Role of dietary salt in hypertension

Biochemical interaction of salt sensitivity: a key player for the development of essential hypertension

Worldwide, more than 1 billion people have elevated blood pressure, with up to 45% of adults affected by the disease. In 2016 the global health study report on patients from 67 countries was released in Lancet, which identified hypertension as the world's leading cause for death and disability-adjusted years since 1990. This paper aims to analyze the pathophysiological connection between hemodynamic inflammatory reactions through sodium balance, salt sensitivity, and potential pathophysiological reactions. Besides, we explore how sodium consumption enhances the expression of transient receptor potential channel 3 (TrpC3) mRNA and facilitates the release of calcium inside immune cell groups, together with elevated blood pressure in essential hypertensive patients.

Effects of sodium intake on postural lightheadedness: Results from the DASH-sodium trial

Lightheadedness after standing contributes to adverse clinical events, including falls. Recommendations for higher sodium intake to treat postural lightheadedness have not been evaluated in a trial setting. The Dietary Approaches to Stop Hypertension (DASH)-Sodium trial (1998-1999) tested the effects of the DASH diet and sodium reduction on blood pressure (BP). Participants were randomly assigned to DASH or a typical Western diet (control). During either diet, participants ate three sodium levels (50, 100, 150 meq/d at 2100 kcal) in random order for 30-days, separated by 5-day breaks. Participants reported the presence and severity of postural lightheadedness at baseline and after each feeding period. There were 412 participants (mean age 48 years; 57% women; 57% black). Mean baseline SBP/DBP was 135/86 mm Hg; 9.5% reported baseline lightheadedness. Among those consuming the DASH diet, high vs low sodium increased lightheadedness (OR 1.71; 95% CI: 1.01, 2.90; P = 0.047) and severity of lightheadedness (P = 0.02), but did not affect lightheadedness in those consuming the control diet (OR 0.77; 95% CI: 0.46, 1.29; P = 0.32). Among those consuming high vs low sodium in the context of the DASH diet, adults <60 vs ≥60 years old experienced more lightheadedness (P-interaction = 0.04), along with obese vs non-obese adults (P-interaction = 0.01). In the context of the DASH diet, higher sodium intake was associated with more frequent and severe lightheadedness. These findings challenge traditional recommendations to increase sodium intake to prevent lightheadedness.

Blood Pressure Regulation: Reviewing Evidence for Interplay Between Common Dietary Sugars and Table Salt

A popular concept is that the significant global progression in prevalence and intensification of elevated blood pressure (BP) levels is due in part to dietary indiscretions. Excess intake of several food sources causing overweight/obesity plays an important role in BP perturbations. However, certain nutrients are involved in ways other than via body fat accumulation, particularly table salt (sodium chloride) and popular refined carbohydrates like dietary sugars (sucrose, fructose, high fructose corn syrup). In nondiabetics and diabetics, several functions of salt and sugar influence BP and metabolism. For example, salt intake is linked to volume expansion, insulin resistance, and hypertension, while sugar intake is associated with enhanced salt sensitivity via urinary sodium retention, insulin resistance, and hypertension. The key postulate evaluated here is that when two popular nutrients-salt and dietary sugars-are consumed together in adequate amounts, their respective individual BP effects are significantly amplified. In previous laboratory studies, a sugar challenge did not increase BP in the face of marked sodium depletion, and combining sugar and salt challenges caused a synergistic BP elevation. Among examples of amplification on the clinical side, the greatest increases in BP following sugar challenges were seen in diabetic subjects having the highest sodium excretion. Interplay between table salt and common dietary sugars in BP regulation is a reasonable postulate and should be carefully considered when developing optimal prevention and treatment regimens to ameliorate the worldwide crisis arising from harmful elevated BP levels.

Potassium Chloride-Based Salt Substitutes: A Critical Review with a Focus on the Patent Literature

High dietary sodium intake (DSI) represents a major health-related public issue in most countries all over the world. Such a diet can lead to increased risk of hypertension and related cardiovascular diseases. This situation has resulted in important public policies for various salt reduction strategies. One of these is based on the use of salt substitutes or salts with reduced sodium content. Among several options, potassium chloride (KCl) has proved to be a key nutritional ingredient for this purpose. It provides similar properties like common salt (NaCl), but with several unwanted side effects, of which the most important have relatively offensive side tastes: bitter, acrid, and metallic. To successfully formulate KCl-based salt substitutes, numerous taste-improving agents and formulation concepts have been used. The field of salt substitutes is mainly described in the patent literature. Since patents are both scientific and legal documents, careful and critical consideration is required when using them as a source of scientific information. This review brings a deep insight into the area of KCl-based salt substitutes with a focus on the patent literature through the eyes of food science and technology. The most important classes of taste-improving agents that have been employed in numerous formulation concepts of KCl-based salt substitutes are nutritionally acceptable mineral salts; food acids, amino acids, and their nutritionally acceptable salts; simple carbohydrates and sugar substitutes; food polymers; umami ingredients; spices, vegetables, and flavors; miscellaneous taste improvers; as well as a plethora of their specific combinations. A critical review of the respective patent literature is given.

Interaction between Single Nucleotide Polymorphism and Urinary Sodium, Potassium, and Sodium-Potassium Ratio on the Risk of Hypertension in Korean Adults

Hypertension is a complex disease explained with diverse factors including environmental factors and genetic factors. The objectives of this study were to determine the interaction effects between gene variants and 24 h estimated urinary sodium and potassium excretion and sodium-potassium excretion ratios on the risk of hypertension. A total of 8839 participants were included in the genome-wide association study (GWAS) to find genetic factors associated with hypertension. Tanaka and Kawasaki formulas were applied to estimate 24 h urinary sodium and potassium excretion. A total of 4414 participants were included in interaction analyses to identify the interaction effects of gene variants according to 24 h estimated urinary factors on the risk of hypertension. CSK rs1378942 and CSK-MIR4513 rs3784789 were significantly modified by urinary sodium-potassium excretion ratio. In addition, MKLN rs1643270 with urinary potassium excretion, LOC101929750 rs7554672 with urinary sodium and potassium excretion, and TENM4 rs10466739 with urinary sodium-potassium excretion ratio showed significant interaction effects. The present study results indicated that the mutant alleles of CSK rs1378942 and CSK-MIR4513 rs3784789 had the strongest protective effects against hypertension in the middle group of 24 h estimated urinary sodium-potassium excretion ratio. Further studies are needed to replicate these analyses in other populations.

The Effect of the Sodium to Potassium Ratio on Hypertension Prevalence: A Propensity Score Matching Approach

This study investigated the effect of the sodium to potassium ratio on hypertension prevalence and blood pressure. The study population was constructed by pooling the Korean National Health and Nutrition Examination Surveys between 2010 and 2014. The study population was divided into quartiles based on the sodium to potassium ratio, and the effect was inferred by the difference in hypertension prevalence across quartiles by six pairwise comparisons using a propensity score matching technique. The quartiles with the higher sodium to potassium ratio had higher hypertension prevalence rates based on the following pairwise comparisons: the first vs. third quartile, the first vs. fourth quartile, the second vs. third quartile, and the second vs. fourth quartile. The prevalence differences were 2.74% point (p < 0.05), 3.44% point (p < 0.01), 2.47% point (p < 0.05), and 2.95% point (p < 0.01), respectively. In addition, statistically significant higher systolic (p < 0.05) and diastolic blood pressure (p < 0.01) was observed in the second quartiles compared to the first quartiles. Because a strong association was also detected between the sodium to potassium ratio and blood pressure even at a low level of sodium to potassium ratio, a lower sodium to potassium ratio diet than a usual diet is recommended to control high blood pressure in Korea.

Childbearing May Increase the Risk of Nondiabetic Cataract in Chinese Women's Old Age

Backgrounds. Ocular changes may arise during pregnancy and after childbirth, but very few studies have reported the association between childbearing and cataract among older adults. Methods. 14,292 individuals aged 60+ years were recruited in Xiamen, China, in 2013. Physician-diagnosed cataract and diabetes status were assessed by a self-reported questionnaire. Childbearing status was measured by number of children (NOC). Structural equation modeling (SEM) analysis was conducted to examine the relationships among NOC, diabetes, and cataract. Gender-specific logistic models regressing nondiabetic cataract on NOC were performed by adjusting some covariates. Results. 14,119 participants had complete data, of whom 5.01% suffered from cataract, with higher prevalence in women than men (6.41% versus 3.51%). Estimates of SEM models for women suggested that both NOC and diabetes were risk factors for cataract and that no correlation existed between NOC and diabetes. Women who had one or more children faced roughly 2–4 times higher risk of nondiabetic cataract than their childless counterparts (OR [95% CI] = 3.88 [1.24, 17.71], 3.21 [1.04, 14.52], 4.32 [1.42, 19.44], 4.41 [1.46, 19.74], and 3.98 [1.28, 18.10] for having 1, 2, 3, 4-5, and 6 or more children, resp.). Conclusions. Childbearing may increase the risk of nondiabetic cataract in Chinese women's older age.

Gene expression responses of threespine stickleback to salinity: implications for salt-sensitive hypertension

Despite recent success with genome-wide association studies (GWAS), identifying hypertension (HTN)-susceptibility loci in the general population remains difficult. Here, we present a novel strategy to address this challenge by studying salinity adaptation in the threespine stickleback, a fish species with diverse salt-handling ecotypes. We acclimated native freshwater (FW) and anadromous saltwater (SW) threespine sticklebacks to fresh, brackish, and sea water for 30 days, and applied RNA sequencing to determine the gene expression in fish kidneys. We identified 1844 salt-responsive genes that were differentially expressed between FW sticklebacks acclimated to different salinities and/or between SW and FW sticklebacks acclimated to full-strength sea water. Significant overlap between stickleback salt-responsive genes and human genes implicated in HTN was detected (P < 10⁻⁷, hypergeometric test), suggesting a possible similarity in genetic mechanisms of salt handling between threespine sticklebacks and humans. The overlapping genes included a newly discovered HTN gene—MAP3K15, whose expression in FW stickleback kidneys decreases with salinity. These also included genes located in the GWAS loci such as AGTRAP-PLOD1 and CYP1A1-ULK3, which contain multiple potentially causative genes contributing to HTN susceptibility that need to be prioritized for study. Taken together, we show that stickleback salt-responsive genes provide valuable information facilitating the identification of human HTN genes. Thus, threespine sticklebacks may be used as a model, complementary to existing animal models, in human HTN research.

Long-term effects of maternal diabetes on blood pressure and renal function in rat male offspring

Aims/Hypothesis

Gestational diabetes mellitus (GDM) is increasing rapidly worldwide. Previous animal models were established to study consequences of offspring after exposure to severe intrauterine hyperglycemia. In this study we are aiming to characterize the blood pressure levels and renal function of male offspring obtained from diabetic mothers with moderate hyperglycemia.

Methods

We established a rat model with moderate hyperglycemia after pregnancy by a single intraperitoneal injection of streptozotocin (STZ). The male offspring were studied and fed with either normal diet or high salt diet after weaning. Arterial pressure and renal function were measured.

Results

Arterial pressure of male offspring increased from 12 weeks by exposure to intrauterine moderate hyperglycemia. At 20 weeks, high salt diet accelerated the blood pressure on diabetic offspring compared to diabetic offspring fed with normal diet. We found offspring exposed to intrauterine moderate hyperglycemia had a trend to have a higher creatinine clearance rate and significant increase of urinary N-acetyl-β-D-glucosaminidase (NAG) excretion indicating an early stage of nephropathy progression.

Conclusions/Interpretation

We observed the high blood pressure level and early renal dysfunction of male offspring obtained from diabetic mothers with moderate hyperglycemia. Furthermore, we investigated high salt diet after weaning on offspring exposed to intrauterine hyperglycemia could exacerbate the blood pressure and renal function. Renin angiotensin system (RAS) plays an important role in hypertension pathogenesis and altered gene expression of RAS components in offspring with in utero hyperglycemia exposure may account for the programmed hypertension. Therefore, our study provides evidence “fetal programming” of maternal diabetes is critical for metabolic disease development.

N-geranyl cyclopropyl-carboximide modulates salty and umami taste in humans and animal models

Effects of N-geranyl cyclopropyl-carboxamide (NGCC) and four structurally related compounds (N-cyclopropyl E2,Z6-nonadienamide, N-geranyl isobutanamide, N-geranyl 2-methylbutanamide, and allyl N-geranyl carbamate) were evaluated on the chorda tympani (CT) nerve response to NaCl and monosodium glutamate (MSG) in rats and wild-type (WT) and TRPV1 knockout (KO) mice and on human salty and umami taste intensity. NGCC enhanced the rat CT response to 100 mM NaCl + 5 μM benzamil (Bz; an epithelial Na(+) channel blocker) between 1 and 2.5 μM and inhibited it above 5 μM. N-(3-methoxyphenyl)-4-chlorocinnamid (SB-366791, a TRPV1t blocker) inhibited the NaCl+Bz CT response in the absence and presence of NGCC. Unlike the WT mice, no NaCl+Bz CT response was observed in TRPV1 KO mice in the absence or presence of NGCC. NGCC enhanced human salt taste intensity of fish soup stock containing 60 mM NaCl at 5 and 10 μM and decreased it at 25 μM. Rat CT responses to NaCl+Bz and human salt sensory perception were not affected by the above four structurally related compounds. Above 10 μM, NGCC increased the CT response to MSG+Bz+SB-366791 and maximally enhanced the response between 40 and 60 μM. Increasing taste cell Ca(2+) inhibited the NGCC-induced increase but not the inosine monophosphate-induced increase in glutamate response. Addition of 45 μM NGCC to chicken broth containing 60 mM sodium enhanced the human umami taste intensity. Thus, depending upon its concentration, NGCC modulates salt taste by interacting with the putative TRPV1t-dependent salt taste receptor and umami taste by interacting with a Ca(2+)-dependent transduction pathway.

Increased depressor response to N-arachidonoyl-dopamine during high salt intake: role of the TRPV1 receptor

OBJECTIVE

This study was designed to test the hypothesis that the systemic administration of N-arachidonoyl-dopamine (NADA), an endovanilloid, causes a depressor effect via activation of transient receptor potential vanilloid type 1 (TRPV1) channels during high-salt intake.

METHODS

Wistar rats were fed a normal (0.4%) or high (4%) sodium diet for 10 days, and arteries and veins were cannulated for measurement of mean arterial pressure (MAP) or injection of drugs and collection of plasma. Radioimmunoassay and western blot were used to determine the plasma calcitonin gene-related peptide (CGRP) level and TRPV1 protein content, respectively.

RESULTS

The NADA-induced dose-dependent decrease in MAP was greater in high-sodium than normal-treated rats, and was abolished by capsazepine, a selective TRPV1 antagonist, or CGRP8-37, a selective CGRP receptor antagonist, but not by SR141716A, a selective cannabinoid 1 receptor antagonist. Capsaicin, a selective TRPV1 receptor agonist, or CGRP dose-dependently decreased MAP in normal or high-sodium-treated rats, with a greater effect in the latter. Baseline and NADA-induced increases in plasma CGRP levels were higher in high-sodium than normal-treated rats. TRPV1 protein expression in mesenteric arteries was higher in high-sodium than normal-treated rats. In vitro, NADA caused a greater CGRP release from mesenteric arteries of high-sodium than normal-treated rats, which was blocked by capsazepine.

CONCLUSION

High sodium increases the sensitivity of blood pressure responses to NADA. The enhanced depressor effect induced by NADA during high-sodium intake is prevented by blockade of the TRPV1 or CGRP receptors, but not cannabinoid 1 receptor. High sodium upregulates mesenteric TRPV1 expression, and increases NADA-induced CGRP release in vitro and in vivo.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Recombinant adeno-associated virus-mediated delivery of antisense angiotensin II receptor 1 gene attenuates hypertension development

AIM

The renin-angiotensin system plays a crucial role in the development and establishment of hypertension, and the pharmacological blockade of the system results in a reduction in blood pressure. In the present study, we investigated whether the effects of a novel, double-stranded, recombinant adeno-associated virus vector (rAAV)-mediated antisense angiotensin II receptor 1 (AT1R) gene efficiently prevents the development of hypertension induced by a high-salt diet in adult, male Sprague-Dawley (SD) rats.

METHODS

A rAAV was prepared with a cassette containing a cytomegalovirus promoter and partial cDNA (660 base pairs) for the AT1R inserted in the antisense direction (rAAV-AT1-AS). A single tail vein injection of the rAAV-AT1-AS or rAAV-GFP (green fluorescent protein, a reporter gene) was performed in adult, male SD rats. Two weeks after injection, the animals were fed a diet containing 8% NaCl, and the systolic blood pressure was measured weekly using the tail-cuff method for 12 weeks.

RESULTS

The high-salt diet induced a significant rise in systolic blood pressure in the rAAV-GFP-treated animals; however, the rAAV-AT1-AS treatment attenuated the rise in blood pressure (142.7+/-4.5 mmHg vs 117+/-3.8 mmHg, P<0.01), and the hypotensive effect was maintained until the experiments ended at 12 weeks. In the rAAV-GFP-treated animals AT1 was overexpressed in various tissues, especially in the aorta and kidney at mRNA levels; in contrast, rAAV-AT1-AS treatment markedly attenuated AT1 expression. Furthermore, rAAV-AT1-AS treatment prevented target organ damages from hypertension, including cardiac dysfunction and renal injury compared to the rAAV-GFP group.

CONCLUSION

These results suggest that rAAVmediated anti-AT1 delivery attenuates the development of hypertension and protects against renal injury and cardiac remodeling.

Elevated sodium chloride concentrations enhance the bystander effects induced by low dose alpha-particle irradiation

Previous studies have shown that high NaCl can be genotoxic, either alone or combined with irradiation. However, little is known about the relationship between environmental NaCl at elevated conditions and radiation-induced bystander effects (RIBE). RIBE, which has been considered as non-targeted bystander responses, has been demonstrated to occur widely in various cell lines. In the present study, RIBE under the elevated NaCl culture condition was assessed in AG 1522 cells by both the induction of gamma-H2AX, a reliable marker of DNA double-strand break (DSB) for the early process (<1h post irradiation), and the generation of micronuclei (MN), a sensitive marker for relative long process of RIBE. Our results showed that in the absence of irradiation, NaCl at elevated concentration such as 8.0, 9.0 and 10.0g/L did not significantly increase the frequency of gamma-H2AX foci-positive cells and the number of foci per positive cell comparing with that NaCl at a normal concentration (6.8g/L). However, with 0.2cGy alpha-particle irradiation, the induced fraction of gamma-H2AX foci-positive cells and the number of induced gamma-H2AX foci per positive cell were significantly increased in both irradiated and adjacent non-irradiated regions. Similarly, the induction of MN by 0.2cGy alpha-particle irradiation also increased with the elevated NaCl concentrations. With N(G)-methyl-l-arginine, an inhibitor of nitric oxide synthase, the induced fraction of foci-positive cells was effectively inhibited both in 0.2cGy alpha-particle irradiated and adjacent non-irradiated regions under either normal or elevated NaCl conditions. These results suggested that the cultures with elevated NaCl medium magnified the damage effects induced by the low dose alpha-particle irradiation and nitric oxide generated by irradiation was also very important in this process.

Endocannabinoid Regulates Blood Pressure via Activation of the Transient Receptor Potential Vanilloid Type 1 in Wistar Rats Fed a High-Salt Diet

This study was designed to examine the role of the endocannabinoids in blood pressure regulation during high sodium (HS) intake. HS (4% Na+ by weight) intake for 3 weeks increased baseline mean arterial pressure (MAP, mm Hg) compared with normal sodium (NS, 0.4% Na+ by weight)-treated male Wistar rats. Capsazepine (3 mg/kg), a selective transient receptor potential vanilloid type 1 (TRPV1) antagonist, caused a greater increase in MAP (mm Hg) in HS-treated compared with NS-treated rats (13+/-3 versus 4+/-2, p<0.05), whereas calcitonin gene-related peptide (CGRP) dose-dependently decreased MAP in both HS- and NS-treated rats with a more profound effect in the former. HS increased plasma anandamide levels analyzed by liquid chromatography/electrospray tandem mass spectrometry (NS, 2.40+/-0.31 versus HS, 4.05+/-0.47 pmol/ml, p<0.05) and plasma CGRP levels determined by radioimmunoassay (NS, 36.6+/-3.8 versus HS, 55.7+/-6.4 pg/ml, p<0.05). Methanandamide, a metabolically stable analog of anandamide, caused a greater CGRP release in mesenteric arteries isolated from HS-treated compared with NS-treated rats. Western blot showed that expression of receptor activity-modifying protein 1, a subunit of the CGRP receptor, in mesenteric arteries was greater in HS-treated compared with NS-treated rats. These results show that HS intake increases production of anandamide, which may serve as an endovanilloid to activate TRPV1, leading to release of CGRP to blunt salt-induced increases in blood pressure. These data support the notion that TRPV1 may act as a molecular target for salt-induced elevation of endovanilloid compounds to regulate blood pressure.

Heme-oxygenase upregulation ameliorates angiotensin II-induced tubulointerstitial injury and salt-sensitive hypertension

BACKGROUND

Heme oxygenase-1 (HO-1) has been implicated in the modulation of several diseases including hypertension (HTN) and renal injury. The tubulointerstitial (TI) injuries are supposed to be the main determinants for the development of salt-sensitive HTN. Therefore, this study examined the role of HO-1 in angiotensin II (AngII)-induced TI injury and salt-sensitive HTN.

METHODS

Sprague-Dawley rats on a high salt diet were treated by AngII infusion plus either hemin, an inducer of HO-1, or hemin + zinc protoporphyrin, a HO-1 inhibitor, for 2 weeks, and then followed for 6 weeks.

RESULTS

The AngII infusion resulted in acute HTN and proteinuria. Light microscopy revealed focal areas of tubular atrophy with mononuclear cell infiltration and interstitial expansion. The overexpression of osteopontin and TGF-beta(1) accompanied by diminished expression of rat endothelial cell antigen-1, the hallmarks of TI injury, were observed. At 2 weeks, all interventions were withdrawn and systolic blood pressure returned towards normal. After a brief normal salt diet, rats were again placed on high salt diet, resulting in progressive increase in systolic blood pressure in the HO-1-inhibited group.

CONCLUSION

The induction of HO-1 attenuated the development of HTN, suggesting that HO-1 plays a crucial role in significant attenuation of AngII-mediated TI injury and resultant salt-sensitive HTN.

Dysfunction of paracellin-1 by dephosphorylation in Dahl salt-sensitive hypertensive rats

A high-salt diet reduced the levels of renal cAMP content and serine-phosphorylated paracellin-1 in Dahl salt-sensitive hypertensive rats. In MDCK cells expressing paracellin-1, protein kinase A inhibitor reduced the serine-phosphorylated paracellin-1 and transepithelial Mg(2+) transport, suggesting that a dephosphorylation of paracellin-1 induces the reduction of Mg(2+) reabsorption in salt-sensitive hypertension.

Long-term compliance with salt restriction in Japanese hypertensive patients

The purpose of the present study was to investigate the long-term compliance with salt restriction in Japanese hypertensive patients. Subjects included 389 patients, 230 women and 159 men, mean age 58+/-11 years, who underwent successful 24-h home urine collection more than three times over an interval of a year. Urinary salt, potassium, and creatinine were measured. Additionally, family history, habitual alcohol intake, smoking habit, physical activities, and job status were assessed by use of a questionnaire. During the follow-up period (average 3.5 years), participants underwent urine collection 4.6 times in average. Urinary salt excretion at the last visit was significantly lower than that at the first visit (8.7+/-3.4 vs. 9.6+/-4.1 g/day; p<0.01). Urinary potassium excretion also decreased significantly during this period (from 2.0+/-0.7 to 1.9+/-0.7 g/day; p<0.05). Among the mean 4.6 urine collections, 45.2% (men 34.6%, women 52.6%) of the patients successfully achieved <6 g (100 mmol of sodium)/day of salt excretion on at least one occasion. The rate of achievement of averaged urinary salt excretion <6 g/day dropped to 10.3% (men 4.4%, women 14.3%). Only 2.3% (men 0.6%, women 3.5%) of the patients achieved <6 g/day on all occasions. There were no significant differences in age, habitual alcohol intake, smoking habit, physical activities, or job status between patients who complied with the salt-restricted diet and those who did not. Results suggest that long-term compliance with salt restriction is poor in Japanese hypertensive patients. Since no specifically defining characteristics were found in the compliant patients, repeated measurements of urinary salt excretion seem to be important to encourage salt restriction.

Hypertension, Na+/Ca2+ exchanger, and Na+, K+-ATPase

Hypertension is the most prevalent risk factor for stroke, myocardial infarction, or end-stage renal failure. The critical importance of excess salt intake in the pathogenesis of hypertension is widely recognized, but the mechanisms whereby salt intake elevates blood pressure have puzzled researchers. Recent studies using Na+/Ca2+ exchange inhibitors and genetically engineered mice provide evidence that vascular Na+/Ca2+ exchanger type 1 (NCX1) is involved in the development of salt-dependent hypertension. Endogenous cardiac glycosides, which may contribute to salt-dependent hypertension, seem to be necessary for NCX1-mediated hypertension. Intriguingly, studies using knock-in mice with modified cardiac glycoside binding affinity of Na+,K+-ATPases provide a clear demonstration that this cardiac glycoside-binding site plays an important role in blood pressure regulation. Taken all together: (1) endogenous cardiac glycosides are secreted after high salt intake; (2) these cardiac glycosides inhibit Na+,K+-ATPase in vascular smooth muscle cells; (3) this inhibition results in the elevation of local Na+ on the submembrane area; and (4) this elevation of local Na+ facilitates Ca2+ entry through NCX1, resulting in vasoconstriction. This proposed pathway may have enabled us to explain how to link dietary salt to hypertension.

Role of dietary salt in hypertension

Certain things have not changed since my colleague and I last reviewed the role of dietary salt in hypertension [Haddy, F.J., Pamnani, M.B., 1995. Role of dietary salt in hypertension. Journal of the American College of Nutrition 14, 428-438]. Over half of hypertensives are still salt sensitive, i.e., they respond to a high NaCl intake with a rise in blood pressure. This can be ameliorated by restricting NaCl intake, supplementing potassium intake, and consuming diuretics. Some things have changed. We now have more insight into mechanism; we suspected that volume expansion and endogenous Na(+),K(+)-ATPase inhibitors were the connection between excessive salt intake and the hypertension, but we were not certain as to the nature of the inhibitors. Now it appears that the inhibitors are steroids released from the adrenal gland and are members of the cardenolide family, e.g., ouabain, and the bufadienolide family, e.g., marinobufagenin. This presents new possibilities in therapy, including antibodies to these agents and competitive inhibitors to their binding to Na(+),K(+)-ATPase.

Young Scholars Award Lecture: Intratubular angiotensinogen in hypertension and kidney diseases

Recent findings related to the renin-angiotensin system have provided a more elaborated understanding of the pathophysiology of hypertension and kidney diseases. These findings have led to unique concepts and issues regarding the intrarenal renin-angiotensin system. Angiotensinogen is the only known substrate for renin that is the rate-limiting enzyme of the renin-angiotensin system. Because the level of angiotensinogen in human beings is close to the Michaelis-Menten constant value for renin, changes in angiotensinogen levels can control the activity of the renin-angiotensin system, and its upregulation may lead to elevated angiotensin peptide levels and increases in blood pressure. Enhanced intrarenal angiotensinogen mRNA or protein levels or both have been observed in multiple models of hypertension including angiotensin II-dependent hypertensive rats, Dahl salt-sensitive hypertensive rats, and spontaneously hypertensive rats, as well as in kidney diseases including diabetic nephropathy, immunoglobulin A (IgA) nephropathy, and radiation nephropathy. Renal angiotensinogen is formed primarily in proximal tubular cells and is secreted into the tubular fluid. Urinary angiotensinogen excretion rates show a clear relationship to kidney angiotensin II contents and kidney angiotensinogen levels, suggesting that urinary angiotensinogen may serve as an index of the intrarenal renin-angiotensin system status. Establishment of concise and accurate methods to measure human angiotensinogen may allow clinical studies that would provide important information regarding the roles of intrarenal angiotensinogen in the development and progression of hypertension and kidney diseases.

A Novel Mechanism Contributing to Development of Dahl Salt–Sensitive Hypertension

To determine the role of the transient receptor potential vanilloid type 1 (TRPV1) channels in development of hypertension in Dahl salt-sensitive (DS) rats fed a high-salt diet (HS), male DS and Dahl salt-resistant (DR) rats were maintained on a low-salt diet (LS) or HS for 3 weeks. HS significantly increased systolic blood pressure in DS+HS rats compared with DS+LS, DR+HS, and DR+LS rats. Intravenous bolus injection of capsazepine (3 mg/kg), a selective TRPV1 antagonist, significantly increased mean arterial pressure in conscious DR+HS rats compared with DR+LS, DS+/-HS, and DS+/-LS rats. In contrast, capsaicin (10 or 30 microg/kg), a selective TRPV1 agonist, dose-dependently decreased mean arterial pressure in all of the groups with the most profound magnitude in DR+HS rats compared with the other 3 groups. TRPV1 expression in mesenteric resistance arteries and the renal cortex and medulla, calcitonin gene-related peptide levels in dorsal root ganglia, and calcitonin gene-related peptide-positive sensory nerve density in mesenteric resistance arteries were significantly decreased in DS+HS rats compared with DS+LS, DR+HS, and DR+LS rats. Taken together, our data indicate that the TRPV1 receptor is activated and its expression upregulated during HS intake in DR rats, which acts to prevent salt-induced increases in blood pressure. In contrast, TRPV1 expression and function are impaired in DS rats, which renders DS rats sensitive to salt load in terms of blood pressure regulation.

Vascular Na+/Ca2+exchanger: implications for the pathogenesis and therapy of salt-dependent hypertension

The Na+/Ca2+exchanger is an ion transporter that exchanges Na+and Ca2+in either Ca2+efflux or Ca2+influx mode, depending on membrane potential and transmembrane ion gradients. In arterial smooth muscle cells, the Na+/Ca2+exchanger is thought to participate in the maintenance of vascular tone by regulating cytosolic Ca2+concentration. Recent pharmacological and genetic engineering studies have revealed that the Ca2+influx mode of vascular Na+/Ca2+exchanger type-1 (NCX1) is involved in the pathogenesis of salt-dependent hypertension. SEA0400, a specific Na+/Ca2+exchange inhibitor that preferentially blocks the Ca2+influx mode, lowers arterial blood pressure in salt-dependent hypertensive models, but not in normotensive rats or other types of hypertensive rats. Furthermore, heterozygous mice with reduced expression of NCX1 are resistant to development of salt-dependent hypertension, whereas transgenic mice with vascular smooth muscle-specific overexpression of NCX1 readily develop hypertension after high-salt loading. SEA0400 reverses the cytosolic Ca2+elevation and vasoconstriction induced by nanomolar ouabain, as well as humoral factors in salt-loaded animals. One possibility is that circulating endogenous cardiotonic steroids may be necessary for NCX1-mediated hypertension. These findings help to explain how arterial smooth muscle cells in blood vessels contribute to salt-elicited blood pressure elevation and suggest that NCX1 inhibitors might be therapeutically useful for salt-dependent hypertension.

Salt-sensitive hypertension, Na+/Ca2+ exchanger, and vascular smooth muscle

Hypertension is the most common chronic disease and is the leading risk factor for death caused by stroke, myocardial infarction, and end-stage renal failure. The critical importance of excess salt intake in the pathogenesis of hypertension is widely recognized. However, the molecular mechanisms underlying salt-sensitive hypertension remain obscure. Recent studies using selective Na(+)/Ca(2+) exchanger (NCX) inhibitors and genetically engineered mice provide compelling evidence that salt-sensitive hypertension is triggered by Ca(2+) entry through NCX type 1 (NCX1) in arterial smooth muscle. Cardiotonic steroids, such as endogenous ouabain, which may contribute to the pathogenesis of salt-sensitive hypertension, seem to be necessary for NCX1-mediated hypertension. These findings have enabled us to explain how high salt intake leads to hypertension and further to describe the potential of vascular NCX1 as a new therapeutic or diagnostic target for salt-sensitive hypertension.

Salt-sensitive hypertension is triggered by Ca2+ entry via Na+/Ca2+ exchanger type-1 in vascular smooth muscle

Excessive salt intake is a major risk factor for hypertension. Here we identify the role of Na(+)/Ca(2+) exchanger type 1 (NCX1) in salt-sensitive hypertension using SEA0400, a specific inhibitor of Ca(2+) entry through NCX1, and genetically engineered mice. SEA0400 lowers arterial blood pressure in salt-dependent hypertensive rat models, but not in other types of hypertensive rats or in normotensive rats. Infusion of SEA0400 into the femoral artery in salt-dependent hypertensive rats increases arterial blood flow, indicating peripheral vasodilation. SEA0400 reverses ouabain-induced cytosolic Ca(2+) elevation and vasoconstriction in arteries. Furthermore, heterozygous NCX1-deficient mice have low salt sensitivity, whereas transgenic mice that specifically express NCX1.3 in smooth muscle are hypersensitive to salt. SEA0400 lowers the blood pressure in salt-dependent hypertensive mice expressing NCX1.3, but not in SEA0400-insensitive NCX1.3 mutants. These findings indicate that salt-sensitive hypertension is triggered by Ca(2+) entry through NCX1 in arterial smooth muscle and suggest that NCX1 inhibitors might be useful therapeutically.

Relationship between the Awareness of Salt Restriction and the Actual Salt Intake in Hypertensive Patients

A 24-h home urine collection was conducted to estimate accurate salt intake in hypertensive outpatients. Using 24-h urinary creatinine excretion as a criterion for success, urine samples were obtained from 534 hypertensive patients. The urinary salt excretion of hypertensive outpatients ranged widely from 1.5 to 23.4 g/day (mean value 9.7 +/- 3.9 g/day). Urinary salt excretion was higher in males than in females (10.6 +/- 4.0 vs. 9.2 +/- 3.7 g/day, p<0.01). Based on the questionnaires, the patients were divided into salt-conscious patients, or those who were careful to reduce their daily salt intake, and non-salt-conscious patients. It was found that urinary salt excretion was lower in the salt-conscious group than in the non-salt-conscious group (9.4 +/- 3.8 vs. 10.6 +/- 4.0 g/day, p<0.01), but that urinary salt excretion adjusted for body weight was not significantly different between the two groups (0.16 +/- 0.06 vs. 0.17 +/- 0.07 g/kg/day). Our results suggest that there was no obvious reduction in the actual salt intake in salt-conscious patients, suggesting the importance of monitoring salt intake by 24-h home urine collection and informing patients of their actual salt intake as a means of encouraging the achievement of salt restriction.

Gustatory Evaluation of Still and Carbonated Waters: A Preference Rating Study

We studied the sensory preference for six still waters and four carbonated waters, nonflavored, by 11 tasting experts (4 women and 7 men). Five tasters rated the still waters, four tasters rated the carbonated water, and seven tasters rated twice on each of the still waters when evaluated with a dry red wine. All ratings were performed through answering a set of questions regarding the specific taste and/or smell of the waters. All tasters and the statistician were blinded to the water brands during rating and analysis. Multidimensional preference analysis and correspondence analysis were used to portray the underlying sensory preference. Still waters with higher mineral content tended to be less favorable for drinking purposes. On the other hand, carbonated waters with more minerals (but not over a certain limit) were favorable, and still waters with higher mineral content were preferable as mouth cleaners for red wine. The methodology can be carried to the food and beverage industries, to the functional foods industry, and to medical research where the preference of patients toward certain medications is of interest.

Enhancement of intrarenal angiotensinogen in Dahl salt-sensitive rats on high salt diet

This study was performed to examine whether there is an inappropriate regulation of intrarenal angiotensinogen in Dahl-salt sensitive rats (DS) fed a high salt diet (HS). Dahl salt-resistant rats (DR) and DS were maintained on HS (8% NaCl) or low salt diet (LS, 0.3% NaCl) for 4 weeks. Systolic blood pressure (SBP), measured by tail-cuff plethysmography, was unaltered in DR (DR+HS, 127+/-3 mm Hg, n=5; DR+LS, 126+/-3, n=5); however, SBP was significantly increased in DS+HS (208+/-7, n=9) compared with DS+LS (134+/-2, n=5). HS suppressed plasma renin activity in both strains (0.7+/-0.2 ng of angiotensin I/mL per hour in DS+HS, 3.1+/-0.5 in DS+LS, 0.8+/-0.2 in DR+HS, 5.1+/-0.7 in DR+LS). Plasma angiotensinogen levels, measured by Western blot analysis, were also suppressed by HS in both strains (36 919+/-2170 integrated densitometric unit in DS+HS, 53 028+/-2752 in DS+LS, 44 722+/-1721 in DR+HS, 55782+/-3785 in DR+LS). However, kidney angiotensinogen levels were significantly increased in DS+HS (75 850+/-4171, integrated densitometric unit) compared with DS+LS (47 232+/-3470), DR+HS (44 748+/-8236), and DR+LS (42 504+/-4052). Urinary excretion of angiotensinogen, measured by radioimmunoassay of angiotensin I after incubation with excess renin, had a similar profile. Urinary excretion of angiotensinogen was significantly increased in DS+HS (2958+/-531 pmol/d) compared with DS+LS (56+/-4), DR+HS (31+/-12), and DR+LS (21+/-7). These data indicate that intrarenal angiotensinogen is enhanced in DS+HS, which is reflected by the increased urinary excretion of angiotensinogen. The results suggest that DS on HS have an inappropriate augmentation of intrarenal angiotensinogen, which may contribute to impaired sodium excretion during a high salt diet and the development of hypertension in this strain.

AT(1) receptor regulation in salt-sensitive hypertension

The molecular events governing salt-sensitive hypertension are currently unknown. Because the renin-ANG system plays a central role in blood pressure regulation and electrolyte balance, it may be closely involved in the phenomenon of salt sensitivity. Therefore, we examined the effect of a high-salt diet (8%) and a low-salt diet (0.4%) on ANG II-caused vascular constriction and ANG II type 1 (AT(1)) receptor expression in aorta, brain, and kidney of Dahl S (salt-sensitive) and Dahl R (salt-resistant) rats by means of radioligand binding assays and quantitative PCR. NaCl diet at 8% led to a significant increase of blood pressure in Dahl S but not in Dahl R rats. High-sodium intake caused a profound decrease of ANG II-induced aortic vasoconstriction in both Dahl R and Dahl S rats. The underlying mechanism was a downregulation of aortic AT(1) receptor density and AT(1) receptor mRNA. AT(1) receptor mRNA was downregulated to 57.8% in Dahl R and 59.0% in Dahl S rats by an 8% NaCl diet compared with a 0.4% NaCl diet (P < 0.05). There was a similar decrease in aortic AT(1) receptor density. Additionally, AT(1) receptor mRNA was also downregulated in the kidney but upregulated the brain of Dahl R and S rats on a high-salt diet. Thus high NaCl intake causes organ-specific AT(1) receptor regulation in Dahl R and in Dahl S rats despite the differential blood pressure regulation in these animal models in response to a high-salt diet. These findings suggest that the regulation of vascular AT(1) receptors is influenced by numerous factors such as the renin-ANG system and obviously by various other events that are currently only partly understood.

Daily response of blood pressure to day-to-day variation of urinary sodium to potassium ratio

The relationship between blood pressure and urinary sodium-to-potassium (Na/K) ratio was assessed in eight healthy men, none of whom used antihypertensive medications. Blood pressure and urinary sodium and potassium concentrations were measured for 11 to 33 days without any dietary restriction. For two of the eight subjects, the urinary Na/K ratio significantly correlated with systolic blood pressure (r=0.70 and 0.45, respectively), and in one of the two subjects, the urinary ratio also positively correlated with diastolic blood pressure (r=0.72). In the others, no relationship between the ratio and blood pressure was observed (r=-0.24 to 0.26). The results indicate that, in some individuals, the daily variation of urinary Na/K ratio is closely correlated with day-to-day changes in blood pressure level, and suggest that the urinary Na/K ratio is useful in the management of the daily sodium and potassium intake balance of hypertensive patients who need to restrict salt intake.

Variation in the mineral content of commercially available bottled waters: implications for health and disease

PURPOSE

Although the annual consumption of bottled water in North America is 12.7 gallons per capita, little is known about the potential health effects of these waters. We reviewed the amounts of major minerals found in commercially available bottled waters, the recommended daily allowances for these minerals, and their beneficial and harmful effects.

METHODS

We obtained the mineral content of various commercially available bottled waters in North America and Europe from The Pocket Guide to Bottled Water. We then conducted a Medline search to identify articles examining the beneficial and harmful effects of magnesium, sodium, and calcium.

RESULTS

Great variation exists in the mineral content of commercially available bottled waters. Among the bottled waters that we reviewed, the magnesium content ranges from 0 to 126 mg per liter, the sodium content ranges from 0 to 1,200 mg per liter, and the calcium content ranges from 0 to 546 mg per liter. Epidemiologic and clinical studies suggest that magnesium may reduce the frequency of sudden death, that sodium contributes to the occurrence of hypertension, and that calcium may help prevent osteoporosis.

CONCLUSION

The ideal bottled water should be rich in magnesium and calcium and have a low sodium content. Because there is great variation in the mineral content of commercially available bottled waters, the actual mineral content of bottled water should be considered when selecting one for consumption.

Region of birth and black diets: the Harlem Household Survey

OBJECTIVES

This study compared dietary risk factors among Southern-born and other Blacks in Central Harlem.

METHODS

A survey of residents of Central Harlem was used to compute a "healthy diet" score for 621 subjects.

RESULTS

Southern-born respondents had the highest-risk diets. Although their numbers were small, Caribbean-born respondents, particularly those younger than 45 years, had the lowest-risk diets.

CONCLUSIONS

The variation in diets in Central Harlem was considerable, with Southern-born Blacks at highest dietary risk for chronic diseases. These results remain to be tested elsewhere, as does the contribution of other chronic disease risk factors.

Salt induces vascular AT1 receptor overexpression in vitro and in vivo

The molecular events governing salt-sensitive hypertension are currently unknown. Because the renin-angiotensin system plays a central role in blood pressure regulation, as well as electrolyte balance, it may be closely involved in the phenomenon of salt sensitivity. Therefore, we examined the effect of a high salt diet (8%) on aortic angiotensin type 1 (AT1) receptor expression in Sprague-Dawley rats by means of radioligand binding assays and quantitative polymerase chain reaction. High salt intake caused an increase of AT1 receptor mRNA and AT1 receptor density to approximately 160% compared with control levels. Northern analysis revealed that incubation of vascular smooth muscle cells (VSMCs) with an increased concentration of sodium chloride (by 10 mmol/L) caused a time-dependent elevation of AT1 receptor mRNA levels, with a maximum of 241+/-28% after 24 hours. There was a similar increase in AT1 receptor density in VSMCs in response to sodium chloride, as assessed by radioligand binding assays. The salt-induced AT1 receptor upregulation led to an enhanced functional response of VSMCs on stimulation with angiotensin II, since the angiotensin II-elicited intracellular calcium response was significantly increased in cells preincubated for 24 hours with the high salt concentration. Thus, sodium chloride may directly induce AT1 receptor upregulation in vitro as well as in vivo; this suggests a potential mechanism participating in salt-induced hypertension because the AT1 receptor activation is tightly coupled to blood pressure regulation.

Hypertension hemodynamics

The hemodynamic factors in hypertension should be evaluated in terms of early versus late stages, autoregulation versus amplifying mechanisms, and arterial compliance versus arteriolar vasoconstrictive responses. In addition, evaluation of hemodynamic changes in hypertension should include the role of vascular endothelium, genetic factors, volume factors, salt intake, vascular reactivity, presence or absence of left ventricular hypertrophy or left ventricular diastolic dysfunction, and finally the presence of left ventricular systolic failure. Whether therapy directed by knowledge of hemodynamic profiling will be more efficacious or more cost-effective than standard therapy in reducing morbidity and mortality of hypertension needs to be proven.

Hypertension-related morbidity and mortality in the southeastern United States

Stroke mortality is higher in the Southeast compared with other regions of the United States. The prevalence of hypertension is also higher (black men = 35%, black women = 37.7%, white men = 26.5%, white women = 21.5%), and the proportion of patients whose hypertension is being controlled is poor, especially in white and black men. The prevalence of hypertension-related complications other than stroke is also higher in the Southeast. The five states with the highest death rates for congestive heart failure are all in the southern region. Of the 15 states with the highest rates of end-stage renal disease, 10 are in the Southeast. Obesity is very prevalent (24% to 28%) in the Southeast. Although Michigan tops the ranking for all states, 6 of the top 15 states are in the Southeast, as are 7 of the 10 states with the highest reported prevalence regarding no leisure-time physical activity. Similar to other areas of the United States, dietary sodium and saturated fat intake are high in the Southeast; dietary potassium intake appears to be relatively low. Other factors that may be associated with the high prevalence, poor control, and excess morbidity and mortality of hypertension-related complications in the Southeast include misperceptions of the seriousness of the problem, the severity of the hypertension, lack of adequate follow-up, reduced access to health care, the cost of treatment, and possibly, low birth weights. The Consortium of Southeastern Hypertension Control (COSEHC) is a nonprofit organization created in 1992 in response to a compelling need to improve the disproportionate hypertension-related morbidity and mortality throughout this region. The purpose of this position paper is to summarize the data that document the problem, the consequences, and possible causative factors.