NaCl-induced renal vasoconstriction in salt-sensitive African Americans: antipressor and hemodynamic effects of potassium bicarbonate

High dietary salt intake attenuates nitric oxide mediated endothelium-dependent vasodilation and increases oxidative stress in pregnancy

OBJECTIVE

This study aimed to investigate the impact of dietary salt intake during normal pregnancy on maternal microvascular and macrovascular endothelium-dependent reactivity and oxidative stress level.

MATERIALS AND METHODS

In this cross-sectional study, based on their 24-h urinary sodium excretion, pregnant women (37-40 weeks of gestation) were divided into three groups: normal salt (<5.75 g/day, N  = 12), high salt (5.75-10.25 g/day, N  = 36), and very high salt (VHS;>10.25 g/day, N  = 17). Forearm skin microvascular reactivity in response to vascular occlusion, local heating (LTH) and iontophoresis of acetylcholine (AChID), as well as brachial artery flow mediated dilation (FMD) were measured. Serum nitric oxide, endocan, 8-iso-prostaglandin F2α (8-iso-PGF2α), thiobarbituric acid reactive substances (TBARS), and ferric-reducing ability of plasma assay were measured as biomarkers of endothelial function/activation and oxidative stress.

RESULTS

Brachial artery FMD, microvascular AChID, and LTH were significantly decreased in VHS compared with NS group, while LTH was also decreased in normal salt compared with high salt group. Nitric oxide was significantly decreased in both high salt and VHS groups compared with normal salt. Endocan, 8-iso-PGF2α, and TBARS were significantly increased in VHS compared with the normal salt group.

CONCLUSION

High dietary salt intake is associated with decreased nitric oxide mediated endothelium-dependent vasodilation in peripheral microcirculation and macrocirculation of healthy pregnant women due to increased oxidative stress.

Salt Sensitivity of Blood Pressure in Black People: The Need to Sort Out Ancestry Versus Epigenetic Versus Social Determinants of Its Causation

Race is a social construct, but self-identified Black people are known to have higher prevalence and worse outcomes of hypertension than White people. This may be partly due to the disproportionate incidence of salt sensitivity of blood pressure in Black people, a cardiovascular risk factor that is independent of blood pressure and has no proven therapy. We review the multiple physiological systems involved in regulation of blood pressure, discuss what, if anything is known about the differences between Black and White people in these systems and how they affect salt sensitivity of blood pressure. The contributions of genetics, epigenetics, environment, and social determinants of health are briefly touched on, with the hope of stimulating further work in the field.

Salty Subjects: Unpacking Racial Differences in Salt-Sensitive Hypertension

PURPOSE OF REVIEW

To review underlying mechanisms and environmental factors that may influence racial disparities in the development of salt-sensitive blood pressure.

RECENT FINDINGS

Our group and others have observed racial differences in diet and hydration, which may influence salt sensitivity. Dietary salt elicits negative alterations to the gut microbiota and immune system, which may increase hypertension risk, but little is known regarding potential racial differences in these physiological responses. Antioxidant supplementation and exercise offset vascular dysfunction following dietary salt, including in Black adults. Furthermore, recent work proposes the role of racial differences in exposure to social determinants of health, and differences in health behaviors that may influence risk of salt sensitivity. Physiological and environmental factors contribute to the mechanisms that manifest in racial differences in salt-sensitive blood pressure. Using this information, additional work is needed to develop strategies that can attenuate racial disparities in salt-sensitive blood pressure.

Mechanism-based strategies to prevent salt sensitivity and salt-induced hypertension

High-salt diets are a major cause of hypertension and cardiovascular (CV) disease. Many governments are interested in using food salt reduction programs to reduce the risk for salt-induced increases in blood pressure and CV events. It is assumed that reducing the salt concentration of processed foods will substantially reduce mean salt intake in the general population. However, contrary to expectations, reducing the sodium density of nearly all foods consumed in England by 21% had little or no effect on salt intake in the general population. This may be due to the fact that in England, as in other countries including the U.S.A., mean salt intake is already close to the lower normal physiologic limit for mean salt intake of free-living populations. Thus, mechanism-based strategies for preventing salt-induced increases in blood pressure that do not solely depend on reducing salt intake merit attention. It is now recognized that the initiation of salt-induced increases in blood pressure often involves a combination of normal increases in sodium balance, blood volume and cardiac output together with abnormal vascular resistance responses to increased salt intake. Therefore, preventing either the normal increases in sodium balance and cardiac output, or the abnormal vascular resistance responses to salt, can prevent salt-induced increases in blood pressure. Suboptimal nutrient intake is a common cause of the hemodynamic disturbances mediating salt-induced hypertension. Accordingly, efforts to identify and correct the nutrient deficiencies that promote salt sensitivity hold promise for decreasing population risk of salt-induced hypertension without requiring reductions in salt intake.

High dietary salt intake increases urinary NGAL excretion and creatinine clearance in healthy young adults

In rodents and older patients with elevated blood pressure (BP), high dietary sodium increases excretion of biomarkers of kidney injury, but it is unclear whether this effect occurs in healthy young adults. The purpose of this study was to determine whether short-term high dietary salt increases urinary excretion of the kidney injury biomarkers neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) in healthy young adults. Twenty participants participated in a double-blind, placebo-controlled, randomized crossover study. For 10 days each, participants were asked to consume salt (3,900 mg sodium) or placebo capsules. We measured BP during each visit, obtained 24-h urine samples for measurements of electrolytes, NGAL, and KIM-1, and assessed creatinine clearance. Compared with placebo, salt loading increased daily urinary sodium excretion (placebo: 130.3 ± 62.4 mmol/24 h vs. salt: 287.2 ± 72.0 mmol/24 h, P < 0.01). There was no difference in mean arterial BP (placebo: 77 ± 7 mmHg vs. salt: 77 ± 6 mmHg, P = 0.83) between conditions. However, salt loading increased the urinary NGAL excretion rate (placebo: 59.8 ± 44.4 ng/min vs. salt: 80.8 ± 49.5 ng/min, P < 0.01) and increased creatinine clearance (placebo: 110.5 ± 32.9 mL/min vs. salt: 145.0 ± 24.9 mL/min, P < 0.01). Urinary KIM-1 excretion was not different between conditions. In conclusion, in healthy young adults 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker NGAL but not KIM-1.NEW & NOTEWORTHY In healthy young adults, 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker neutrophil gelatinase-associated lipocalin despite no change in resting blood pressure.

The Sweet and Salty Dietary Face of Hypertension and Cardiovascular Disease in Lebanon

According to the World Health Organization (WHO), an estimated 1.28 billion adults aged 30–79 years worldwide have hypertension; and every year, hypertension takes 7.6 million lives. High intakes of salt and sugar (mainly fructose from added sugars) have been linked to the etiology of hypertension, and this may be particularly true for countries undergoing the nutrition transition, such as Lebanon. Salt-induced hypertension and fructose-induced hypertension are manifested in different mechanisms, including Inflammation, aldosterone-mineralocorticoid receptor pathway, aldosterone independent mineralocorticoid receptor pathway, renin-angiotensin system (RAS), sympathetic nervous system (SNS) activity, and genetic mechanisms. This review describes the evolution of hypertension and cardiovascular diseases (CVDs) in Lebanon and aims to elucidate potential mechanisms where salt and fructose work together to induce hypertension. These mechanisms increase salt absorption, decrease salt excretion, induce endogenous fructose production, activate fructose-insulin-salt interaction, and trigger oxidative stress, thus leading to hypertension. The review also provides an up-to-date appraisal of current intake levels of salt and fructose in Lebanon and their main food contributors. It identifies ongoing salt and sugar intake reduction strategies in Lebanon while acknowledging the country’s limited scope of regulation and legislation. Finally, the review concludes with proposed public health strategies and suggestions for future research, which can reduce the intake levels of salt and fructose levels and contribute to curbing the CVD epidemic in the country.

Salt-Sensitive Hypertension, Renal Injury, and Renal Vasodysfunction Associated With Dahl Salt-Sensitive Rats Are Abolished in Consomic SS.BN1 Rats

Background

Abnormal renal hemodynamic responses to salt‐loading are thought to contribute to salt‐sensitive (SS) hypertension. However, this is based largely on studies in anesthetized animals, and little data are available in conscious SS and salt‐resistant rats.

Methods and Results

We assessed arterial blood pressure, renal function, and renal blood flow during administration of a 0.4% NaCl and a high‐salt (4.0% NaCl) diet in conscious, chronically instrumented 10‐ to 14‐week‐old Dahl SS and consomic SS rats in which chromosome 1 from the salt‐resistant Brown‐Norway strain was introgressed into the genome of the SS strain (SS.BN1). Three weeks of high salt intake significantly increased blood pressure (20%) and exacerbated renal injury in SS rats. In contrast, the increase in blood pressure (5%) was similarly attenuated in Brown‐Norway and SS.BN1 rats, and both strains were completely protected against renal injury. In SS.BN1 rats, 1 week of high salt intake was associated with a significant decrease in renal vascular resistance (−8%) and increase in renal blood flow (15%). In contrast, renal vascular resistance failed to decrease, and renal blood flow remained unchanged in SS rats during high salt intake. Finally, urinary sodium excretion and glomerular filtration rate were similar between SS and SS.BN1 rats during 0.4% NaCl and high salt intake.

Conclusions

Our data support the concept that renal vasodysfunction contributes to blood pressure salt sensitivity in Dahl SS rats, and that genes on rat chromosome 1 play a major role in modulating renal hemodynamic responses to salt loading and salt‐induced hypertension.

Sodium Intake Is Associated With Renal Resistive Index in an Adult Population-Based Study

Renal resistive index (RRI) has been associated with adverse renal and cardiovascular outcomes. Although traditionally considered a marker of intrinsic renal damage, RRI could also reflect systemic vascular dysfunction. As sodium intake was linked to alterations in vascular properties, we wished to characterize the association of salt consumption with RRI in the general adult population. Participants were recruited in a population-based study in Switzerland. RRI was measured by ultrasound in 3 segmental arteries. Sodium intake (UNa; mmol/24 h) was estimated on 24-hour urine samples. Carotido-femoral pulse wave velocity was obtained by applanation tonometry. Mixed multivariate regression models were used with RRI or pulse wave velocity as independent variables and UNa as dependent variable, adjusting for possible confounders. We included 1002 patients in the analyses with 528 (52.7%) women and mean age of 47.2±17.4. Mean values of UNa and RRI were 141.8±61.1 mmol/24 h and 63.8±5.5%, respectively. In multivariate analysis, UNa was positively associated with RRI (P=0.002) but not with pulse wave velocity (P=0.344). Plasma renin activity and aldosterone did not modify the relationship between UNa and RRI (P=0.087 for interaction). UNa/urinary potassium ratio was positively associated with pulse wave velocity ≥12 m/s (P=0.033). Our results suggest that dietary salt consumption has a direct impact on renal hemodynamic in the adult general population. Alterations in vascular properties likely explain those findings, but inadequate renal vaso-motor response is also possible. Sodium intake could thus potentially be linked to underlying structural systemic damages affecting this population.

Should we eat more potassium to better control blood pressure in hypertension?

Changes in lifestyle and nutrition are recommended as the first-step approach to the management of hypertension by all national and international guidelines. Today, when considering nutritional factors in hypertension, almost all the attention is focused on the reduction of salt intake to improve blood pressure (BP) control. Changes in potassium intake are only briefly evoked in guidelines. Few physicians actually think about proposing to eat more foods that are high in potassium (fruits, vegetables, nuts) to better control BP. Yet, during the last 40 years, increasing evidence has accumulated demonstrating that increasing potassium intake, either with food products or with supplements, is associated with significant reductions of both systolic and diastolic BP. The hypotensive effect of potassium is particularly marked in patients with hypertension and in subjects with a very high sodium intake, suggesting that potassium counterbalances the effects of sodium. In addition, several meta-analyses have now confirmed that high potassium intake reduces the risk of stroke by ∼ 25%. Finally, increasing potassium in the diet may perhaps be beneficial for some renal patients, as post hoc analyses have suggested that a high potassium intake may retard the decline of renal function in patients with early chronic kidney disease (CKD) stages. However, high potassium intake may be risky and sometimes even dangerous in hypertensive patients with CKD stages 3-5, specifically diabetics. In this context, however, as the level of evidence remains low, more prospective clinical studies are needed. The goal of this review is to discuss the actual evidence that supports the recommendation to eat more potassium in order to better control BP in essential hypertension and to review the restrictions in CKD patients with hypertension.

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

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

The American Heart Association Scientific Statement on salt sensitivity of blood pressure: Prompting consideration of alternative conceptual frameworks for the pathogenesis of salt sensitivity?

: Recently, the American Heart Association (AHA) published a scientific statement on salt sensitivity of blood pressure which emphasized a decades old conceptual framework for the pathogenesis of this common disorder. Here we examine the extent to which the conceptual framework for salt sensitivity emphasized in the AHA Statement accommodates contemporary findings and views of the broader scientific community on the pathogenesis of salt sensitivity. In addition, we highlight alternative conceptual frameworks and important contemporary theories of salt sensitivity that are little discussed in the AHA Statement. We suggest that greater consideration of conceptual frameworks and theories for salt sensitivity beyond those emphasized in the AHA Statement may help to advance understanding of the pathogenesis of salt-induced increases in blood pressure and, in consequence, may lead to improved approaches to preventing and treating this common disorder.

Simulating a virtual population's sensitivity to salt and uninephrectomy

Salt sensitivity, with or without concomitant hypertension, is associated with increased mortality. Reduced functional renal mass plays an important role in causing salt-sensitive hypertension for many individuals. Factors that are important in the condition of decreased renal mass and how they affect blood pressure (BP) or salt sensitivity are unclear. We used HumMod, an integrative mathematical model of human physiology, to create a heterogeneous population of 1000 virtual patients by randomly varying physiological parameters. We examined potential physiological mechanisms responsible for the change in BP in response to high-salt diet (8× change in salt intake for three weeks) with full kidney mass and again after the removal of one kidney in the same group of virtual patients. We used topological data analysis (TDA), a clustering algorithm tool, to analyse the large dataset and separate patient subpopulations. TDA distinguished five unique clusters of salt-sensitive individuals (more than 15 mmHg change in BP with increased salt). While these clusters had similar BP responses to salt, different collections of variables were responsible for their salt sensitivity, e.g. greater reductions in glomerular filtration rate (GFR) or impairments in the renin-angiotensin system. After simulating uninephrectomy in these virtual patients, the three most salt-sensitive clusters were associated with a blunted increase in renal blood flow (RBF) and higher increase in loop and distal sodium reabsorption when compared with the salt-resistant population. These data suggest that the suppression of sodium reabsorption and renin-angiotensin system is key for salt resistance, and RBF in addition to GFR may be an important factor when considering criteria for kidney donors. Here, we show that in our model of human physiology, different derangements result in the same phenotype. While these concepts are known in the experimental community, they were derived here by considering only the data obtained from our virtual experiments. These methodologies could potentially be used to discover patterns in patient sensitivity to dietary change or interventions and could be a revolutionary tool in personalizing medicine.

Novel Paradigms of Salt and Hypertension

Salt resistance/sensitivity refers specifically to the effect of dietary sodium chloride (salt) intake on BP. Increased dietary salt intake promotes an early and uniform expansion of extracellular fluid volume and increased cardiac output. To compensate for these hemodynamic changes and maintain constant BP in salt resistance, renal and peripheral vascular resistance falls and is associated with an increase in production of nitric oxide. In contrast, the decline in peripheral vascular resistance and the increase in nitric oxide are impaired or absent in salt sensitivity, promoting an increase in BP in these individuals. Endothelial dysfunction may pose a particularly significant risk factor in the development of salt sensitivity and subsequent hypertension. Vulnerable salt-sensitive populations may have in common underlying endothelial dysfunction due to genetic or environmental influences. These individuals may be very sensitive to the hemodynamic stress of increased effective blood volume, setting in motion untoward molecular and biochemical events that lead to overproduction of TGF-β, oxidative stress, and limited bioavailable nitric oxide. Finally, chronic high-salt ingestion produces endothelial dysfunction, even in salt-resistant subjects. Thus, the complex syndrome of salt sensitivity may be a function of the endothelium, which is integrally involved in the vascular responses to high salt intake.

Dipping in Ambulatory Blood Pressure Monitoring Correlates With Overnight Urinary Excretion of Catecholamines and Sodium

Nondipping blood pressure (BP) is associated with increased morbidity and mortality. This study examines the relationship of "dipping" in 24-hour ambulatory BP monitoring (ABPM) with awake and sleeping urinary norepinephrine (NE) and epinephrine (EPI), and that of urinary NE and EPI with urinary sodium (UNa). Fifty nondippers and 65 dippers were included in the present study. Collected data included age, sex, body mass index, history of hypertension, current antihypertensive treatment, ABPM data, and NE, EPI, and UNa values. Hierarchical multiple regression analysis with the night-to-day ratio (NDR) of systolic BP as a dependent variable showed that the composite term of the NDRs of urinary NE and EPI was a significant predictor for dipping. Results also show a differential role of NE and EPI in circadian UNa excretion in dippers and nondippers. These results indicate that the sympathetic nervous system is involved in the regulation of circadian BP variations and UNa excretion.

Salt-sensitive hypertension: mechanisms and effects of dietary and other lifestyle factors

Salt sensitivity, which is an increase in blood pressure in response to high dietary salt intake, is an independent risk factor for cardiovascular disease and mortality. It is associated with physiological, environmental, demographic, and genetic factors. This review focuses on the physiological mechanisms of salt sensitivity in populations at particular risk, along with the associated dietary factors. The interplay of mechanisms such as the renin-angiotensin aldosterone system, endothelial dysfunction, ion transport, and estrogen decrease in women contributes to development of salt sensitivity. Because of their effects on these mechanisms, higher dietary intakes of potassium, calcium, vitamin D, antioxidant vitamins, and proteins rich in L-arginine, as well as adherence to dietary patterns similar to the DASH (Dietary Approaches to Stop Hypertension) diet, can be beneficial to salt-sensitive populations. In contrast, diets similar to the typical Western diet, which is rich in saturated fats, sucrose, and fructose, together with excessive alcohol consumption, may exacerbate salt-sensitive changes in blood pressure. Identifying potential mechanisms of salt sensitivity in susceptible populations and linking them to protective or harmful dietary and lifestyle factors can lead to more specific guidelines for the prevention of hypertension and cardiovascular disease.

Race/ethnicity determines the relationships between oxidative stress markers and blood pressure in individuals with high cardiovascular disease risk

Oxidative stress (OS) and cardiovascular (CV) reactivity are related to CV morbidity and mortality. However, little is known about the relationships between these CV risk factors and their confounders. We hypothesize that higher OS is linked to higher blood pressure (BP) reactivity to acute laboratory stressors and in the natural setting. We studied 137 subjects with a family history of hypertension and early myocardial infarction. There were 63 European Americans (EAs) (38 males) and 74 African Americans (AAs) (35 males), aged 19-36 (27.6±3.1). The protocol included a competitive video game, cold stressor and ambulatory BP recording. Blood samples were drawn six times for OS markers (8-hydroxydeoxyguanosine (8-OHdG) and 8-Isoprostane) assay. Repeated measures analyses of covariance were used to test for mean differences and Pearson correlations were used to test OS and BP associations. There were no significant race/ethnicity differences in BP reactivity to either stressor (both P's>0.48). 8-OHdG levels were significantly lower across all time points for AAs than for EAs (P<0.05), while levels of 8-isoprostane did not differ significantly (P>0.10). Averaged 8-OHdG levels significantly correlated with systolic blood pressure (SBP) reactivity (r=0.45, <0.01) and 24-h, daytime and nighttime SBP (r range=0.37-0.42, all P's<0.02) for EAs but not for AAs, whereas 8-isoprostane levels were significantly correlated with reactive SBP and nighttime diastolic blood pressure (DBP) (both r's=0.38, P<0.01) for AAs but not for EAs. These findings suggest a link between OS and BP changes in subjects at high risk for CV disease (CVD). Further, race/ethnicity determines which OS marker will impact BP variation implying race/ethnicity differences in OS-related mechanisms of CVD.

Translation and validation of the dietary approaches to stop hypertension for koreans intervention: culturally tailored dietary guidelines for Korean Americans with high blood pressure

BACKGROUND

Lifestyle modification strategies such as adoption of the Dietary Approaches to Stop Hypertension (DASH) diet are now recognized as an integral part of high blood pressure (HBP) management. Although the high prevalence of HBP among Korean Americans (KAs) is well documented, few dietary interventions have been implemented in this population, in part because of a lack of culturally relevant nutrition education guidelines. Translating and testing the efficacy of culturally relevant dietary recommendations using a well-established dietary guideline such as DASH are imperative for promoting better cardiovascular health for this high-risk cultural group.

OBJECTIVE

The aims of this study were to systematically translate and validate a culturally modified DASH for Koreans (K-DASH) and obtain preliminary evidence of efficacy.

METHODS

A 2-step approach of intervention translation and efficacy testing, together with close adherence to principles of community-based participatory research, was used to maximize community input. A 1-group pre-post design with 24-hour urine and 24-hour ambulatory blood pressure monitoring comparisons was used to test the initial feasibility and efficacy of the K-DASH intervention.

RESULTS

A total of 28 KAs with HBP participated in a 10-week dietary intervention consisting of group education sessions and individual counseling. Both systolic blood pressure and diastolic blood pressure, as measured by ambulatory blood pressure monitoring, were significantly decreased at postintervention evaluation (systolic blood pressure, -4.5 mm Hg; diastolic blood pressure, -2.6 mm Hg; P < .05). Serum low-density lipoprotein cholesterol was significantly decreased (-7.3 mg/dL; P < .05). Serum potassium and ascorbic acid levels were also improved in the reference range. Urine potassium level was significantly increased, supporting increased fruit and vegetable consumption.

CONCLUSION

This pilot study has (a) demonstrated that a cultural adaptation of DASH using community-based participatory research methodology produced a culturally relevant and efficacious dietary intervention for the KAs with HBP and (b) provided strong preliminary evidence for the efficacy of the K-DASH intervention in reducing HBP in hypertensive KAs.

Relationship of resistant hypertension and treatment outcomes with total arterial compliance in a predominantly African American hypertensive cohort

Resistant hypertension (RH) affects 8% to 30% of hypertensive patients. Blood pressure (BP) reflects the interaction between vascular compliance, resistance to flow, intravascular volume, and cardiac contractility. The relationship of RH with total arterial compliance index (TACI) has not been adequately explored. The RH period prevalence (RH at baseline or follow-up) was determined in a hypertensive cohort (N=156) and compared across quartiles of TACI. Age- and sex-adjusted systolic BP, diastolic BP, and antihypertensive therapeutic intensity score (TIS) were also determined at the time of first BP control. The cohort was 85.3% African American and 67.3% female. Median follow-up was 7 months. The prevalence of RH at baseline was 14.7% while the period prevalence was 43.6%. The period prevalence of RH by ascending quartile for TACI was 66%, 36.8%, 40%, and 30.8% (P=.008). The average BP and antihypertensive TIS at first BP control across TACI quartiles was 122.3/73.4 mm Hg (2.26), 120.7/72.5 mm Hg (1.88), 122.4/75.3 mm Hg (1.71), and 120.0/79.4 mm Hg (1.64) (P=.62, P=.03, P=.13). Low TACI was linked to higher RH prevalence and antihypertensive TIS at first attainment of goal BP according to the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure. TACI provides prognostic information that is clinically and perhaps pathophysiologically relevant in RH.

Therapy of hypertension in African Americans

Hypertension in African Americans is a major clinical and public health problem because of the high prevalence and premature onset of elevated blood pressure (BP) as well as the high burden of co-morbid factors that lead to pharmacological treatment resistance (obesity, diabetes mellitus, depressed glomerular filtration rate, and albuminuria). BP control rates are lower in African Americans, especially men, than in other major race/ethnicity-sex groups; overall control rates are 29.9% for non-Hispanic Black men. Optimal antihypertensive treatment requires a comprehensive approach that encompasses multifactorial lifestyle modifications (weight loss, salt and alcohol restriction, and increased physical activity) plus drug therapy. The most important initial step in the evaluation of patients with elevated BP is to appropriately risk stratify them to allow determination of whether they are truly hypertensive and also to determine their goal BP levels. The overwhelming majority of African American hypertensive patients will require combination antihypertensive drug therapy to maintain BP consistently below target levels. The emphasis is now appropriately on utilizing the most effective drug combinations for the control of BP and protection of target-organs in this high-risk population. When BP is >15/10 mmHg above goal levels, combination drug therapy is recommended. The preferred combination is a calcium antagonist/angiotensin-converting enzyme inhibitor or, alternatively, in edematous and/or volume overload states, a thiazide diuretic/angiotensin-converting inhibitor.

Non-pharmacological aspects of blood pressure management: what are the data?

Hypertension affects 29% of US adults and is a significant risk factor for cardiovascular morbidity and mortality. Epidemiological data support contribution of several dietary and other lifestyle-related factors to the development of high blood pressure (BP). Several clinical trials investigated the efficacy of non-pharmacological interventions and lifestyle modifications to reduce BP. Best evidence from randomized controlled trials supports BP-lowering effects of weight loss, the Dietary Approaches to Stop Hypertension (DASH) diet, and dietary sodium (Na(+)) reduction in those with prehypertension, with more pronounced effects in those with hypertension. In hypertensive participants, the effects on BP of DASH combined with low Na(+) alone or with the addition of weight loss were greater than or equal to those of single-drug therapy. Trials where food was provided to participants were more successful in showing a BP-lowering effect. However, clinical studies with long-term follow-up revealed that lifestyle modifications were difficult to maintain. Findings from controlled trials of increased potassium, calcium, or magnesium intake, or reduction in alcohol intake revealed modest BP-lowering effects and are less conclusive. The reported effects of exercise independent of weight loss on BP are inconsistent.

Hypertension in special populations: chronic kidney disease, organ transplant recipients, pregnancy, autonomic dysfunction, racial and ethnic populations

The benefits of appropriate blood pressure (BP) control include reductions in proteinuria and possibly a slowing of the progressive loss of kidney function. Overall, medication therapy to lower BP during pregnancy should be used mainly for maternal safety because of the lack of data to support an improvement in fetal outcome. The major goal of hypertension treatment in those with baroreceptor dysfunction is to avoid the precipitous, severe BP elevations that characteristically occur during emotional stimulation. The treatment of hypertension in African Americans optimally consists of comprehensive lifestyle modifications along with pharmacologic treatments, most often with combination, not single-drug, therapy.

Are all individuals equally sensitive in the blood pressure to high salt intake? (Review article)

It has been reported that only one-third of normotensive subjects and half of hypertensive patients are salt-sensitive. Many causes of salt-sensitivity have been proposed. Our suggestion is that a reduced urinary kallikrein level may be one cause, since mutant kininogen-deficient rats, which cannot generate kinin in the urine, are salt-sensitive. Renal kallikrein is secreted by the connecting tubule cells of the kidney, which are located just distal to the macula densa or the tubuloglomerular feedback system. Excess amounts of sodium taken overflow into the distal tubules and are reabsorbed in the collecting ducts. Kinins generated inhibit sodium reabsorption in the collecting ducts. Both blacks and whites with essential hypertension excrete less urinary kallikrein than do their normotensive counterparts, but the mean value in "normotensive blacks" were not different from that in "hypertensive whites". African-Americans consume less potassium than whites. Potassium and ATP-sensitive potassium channel blockers are releasers of renal kallikrein. In a small-scale study, sodium loading caused more increase in the systolic blood pressure in urinary low-kallikrein group than in urinary high-kallikrein group. Large-scale clinical studies, under strict control of potassium intake, are needed to elucidate the relationship between salt-sensitivity and urinary kallikrein levels.

The effect of a dietary supplement of potassium chloride or potassium citrate on blood pressure in predominantly normotensive volunteers

Blood pressure (BP) shows a continuous relationship with the risk of CVD. There is substantial evidence that dietary potassium exerts an anti-pressor effect. Most clinical trials have used KCl. However, the chloride ion may have a pressor effect and in foods potassium is associated with organic anions. In a double-blind randomized placebo-controlled trial we explored the effect on BP of two salts of potassium, KCl and potassium citrate (K-cit), in predominantly young healthy normotensive volunteers. The primary outcome was the change in mean arterial pressure as measured in a clinic setting. After 6 weeks of supplementation, compared with the placebo group (n 31), 30 mmol K-cit/d (n 28) changed mean arterial pressure by -5.22 mmHg (95% CI -8.85, -4.53) which did not differ significantly from that induced by KCl (n 26), -4.70 mmHg (-6.56, -2.84). The changes in systolic and diastolic BP were -6.69 (95% CI -8.85, -4.43) and -4.26 (95% CI -6.31, -2.21) mmHg with K-cit and -5.24 (95% CI -7.43, -3.06) and -4.30 (95% CI -6.39, -2.20) mmHg with KCl, and did not differ significantly between the two treatments. Changes in BP were not related to baseline urinary electrolytes. A greater treatment-related effect was observed in those with higher systolic BP. Increasing dietary potassium could therefore have a significant impact on the progressive rise in BP in the entire population.

Sodium-selective salt sensitivity: its occurrence in blacks

We tested the hypothesis that the Na(+) component of dietary NaCl can have a pressor effect apart from its capacity to complement the extracellular osmotic activity of Cl(-) and, thus, expand plasma volume. We studied 35 mostly normotensive blacks who ingested a low-NaCl diet, 30 mmol/d, for 3 weeks, in the first and third of which Na(+) was loaded orally with either NaHCO(3) or NaCl, in random order (250 mmol/d). In subjects adjudged to be salt sensitive (n=18; Delta mean arterial pressure: >or=5 mm Hg with NaCl load), but not in salt-resistant subjects (n=17), loading with NaHCO(3) was also pressor. The pressor effect of NaHCO(3) was half that of NaCl: mean arterial pressure (millimeters of mercury) increased significantly from 90 on low NaCl to 95 with NaHCO(3) and to 101 with NaCl. The pressor effect of NaCl strongly predicted that of NaHCO(3.) As judged by hematocrit decrease, plasma volume expansion with NaCl was the same in salt-resistant and salt-sensitive subjects and twice that with NaHCO(3), irrespective of the pressor effect. In salt-sensitive subjects, mean arterial pressure varied directly with plasma Na(+) concentration attained with all Na(+) loading. In salt-sensitive but not salt-resistant subjects, NaHCO(3) and NaCl induced decreases in renal blood flow and increases in renal vascular resistance; changes in renal blood flow were not different with the 2 salts. Responses of renal blood flow and renal vascular resistance to NaHCO(3) were strongly predicted by those to NaCl. In establishing the fact of "sodium-selective" salt sensitivity, the current observations demonstrate that the Na(+) component of NaCl can have pressor and renal vasoconstrictive properties apart from its capacity to complement Cl(-) in plasma volume expansion.

What initiates the pressor effect of salt in salt-sensitive humans? Observations in normotensive blacks

We tested the traditional hypothesis that an abnormally enhanced renal reclamation of dietary NaCl alone initiates its pressor effect ("salt sensitivity"). Under metabolically controlled conditions, we grouped 23 normotensive blacks as either salt-sensitive (SS) or salt-resistant (SR), depending on whether or not dietary NaCl loading did or did not increase mean arterial blood pressure (MAP) by >or=5 mm Hg. We determined whether dietary NaCl loading induces greater increases in external Na(+) balance, plasma volume, and cardiac output in SS, compared with any in SR subjects, and differential changes in systemic vascular resistance (SVR) that could account for the pressor differences between SS and SR subjects. Using impedance cardiography, we measured cardiac output and SVR daily at 4-hour intervals throughout the last 3 days of a 7-day period of low NaCl intake (30 mmol per day) and throughout a subsequent 7-day period of NaCl loading (250 mmol per day). In the 11 SS subjects, compared with the 12 SR subjects, NaCl loading induced no greater increases in Na(+) balance, body weight, plasma volume, and cardiac output. Yet, from days 2 to 7 of NaCl loading, changes of MAP in SS diverged progressively from those in SR. From days 2 to 4, progressive increases of MAP in SS subjects reflected importantly impaired decreases of SVR, as judged from "normal" decreases of SVR in SR subjects. In SS and SR subjects combined, changes in both MAP and SVR on day 2 strongly predicted changes in MAP on day 7. In many normotensive blacks, vascular dysfunction is critical to the initiation of a pressor response to dietary NaCl.

Gonadal steroids, salt-sensitivity and renal function

PURPOSE OF REVIEW

The aim of this article is to discuss the impact of male and female sex hormones on renal function and to develop the concept that salt-sensitivity of renal function behaves independently of the systemic blood pressure response to salt and may contribute to renal sex-specific differences.

RECENT FINDINGS

Men exhibit a more rapid age-related decline in renal function than women and some renal diseases are clearly sex dependent. Recent studies have shown that gonadal steroids have an important influence on sodium handling and renal hemodynamics that may offer a key for understanding the sexual dimorphism of the renal function. It has been found that androgens increase proximal sodium reabsorption and intraglomerular pressure by modulating afferent and efferent arteriolar tonus via angiotensin II, endothelin and oxidative stress. In contrast, female sex hormones lead to a renal vasodilation and decrease filtration fraction.

SUMMARY

Some newly discovered mechanisms triggering the salt-sensitivity of the renal function and the interaction between gonadal steroids and components of the renin cascade may play an important role in the dimorphism of renal response to salt.

The Evolution-Informed Optimal Dietary Potassium Intake of Human Beings Greatly Exceeds Current and Recommended Intakes

An organism best fits the environment described by its genes, an environment that prevailed during the time period (millions of years) when evolution naturally selected the genes of its ancestors-those who survived to pass on their genes. When an organism's current environment differs from its ancestral one, the environment's mismatch with the organism's genome may result in functional disadvantages for the organism. The genetically conditioned nutritional requirements of human beings established themselves over millions of years in which ancestral hominins, living as hunter-gatherers, ate a diet markedly different from that of agriculturally dependent contemporary human beings. In that context, we sought to quantify the ancestral-contemporary dietary difference with respect to the supply of one of the body's major mineral nutrients: potassium. In 159 retrojected Stone Age diets, human potassium intake averaged 400 +/- 125 mEq/d, which exceeds current and recommended intakes by more than a factor of 4. We accounted for the transition to the relatively potassium-poor modern diet by the fact that the modern diet has substantially replaced Stone Age amounts of potassium-rich plant foods (especially fruits, leafy greens, vegetable fruits, roots, and tubers), with energy-dense nutrient-poor foods (separated fats, oils, refined sugars, and refined grains), and with potassium-poor energy-rich plant foods (especially cereal grains) introduced by agriculture (circa 10,000 years ago). Given the fundamental physiologic importance of potassium, such a large magnitude of change in potassium intake invites the consideration in human beings of whether the quantitative values of potassium-influenced physiologic phenomena (eg, blood pressure, insulin and aldosterone secretion rates, and intracellular pH) currently viewed as normal, in fact disaccord with genetically conditioned norms. We discuss the potential implications of our findings in respect to human health and disease.

Relationship and interaction between sodium and potassium

Compared with the Stone Age diet, the modern human diet is both excessive in NaCl and deficient in fruits and vegetables which are rich in K+ and HCO3- -yielding organates like citrate. With the modern diet, the K+/Na+ ratio and the HCO3-/Cl- ratio have both become reversed. Yet, the biologic machinery that evolved to process these dietary electrolytes remains largely unchanged, genetically fixed in Paleolithic time. Thus, the electrolytic mix of the modern diet is profoundly mismatched to its processing machinery. Dietary potassium modulates both the pressor and hypercalciuric effects of the modern dietary excess of NaCl. A marginally deficient dietary intake of potassium amplifies both of these effects, and both effects are dose-dependently attenuated and may be abolished either with dietary potassium or supplemental KHCO3. The pathogenic effects of a dietary deficiency of potassium amplify, and are amplified by, those of a dietary excess of NaCl and in some instances a dietary deficiency of bicarbonate precursors. Thus, in those ingesting the modern diet, it may not be possible to discern which of these dietary electrolytic dislocations is most determining of salt-sensitive blood pressure and hypercalciuria, and the hypertension, kidney stones, and osteoporosis they may engender. Obviously abnormal plasma electrolyte concentrations rarely characterize these dietary electrolytic dislocations, and when either dietary potassium or supplemental KHCO3 corrects the pressor and hypercalciuric effects of these dislocations, the plasma concentrations of sodium, potassium, bicarbonate and chloride change little and remain well within the normal range.

A missing link between a high salt intake and blood pressure increase

It is widely accepted that a high sodium intake triggers blood pressure rise. However, only one-third of the normotensive subjects were reported to show salt-sensitivity in their blood pressure. Many factors have been proposed as causes of salt-sensitive hypertension, but none of them provides a satisfactory explanation. We propose, on the basis of accumulated data, that the reduced activity of the kallikrein-kinin system in the kidney may provide this link. Renal kallikrein is secreted by the distal connecting tubular cells and all kallikrein-kinin system components are distributed along the collecting ducts in the distal nephron. Bradykinin generated is immediately destroyed by carboxypeptidase Y-like exopeptidase and neutral endopeptidase, both quite independent from the kininases in plasma, such as angiotensin converting enzyme. The salt-sensitivity of the blood pressure depends largely upon ethnicity and potassium intake. Interestingly, potassium and ATP-sensitive potassium (K(ATP)) channel blockers accelerate renal kallikrein secretion and suppress blood pressure rises in animal hypertension models. Measurement of urinary kallikrein may become necessary in salt-sensitive normotensive and hypertensive subjects. Furthermore, pharmaceutical development of renal kallikrein releasers, such as K(ATP) channel blockers, and renal kininase inhibitors, such as ebelactone B, may lead to the development of novel antihypertensive drugs.

Salt intake and progression of chronic kidney disease: An overlooked modifiable exposure? A commentary

The relationship between sodium chloride (salt) intake and blood pressure and cardiovascular disease has been debated for decades. Overlooked is whether there is a relationship between dietary electrolyte ingestion (both sodium and potassium) and risk for progression of kidney disease, particularly in patients who manifest early evidence of chronic kidney disease (CKD). Patients with CKD often are salt sensitive and respond to increased ingestion of sodium chloride with increased blood pressure. Of concern is the clinical evidence that salt-sensitive patients respond to increased salt intake, in the physiological range, with increased glomerular filtration fraction and proteinuria. Thus, these salt-induced changes in both systemic blood pressure and the renal microcirculation create a favorable theoretical scenario for progressive renal injury. Increased salt intake also attenuates the antihypertensive effects of most antihypertensive drugs. Consequently, salt intake must be considered a potential modifiable risk factor for the progression of kidney disease.

The renal kallikrein-kinin system: its role as a safety valve for excess sodium intake, and its attenuation as a possible etiologic factor in salt-sensitive hypertension

The distal tubules of the kidney express the full set of the components of the kallikrein-kinin system, which works independently from the plasma kallikrein-kinin system. Studies on the role of the renal kallikrein-kinin system, using congenitally kininogen-deficient Brown-Norway Katholiek rats and also bradykinin B2 receptor knockout mice, revealed that this system starts to function and to induce natriuresis and diuresis when sodium accumulates in the body as a result of excess sodium intake or aldosterone release, for example, by angiotensin II. Thus, it can be hypothesized that the system works as a safety valve for sodium accumulation. The large numbers of studies on hypertensive animal models and on essential hypertensive patients, particularly those with salt sensitivity, indicate a tendency toward the reduced excretion of urinary kallikrein, although this reduction is modified by potassium intake and impaired renal function. We hypothesize that the reduced excretion of the renal kallikrein may be attributable to a genetic defect of factor(s) in renal kallikrein secretion process and may cause salt-sensitive hypertension after salt intake.

Dysfunctional renal nitric oxide synthase as a determinant of salt-sensitive hypertension: mechanisms of renal artery endothelial dysfunction and role of endothelin for vascular hypertrophy and Glomerulosclerosis

This study investigated the role of renal nitric oxide synthase (NOS), endothelin, and possible mechanisms of renovascular dysfunction in salt-sensitive hypertension. Salt-sensitive (DS) and salt-resistant (DR) Dahl rats were treated for 8 wk with high salt diet (4% NaCl) alone or in combination with the ET(A) receptor antagonist LU135252 (60 mg/kg per d). Salt loading markedly increased NOS activity (pmol citrulline/mg protein per min) in renal cortex and medulla in DR but not in DS rats by 270 and 246%, respectively. Hypertension in DS rats was associated with renal artery hypertrophy, increased vascular and renal endothelin-1 (ET-1) protein content, and glomerulosclerosis. In the renal artery but not in the aorta of hypertensive DS rats, endothelium-dependent relaxation to acetylcholine was unchanged; however, endothelial dysfunction due to enhanced prostanoid-mediated, endothelium-dependent contractions and attenuation of basal nitric oxide release was present. Treatment with LU135252 reduced hypertension in part, but completely prevented activation of tissue ET-1 without affecting ET-3 levels. This was associated with a slight increase of renal NOS activity, normalization of endothelial dysfunction and renal artery hypertrophy, and marked attenuation of glomerulosclerosis. Thus, DS rats fail to increase NOS activity in response to salt loading. This abnormality may predispose to activation of the tissue ET-1 system, abnormal renal vasoconstriction, and renal injury. Chronic ET(A) receptor blockade normalized salt-induced changes in the renal artery and reduced glomerular injury, suggesting therapeutic potential for ET antagonists in salt-sensitive forms of hypertension.