9% vs. 19.5%) and occurred earlier (120 vs. 180 min) during HHD. Syndecan-1 levels were significantly higher at 120 min during HHD compared with SHD ( P < 0.05). Overall, syndecan-1 shedding was higher during HHD compared with SHD (means: 40.4 vs. 19.0 arbitrary units, P = 0.06). Lower predialysis plasma Na+ and osmolality were associated with greater intradialytic increases in syndecan-1 levels (both groups, P = 0.001). The rise in plasma syndecan-1 levels was more pronounced and occurred earlier during hemodialysis with higher plasma Na+ levels. Although we cannot prove that the rise in plasma syndecan-1 originates from the endothelial glycocalyx, our findings are compatible with Na+-driven endothelial glycocalyx-derived syndecan-1 shedding.

The effect of uric acid and urinary sodium excretion on prehypertension: a nationwide population-based study

Background

This study examined the effect of serum uric acid (SUA) level and urinary sodium excretion on blood pressure as well as their combined effect on prehypertension in a Korean population.

Method

Data from the 7th Korea National Health and Nutrition Examination Survey for adults (≥ 19 years of age) were used. The participants were classified into two groups, normotension and prehypertension, according to the JNC-7 definition. Logistic regression was carried out and adjusted for traditionally regarded confounders of blood pressure. All analyses considered a complex sampling design. A multivariate analysis was performed on subgroups defined according to their SUA level and urinary sodium excretion.

Results

The 4200 participants were divided into normotension (n = 2646) and prehypertension (n = 1554) groups. In the univariate analysis, patient age, male sex, concurrent comorbidity (diabetes mellitus, cardiovascular disease, stroke, dyslipidemia, and chronic kidney disease), uric acid, and urinary sodium excretion were associated with prehypertension. After adjusting for baseline covariates, both the SUA level and urinary sodium excretion were significant predictors of incident prehypertension (SUA, per 1 mg/dL increase, odds ratio [OR] 1.216, 95% confidence interval [95% CI] 1.131–1.309; urinary sodium excretion, per 1 g/day increase, OR 1.067, 95% CI 1.019–1.117). Additionally, simultaneously higher tertiles of SUA and urinary sodium excretion resulted in higher ORs for prehypertension.

Conclusion

Increased SUA is a significant risk marker for the development of prehypertension in normotensives. Simultaneously high SUA and urinary sodium excretion amplified the effect on the development of prehypertension. Our findings suggest that lowering SUA levels and reducing sodium intake will contribute to preventing hypertension.

Excessive dietary salt promotes aortic stiffness in murine renovascular hypertension

Renovascular hypertension is characterized by activation of the renin-angiotensin-aldosterone system, blunted natriuretic responses, and elevated sympathetic nerve activity. Excess dietary salt intake exaggerates arterial blood pressure (ABP) in multiple models of experimental hypertension. The present study tested whether a high-salt diet exaggerated ABP and vascular dysfunction in a 2-kidney, 1-clip (2K1C) murine model. Male C57BL/6J mice (8-12 wk) were randomly assigned, and fed a 0.1% or 4.0% NaCl diet, and instrumented with telemetry units to measure ABP. Then, the 2K1C model was produced by placing a cuff around the right renal artery. Systolic, diastolic, and mean ABP were significantly higher in mice fed 4.0% vs. 0.1% NaCl at 1 wk but not after 3 wk. Interestingly, 2K1C hypertension progressively increased arterial pulse pressure in both groups; however, the magnitude was significantly greater in mice fed 4.0% vs. 0.1% NaCl at 3 wk. Moreover, pulse wave velocity was significantly greater in 2K1C mice fed 4.0% vs. 0.1% NaCl diet or sham-operated mice fed either diet. Histological assessment of aortas indicated no structural differences among groups. Finally, endothelium-dependent vasodilation was significantly and selectively attenuated in the aorta but not mesenteric arteries of 2K1C mice fed 4.0% NaCl vs. 0.1% NaCl or sham-operated control mice. The findings suggest that dietary salt loading transiently exaggerates 2K1C renovascular hypertension but promotes chronic aortic stiffness and selective aortic vascular dysfunction.NEW & NOTEWORTHY High dietary salt exaggerates hypertension in multiple experimental models. Here we demonstrate that a high-salt diet produces a greater increase in arterial blood pressure at 1 wk after induction of 2-kidney, 1-clip (2K1C) hypertension but not at 3 wk. Interestingly, 2K1C mice fed a high-salt diet displayed an exaggerated pulse pressure, elevated pulse wave velocity, and reduced endothelium-dependent vasodilation of the aorta but not mesenteric arteries. These findings suggest that dietary salt may interact with underlying cardiovascular disease to promote selective vascular dysfunction and aortic stiffness.

Food Products That May Cause an Increase in Blood Pressure

PURPOSE OF REVIEW

To review latest reports of the food products which might increase blood pressure and therefore might participate in the pathogenesis of hypertension.

RECENT FINDINGS

Results of clinical study suggest that consumption of high-sodium food leads to transient increase in plasma sodium concentration. This is accompanied by blood pressure increase. Results of both clinical and experimental studies suggest direct vasculotoxic effects of sodium. Increased plasma sodium concentration could mediate its effects on blood pressure by changes in endothelial cell stiffness and glycocalyx integrity. Energy drinks are non-alcoholic beverages with increasing popularity. Clinical, interventional, randomized, placebo controlled, and cross-sectional studies showed that energy drinks may increase arterial blood pressure. Blood pressure increase after exposure for the energy drinks is mainly related to the caffeine content in these drinks. Many case reports were published concerning the clinically significant increase in blood pressure caused by the consumption of liquorice root or food products containing liquorice, such as candies, tea, Pontefract cookies, and chewing gum. Liquorice contains a precursor of glycyrrhetic acid. Glycyrrhetic acid reduces the activity of the 11β-hydroxysteroid dehydrogenase type 2 (11ß-HSD2) isoenzyme, which leads to activation of the mineralocorticoid receptor by cortisol in the distal convoluted tubule resulting in hypertension, hypokalemia, and metabolic alkalosis. The relationship between chronic alcohol intake and blood pressure is well established on the basis of a diverse body of evidence including animal experiments, epidemiological studies, mendelian randomization studies, and interventional studies. Results of recent studies suggested that binge drinking (i.e., episodic consumption of a very high amount of alcohol beverages) has pronounced hypertensinogenic effects. Recently, it was documented that also low doses of alcohol may increase the risk of cardiovascular complications. Therefore, the amount of alcohol consumption that is safe is zero. High-salt food products, energy drinks, food products containing liquorice, and alcoholic beverages have hypertensinogenic properties. Patients with hypertension and other cardiovascular diseases should avoid even accidental consumption of these food products.

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.

Hyponatremia Is Protective Against the Development of Portal Vein Thrombosis in Patients Undergoing Liver Transplant

BACKGROUND

Both hyponatremia and portal vein thrombosis (PVT) reflect the severity of liver dysfunction and are independently associated with increased morbidity in cirrhotic patients. In this study, we analyzed effects of hyponatremia on PVT development.

METHODS

Data on adult liver transplants (LTs) in the Model for End-Stage Liver Disease era through September 2016 were obtained. Receiver operating curves and multivariable logistic regression models were constructed to evaluate the association between serum sodium level and PVT. Based on the receiver operating curves, hyponatremia was defined as a sodium level below 125 mEq/L.

RESULTS

Of the 49,155 recipients included, 16% had hyponatremia (n = 7828) and 9% had PVT (n = 4414) at transplant. Subjects with hyponatremia had lower rates of PVT at the time of LT (4.4% vs 10.1%, P < .001), incidence of nonalcoholic steatohepatitis (10.8% vs 16.5%, P < .001), diabetes (19.7% vs 24.3%, P < .001), and need for dialysis (8.8% vs 16.0%, P < .001) as well as higher rates of chronic hepatitis C and B (37.6% vs 29.1%, P < .001 and 2.9% vs 1.7%, P < .001). Multivariable regression analysis confirmed that hyponatremia was independently associated with a decreased likelihood of PVT (odds ratio [OR], 0.44, P < .001). African American patients had a lower incidence of PVT (OR, 0.70; P < .001). Variables associated with a higher incidence of PVT were: nonalcoholic steatohepatitis (OR, 1.15; P = .005), moderate-to-severe ascites (OR, 1.10; P = .008), and Hispanic ethnicity (OR, 1.2; P < .001).

CONCLUSION

Hyponatremia is associated with a lower rate of PVT independent of severity of liver disease and other thrombotic risk factors. This protective effect should be taken into consideration during the perioperative management of hyponatremia in patients undergoing LT.

Serum Sodium and Pulse Pressure in SPRINT

BACKGROUND

High dietary sodium intake may induce a small, yet physiologically relevant rise in serum sodium concentration, which associates with increased systolic blood pressure. Cellular data suggest that this association is mediated by increased endothelial cell stiffness. We hypothesized that higher serum sodium levels were associated with greater arterial stiffness in participants in the Systolic Blood Pressure Intervention Trial (SPRINT).

METHODS

Multivariable linear regression was used to examine the association between baseline serum sodium level and (i) pulse pressure (PP; n = 8,813; a surrogate measure of arterial stiffness) and (ii) carotid-femoral pulse wave velocity (CFPWV; n = 591 in an ancillary study to SPRINT).

RESULTS

Baseline mean ± SD age was 68 ± 9 years and serum sodium level was 140 ± 2 mmol/L. In the PP analysis, higher serum sodium was associated with increased baseline PP in the fully adjusted model (tertile 3 [≥141 mmol] vs. tertile 2 [139-140 mmol]; β = 0.87, 95% CI = 0.32 to 1.43). Results were similar in those with and without chronic kidney disease. In the ancillary study, higher baseline serum sodium was not associated with increased baseline CFPWV in the fully adjusted model (β = 0.35, 95% CI = -0.14 to 0.84).

CONCLUSIONS

Among adults at high risk for cardiovascular events but free from diabetes, higher serum sodium was independently associated with baseline arterial stiffness in SPRINT, as measured by PP, but not by CFPWV. These results suggest that high serum sodium may be a marker of risk for increased PP, a surrogate index of arterial stiffness.

Endothelial Nanomechanics in the Context of Endothelial (Dys)function and Inflammation

SIGNIFICANCE

Stiffness of endothelial cells is closely linked to the function of the vasculature as it regulates the release of vasoactive substances such as nitric oxide (NO) and reactive oxygen species. The outer layer of endothelial cells, consisting of the glycocalyx above and the cortical zone beneath the plasma membrane, is a vulnerable compartment able to adapt its nanomechanical properties to any changes of forces exerted by the adjacent blood stream. Sustained stiffening of this layer contributes to the development of endothelial dysfunction and vascular pathologies. Recent Advances: The development of specific techniques to quantify the mechanical properties of cells enables the detailed investigation of the mechanistic link between structure and function of cells.

CRITICAL ISSUES

Challenging the mechanical stiffness of cells, for instance, by inflammatory mediators can lead to the development of endothelial dysfunction. Prevention of sustained stiffening of the outer layer of endothelial cells in turn improves endothelial function.

FUTURE DIRECTIONS

The mechanical properties of cells can be used as critical marker and test system for the proper function of the vascular system. Pharmacological substances, which are able to improve endothelial nanomechanics and function, could take a new importance in the prevention and treatment of vascular diseases. Thus, detailed knowledge acquisition about the structure/function relationship of endothelial cells and the underlying signaling pathways should be promoted.

Antihypertensive effect of the methanolic extract from Eruca sativa Mill., (Brassicaceae) in rats: Muscarinic receptor-linked vasorelaxant and cardiotonic effects

ETHNOPHARMACOLOGICAL RELEVANCE

Eruca sativa Mill., (Brassicaceae) is a popular remedy for the treatment of hypertension in Pakistan. However, direct effect of the extract and its fractions on blood pressure and vascular tone are unknown.

AIM OF THE STUDY

This investigation was aimed to explore the pharmacological base for the traditional use of E. sativa in hypertension.

MATERIALS AND METHODS

In-vivo blood pressure study was carried out using normotensive and high salt-induced hypertensive rats under anaesthesia. The cardiovascular mechanisms were explored using rat aorta and atria in-vitro. Preliminary phytochemical analysis, spectrophotometric detection of total phenols, flavonoids and HPLC analysis of crude extract were performed using quercetin and erucin as marker compounds.

RESULTS

Intravenous injection of crude extract induced a fall in mean arterial pressure (MAP) in both normotensive (max fall: 41.79 ± 1.55% mmHg) and hypertensive (max fall: 58.25 ± 0.91% mmHg) rats. Atropine (1 mg/kg) pretreatment attenuated this effect significantly (p < 0.001), suggesting the involvement of muscarinic receptor in its antihypertensive effect. Fractions also induced atropine-sensitive antihypertensive effect. Similarly, oral administration of crude and aqueous extracts resulted a fall in MAP in the hypertensive rats. In isolated rat aortic rings from normotensive rats, crude extract and fractions induced an endothelium-dependent relaxation. This relaxation was partially inhibited with _L-NAME and atropine pretreatment and with denudation of aortic rings, indicating involvement of muscarinic receptor-linked nitric oxide (NO). In aorta from the hypertensive rats, crude extract and fractions induced endothelium-independent relaxation. This relaxation was not affected by pretreatment with _L-NAME or atropine. Crude extract and fractions also suppressed phenylephrine contractions in Ca⁺² free/EGTA medium. In isolated rat atrial preparations, crude extract and fractions induced negative inotropic and chronotropic effects with a positive inotropic effect by the n-hexane fraction, which were not affected with atropine pretreatment. Phytochemical screening and spectrophotometric analysis indicated the presence of phenols and flavonoids, whereas HPLC analysis of crude extract revealed the presence of quercetin (flavonoid) and erucin (isothiocyanate).

CONCLUSION

The results suggest that E. sativa is an antihypertensive remedy which is mainly due to its vasodilatory and partly cardiac effects. Muscarinic receptors-linked NO release and dual inhibitory effect on Ca⁺² influx and release underlie the vasodilation. This finding provides pharmacological base to the traditional use of E. sativa in hypertension. The presence of quercetin and erucin further support this finding.

Effect of plasma sodium concentration on blood pressure regulators during hemodialysis: a randomized crossover study

Background

Intradialytic hypotension is a common complication of hemodialysis. The Hemocontrol biofeedback system, improving intradialytic hemodynamic stability, is associated with an initial transient increase in plasma sodium levels. Increases in sodium could affect blood pressure regulators.

Methods

We investigated whether Hemocontrol dialysis affects vasopressin and copeptin levels, endothelial function, and sympathetic activity in twenty-nine chronic hemodialysis patients. Each patient underwent one standard hemodialysis and one Hemocontrol hemodialysis. Plasma sodium, osmolality, nitrite and nitrate (NOx), endothelin-1, angiopoietins-1 and 2, and methemoglobin as measures of endothelial function, plasma catecholamines as indices of sympathetic activity and plasma vasopressin and copeptin levels were measured six times during each modality. Blood pressure, heart rate, blood volume, and heart rate variability were repeatedly monitored. Generalized Estimating Equations was used to compare the course of the parameters during the two treatment modalities.

Results

Plasma sodium and osmolality were significantly higher during the first two hours of Hemocontrol hemodialysis. Overall, mean arterial pressure (MAP) was higher during Hemocontrol dialysis. Neither the measures of endothelial function and sympathetic activity nor copeptin levels differed between the two dialysis modalities. In contrast, plasma vasopressin levels were significantly higher during the first half of Hemocontrol dialysis. The intradialytic course of vasopressin was associated with the course of MAP.

Conclusions

A transient intradialytic increase in plasma sodium did not affect indices of endothelial function or sympathetic activity compared with standard hemodialysis, but coincided with higher plasma vasopressin levels. The beneficial effect of higher intradialytic sodium levels on hemodynamic stability might be mediated by vasopressin.

Trial registration

ClinicalTrials.gov. Identifier: NCT03578510. Date of registration: July 5th, 2018. Retrospectively registered.

Postulating the major environmental condition resulting in the expression of essential hypertension and its associated cardiovascular diseases: Dietary imprudence in daily selection of foods in respect of their potassium and sodium content resulting in oxidative stress-induced dysfunction of the vascular endothelium, vascular smooth muscle, and perivascular tissues

We hypothesize that the major environmental determinant of the expression of essential hypertension in America and other Westernized countries is dietary imprudence in respect of the consumption of daily combinations of foods containing suboptimal amounts of potassium and blood pressure-lowering phytochemicals, and supraphysiological amounts of sodium. We offer as premise that Americans on average consume suboptimal amounts of potassium and blood pressure-lowering phytochemicals, and physiologically excessive amounts of sodium, and that such dietary imprudence leads to essential hypertension through oxidative stress-induced vascular endothelial and smooth muscle dysfunction. Such dysfunctions restrict nitric oxide bioavailability, impairing endothelial cell-mediated relaxation of the underlying vascular smooth muscle, initiating and maintaining inappropriately increased peripheral and renal vascular resistance. The biochemical steps from oxidative stress to vascular endothelial dysfunction and its pernicious cardiovascular consequences are well established and generally accepted. The unique aspect of our hypothesis resides in the contention that Americans' habitual consumption of foods resulting in suboptimal dietary intake of potassium and supraphysiological intake of sodium result in oxidative stress, the degree of which, we suggest, will correlate with the degree of deviation of potassium and sodium intake from optimal. Because suboptimal intakes of potassium reflect suboptimal intakes of fruits and vegetables, associated contributors to oxidative stress include suboptimal intakes of magnesium, nitrate, polyphenols, carotenoids, and other phytochemical antioxidants for which fruits and vegetables contain abundant amounts. Currently Americans consume potassium-to-sodium in molar ratios of less than or close to 1.0 and the Institute of Medicine (IOM) recommends a molar ratio of 1.2. Ancestral diets to which we are physiologically adapted range from molar ratios of 5.0 to 10.0 or higher. Accordingly, we suggest that the average American is usually afflicted with oxidative stress-induced vascular endothelial dysfunction, and therefore the standards for normal blood pressure and pre-hypertension often reflect a degree of clinically significant hypertension. In this article, we provide support for those contentions, and indicate the findings that the hypothesis predicts.

Association between urinary sodium excretion and uric acid, and its interaction on the risk of prehypertension among Chinese young adults

High uric acid (UA) level and high salt intake are reportedly associated with cardiovascular disease. This study investigated the association between UA and urinary sodium excretion, as well as its interaction on the risk of prehypertension. A total of 1869 participants without hypertension were recruited from a previously established cohort in Shaanxi Province, China. The participants were classified as normotensive or prehypertensive on the basis of their blood pressure. Increasing quartiles of sodium excretion were associated with high urinary UA/creatinine levels in prehypertensive participants. Estimated sodium excretion positively correlated with urinary UA/creatinine excretions in the prehypertensive group. In addition, the multivariate-adjusted odds ratios for prehypertension compared with normotension were 1.68 (1.27–2.22) for sodium excretion and 1.71 (1.21–2.42) for serum UA. Increasing sodium excretion and serum UA were associated with higher risk of prehypertension. Compared with the lowest quartiles, the highest sodium excretion and serum UA quartiles entailed 3.48 times greater risk of prehypertension. Sodium excretion is associated with urinary UA excretion in prehypertensive participants. The present study shows that high levels of salt intake and serum UA simultaneously are associated with a higher risk of prehypertension.

Effect of Salt Intake on Plasma and Urinary Uric Acid Levels in Chinese Adults: An Interventional Trial

Uric acid (UA) has been proposed as an important risk factor for cardiovascular and renal morbidity. We conducted an interventional trial to assess effects of altered salt intake on plasma and urine UA levels and the relationship between UA levels and salt sensitivity in humans. Ninety subjects (18–65 years old) were sequentially maintained on a normal diet for 3 days at baseline, a low-salt diet for 7 days (3.0 g/day, NaCl), and a high-salt diet for an additional 7 days (18.0 g/day of NaCl). Plasma UA levels significantly increased from baseline to low-salt diet and decreased from low-salt to high-salt diet. By contrast, daily urinary levels of UA significantly decreased from baseline to low-salt diet and increased from low-salt to high-salt diet. The 24 h urinary sodium excretions showed inverse correlation with plasma UA and positive correlation with urinary UA excretions. Additionally, salt-sensitive subjects presented significantly higher plasma UA changes in comparison to salt-resistant subjects, and a negative correlation was observed between degree of salt sensitivity and plasma UA difference. The present study indicates that variations in dietary salt intake affect plasma and urine UA levels, and plasma UA may be involved in pathophysiological process of salt sensitivity.

Dietary salt blunts vasodilation by stimulating epithelial sodium channels in endothelial cells from salt-sensitive Dahl rats

BACKGROUND AND PURPOSE

Our recent studies show that the reduced activity of epithelial sodium channels (ENaC) in endothelial cells accounts for the adaptation of vasculature to salt in Sprague-Dawley rats. The present study examines a hypothesis that enhanced ENaC activity mediates the loss of vasorelaxation in Dahl salt-sensitive (SS) rats.

EXPERIMENTAL APPROACH

We used the cell-attached patch-clamp technique to record ENaC activity in split-open mesenteric arteries. Western blot and immunofluorescence staining were used to evaluate the levels of aldosterone, ENaC, eNOS and NO. Blood pressure was measured with the tail-cuff method and the artery relaxation was measured with the wire myograph assay.

KEY RESULTS

High-salt (HS) diet significantly increased plasma aldosterone and ENaC activity in the endothelial cells of Dahl SS rats. The endothelium-dependent artery relaxation was blunted by HS challenge in these rats. Amiloride, a potent blocker of ENaC, increased both phosphorylated eNOS and NO and therefore prevented the HS-induced loss of vasorelaxation. As, in SS rats, endogenous aldosterone was already elevated by HS challenge, exogenous aldosterone did not further elevate ENaC activity in the rats fed with HS. Eplerenone, a mineralocorticoid receptor antagonist, attenuated the effects of HS on both ENaC activity and artery relaxation.

CONCLUSIONS AND IMPLICATIONS

These data suggest that HS diet blunts artery relaxation and causes hypertension via a pathway associated with aldosterone-dependent activation of ENaC in endothelial cells. This pathway provides one of the mechanisms by which HS causes hypertension in Dahl SS rats.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

The Effect of Salt Intake and Potassium Supplementation on Serum Gastrin Levels in Chinese Adults: A Randomized Trial

Excess dietary salt is strongly correlated with cardiovascular disease, morbidity, and mortality. Conversely, potassium likely elicits favorable effects against cardiovascular disorders. Gastrin, which is produced by the G-cells of the stomach and duodenum, can increase renal sodium excretion and regulate blood pressure by acting on the cholecystokinin B receptor. The aim of our study was to assess the effects of altered salt and potassium supplementation on serum gastrin levels in humans. A total of 44 subjects (38–65 years old) were selected from a rural community in northern China. All subjects were sequentially maintained on a relatively low-salt diet for 7 days (3.0 g/day of NaCl), a high-salt diet for 7 days (18.0 g/day of NaCl), and then a high-salt diet supplemented with potassium for another 7 days (18.0 g/day of NaCl + 4.5 g/day of KCl). The high-salt intake significantly increased serum gastrin levels (15.3 ± 0.3 vs. 17.6 ± 0.3 pmol/L). This phenomenon was alleviated through potassium supplementation (17.6 ± 0.3 vs. 16.5 ± 0.4 pmol/L). Further analyses revealed that serum gastrin was positively correlated with 24 h urinary sodium excretion (r = 0.476, p < 0.001). By contrast, gastrin level was negatively correlated with blood pressure in all dietary interventions (r = −0.188, p = 0.031). The present study indicated that variations in dietary salt and potassium supplementation affected the serum gastrin concentrations in the Chinese subjects.

Sodium and Its Role in Cardiovascular Disease - The Debate Continues

Guidelines have recommended significant reductions in dietary sodium intake to improve cardiovascular health. However, these dietary sodium intake recommendations have been questioned as emerging evidence has shown that there is a higher risk of cardiovascular disease with a low sodium diet, including in individuals with type 2 diabetes. This may be related to the other pleotropic effects of dietary sodium intake. Therefore, despite recent review of dietary sodium intake guidelines by multiple organizations, including the dietary guidelines for Americans, American Diabetes Association, and American Heart Association, concerns about the impact of the degree of sodium restriction on cardiovascular health continue to be raised. This literature review examines the effects of dietary sodium intake on factors contributing to cardiovascular health, including left ventricular hypertrophy, heart rate, albuminuria, rennin-angiotensin-aldosterone system activation, serum lipids, insulin sensitivity, sympathetic nervous system activation, endothelial function, and immune function. In the last part of this review, the association between dietary sodium intake and cardiovascular outcomes, especially in individuals with diabetes, is explored. Given the increased risk of cardiovascular disease in individuals with diabetes and the increasing incidence of diabetes worldwide, this review is important in summarizing the recent evidence regarding the effects of dietary sodium intake on cardiovascular health, especially in this population.

Involvement of systemic venous congestion in heart failure

Systemic venous congestion has gained significant importance in the interpretation of the pathophysiology of acute heart failure, especially in the development of renal function impairment during exacerbations. In this study, we review the concept, clinical characterisation and identification of venous congestion. We update current knowledge on its importance in the pathophysiology of acute heart failure and its involvement in the prognosis. We pay special attention to the relationship between abdominal congestion, the pulmonary interstitium as filtering membrane, inflammatory phenomena and renal function impairment in acute heart failure. Lastly, we review decongestion as a new therapeutic objective and the measures available for its assessment.

Effects of Salt Loading on Plasma Osteoprotegerin Levels and Protective Role of Potassium Supplement in Normotensive Subjects

BACKGROUND

Excess dietary salt is strongly correlated with cardiovascular disease, morbidity, and mortality. Conversely, potassium likely elicits favorable effects on cardiovascular disorders. In epidemiological studies, increased plasma osteoprotegerin (OPG) concentrations are associated with atherosclerosis and vascular deaths. Our study was designed to examine the effects of salt intake and potassium supplementation on plasma OPG levels in normotensive subjects.Methods and Results:The 18 normotensive subjects were selected from a rural community in China. They were sequentially maintained on low-salt diet for 7 days (3 g/day, NaCl), high-salt diet for 7 days (18 g/day), and high-salt diet with potassium supplementation for 7 days (18 g/day of NaCl+4.5 g/day of KCl). High-salt intake enhanced plasma OPG levels (252.7±13.9 vs. 293.4±16.1 pg/mL). This phenomenon was abolished through potassium supplementation (293.4±16.1 vs. 235.1±11.3 pg/mL). Further analyses revealed that the OPG concentration positively correlated with 24-h urinary sodium excretion (r=0.497, P<0.01). By contrast, OPG concentration negatively correlated with 24-h urinary potassium excretion (r=0.594, P<0.01).

CONCLUSIONS

Salt loading can enhance the production of circulating OPG. Potassium supplementation can reverse the effects of excessive OPG. Our study results may improve our understanding of the roles of salt and potassium in the risk of cardiovascular disorders.

Mechanotransduction of the endothelial glycocalyx mediates nitric oxide production through activation of TRP channels

The endothelial surface glycocalyx (ESG) is a carbohydrate-rich layer found on the vascular endothelium, serving critical functions in the mechanotransduction of blood flow-induced forces. One of the most important protective functions of the ESG is to mediate the production of nitric oxide (NO) in response to blood flow. However, the detailed mechanism underlying ESG's mechanotransduction of the production of NO has not been completely identified. Herein, using the cultured rat brain microvascular endothelial cells (bEnd.3) as a model system, we have implemented a combined atomic force and fluorescence microscopy approach to show that the ESG senses and transduces vertical mechanical stretch to produce NO. This rapid NO production is dependent on the presence of both heparan sulfate (HS) and hyaluronic acid (HA) in ESG, as the removal of HS and/or HA leads to a significant decrease in NO production. Moreover, the production of NO is dependent on the intake of Ca²⁺ via endothelial transient receptor potential (TRP) channels. Together, our results demonstrate the molecular mechanism of rapid production of NO in response to vertical mechanical stretch.

Th17/Treg Imbalance Induced by Dietary Salt Variation Indicates Inflammation of Target Organs in Humans

The functions of T helper 17 (Th17) and regulatory T (Treg) cells are tightly orchestrated through independent differentiation pathways that are involved in the secretion of pro- and anti-inflammatory cytokines induced by high-salt dietary. However, the role of imbalanced Th17/Treg ratio implicated in inflammation and target organ damage remains elusive. Here, by flow cytometry analysis, we demonstrated that switching to a high-salt diet resulted in decreased Th17 cells and reciprocally increased Treg cells, leading to a decreased Th17/Treg ratio. Meanwhile, Th17-related pathway was down-regulated after one day of high salt loading, with the increase in high salt loading as shown by microarray and RT-PCR. Subsequently, blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) observed hypoxia in the renal medulla (increased R2^* signal) during high-salt loading, which was regressed to its baseline level in a step-down fashion during low-salt feeding. The flow-mediated vasodilatation (FMD) of the branchial artery was significantly higher on the first day of high salt loading. Collectively, these observations indicate that a short-term increase in dietary salt intake could induce reciprocal switches in Th17/Treg ratio and related cytokines, which might be the underlying cellular mechanism of high-salt dietary induced end organ inflammation and potential atherosclerotic risk.

High salt intake as a multifaceted cardiovascular disease: new support from cellular and molecular evidence

Scientists worldwide have disseminated the idea that increased dietary salt increases blood pressure. Currently, salt intake in the general population is ten times higher than that consumed in the past and at least two times higher than the current recommendation. Indeed, a salt-rich diet increases cardiovascular morbidity and mortality. For a long time, however, the deleterious effects associated with high salt consumption were only related to the effect of salt on blood pressure. Currently, several other effects have been reported. In some cases, the deleterious effects of high salt consumption are independently associated with other common risk factors. In this article, we gather data on the effects of increased salt intake on the cardiovascular system, from infancy to adulthood, to describe the route by which increased salt intake leads to cardiovascular diseases. We have reviewed the cellular and molecular mechanisms through which a high intake of salt acts on the cardiovascular system to lead to the progressive failure of a healthy heart.

Salt, Angiotensin II, Superoxide, and Endothelial Function

Proper function of the vascular endothelium is essential for cardiovascular health, in large part due to its antiproliferative, antihypertrophic, and anti-inflammatory properties. Crucial to the protective role of the endothelium is the production and liberation of nitric oxide (NO), which not only acts as a potent vasodilator, but also reduces levels of reactive oxygen species, including superoxide anion (O2•-). Superoxide anion is highly injurious to the vasculature because it not only scavenges NO molecules, but has other damaging effects, including direct oxidative disruption of normal signaling mechanisms in the endothelium and vascular smooth muscle cells. The renin-angiotensin system plays a crucial role in the maintenance of normal blood pressure. This function is mediated via the peptide hormone angiotensin II (ANG II), which maintains normal blood volume by regulating Na+ excretion. However, elevation of ANG II above normal levels increases O2•- production, promotes oxidative stress and endothelial dysfunction, and plays a major role in multiple disease conditions. Elevated dietary salt intake also leads to oxidant stress and endothelial dysfunction, but these occur in the face of salt-induced ANG II suppression and reduced levels of circulating ANG II. While the effects of abnormally high levels of ANG II have been extensively studied, far less is known regarding the mechanisms of oxidant stress and endothelial dysfunction occurring in response to chronic exposure to abnormally low levels of ANG II. The current article focuses on the mechanisms and consequences of this less well understood relationship among salt, superoxide, and endothelial function.

Association between pre hemodialysis serum sodium concentration and blood pressure: results from a retrospective analysis from the international monitoring dialysis outcomes (MONDO) initiative

A recent study from the United Kingdom indicates an association between pre hemodialysis (HD) serum sodium (SNa(+)) and systolic and diastolic blood pressure (SBP and DBP) in chronic HD patients. We extend this analysis to an international cohort of incident HD patients. The Monitoring Dialysis Outcomes initiative encompasses patients from 41 countries. Over 2 years monthly pre-HD SNa(+) levels were used as predictors of pre-HD SBP and DBP in a linear mixed model (LMM) adjusted for age, gender, interdialytic weight gain, diabetes, serum albumin and calcium. Similar models were constructed with DBP as outcome. Analyses were carried out stratified by continent (North and South America; Europe and Asia). LMMs were also constructed for the entire observation period of 2 years, and separately the first and the second year after HD initiation. We studied 17 050 incident patients and found SNa(+) to have a significant slope estimate in the LMM predicting pre-HD SBP and DBP (ranging from 0.22 to 0.29 and 0.10 to 0.21 mm Hg per mEq l(-1), respectively, between the continents). The findings were similar in subsets of SBP and SNa(+) tertiles, and separately analyzed for the first and second year. Our analysis shows an independent association between SNa, SBP and DBP in a large intercontinental database, indicating that this relation is a profound biological phenomenon in incident and prevalent HD patients, generalizable to an international level and independent of SBP and DBP magnitude.

Anti-hypertensive effect of Lycium barbarum L. with down-regulated expression of renal endothelial lncRNA sONE in a rat model of salt-sensitive hypertension

The present study aims to test whether Lycium barbarum L. has anti-hypertensive effect through regulating expression of lncRNA sONE in a rat model of salt-sensitive hypertension. Nine weeks old borderline hypertensive rats (BHRs) were divided into 4 groups receiving high (8% NaCl), medium (0.25% NaCl, as control group), and low salt diet (0.015% NaCl) for 16 weeks, respectively, while the fourth group (high salt + L. barbarum group) fed with high salt diet for 12 weeks, then followed by 8% NaCl and L. barbarum treatment for 4 weeks. Body weight and blood pressure were recorded biweekly. Salt-sensitive hypertension was successfully induced by 12-week high salt diet in BHR model. Blood pressure was significantly increased in the model (P < 0.05), and L. barbarum treatment reversed the elevated blood pressure to normal level. Expression of lncRNA sONE was significantly reduced and eNOS expression level was dramatically improved in the hypertension model rats with the L. barbarum compared with that receiving high salt diet. Our results indicated that L. barbarum L. had anti-hypertensive effect and might lower blood pressure by suppressing the expression of lncRNA sONE in BHR model.

High dietary sodium reduces brachial artery flow-mediated dilation in humans with salt-sensitive and salt-resistant blood pressure

Recent studies demonstrate that high dietary sodium (HS) impairs endothelial function in those with salt-resistant (SR) blood pressure (BP). The effect of HS on endothelial function in those with salt-sensitive (SS) BP is not currently known. We hypothesized that HS would impair brachial artery flow-mediated dilation (FMD) to a greater extent in SS compared with SR adults. Ten SR (age 42 ± 5 yr, 5 men, 5 women) and 10 SS (age 39 ± 5 yr, 5 men, 5 women) healthy, normotensive participants were enrolled in a controlled feeding study consisting of a run-in diet followed by a 7-day low dietary sodium (LS) (20 mmol/day) and a 7-day HS (300 mmol/day) diet in random order. Brachial artery FMD and 24-h BP were assessed on the last day of each diet. SS BP was individually assessed and defined as a change in 24-h mean arterial pressure (MAP) of >5 mmHg between the LS and HS diets (ΔMAP: SR -0.6 ± 1.2, SS 7.7 ± 0.4 mmHg). Brachial artery FMD was lower in both SS and SR individuals during the HS diet (P < 0.001), and did not differ between groups (P > 0.05) (FMD: SR LS 10.6 ± 1.3%, SR HS 7.2 ± 1.5%, SS LS 12.5 ± 1.7%, SS HS 7.8 ± 1.4%). These data indicate that an HS diet impairs brachial artery FMD to a similar extent in adults with SS BP and SR BP.

Salt and sugar: their effects on blood pressure

Both dietary salt and sugar are related to blood pressure (BP). The evidence for salt is much stronger, and various types of studies have consistently shown that salt is a major cause of raised BP, and a reduction from the current intake of ≈ 9-12 g/day in most countries of the world to the recommended level of 5-6 g/day lowers BP in both hypertensive and normotensive individuals, in men and women, in all age groups and in all ethnic groups. Countries such as Finland and the UK that have successfully reduced salt intake have demonstrated a reduction in population BP and cardiovascular mortality, with major cost savings to the health service. The mechanisms whereby salt raises BP are not fully understood. The traditional concepts focus on the tendency for an increase in extracellular fluid volume. Increasing evidence suggests that small increases in plasma sodium may play an important role. There are several other factors that also increase BP, one of which is added sugars. The current high intake of added sugars increases obesity which, in turn, raises BP. Recent studies also suggest that added sugars, particularly those in soft drinks, may have a direct effect on BP. However, the relationship between soft drink consumption and BP could be, at least partially, mediated by the effect of salt intake on increasing soft drink consumption. Actions to reduce salt and sugar intake across the whole population will have major beneficial effects on health along with major cost savings.

A vascular mechanism for high-sodium-induced insulin resistance in rats

AIMS/HYPOTHESIS

High sodium (HS) effects on hypertension are well established. Recent evidence implicates a relationship between HS intake and insulin resistance, even in the absence of hypertension. The aim of the current study was to determine whether loss of the vascular actions of insulin may be the driving factor linking HS intake to insulin resistance.

METHODS

Sprague Dawley rats were fed a control (0.31% wt/wt NaCl) or HS (8.00% wt/wt NaCl) diet for 4 weeks and subjected to euglycaemic-hyperinsulinaemic clamp (10 mU min(-1) kg(-1)) or constant-flow pump-perfused hindlimb studies following an overnight fast. A separate group of HS rats was given quinapril during the dietary intervention and subjected to euglycaemic-hyperinsulinaemic clamp as above.

RESULTS

HS intake had no effect on body weight or fat mass or on fasting glucose, insulin, endothelin-1 or NEFA concentrations. However, HS impaired whole body and skeletal muscle glucose uptake, in addition to a loss of insulin-stimulated microvascular recruitment. These effects were present despite enhanced insulin signalling (Akt) in both liver and skeletal muscle. Constant-flow pump-perfused hindlimb experiments revealed normal insulin-stimulated myocyte glucose uptake in HS-fed rats. Quinapril treatment restored insulin-mediated microvascular recruitment and muscle glucose uptake in vivo.

CONCLUSIONS/INTERPRETATION

HS-induced insulin resistance is driven by impaired microvascular responsiveness to insulin, and is not due to metabolic or signalling defects within myocytes or liver. These results imply that reducing sodium intake may be important not only for management of hypertension but also for insulin resistance, and highlight the vasculature as a potential therapeutic target in the prevention of insulin resistance.

Aortic and carotid arterial stiffness and epigenetic regulator gene expression changes precede blood pressure rise in stroke-prone Dahl salt-sensitive hypertensive rats

Multiple clinical studies show that arterial stiffness, measured as pulse wave velocity (PWV), precedes hypertension and is an independent predictor of hypertension end organ diseases including stroke, cardiovascular disease and chronic kidney disease. Risk factor studies for arterial stiffness implicate age, hypertension and sodium. However, causal mechanisms linking risk factor to arterial stiffness remain to be elucidated. Here, we studied the causal relationship of arterial stiffness and hypertension in the Na-induced, stroke-prone Dahl salt-sensitive (S) hypertensive rat model, and analyzed putative molecular mechanisms. Stroke-prone and non-stroke-prone male and female rats were studied at 3- and 6-weeks of age for arterial stiffness (PWV, strain), blood pressure, vessel wall histology, and gene expression changes. Studies showed that increased left carotid and aortic arterial stiffness preceded hypertension, pulse pressure widening, and structural wall changes at the 6-week time-point. Instead, differential gene induction was detected implicating molecular-functional changes in extracellular matrix (ECM) structural constituents, modifiers, cell adhesion, and matricellular proteins, as well as in endothelial function, apoptosis balance, and epigenetic regulators. Immunostaining testing histone modifiers Ep300, HDAC3, and PRMT5 levels confirmed carotid artery-upregulation in all three layers: endothelial, smooth muscle and adventitial cells. Our study recapitulates observations in humans that given salt-sensitivity, increased Na-intake induced arterial stiffness before hypertension, increased pulse pressure, and structural vessel wall changes. Differential gene expression changes associated with arterial stiffness suggest a molecular mechanism linking sodium to full-vessel wall response affecting gene-networks involved in vascular ECM structure-function, apoptosis balance, and epigenetic regulation.

Salt loading has a more deleterious effect on flow-mediated dilation in salt-resistant men than women

BACKGROUND AND AIMS

Dietary sodium loading has been shown to adversely impact endothelial function independently of blood pressure (BP). However, it is unknown whether dietary sodium loading impacts endothelial function differently in men as compared to women. The aim of this study was to test the hypothesis that endothelial-dependent dilation (EDD) would be lower in men as compared to women in response to a high sodium diet.

METHODS AND RESULTS

Thirty subjects (14F, 31±2y; 16M, 29±2y) underwent a randomized, crossover, controlled diet study consisting of 7 days of low sodium (LS; 20 mmol/day) and 7 days of high sodium (HS; 300-350 mmol/day). Salt-resistance was determined by a change in 24-hr mean arterial pressure (MAP) ≤ 5 mm Hg between HS and LS as assessed on day 7 of each diet. Blood and 24-hr urine were also collected and EDD was assessed by brachial artery flow-mediated dilation (FMD). By design, MAP was not different between LS and HS conditions and urinary sodium excretion increased on HS diet (P < 0.01). FMD did not differ between men and women on the LS diet (10.2 ± 0.65 vs. 10.7 ± 0.83; P > 0.05) and declined in both men and women on HS (P < 0.001). However, FMD was lower in men as compared to women on HS (5.7 ± 0.5 vs. 8.6 ± 0.86; P < 0.01).

CONCLUSIONS

HS reduced FMD in both men and women. In response to an HS diet, FMD was lower in men compared to women suggesting a greater sensitivity of the vasculature to high sodium in men.

Rationale and design of the Myocardial Microinjury and Cardiac Remodeling Extension Study in the Sodium Lowering in Dialysate trial (Mac-SoLID study)

Background

The Sodium Lowering in Dialysate (SoLID) trial is an ongoing a multi-center, prospective, randomised, single-blind (assessor), controlled, parallel assignment clinical trial, enrolling 96 home and self-care hemodialysis (HD) patients from 7 centers in New Zealand. The trial will evaluate the hypothesis that lower dialysate [Na+] during HD results in lower left ventricular (LV) mass. Since it’s inception, observational evidence has suggested increased mortality risk with lower dialysate [Na+], possibly due to exacerbation of intra-dialytic hypotension and subsequent myocardial micro-injury. The Myocardial Micro-injury and Cardiac Remodeling Extension Study in the Sodium Lowering In Dialysate Trial (Mac-SoLID study) aims to determine whether lower dialysate [Na+] results in (i) increased levels of high-sensitivity Troponin T (hsTnT), a well-established marker of intra-dialytic myocardial micro-injury in HD populations, and (ii) increased fixed LV segmental wall motion abnormalities, a marker of recurrent myocardial stunning and micro-injury, and (iii) detrimental changes in LV geometry due to maladaptive homeostatic mechanisms.

Methods/design

The SoLID trial and the Mac-SoLID study are funded by the Health Research Council of New Zealand. Key exclusion criteria: patients who dialyse > 3.5 times per week, pre-dialysis serum sodium <135 mM, and maintenance haemodiafiltration. In addition, some medical conditions, treatments or participation in other dialysis trials that contraindicate the study intervention or confound its effects, will be exclusion criteria. The intervention and control groups will receive dialysate sodium 135 mM and 140 mM respectively, for 12 months. The primary outcome measure for the Mac-SOLID study is repeated measures of [hsTnT] at 0, 3, 6, 9, and 12 months. The secondary outcomes will be assessed using cardiac magnetic resonance imaging (MRI), and comprise LV segmental wall motion abnormality scores, LV mass to volume ratio and patterns of LV remodeling at 0 and 12 months.

Discussion

The Mac-SoLID study enhances and complements the SoLID trial. It tests whether potential gains in cardiovascular health (reduced LV mass) which low dialysate [Na+] is expected to deliver, are counteracted by deterioration in cardiovascular health through alternative mechanisms, namely repeated LV stunning and micro-injury.

Trial registration

Australian and New Zealand Clinical Trials Registry number: ACTRN12611000975998.

Feedforward activation of endothelial ENaC by high sodium

Kidney epithelial sodium channels (ENaCs) are known to be inactivated by high sodium concentrations (feedback inhibition). Recently, the endothelial sodium channel (EnNaC) was identified to control the nanomechanical properties of the endothelium. EnNaC-dependent endothelial stiffening reduces the release of nitric oxide, the hallmark of endothelial dysfunction. To study the regulatory impact of sodium on EnNaC, endothelial cells (EA.hy926 and ex vivo mouse endothelium) were incubated in aldosterone-free solutions containing either low (130 mM) or high (150 mM) sodium concentrations. By applying atomic force microscopy-based nanoindentation, an unexpected positive correlation between increasing sodium concentrations and cortical endothelial stiffness was observed, which can be attributed to functional EnNaC. In particular, an acute rise in sodium concentration (+20 mM) was sufficient to increase EnNaC membrane abundance by 90% and stiffening of the endothelial cortex by 18%. Despite the absence of exogenous aldosterone, these effects were prevented by the aldosterone synthase inhibitor FAD286 (100 nM) or the mineralocorticoid receptor (MR)-antagonist spironolactone (100 nM), indicating endogenous aldosterone synthesis and MR-dependent signaling. Interestingly, in the presence of high-sodium concentrations, FAD286 increased the transcription of the MR by 69%. Taken together, a novel feedforward activation of EnNaC by sodium is proposed that contrasts ENaC feedback inhibition in kidney.

Vascular Response to Graded Angiotensin II Infusion in Offspring Subjected to High-Salt Drinking Water during Pregnancy: The Effect of Blood Pressure, Heart Rate, Urine Output, Endothelial Permeability, and Gender

Introduction. Rennin-angiotensin system and salt diet play important roles in blood pressure control. We hypothesized that the high-salt intake during pregnancy influences the degree of angiotensin-dependent control of the blood pressure in adult offspring. Methods. Female Wistar rats in two groups (A and B) were subjected to drink tap and salt water, respectively, during pregnancy. The offspring were divided into four groups as male and female offspring from group A (groups 1 and 2) and from group B (groups 3 and 4). In anesthetized matured offspring mean arterial pressure (MAP), heart rate and urine output were measured in response to angiotensin II (AngII) (0-1000 ng/kg/min, iv) infusion. Results. An increase in MAP was detected in mothers with salt drinking water (P < 0.05). The body weight increased and kidney weight decreased significantly in male offspring from group 3 in comparison to group 1 (P < 0.05). MAP and urine volume in response to AngII infusion increased in group 3 (P < 0.05). These findings were not observed in female rats. Conclusion. Salt overloading during pregnancy had long-term effects on kidney weight and increased sex-dependent response to AngII infusion in offspring (adult) that may reveal the important role of diet during pregnancy in AngII receptors.

Blood pressure and amiloride-sensitive sodium channels in vascular and renal cells

Sodium transport in the distal nephron is mediated by epithelial sodium channel activity. Proteolytic processing of external domains and inhibition with increased sodium concentrations are important regulatory features of epithelial sodium channel complexes expressed in the distal nephron. By contrast, sodium channels expressed in the vascular system are activated by increased external sodium concentrations, which results in changes in the mechanical properties and function of endothelial cells. Mechanosensitivity and shear stress affect both epithelial and vascular sodium channel activity. Guyton's hypothesis stated that blood pressure control is critically dependent on vascular tone and fluid handling by the kidney. The synergistic effects, and complementary regulation, of the epithelial and vascular systems are consistent with the Guytonian model of volume and blood pressure regulation, and probably reflect sequential evolution of the two systems. The integration of vascular tone, renal perfusion and regulation of renal sodium reabsorption is the central underpinning of the Guytonian model. In this Review, we focus on the expression and regulation of sodium channels, and we outline the emerging evidence that describes the central role of amiloride-sensitive sodium channels in the efferent (vascular) and afferent (epithelial) arms of this homeostatic system.

Vascular endothelium: a vulnerable transit zone for merciless sodium

In humans, when plasma sodium concentration rises slightly beyond 140 mM, vascular endothelium sharply stiffens and nitric oxide release declines. In search of a vascular sodium sensor, the endothelial glycocalyx was identified as being a negatively charged biopolymer capable of selectively buffering sodium ions. Sodium excess damages the glycocalyx and renders vascular endothelium increasingly permeable for sodium. In the long term, sodium accumulates in the interstitium and gradually damages the organism. It was discovered that circulating red blood cells (RBC) 'report' surface properties of the vascular endothelium. To some extent, the RBC glycocalyx mirrors the endothelial glycocalyx. A poor (charge-deprived) endothelial glycocalyx causes a poor RBC glycocalyx and vice versa. This observation led to the assumption that the current state of an individual's vascular endothelium in terms of electrical surface charges and sodium-buffering capabilities could be read simply from a blood sample. Recently, a so-called salt blood test was introduced that quantifies the RBC sodium buffer capacity and thus characterizes the endothelial function. The arguments are outlined in this article spanning a bridge from cellular nano-mechanics to clinical application.

The effect of high salt intake on endothelial function: reduced vascular nitric oxide in the absence of hypertension

Within the last 25 years, it has become increasingly clear that high dietary salt intake represents a risk factor for the development of cardiovascular disease that is independent of its well-known ability to increase arterial pressure in some individuals. Studies in normotensive experimental animals and human subjects have revealed that a key feature of this pressure-independent effect of dietary salt is a profound reduction in vascular nitric oxide (NO) bioavailability that limits endothelium-dependent dilation. This reduction in NO is strongly associated with increased levels of reactive oxygen species (ROS) generated by NAD(P)H oxidase, xanthine oxidase or uncoupled endothelial NO synthase within the vascular wall, leading not only to scavenging of NO but also to disruption of some signaling pathways that mediate its production. The mechanistic link between high salt intake and elevated levels of enzymatically generated ROS in the peripheral vasculature is not clear, but a reduction in circulating angiotensin II may play a key role in this regard. Additional studies are needed to further elucidate the mechanisms, both at the systemic level and within the vascular wall, that trigger these salt-induced deficits in endothelial function, and to further clarify how the attendant loss of NO may disrupt tissue blood flow regulation and ultimately lead to adverse cardiovascular events.