Sodium is more important than calcium in essential hypertension

A Method for Estimating 24-Hour Urinary Sodium Excretion by Casual Urine Specimen in Chinese Hypertensive Patients

BACKGROUND

High salt intake is a known risk factor of hypertension, which in turn increases the risk of stroke and cardiovascular diseases. The aim of this study was to develop and evaluate a method for predicting 24-hour urinary sodium excretion (UNa24h) using casual urine specimens in Chinese hypertensive patients.

METHODS

A total of 966 patients with hypertension were included from 8 provinces across China. A UNa24h prediction model (Sun_C method) was developed for males and females using linear regression based on age, weight, sodium concentration in the spot urine (UNaspot), and creatinine concentration in the spot urine (UCrspot). The data were split into the training (70%) and testing (30%) sets to, respectively, develop and evaluate the Sun_C method.

RESULTS

Compared with the Kawasaki, INTERSALT, and Tanaka methods, Sun_C method achieved a low and consistent mean bias (1.1 mmol/d) within the range from 106 to 212 mmol/d of UNa24h (equivalent to NaCl intake of 6-12 g/d). In addition, the Sun_C method showed no significant difference between the measured and estimated UNa24h in a paired t-test (P = 0.689). At individual level, Sun_C method had 79.8% of individuals at the cutoff under ±30% level.

CONCLUSIONS

Sun_C method may prove a reasonable method to estimate the daily dietary sodium intakes (particularly in the range of 6-12 g/d of NaCl) in Chinese hypertensive patients using spot urine measurements. As the amount of data increases in the future, the performance of our formulae will be further improved.

Mechanistic interactions of uromodulin with the thick ascending limb: perspectives in physiology and hypertension

Hypertension is a significant risk factor for cardiovascular disease and mortality worldwide. The kidney is a major regulator of blood pressure and electrolyte homeostasis, with monogenic disorders indicating a link between abnormal ion transport and salt-sensitive hypertension. However, the association between salt and hypertension remains controversial. Thus, there is continued interest in deciphering the molecular mechanisms behind these processes. Uromodulin (UMOD) is the most abundant protein in the normal urine and is primarily synthesized by the thick ascending limb epithelial cells of the kidney. Genome-wide association studies have linked common UMOD variants with kidney function, susceptibility to chronic kidney disease and hypertension independent of renal excretory function. This review will discuss and provide predictions on the role of the UMOD protein in renal ion transport and hypertension based on current observational, biochemical, genetic, pharmacological and clinical evidence.

Estimating the urinary sodium excretion in patients with chronic kidney disease is not useful in monitoring the effects of a low-salt diet

Background

Several epidemiologic studies have suggested that the urine sodium excretion (USE) can be estimated in lieu of performing 24-hour urine collection. However, this method has not been verified in patients with chronic kidney disease (CKD) or in an interventional study. The purpose of this study was to evaluate the usefulness of estimating USE in a prospective low-salt diet education cohort (ESPECIAL).

Methods

A new formula was developed on the basis of morning fasting urine samples from 228 CKD patients in the ESPECIAL cohort. This formula was compared to the previous four formulas in the prediction of 24-hour USE after treatment with olmesartan and low-salt diet education.

Results

Most previously reported formulas had low predictability of the measured USE based on the ESPECIAL cohort. Only the Tanaka formula showed a small but significant bias (9.8 mEq/day, P < 0.05) with a low correlation (r = 0.34). In contrast, a new formula showed improved bias (-0.1 mEq/day) and correlation (r = 0.569) at baseline. This formula demonstrated no significant bias (-1.2 mEq/day) with the same correlation (r = 0.571) after 8 weeks of treatment with olmesartan. Intensive low-salt diet education elicited a significant decrease in the measured USE. However, none of the formulas predicted this change in the measured urine sodium after diet adjustment.

Conclusion

We developed a more reliable formula for estimating the USE in CKD patients. Although estimating USE is applicable in an interventional study, it may be unsuitable for estimating the change of individual sodium intake in a low-salt intervention study.

Acute effects of salt on blood pressure are mediated by serum osmolality

It is classically thought that it is the amount of salt that is critical for driving acute blood pressure responses. However, recent studies suggest that blood pressure responses, at least acutely, may relate to changes in serum osmolality. Here, we test the hypothesis that acute blood pressure responses to salt can be altered by concomitant water loading. Ten healthy patients free of any disease and medication underwent 4 interventions each a week apart in which they took 300 mL of lentil soup with no salt (visit 1), lentil soup with 3 g salt (visit 2), or lentil soup with 3 g salt and 500 mL water (visit 3) or 750 mL water (visit 4). At each visit, hourly blood measurements and blood pressure measurements (baseline, 1st, 2nd, 3rd, and 4th hour) were performed and plasma osmolarity, sodium and copeptin levels were measured. Patients receiving the 3 g salt showed a 6 mOsm/L change in osmolality with a 2.5 mmol/L change in plasma sodium and 10 mm Hg rise in systolic blood pressure at 2 hours. When the same patients drank salty soup with water, the changes in plasma osmolarity, plasma sodium, and blood pressure were prevented. The ability to raise blood pressure acutely with salt appears dependent on changes in plasma osmolality rather than the amount of salt. Our findings suggest that concurrent intake of water must be considered when evaluating the role of salt in blood pressure.

Beyond Blood Pressure Screening: A Rationale for Promoting the Primary Prevention of Hypertension

High blood pressure is a major public health problem in the United States. However, the underlying reasons for the chronic elevation of blood pressure (BP) are unknown in most cases of hypertension (HT), and medical care has focused on lowering already elevated BP, primarily by pharmacologic means. Although an important factor in the development of HT appears to be a genetic predisposition, other potentially modifiable lifestyle risk factors associated with elevated BP have been identified. This article describes the scientific rationale for encouraging health promotion specialists to focus on the primary prevention of abnormally elevated blood pressure. Nonbehavioral risk factors such as increasing age, history of HT, Black ancestry, and consistent BP readings in the higher range of normality, and behavioral factors including dietary excesses and deficiencies, excessive body fat, a sedentary life style, and frequent episodes of unmanageable emotional stress are addressed. Recommendations are made based on scientific evidence supporting the relationships between these risk factors and the development of HT.

The blood pressure-salt sensitivity paradigm: pathophysiologically sound yet of no practical value

Sodium plays an important pathophysiological role in blood pressure (BP) values and in the development of hypertension, and epidemiological studies such as the Intersalt Study have shown that the increase in BP occurring with age is determined by salt intake. Recently, a meta-analysis of 13 prospective studies has also shown the close relationship between excess sodium intake and higher risk of stroke and total cardiovascular events. However, the BP response to changing salt intake displayed a marked variability, as first suggested by Kawasaki et al. (The effect of high-sodium and low-sodium intakes on blood pressure and other related variables in human subjects with idiopathic hypertension. Am J Med 1978; 64: 193-198) and later by Weinberger et al. (Definitions and characteristics of sodium sensitivity and blood pressure resistance. Hypertension 1986; 8: II127-II134), who recognized the heterogeneity of the BP response to salt and developed the concept of salt sensitivity. We have a large body of evidence in favour of a major role of metabolic and neuro-hormonal factors in determining BP salt sensitivity in association with the effect of genetic variation. There is evidence that salt sensitivity influences the development of organ damage, even independently-at least in part-of BP levels and the occurrence of hypertension. In addition, several observational studies indicate that salt sensitivity is clearly associated with a higher rate of cardiovascular events and mortality, independently of BP levels and hypertension. A cluster of factors with well-known atherogenic potential such as hyperinsulinaemia, dyslipidaemia and microalbuminuria-all known to be prevalent in salt-sensitive hypertension-might at least partially explain the increased cardiovascular risk observed in salt sensitive individuals. The gold standard for the evaluation of BP salt sensitivity is the BP response to a moderate reduction of salt intake for several weeks; nevertheless, these protocols often suffer of poor patient compliance to dietary instructions. To overcome this problem, short-term tests have been proposed that evaluate either large differences in salt intake for a few days or the response to intravenous administration of saline solution and short-acting diuretics. Recently, the use of ambulatory BP measurement has been proposed for the clinical assessment of BP salt sensitivity. Noteworthy, BP salt sensitivity, in whomever or however assessed, behaves as a continuous variable but salt sensitivity is used as a categorical parameter, with salt-sensitive individuals being defined as those with a difference in BP between low- and high-sodium intake >10%, and salt-resistant subjects those in whom BP does not increase or shows an increase <5% under sodium loading. The general conclusion that can and should be drawn from the above considerations is that the paradigm of salt sensitivity, despite its important pathophysiological meaning, is not helpful, so far, to the practising physician in clinical practice nor is it relevant or useful to the design and implementation of a population-based strategy of salt intake reduction; however, further studies are warranted for an accurate assessment of the salt-sensitivity phenotype in clinical practice. In the absence of a population strategy for salt intake reduction, the aim should be the generation of a 'low sodium environment' allowing for a dietary salt intake tailored on true human requirements and not on deleterious lifestyle habits.

The discovery of hypertension: evolving views on the role of the kidneys, and current hot topics

Primary hypertension is increasingly common and is associated with significant morbidity. Here, we review the history of its discovery and rise during the last century with an emphasis on studies trying to identify its cause. Early studies identified a defect in sodium excretion by the kidney as being central to the pathogenesis. Recent studies have focused on a variety of genetic, congenital (fetal programming), and acquired mechanisms for causing the defect in natriuresis. Certain risk factors are apparent, including genetic polymorphisms that regulate sodium excretion, a congenital reduction in nephron number, obesity and hyperleptinemia, an elevated sympathetic nervous system, diet (salt and fructose), and metabolic (hyperuricemia) mechanisms. The kidney shows evidence for renal arteriolar vasoconstriction, an intrarenal inflammatory response, local oxidative stress, and intrarenal activation of the renin-angiotensin system. Recent studies suggest that intrarenal T cells have an important role in causing hypertension to be persistent, likely due to the induction of a local autoimmune response to neoantigens such as heat shock protein 70 and protein aggregates formed by isoketals resulting from lipid peroxidation. Salt retention due to impairment in pressure-diuresis leads to the release of cardiotonic steroids and central nervous system effects that cause systemic vasoconstriction and a rise in blood pressure. Some recent studies suggest that salt may increase blood pressure not simply by effects on extracellular volume but rather as a consequence of hyperosmolarity. These new insights could lead to new approaches for the prevention and treatment of this important disease.

Effect of γ-aminobutyric acid and nattokinase-enriched fermented beans on the blood pressure of spontaneously hypertensive and normotensive Wistar-Kyoto rats

In this study we have evaluated the changes in arterial blood pressure in spontaneously hypertensive rats (SHR) caused by the short-term intake of Bacillus subtilis B060-fermented beans with significant γ-aminobutyric acid (GABA) and nattokinase activity. After being weaned, 7-week-old male SHR and 7-week-old male Wistar–Kyoto (WKY) rats were randomized into seven groups. Until the 8^th week of life, the rats in each group were given one of the following: Group 1, high dose of GABA and nattokinase in the SHR (SHD); Group 2, medium dose of GABA and nattokinase in the SHR (SMD); Group 3, low dose of GABA and nattokinase in the SHR (SLD); Group 4, negative control in the SHR (SD); Group 5, positive control in the SHR (SM); Group 6, high dose of GABA and nattokinase in the WKY (WHD); and Group 7, negative control in the WKY (WD). Distilled water served as the negative control, and captopril (50 mg/kg), a known ACE inhibitor, served as the positive control. Systolic blood pressure and diastolic blood pressure values were measured weekly from the 8^th week to the 16^th week of life using the tail-cuff method. A definite decrease in systolic and diastolic blood pressure values could be observed in the rats treated with captopril and in the rats that received GABA and nattokinase. The greatest antihypertensive effect was observed when the pharmacological treatment was administered. The effect of the daily intake of fermented beans containing GABA and nattokinase may be helpful in controlling blood pressure levels in hypertensive model animals. The fermentation of beans with B. subtilis B060 may therefore constitute a successful strategy for producing a functional food with antihypertensive activity.

High sodium and low potassium intake in patients with Type 2 diabetes

AIMS

To document dietary sodium and potassium intake and adherence to the Australian National Heart Foundation (NHF) guidelines in patients with Type 2 diabetes mellitus attending an Australian tertiary referral and university teaching hospital.

METHODS

In a longitudinal study, 24h urinary sodium (uNa), potassium (uK), creatinine (uCr), urea (uUrea) and glucose (uGlu) excretions, urine volume (uVol) and body mass index were recorded in 122 regular attenders over an 8 year period (2001-2008; mean of 1.9 samples/patient/year). In a cross-sectional study, the same measurements were recorded in patients providing urine samples in the month of June from 2001 to 2009 (782 patients, averaging 87/year).

RESULTS

In the longitudinal study, uNa (mmol/24 h) was 170 ± 53 (mean ± SD) in males and 142 ± 51 in females, whereas uK (mmol/24 h) was 75 ± 22 in males and 62 ± 18 in females. Once adjusted for insensible losses, only 3% of males and 14% of females met the NHF dietary sodium intake guidelines, and 14% of males and 3% of female patients met the NHF dietary potassium guidelines. Body mass index, uUrea, uVol and uGlu were independent predictors of uNa (adjusted r(2) =0.57, P<0.0001). The mean intra-individual coefficient of variation of the corrected uNa was 21 ± 1%. The cross-sectional study confirmed these findings, and no temporal trends were observed. There was no correlation with glycated haemoglobin to suggest natriuresis with hyperglycaemia.

CONCLUSIONS

Most patients with Type 2 diabetes mellitus do not meet NHF sodium or potassium intake guidelines. A diet high in sodium and low in potassium may contribute to the development of hypertension and to resistance to blood-pressure-lowering therapies.

Development and validation of a short questionnaire to assess sodium intake

Objectives

To develop and validate a short food-frequency questionnaire to assess habitual dietary salt intake in South Africans and to allow classification of individuals according to intakes above or below the maximum recommended intake of 6 g salt day−1.

Design

Cross-sectional validation study in 324 conveniently sampled men and women.

Methods

Repeated 24-hour urinary Na values and 24-hour dietary recalls were obtained on three occasions. Food items consumed by >5% of the sample and which contributed ≥50 mg Na serving−1 were included in the questionnaire in 42 categories. A scoring system was devised, based on Na content of one index food per category and frequency of consumption.

Results

Positive correlations were found between Na content of 35 of the 42 food categories in the questionnaire and total Na intake, calculated from 24-hour recall data. Total Na content of the questionnaire was associated with Na estimations from 24-hour recall data (r = 0.750; P < 0.0001; n = 328) and urinary Na (r = 0.152; P = 0.0105; n = 284). Urinary Na was higher for subjects in tertile 3 than tertile 1 of questionnaire Na content (P < 0.05). Questionnaire Na content of <2400 and ≥2400 mg day−1 equated to a reference cut-off score of 48 and corresponded to mean (standard deviation) urinary Na values of 145 (68) and 176 (99) mmol day−1, respectively (P < 0.05). Sensitivity and specificity against urinary Na ≥100 and <100 mmol day−1 was 12.4% and 93.9%, respectively.

Conclusion

A 42-item food-frequency questionnaire has been shown to have content-, construct- and criterion-related validity, as well as internal consistency, with regard to categorising individuals according to their habitual salt intake; however, the devised scoring system needs to show improved sensitivity.

Placental oxidative stress in a rat model of preeclampsia

The onset of preeclampsia is associated with increased maternal insult that could affect placental function. By increasing sodium intake (0.9% or 1.8% NaCl in drinking water) during the last week of gestation in the rat, we developed an animal model that shows many characteristics of preeclampsia such as increased blood pressure, decreased circulatory volume and diminished activity of the renin-angiotensin-aldosterone system. The aim of the present study was to determine in this model whether maternal perturbations in pregnancy lead to placental oxidative stress. Sprague-Dawley pregnant rats receiving salted-water were compared to not-supplemented pregnant rats. Markers of oxidative stress, ensuing cell death, and changes in the production of vasoactive substances (prostanoids: thromboxane, TxB(2); and prostacyclin, PGF(1alpha)) and the pro-inflammatory cytokine tumour necrosis factor-alpha (TNF-alpha) were measured in the placenta. In tissue from pregnant rats on 1.8% NaCl supplement, 8-iso-PGF(2alpha) levels, TxB(2)/6-keto-PGF(1alpha) ratios, total TNF-alpha RNA expression, as well as the apoptotic index (Bax/Bcl-2 ratio) and endothelial nitric oxide synthase protein expression increase while total glutathione content decreases. These findings demonstrate that maternal insult during gestation induced an imbalance in the oxidative environment in the placenta favouring oxidation. This was accompanied by an increased synthesis of vasoconstrictive substances and TNF-alpha by the placenta as well as the increased rate of placental cell apoptosis.

HYPERTENSION IN HEMODIALYSIS PATIENTS: Dietary Sodium Restriction for Hypertension in Dialysis Patients

A close relationship between sodium and hypertension exists and this relationship is even more pronounced in renal failure and dialysis patients. Hypertension is one of the strongest predictors of poor outcome in dialysis patients. Almost all end-stage renal disease (ESRD) patients have hypertension and positive sodium balance, resulting in extracellular volume (ECV) expansion-the most important contributing factor to hypertension. Thus the effective management of hypertension requires normalization of the sodium balance and ECV. Two important methods to achieve this are limiting interdialytic weight gain (IDWG) and a dialysis process that is able to remove all IDWG and consistently attain dry weight. Since IDWG is directly dependent on sodium intake and the resulting thirst, sodium restriction is the most effective way to limit IDWG. Ultrafiltration and dialysate sodium concentration influence sodium removal, ECV control, and blood pressure (BP) control. Thus the dialysis session should be long enough to achieve dry weight and frequent enough to maintain appropriate BP.

Reduced activity of the kallikrein-kinin system predominates over renin-angiotensin system overactivity in all conditions of sodium balance in essential hypertensives and family-related hypertension

OBJECTIVE

To study the renin-angiotensin-aldosterone and kallikrein-kinin systems in essential hypertensives and offspring of hypertensive parents during different sodium loads, and to explore their possible influence on renal hemodynamics.

METHODS

Forty-five essential hypertensives (35 +/- 4 years old, 25 males), 30 offspring of hypertensive parents (26 +/- 8 years old, 16 males) and 30 normotensive controls (28 +/- 5 years old, 20 males) were submitted to three different sodium loads (high, 250 mmol/l; normal, 140 mmol/l; and low, 20 mmol/l). Blood pressure, plasma renin activity, serum aldosterone, total kallikrein and urinary kallikrein-like activity were measured after each period. Effective renal plasma flow and glomerular filtration rate were also measured. In essential hypertensive subjects, renal hemodynamic and hormonal parameters were also measured after 3 days of 20 mg enalapril administration.

RESULTS

Plasma renin activity and serum aldosterone were higher in normotensives, essential hypertensives and offspring of hypertensive parents only during low sodium intake, whereas urinary kallikrein activity was lower in hypertensive offspring and essential hypertensives, compared with normotensives, during the three diet conditions. Effective renal plasma flow was found to be reduced in hypertensives and normotensive offspring, while the glomerular filtration rated was similar in the three groups. Angiotensin converting enzyme inhibitor (ACEI) administration to essential hypertensives for 3 days normalized effective renal plasma flow, increased plasma renin activity and decreased aldosterone and urinary kallikrein activity.

CONCLUSIONS

Our observations confirmed the presence of a hormonal imbalance between the renin-angiotensin-aldosterone system and the kallikrein-kinin system, not only in essential hypertensives but also in the offspring of hypertensive parents. This imbalance probably affects the renal circulation and sodium homeostasis, since there was reduced effective renal plasma flow in both populations compared with normotensive subjects. The positive effect of ACEI, resulting in normalization of the effective renal plasma flow in essential hypertensive patients, suggests the involvement of both systems in impaired renal circulation.

Blood pressure and urinary excretion of electrolytes in Spanish schoolchildren

Despite the importance of hypertension in adults, its effects on child health are poorly understood. This cross-sectional epidemiological study was designed to look for a relationship between elevated blood pressure (BP) in children and 24-h urinary excretion of sodium (Na) and potassium (K), and between BP and dietary salt intake. The study population was all 59 856 schoolchildren aged 6 to 14 years in the province of Almería in southern Spain, among whom 613 participants were chosen randomly for study. We measured 24-h urinary Na and K concentrations, systolic and diastolic BP, body weight and height. There was a weak correlation between Na excretion and systolic BP (r = 0.18, 95% confidence interval 0.10-0.26), and between K excretion and systolic BP (r = 0.49, 95% CI = 0.04-0.20). Body weight was the variable that best correlated with systolic (r = 0.49, 95% CI = 0.43-0.55) and diastolic BP, and with Na excretion (r = 0.48, 95% CI = 0.42-0.55). Multiple regression analysis also showed that body weight was the variable that best correlated with systolic BP (b = 0.58), although the variables in the equation explained little of the total variability in BP (26%). These correlations were significant at P < 0.05. In conclusion urinary electrolytes correlated poorly with BP in a sample of Spanish schoolchildren. Body weight was the only variable that showed a weak relationship with BP and Na excretion.

Salt sensitivity is associated with an increased mortality in both normal and hypertensive humans

While a variety of studies have demonstrated the heterogeneity of the blood pressure response to salt loading and depletion, none has examined the relationship of these responses to mortality. We conducted a follow-up study of 430 normal and 278 hypertensive subjects studied as long ago as 28 years by techniques to assess their blood pressure responses to salt and volume expansion and depletion (salt sensitivity). We found that 123 (21%) of our study subjects had died in the interval since the initial study. The following measures were found to be significantly associated with the risk for death: blood pressure (systolic, diastolic, mean arterial, and pulse pressures), hypertension, age, salt sensitivity, baseline renin levels (inverse), and body mass index (but not body weight). Normotensive, salt-sensitive subjects had a survival that was no different than that of hypertensive subjects. Only initially normotensive, salt-resistant individuals had improved survival. Studies are continuing in order to elucidate the mechanisms by which salt sensitivity, even in normotensive subjects, may lead to reduced survival.

Higher urinary albumin excretion is associated with abnormal erythrocyte Na(+)/Li(+) countertransport (SLC) in non-modulating essential hypertensives and offspring of hypertensive parents

Non-modulating is a highly reproducible type of sodium-sensitive hypertension. The aim of this study was to evaluate in non-modulating individuals the erythrocyte sodium-lithium countertransport (SLC) abnormalities, which have been mentioned as a marker of non-modulation, and the association with increased microalbuminuria, as a marker of an early kidney impairment. We measured erythrocyte SLC in 10 normotensives (NT, 28 +/- 4 years), 20 offspring of hypertensive parents being 10 modulating (MHO, 25 +/- 6 years) and 10 non-modulating (NMHO, 26 +/- 5 years), and 23 essential hypertensives being 12 modulating (MHT, 34 +/- 5 years) and 11 non-modulating (NMHT, 32 +/- 4 years). In all the subjects studied, microalbuminuria was determined by duplicate 24-h urine collection by radioimmunoassay. In non-modulating offspring of hypertensive parents and essential hypertensives. SLC was significantly elevated when compared either with normotensives without family history of hypertension, modulating offspring of hypertensive parents or essential hypertensives (P < 0.025). Likewise, 24-h urinary albumin excretion was found higher in non-modulating individuals (essential hypertensives and offspring of hypertensive parents) than in modulating individuals (P < 0.01). In conclusion, non-modulators with higher SLC countertransport sodium transport abnormalities showed higher elimination of microalbuminuria suggesting that non-modulators may have an increased risk for developing cardiovascular morbidity and kidney impairment even in normotensive subjects with familiarity history of hypertension.

Abnormal platelet function and calcium handling in Dahl salt-hypertensive rats

The effect of dietary salt on platelet function and Ca(2+) homeostasis was studied in Dahl (DS) rats, a genetic model of salt-sensitive hypertension. DS rats were fed a high-salt (DSHS) or a low-salt diet (DSLS) for up to 4 weeks, and the effects of salt loading on systolic blood pressure, platelet P-selectin expression, and platelet Ca(2+) homeostasis were measured. The high-salt diet increased blood pressure and markedly increased the amount of ionomycin (IM)-releasable Ca(2+) in platelet intracellular stores (Ca(2+)/IM). The alteration in Ca(2+) stores was not prevented when the hypertension was prevented by treatment with hydralazine and reserpine. The Ca(2+) store filling during platelet exposure to 1 mmol/L Ca(2+) for 5 minutes and the rate of sarcoplasmic/endoplasmic Ca(2+) ATPase-dependent Ca(45) uptake were higher in DSHS compared with that in DSLS. There was a decrease in thrombin-induced Ca(2+) influx in platelets from DSHS; consistent with this, agonist-induced P-selectin expression was decreased. In DSLS, nitric oxide accelerated reloading of platelet Ca(2+) stores after their emptying by thrombin but failed to do so in DSHS. These results indicate that in DS rats, a high-salt diet increases sarcoplasmic/endoplasmic Ca(2+) ATPase activity and the Ca(2+)/IM but decreases the reuptake of Ca(2+) caused by nitric oxide. Decreases in Ca(2+) influx and platelet P-selectin expression might be explained by changes in intracellular Ca(2+) stores in DSHS rats, which apparently is a heritable response to a high-salt diet.

Comparison of the mineral content of tap water and bottled waters

OBJECTIVES

Because of growing concern that constituents of drinking water may have adverse health effects, consumption of tap water in North America has decreased and consumption of bottled water has increased. Our objectives were to 1) determine whether North American tap water contains clinically important levels of calcium (Ca2+), magnesium (Mg2+), and sodium (Na+) and 2) determine whether differences in mineral content of tap water and commercially available bottled waters are clinically important.

DESIGN

We obtained mineral analysis reports from municipal water authorities of 21 major North American cities. Mineral content of tap water was compared with published data regarding commercially available bottled waters and with dietary reference intakes (DRIs).

MEASUREMENTS AND MAIN RESULTS

Mineral levels varied among tap water sources in North America and among bottled waters. European bottled waters generally contained higher mineral levels than North American tap water sources and North American bottled waters. For half of the tap water sources we examined, adults may fulfill between 8% and 16% of their Ca2+ DRI and between 6% and 31% of their Mg2+ DRI by drinking 2 liters per day. One liter of most moderate mineralization European bottled waters contained between 20% and 58% of the Ca2+ DRI and between 16% and 41% of the Mg2+ DRI in adults. High mineralization bottled waters often contained up to half of the maximum recommended daily intake of Na+.

CONCLUSION

Drinking water sources available to North Americans may contain high levels of Ca2+, Mg2+, and Na+ and may provide clinically important portions of the recommended dietary intake of these minerals. Physicians should encourage patients to check the mineral content of their drinking water, whether tap or bottled, and choose water most appropriate for their needs.

Salt sensitivity, pulse pressure, and death in normal and hypertensive humans

Although factors such as age, blood pressure, and its responsiveness to changes in sodium balance and extracellular fluid volume status (salt sensitivity) are associated with an increased risk of end-organ disease and cardiovascular events in hypertensive subjects, no such relationship with mortality has been demonstrated for salt sensitivity in normotensive subjects. We conducted long-term follow-up of 430 normal and 278 hypertensive subjects in whom assessment of salt sensitivity of blood pressure was performed as long as 27 years ago. We ascertained the status of 596 subjects (85% of the total population), 123 (21%) of whom had died. The following initial measurements were significantly (P<0.002) associated with subjects who had died compared with subjects known to be alive: age at study, pulse pressure, systolic, diastolic, and mean arterial pressures, hypertension, salt sensitivity, baseline renin levels, and body mass index (but not body weight). A stepwise logistic regression found the following independent predictors of death (odds ratio, 95% CI): age at initial study (1.08, 1.06 to 1.10), baseline blood pressure (1.03, 1.01 to 1.04), sodium sensitivity (1.73, 1.02 to 2.94), and male gender (1.91, 1.15 to 3.17). When survival curves were examined, normotensive salt-sensitive subjects aged >25 years when initially studied were found to have a cumulative mortality similar to that of hypertensive subjects, whereas salt-resistant normotensive subjects had increased survival (P:<0.001). These observations provide unique evidence of a relationship between salt sensitivity and mortality that is independent of elevated blood pressure.

Cardiovascular aging in health

Major focuses of geriatric medicine are cardiovascular diseases with increases in prevalence in older people and how aging might modify the risk factors, clinical manifestations, treatment strategies, and prognoses of these diseases. Quantitative information on age-associated alterations in cardiovascular structure and function in health is essential to define and target the specific characteristics of the cardiovascular aging process that render it the major risk factor for cardiovascular diseases. Such information also is required to differentiate among the limitations of elderly individuals that relate to disease and limitations that may fall within expected normal limits. Differences in cardiovascular function between older and younger individuals have been described extensively in the literature, but confusion often arises in the interpretation of these differences because of a failure to acknowledge or to control for interactions among age, disease, and lifestyle. The Baltimore Longitudinal Study on Aging has made an effort to characterize the effects of aging on multiple aspects of cardiovascular structure and function. The concepts that have evolved from this and other studies are discussed.

Calcium supplementation in patients with essential hypertension: assessment by office, home and ambulatory blood pressure

OBJECTIVE

To study the effects of a high calcium intake in hypertensive patients by blood pressure monitoring.

DESIGN

In a randomized crossover study, patients were assigned to an 8-week calcium supplementation period and an 8-week control period. The subjects were given 25 mmol/day (1 g/day) of calcium as calcium carbonate during the intervention period.

SETTING

A hypertension clinic in a tertiary teaching hospital.

PATIENTS

Sixty untreated or treated hypertensive patients (35 men and 25 women, mean age 58 years) with office systolic/diastolic blood pressure > or = 140/90 mmHg.

MAIN OUTCOME MEASURES

Office blood pressure, home blood pressure (last 7 days), and ambulatory 24 h blood pressure (every 30 min using TM-2421).

RESULTS

The serum calcium concentration and urinary calcium excretion increased significantly with calcium supplementation. Office, home and 24 h blood pressure were lower in the calcium period than in the control period, although the differences were small (mean +/- SEM office blood pressure: 1.2+/-1.2/1.1+/-0.7 mmHg; home blood pressure: 1.9+/-0.7/1.3+/-0.6 mmHg; 24 h blood pressure: 1.2+/-0.8/0.9+/-0.5 mmHg,), and significant only for home systolic and diastolic blood pressures. The difference in home systolic blood pressure was inversely correlated with the level of home blood pressure in the control period and with the difference in urinary calcium. The difference in 24 h systolic blood pressure was positively correlated with the control level of urinary calcium. Age, sex, antihypertensive medication, drinking habit, sodium intake or order of treatment did not significantly influence the effects of calcium supplementation.

CONCLUSIONS

An increase in calcium intake tends to lower office, home and ambulatory blood pressure in hypertensive patients. However, the antihypertensive effect is too small to support the general application of a high calcium intake in the treatment of hypertension.

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.

Renal responses to hypertonic saline infusion in salt-sensitive spontaneously hypertensive rats

In Wistar Kyoto (WKY) and Sprague Dawley rats, high dietary sodium chloride (NaCl) increases natriuretic and diuretic responses to acute isotonic saline infusion, but in NaCl-sensitive spontaneously hypertensive rats (SHR-S), a high-NaCl diet causes negligible increases in natriuretic and diuretic responses. To investigate whether this deficit in sodium and fluid excretion in SHR-S is stimulus (volume)-specific or because of a more generalized alteration in renal function, the present study measured, in SHR-S and Wistar Kyoto rats, natriuretic and diuretic responses to a hypertonic saline infusion (the amount of sodium infused was equal to that infused in a previous, isotonic experiment). Eight-week-old Wistar Kyoto rats, SHR-S, and salt-resistant SHR were given a basal (1%) or high (8%)-NaCl diet for 2 weeks. Intravenous infusion of hypertonic saline increased mean arterial pressure and reduced heart rate in all groups. Baseline sodium excretion was lower in SHR-S compared with salt-resistant SHR with either diet, but after infusion of hypertonic saline, all 6 groups displayed significant increases in sodium and fluid excretion, glomerular filtration rate, and effective renal blood flow (ERBF). The percent-sodium excretion in response to hypertonic saline infusion was slightly, but significantly, lower in SHR-S (compared with salt-resistant SHR) for either the basal or the high-NaCl diet. We conclude that renal responses to hypertonic saline infusion are affected minimally in SHR-S compared with salt-resistant SHR or Wistar Kyoto rats. Therefore, the deficits in renal function observed in SHR-S after volume loading are not reflected in a renal deficit to hypertonic saline challenge.

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.

Erythrocyte sodium-lithium countertransport in non-modulating offspring and essential hypertensive individuals: response to enalapril

Non-modulators are a subset of essential hypertensive individuals in whom renal hemodynamic and adrenal aldosterone responses to angiotensin II fail to modulate appropriately during high dietary salt intake. The main aim of this study was to investigate the familial aggregation of non-modulation and several erythrocyte Na+ transport systems in normotensive and hypertensive individuals as well as offspring of hypertensive parents. An additional aim was to evaluate the effect of treatment with enalapril on erythrocyte Na+ transport. We studied 15 normotensive subjects (6 males, 27+/-6 years), 14 untreated modulating essential hypertensive subjects (7 males, 38+/-7 years), 12 untreated non-modulating essential hypertensive subjects (7 males, 38+/-6 years), 14 modulating offspring of hypertensive parents (8 males, 25+/-6 years), and 14 non-modulating offspring of hypertensive parents (8 males, 26+/-4 years). Blood pressure was recorded with an oscillometric device and renal plasma flow and glomerular filtration rate by clearances of para-aminohippurate and inulin, respectively. Non-modulating subjects were identified as individuals who failed to increase effective renal plasma flow by 30% and decrease filtration fraction by at least 30% 10 days after changing from a low (20 mmol/d) to a high (250 mmol/d) sodium intake. Erythrocyte Na+ transport was characterized by measurements of the Na+-K+ pump, Na+-Li+ countertransport, Na+-K+-Cl- cotransport, passive Na+ permeability, and Na+ content. After the initial studies, hypertensive individuals were treated with enalapril (20 mg/d P.O.) for 6 months, after which erythrocyte Na+ transport measurements were again made. The main findings were that Na+-Li+ countertransport is increased in non-modulating hypertensive subjects and non-modulating offspring of hypertensive parents, that the increase in blood pressure in response to high salt intake is greater in non-modulating than modulating hypertensive subjects, and that enalapril decreases Na+-Li+ countertransport activity to normal in non-modulating hypertensive subjects. These findings provide support for a possible genetic role in the development of salt sensitivity and suggest that Na+-Li+ countertransport and non-modulation are related phenotypes.

Effects of dietary salt and angiotensin-converting enzyme inhibitor on ATP-driven Ca pump and Na/Ca exchange in aortic rings of Dahl rats

We examined effects of dietary salt and cilazapril on ATP-driven Ca pump and Na/Ca exchange system in arterial smooth muscle of Dahl salt-sensitive (DS) rats. Twenty-four DS rats were assigned to 4 groups. H- and H+ rats were fed a high-salt diet. L- and L+ rats were fed a low-salt diet. H+ and L+ were administered cilazapril. Aortic rings were superfused with physiological saline, and isometric tension was measured. Relaxation rates of low-Na(+)-induced contractions were promoted by the removal of external Ca. Cilazapril significantly decreased blood pressure in both the high- and low-salt diet groups. Salt loading reduced relaxation rates in 1.2 mmol/l Na+, and enhanced the increase in relaxation rates from 1.2 mmol/l to normal Na+. A negative correlation was observed between Ca extrusion by the Ca pump and blood pressure, and a positive correlation was observed between Ca extrusion by Na/Ca exchange and blood pressure. The results suggest that the decrease of Ca2+ extrusion by the ATP-driven Ca pump resulting from a high-salt diet might lead to an elevation in the concentration of cellular Ca2+.

High sodium sensitivity implicates nocturnal hypertension in essential hypertension

We investigated the relationship between sodium sensitivity and diurnal variation of blood pressure in patients with essential hypertension. Twenty-eight inpatients with essential hypertension were maintained on high sodium (12 to 15 g NaCl per day) and low sodium (1 to 3 g NaCl per day) diets for 1 week each. Twenty-four-hour blood pressure and urinary sodium excretion were measured at the end of each diet period, and the sodium sensitivity index was calculated as the ratio of the change in mean arterial pressure to the change in urinary sodium excretion rate by sodium restriction. Patients whose average mean arterial pressure was lowered more than 10% by sodium restriction were assigned to the sodium-sensitive group (n = 16); the remaining patients, whose mean arterial pressure was lowered by less than 10%, were assigned to the non-sodium-sensitive group (n = 12). In the non-sodium-sensitive group, mean arterial pressure and heart rate fell during the nighttime, and average values of systolic, diastolic, and mean arterial pressures during the night were significantly lower than those during the day during both low and high sodium diets. On the other hand, in the sodium-sensitive group, there was no nocturnal fall in mean arterial pressure, and none of the systolic, diastolic, and mean arterial pressure values during the nighttime was different from the respective pressure values during the daytime during either sodium diet. The sodium sensitivity index was positively correlated with the fall in mean arterial pressure during the nighttime during a high sodium diet (r = .55, P < .01). These results indicate that in patients with sodium-sensitive essential hypertension, blood pressure fails to fall during the night. High sodium sensitivity may be a marker of greater risk of renal and cardiovascular complications, as has been found in nondippers, patients whose blood pressure fails to fall during the night.

Angiotensin I-converting enzyme gene polymorphism and salt sensitivity in essential hypertension

We undertook the present study in 66 Japanese patients with essential hypertension to identify genetic factors associated with salt sensitivity. Patients were classified into salt-sensitive or salt-resistant groups on the basis of changes in their mean blood pressures from a week of a low salt diet (50 mmol/d) to a week of a high salt diet (340 mmol/d). Salt sensitivity and resistance were studied in relation to a 287-bp insertion/deletion (I/D) polymorphism of the angiotensin I-converting enzyme gene detected by a polymerase chain reaction method and the haptoglobin phenotype determined by polyacrylamide gel electrophoresis. Patients with the angiotensin I-converting enzyme gene genotype II were more apt to be salt sensitive than patients with the ID and DD genotypes, although plasma renin activity was similar in each group. The frequency of the I allele in the salt-sensitive group was significantly higher than that in the salt-resistant group (chi2 = 7.4, odds ratio = 2.78). However, there was no significant relationship between haptoglobin phenotype and salt sensitivity. These data suggest that an I/D polymorphism of the angiotensin I-converting enzyme gene is a genetic factor associated with salt sensitivity of blood pressure independently of plasma renin activity in Japanese patients with essential hypertension.

Salt sensitivity of blood pressure in humans

A variety of different techniques have been used for the assessment of the blood pressure response to changes in salt and water balance in humans. These have generally been found to be reproducible and to yield congruent results. This review surveys the characteristics of subjects identified as salt sensitive and salt resistant by different investigators from demographic and physiological perspectives.

The effect of increased salt intake on blood pressure of chimpanzees

A colony of 26 chimpanzees given a fruit and vegetable diet of very low Na and high K intake were maintained in long-standing, socially stable small groups for three years. Half of them had salt added progressively to their diet during 20 months. This addition of salt within the human dietetic range caused a highly significant rise in systolic, mean and diastolic blood pressure. The change reversed completely by six months after cessation of salt. The effect of salt differed between chimpanzees, some having a large blood pressure rise and others small or no rise. These results in the species phylogenetically closest to humans bear directly on causation of human hypertension, particularly in relation to migration of preliterate people, with low Na diet, to a Western urban lifestyle with increased salt intake. The hedonic liking for salt and avid ingestion was apt during human prehistory involving hunter-gatherer-scavenger existence in the interior of continents with a scarcity of salt, but is maladaptive in urban technological life with salt cheap and freely available.

Alpha 2-adrenoceptors in brain and kidney during development of hypertension in Dahl-Iwai salt-sensitive rats

BACKGROUND

Both renal and extrarenal factors have been considered to contribute to the development of hypertension in Dahl salt-sensitive rats, but contents of both factors have not been established precisely.

AIM

To clarify the role of those factors in the sympathetic nervous system, we examined the regulation of alpha2-adrenoceptors in the lower brainstem and the renal tubular basolateral membranes simultaneously during the development of salt-induced hypertension in Dahl-Iwai salt-sensitive rats.

METHODS

Dahl-Iwai salt-sensitive or resistant rats were fed a high (8.0% NaCl)- or low (0.3%)- salt diet from 4 to 6 or 10 weeks of age. At 4, 6 and 10 weeks of age, the plasma membranes of the lower brainstem and the renal tubular basolateral membranes were obtained simultaneously and alpha 2-adrenoceptors were quantified by a radioligand binding assay using 3H-rauwolscine.

RESULTS

In the salt-sensitive rats, systolic blood pressure was significantly higher in those fed a high-salt diet than in those fed a low-salt diet. In the salt-resistant rats, both the high- and the low-salt groups showed similar blood pressure levels. At 6 weeks of age, alpha 2-receptor densities of the salt-sensitive rats fed a high-salt diet were lower in the lower brainstem and higher in the renal basolateral membranes than those fed a low-salt diet. In contrast, in the salt-resistant rats, both the high- and the low-salt groups had similar densities. At 10 weeks of age, the difference between the high- and the low-salt groups in the salt-sensitive rats disappeared in both the brainstem and the renal basolateral membranes.

CONCLUSIONS

Alpha 2-adrenoceptor regulation in the brainstem and the renal basolateral membranes differs between Dahl-Iwai salt-sensitive and salt-resistant rats. The modulation of alpha 2-adrenoceptors by a high salt intake may be essential particularly in the early phase of the development of salt-induced hypertension.

Alterations in sodium metabolism as an etiological model for hypertension

An adequate matching for race, sex, stage of the menstrual cycle, family history of hypertension, and the amount of sodium and other electrolytes in the diet should be a prerequisite for valid conclusions when interpreting the erythrocyte concentration and fluxes of sodium in essential hypertensive patients in comparison with normal subjects. Alterations in intracellular sodium concentration and transmembrane sodium transport systems as causes of essential hypertension are postulated. This review article describes how this abnormal sodium and calcium metabolism translates into increased systemic vascular resistance through altered vasoactive responses and/or vasculature structural changes.

Milk electrolyte content of Dahl hypertensive and normotensive rats

Milk samples were collected from lightly anesthetized lactating female rats of the Dahl hypertension-sensitive (SS/Jr) and Dahl hypertension-resistent (SR/Jr) inbred strains on postnatal days 8, 14 and 18. These milk samples were stored at 4 degrees C until analyzed for content of calcium (Ca++), magnesium (Mg++), chloride (Cl-), potassium (K+), sodium (Na+), and total protein. Our findings revealed that milk samples from females of the two strains were remarkably similar in content of electrolytes and total protein at each of the three sampling times. The only significant difference from among a total of 18 strain comparisons across the three sample times was that milk levels of Ca++ were significantly higher in SS/Jrs compared to SR/Jrs on postnatal day 14. These findings clearly indicate that these milk constituents do not differ between mothers of the two Dahl strains. Thus, milk concentrations of electrolytes and protein do not appear to serve as an environmental stimulus during the preweanling period for the dramatic age-related increases in arterial pressure characteristic of the SS/Jr strain.

Effect of supplemental dietary calcium on the development of DOCA-salt hypertension in weanling rats

This study characterizes the response to dietary calcium in DOCA-salt hypertension. Body weight, systolic blood pressure, and total serum calcium levels were compared among normotensive control rats, DOCA-salt hypertensive rats treated with calcium carbonate (CaCO3) augmentation, and DOCA-salt hypertensive rats without supplementary dietary calcium. Dietary calcium augmentation prevented the rise of blood pressure that is normally produced by DOCA-salt. Attenuation in systolic blood pressure was independent of weight loss or total serum calcium and may be linked to alterations in calcium homeostasis that are seen in both human and experimental hypertension. Thus this study provides important data that may assist in further explicating the role that alterations in calcium homeostasis play in DOCA-salt hypertension. Further, these data may also be important in the identification of a nonpharmacological intervention for testing in humans.

Salt sensitivity in hypertension. Renal and cardiovascular implications

The mechanisms responsible for the increase in blood pressure response to high salt intake in salt-sensitive patients with essential hypertension are complex and only partially understood. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for such patients to retain salt and develop salt-dependent hypertension. The possible role of vasodilator and natriuretic agents, such as the prostaglandins, endothelium-derived relaxing factor, atrial natriuretic factor, and kinin-kallikrein system, requires further investigation. An association between salt sensitivity and a greater propensity to develop renal failure has been described in certain groups of hypertensive patients, such as blacks, the elderly, and those with diabetes mellitus. Salt-sensitive patients with essential hypertension manifest a deranged renal hemodynamic adaptation to a high dietary salt intake. During a low salt diet, salt-sensitive and salt-resistant patients have similar mean arterial pressure, glomerular filtration rate, effective renal plasma flow, and filtration fraction. On the other hand, during a high salt intake glomerular filtration rate does not change in either group, and effective renal blood flow increases in salt-resistant but decreases in salt-sensitive patients; filtration fraction and glomerular capillary pressure decrease in salt-resistant but increase in salt-sensitive patients. Salt-sensitive patients are also more likely than salt-resistant patients to manifest left ventricular hypertrophy, microalbuminuria, and metabolic abnormalities that may predispose them to cardiovascular diseases. In conclusion, salt sensitivity in hypertension is associated with substantial renal, hemodynamic, and metabolic abnormalities that may enhance the risk of cardiovascular and renal morbidity.

Behavior analysis and the search for the origins of hypertension

Hypertension is a disorder of sodium regulation that develops over time in a context of the interactions of the individual with the environment. Experimental hypertension can be induced in laboratory animals and normotensive humans via increases in sodium intake under conditions of aversive behavioral control. Readiness for avoidance contingencies includes a breathing pattern characterized by subnormal rate and normal tidal volume. Studies with humans have shown that this inhibitory breathing pattern is associated with increased plasma acidity, increased renal sodium reabsorption, increased secretion of digitalis-like hormones that inhibit sodium-pump activity, and increased vasoconstriction and blood pressure. Behavioral research is needed that defines the necessary and sufficient conditions for inhibitory breathing and its role in the development of hypertension.

Effect of dietary sodium chloride on the development of renal glomerular and vascular lesions in hypertensive rats

1. The hypothesis that high levels of NaCl in the diet aggravates hypertension-associated renal vascular lesions was examined in unilaterally nephrectomized deoxycorticosterone acetate treated (DOCA) and two kidney one clip (2K1C) hypertensive rats, as well as normotensive controls. 2. High NaCl diet significantly increased systolic blood pressure (SBP) in DOCA rats, but had little effect on SBP in normal control rats, and did not affect the rise of SBP in 2K1C rats. 3. High NaCl diet was associated with a higher percentage of glomerular lesions and renal arterial and arteriolar lesions in DOCA and 2K1C rats (P < 0.05). 4. Thus high NaCl intake exacerbated renal arterial and arteriolar and glomerular lesions in both DOCA and 2K1C hypertensive rats. In 2K1C rats this effect may be in part independent of blood pressure.