Effect of chronic sodium loading on cardiovascular response in young blacks and whites

Pathophysiology of primary hypertension in children and adolescents

The progress in research on the physiology of the cardiovascular system made in the last 100 years allowed for the development of the pathogenesis not only of secondary forms of hypertension but also of primary hypertension. The main determinants of blood pressure are described by the relationship between stroke volume, heart rate, peripheral resistance, and arterial stiffness. The theories developed by Guyton and Folkow describe the importance of the volume factor and total peripheral resistance. However, none of them fully presents the pathogenesis of essential hypertension. The multifactorial model of primary hypertension pathogenesis developed by Irving Page in the 1940s, called Page's mosaic, covers most of the pathophysiological phenomena observed in essential hypertension. The most important pathophysiological phenomena included in Page's mosaic form a network of interconnected "nodes". New discoveries both from experimental and clinical studies made in recent decades have allowed the original Page mosaic to be modified and the addition of new pathophysiological nodes. Most of the clinical studies confirming the validity of the multifactorial pathogenesis of primary hypertension concern adults. However, hypertension develops in childhood and is even perinatally programmed. Therefore, the next nodes in Page's mosaic should be age and perinatal factors. This article presents data from pediatric clinical trials describing the most important pathophysiological processes associated with the development of essential hypertension in children and adolescents.

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.

Association between salt sensitivity of blood pressure and the risk of hypertension in a Chinese Tibetan population

Epidemiological studies have confirmed salt sensitivity as a crucial risk factor for the development of hypertension. However, few studies have investigated the association between salt sensitivity of blood pressure (SSBP) and hypertension in Chinese Tibetan population. Therefore, we conducted a cross-sectional study based on a Tibetan population to evaluate the association between SSBP and the risk of hypertension. Seven hundred and eighty-four participants with hypertension and 645 participants without hypertension were included from five villages in Tibetan Autonomous Region of Gannan during 2013-2014. The assessment of salt sensitivity (SS) and non-salt sensitivity (NSS) was performed according to mean arterial pressure (MAP) changes by the modified Sullivan's acute oral saline load and diuresis shrinkage test (MSAOSL-DST). Logistic regression models and restricted cubic models were used to examine the association between SSBP and hypertension. There were 554 (70.5%) salt-sensitive participants with hypertension and 412 (63.9%) salt-sensitive participants without hypertension in this study. Compared with individuals with NSS, individuals with SS had a significantly increased risk of hypertension, and the multiple-adjusted odds ratios were 2.582 with 95% confidence interval of 1.357-4.912. Furthermore, a significant linear trend was found between MAP changes and hypertension. Subgroup analyses showed significant and stronger associations between SSBP and the risk of hypertension in the older (age ≥ 55 years old), males and participants who took exercise less than 1 time per week. Our results suggest that SS is associated with an increased risk of hypertension in Tibetan population, indicating a need for clinicians dealing with SSBP to decrease the risk of hypertension.

Barriers to up-titrated antihypertensive strategies in 12 sub-Saharan African countries: the Multination Evaluation of hypertension in Sub-Saharan Africa Study

BACKGROUND

Sub-Saharan Africa (SSA) faces the highest rate of hypertension worldwide. The high burden of elevated blood pressure (BP) in black people has been emphasized. Guidelines recommend two or more antihypertensive medications to achieve a BP control. We aimed to identify factors associated with prescription of up-titrated antihypertensive strategies in Africa.

METHODS

We conducted a cross-sectional study on outpatient consultations for hypertension across 12 SSA countries. Collected data included socioeconomic status, antihypertensive drugs classes, BP measures, cardiovascular risk factors and complication of hypertension. We used ordinal logistic regression to assess factors associated with prescription of up-titrated strategies.

RESULTS

The study involved 2123 treated patients with hypertension. Patients received monotherapy in 36.3 vs. 25.9%, two-drug in 42.2 vs. 45% and three and more drugs strategies in 21.5 vs. 29.1% in low (LIC) and middle (MIC) income countries, respectively. Patients with sedentary lifestyle [OR 1.4 (1.11-1.77)], complication of hypertension [OR 2.4 (1.89-3.03)], former hypertension [OR 3.12 (2.3-4.26)], good adherence [OR 1.98 (1.47-2.66)], from MIC [OR 1.38 (1.10-1.74)] and living in urban areas [OR 1.52 (1.16-1.99)] were more likely to be treated with up-titrated strategies. Stratified analysis shows that in LIC, up-titrated strategies were less frequent in rural than in urban patients (P for trend <0.01) whereas such difference was not observed in MIC.

CONCLUSION

In this African setting, in addition to expected factors, up-titrated drug strategies were associated with country-level income, patient location and finally, the interplay between both in LIC. These results highlight the importance of developing policies that seek to make multiple drug classes accessible particularly in rural and LIC.

Salt sensitivity of blood pressure in childhood and adolescence

Although moderation of sodium intake is recommended population-wide, it remains uncertain who benefits from salt restriction. Salt sensitivity refers to changes in blood pressure in response to sodium intake and may occur with or without hypertension. Unfortunately, there is no practical way to assess salt sensitivity in daily practice. Assessment of salt sensitivity even in research studies is challenging with varying protocols utilized which may contribute to differing results. Building on studies in animals and adults, risk factors and conditions associated with salt sensitivity have been identified in the pediatric and young adult populations. This review presents the limited evidence linking obesity, low birth weight, diabetes, chronic kidney disease, and race/ethnicity with salt sensitivity in children, adolescents, and young adults. The impact of stress on sodium handling is also reviewed. The influence of age on the timing of introduction of dietary salt restriction and the long-term influence of salt sensitivity on risk for hypertension are considered. Lastly, interventions other than salt restriction that may improve salt sensitivity and may inform recommendations to families are reviewed.

Racial Differences in Blood Pressure Control from Users of Antihypertensive Monotherapy: Results from the ELSA-Brasil Study

BACKGROUND

It seems that the worst response to some classes of antihypertensive drugs, especially angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, on the part of the Black population, would at least partially explain the worse control of hypertension among these individuals. However, most of the evidence comes from American studies.

OBJECTIVES

This study aims to investigate the association between self-reported race/skin color and BP control in participants of the Longitudinal Study of Adult Health (ELSA-Brasil), using different classes of antihypertensive drugs in monotherapy.

METHODS

The study involved a cross-sectional analysis, carried out with participants from the baseline of ELSA-Brasil. Blood pressure control was the response variable, participants with BP values ≥140/90 mmHg were considered out of control in relation to blood pressure levels. Race/skin color was self-reported (White, Brown, Black). All participants were asked about the continuous use of medication. Association between BP control and race/skin color was estimated through logistic regression. The level of significance adopted in this study was of 5%.

RESULTS

Of the total of 1,795 users of antihypertensive drugs in monotherapy at baseline, 55.5% declared themselves White, 27.9% Brown, and 16.7% Black. Even after adjusting for confounding variables, Blacks using angiotensin converting enzyme inhibitors (ACEI), angiotensin receptor blocker (ARB), thiazide diuretics (thiazide DIU), and beta-blockers (BB) in monotherapy had worse blood pressure control compared to Whites.

CONCLUSIONS

Our results suggest that in this sample of Brazilian adults using antihypertensive drugs in monotherapy, the differences in blood pressure control between different racial groups are not explained by the possible lower effectiveness of ACEIs and ARBs in Black individuals.

Differential influences of dietary sodium on blood pressure regulation based on race and sex

There are clear differences between men and women, and differences among races, in the incidence and prevalence of hypertension. Furthermore, there is extensive inter-individual variability among humans in the extent to which sodium ingestion alters blood pressure. Orthostatic intolerance and orthostatic hypotension are more common in women; these are often treated with a high salt diet, which has variable efficacy in increasing blood volume and blood pressure. Conversely, people with certain forms of hypertension are often counseled to decrease their sodium intake. Non-Hispanic Black men and women have higher rates of hypertension compared to non-Hispanic White men and women and other racial/ethnic groups. In aggregate, Black women appear to have better orthostatic tolerance than White women. In the present paper, we summarize and evaluate the current evidence for mechanisms of blood pressure regulation in men and women, as well as differences between Black and White groups, with a focus on cardiovascular responses to salt and differences among these groups. We also provide a brief review of factors that are not traditionally considered to be "biological" - such as socio-economic disparities resulting from historic and contemporary inequity across racial groups. These non-biological factors have direct and substantial influences on cardiovascular mechanisms, as well as implications for the influences of salt and sodium intake on blood pressure and cardiovascular health. We conclude that both biological and socio-economic factors provide critical modulating influences when considering the impacts of sodium on cardiovascular health as functions of race and sex.

No evidence of racial disparities in blood pressure salt sensitivity when potassium intake exceeds levels recommended in the US dietary guidelines

On average, black individuals are widely believed to be more sensitive than white individuals to blood pressure (BP) effects of changes in salt intake. However, few studies have directly compared the BP effects of changing salt intake in black versus white individuals. In this narrative review, we analyze those studies and note that when potassium intake substantially exceeds the recently recommended US dietary goal of 87 mmol/day, black adults do not appear more sensitive than white adults to BP effects of short-term or long-term increases in salt intake (from an intake ≤50 mmol/day up to 150 mmol/day or more). However, with lower potassium intakes, racial differences in salt sensitivity are observed. Mechanistic studies suggest that racial differences in salt sensitivity are related to differences in vascular resistance responses to changes in salt intake mediated by vasodilator and vasoconstrictor pathways. With respect to cause and prevention of racial disparities in salt sensitivity, it is noteworthy that 1) on average, black individuals consume less potassium than white individuals and 2) consuming supplemental potassium bicarbonate, or potassium rich foods can prevent racial disparities in salt sensitivity. However, the new US dietary guidelines reduced the dietary potassium goal well below the amount associated with preventing racial disparities in salt sensitivity. These observations should motivate research on the impact of the new dietary potassium guidelines on racial disparities in salt sensitivity, the risks and benefits of potassium-containing salt substitutes or supplements, and methods for increasing consumption of foods rich in nutrients that protect against salt-induced hypertension.

Urinary sodium and potassium excretions in young adulthood and blood pressure by middle age: the Coronary Artery Risk Development in Young Adults (CARDIA) Study

OBJECTIVE

Data are sparse regarding the impact of sodium and potassium intakes on serial blood pressure (BP) levels during long-term follow-up.

METHODS

Among 1007 Coronary Artery Risk Development in Young Adults participants (mean age, 30.2 years; 53% blacks; 57% women) who had at least two 24-h urine samples collected at year 5 (Y5) examination, we assessed associations of urinary sodium and potassium excretions with BP trends and incident hypertension in the subsequent 25 years. Participants were classified by sex-specific medians for averaged 24-h urinary excretions: lower sodium and higher potassium (Na-Lo-K-Hi); higher sodium and lower potassium (Na-Hi-K-Lo); and others.

RESULTS

In the adjusted generalized estimating equation model, SBP and DBP greatly increased in the Na-Hi-K-Lo group (n = 185) compared with the Na-Lo-K-Hi group (n = 185), with statistically significant BP differences at Y20, Y25, and Y30 (mean SBP, 3.93, 4.94, and 4.88 mmHg, respectively; and mean DBP, 4.70, 4.95, and 4.59 mmHg, respectively). During 25-year follow-up, among 926 participants without prevalent hypertension by Y5, 381 (41.1%) developed hypertension. In the adjusted Cox proportional hazards model, the Na-Hi-K-Lo group had hazard ratio (95% confidence interval), 1.45 (1.00-2.10) for incident hypertension compared with the Na-Lo-K-Hi group. The association with incident hypertension was predominant in blacks and white women (race--sex interaction, P = 0.03). Sodium-to-potassium ratio and sodium excretion were positively, whereas potassium excretion was inversely, associated with incident hypertension (all P trend <0.05).

CONCLUSION

Our findings highlight the importance of dietary sodium reduction and higher potassium intake for hypertension prevention among young adults.

The coArtHA trial-identifying the most effective treatment strategies to control arterial hypertension in sub-Saharan Africa: study protocol for a randomized controlled trial

BACKGROUND

Arterial hypertension is the most prevalent risk factor for cardiovascular disease in sub-Saharan Africa. Only a few and mostly small randomized trials have studied antihypertensive treatments in people of African descent living in sub-Saharan Africa.

METHODS

In this open-label, three-arm, parallel randomized controlled trial conducted at two rural hospitals in Lesotho and Tanzania, we compare the efficacy and cost-effectiveness of three antihypertensive treatment strategies among participants aged ≥ 18 years. The study includes patients with untreated uncomplicated arterial hypertension diagnosed by a standardized office blood pressure ≥ 140/90 mmHg. The trial encompasses a superiority comparison between a triple low-dose antihypertensive drug combination versus the current standard of care (monotherapy followed by dual treatment), as well as a non-inferiority comparison for a dual drug combination versus standard of care with optional dose titration after 4 and 8 weeks for participants not reaching the target blood pressure. The sample size is 1268 participants with parallel allocation and a randomization ratio of 2:1:2 for the dual, triple and control arms, respectively. The primary endpoint is the proportion of participants reaching a target blood pressure at 12 weeks of ≤ 130/80 mmHg and ≤ 140/90 mmHg among those aged < 65 years and ≥ 65 years, respectively. Clinical manifestations of end-organ damage and cost-effectiveness at 6 months are secondary endpoints.

DISCUSSION

This trial will help to identify the most effective and cost-effective treatment strategies for uncomplicated arterial hypertension among people of African descent living in rural sub-Saharan Africa and inform future clinical guidelines on antihypertensive management in the region.

TRIAL REGISTRATION

Clinicaltrials.gov NCT04129840 . Registered on 17 October 2019 ( https://www.clinicaltrials.gov/ ).

Is too much salt harmful? Yes

The contribution of high sodium intake to hypertension and to the severity of immune-mediated diseases is still being heatedly debated in medical literature and in the lay media. This review aims to demonstrate two conflicting views on the topic, with the first part citing the detrimental effects of excessive salt consumption. Sodium plays a central role in volume and blood pressure homeostasis, and the positive correlation between sodium intake and blood pressure has been extensively researched. Despite the fact that the average of global daily salt consumption exceeds recommendations of international associations, health damage from excessive salt intake is still controversial. Individual differences in salt sensitivity are in great part attributed to this contradiction. Patients suffering from certain diseases as well as other vulnerable groups-either minors or individuals of full age-exhibit more pronounced blood pressure reduction when consuming a low-sodium diet. Furthermore, findings from the last two decades give insight into the concept of extrarenal sodium storage; however, the long-term consequences of this phenomenon are lesser known. Evidence of the relationship between sodium and autoimmune diseases are cited in the review, too. Nevertheless, further clinical trials are needed to clarify their interplay. In conclusion, for salt-sensitive risk groups in the population, even stricter limits of sodium consumption should be set than for young, healthy individuals. Therefore, the question raised in the title should be rephrased as follows: "how much salt is harmful" and "for whom is elevated salt intake harmful?"

Non-Communicable Diseases on the Rise in Sub-Saharan Africa, the Underappreciated Threat of a Dual Disease Burden

In sub-Saharan Africa, the burden of non-communicable diseases (NCDs) remains under appreciated, but emerging evidence suggests it to be substantial. NCDs such as arterial hypertension, heart diseases, diabetes mellitus and chronic kidney diseases are especially relevant, and put additional strain on the already challenged health systems in this region. Moreover, NCDs appear to be associated with higher mortality and morbidity rates and are more common in younger population groups, in people from sub-Saharan Africa when compared to more developed countries. In this review, we summarize the current literature on the burden of NCDs in sub-Saharan Africa, and highlight the clinical implications of the most relevant etiologies, i.e. arterial hypertension, heart diseases, diabetes mellitus and chronic kidney diseases.

The Na+K+-ATPase Inhibitor Marinobufagenin and Early Cardiovascular Risk in Humans: a Review of Recent Evidence

PURPOSE OF REVIEW

This review synthesizes recent findings in humans pertaining to the relationships between marinobufagenin (MBG), a steroidal Na+/K+-ATPase inhibitor and salt-sensitivity biomarker, and early cardiovascular risk markers.

RECENT FINDINGS

Twenty-four-hour urinary MBG strongly associates with habitual salt intake in young healthy adults (aged 20-30 years). Furthermore, in young healthy adults free of detected cardiovascular disease, MBG associates with increased large artery stiffness and left ventricular mass independent of blood pressure. These findings in human studies corroborate mechanistic data from rat studies whereby stimulation of MBG by a high salt intake or MBG infusion increased vascular fibrosis and cardiac hypertrophy. Twenty-four-hour urinary MBG may be a potential biomarker of early cardiovascular risk. Adverse associations between MBG-which increases with salt consumption-and early cardiovascular risk markers support the global efforts to reduce population-wide salt intake in an effort to prevent and control the burden of non-communicable diseases.

Autonomic activity and its relationship with the endogenous cardiotonic steroid marinobufagenin: the African-PREDICT study

Aim: Marinobufagenin (MBG), a cardiotonic steroid and a natriuretic hormone, is elevated in response to high salt diet consumption. In animal models salt intake stimulates adrenocortical MBG secretion via increased angiotensin II, sympathetic activity and aldosterone. No evidence in humans exists to suggest the involvement of the angiotensinergic-sympatho-excitatory pathway in MBG production. We investigated whether MBG is related to indices of autonomic activity in men and women. Methods: This cross-sectional study included 680 black and white, men and women from the African-PREDICT study (aged 20-30 years). Continuous 24 hr ECG recordings were used to obtain low and high frequency (LF, HF) heart rate variability (HRV). We measured 24 hr urinary MBG excretion and serum aldosterone. Results: We found a positive association of MBG excretion with estimated salt intake (P < 0.001) and aldosterone (P < 0.001) in women and men. In women only, a positive relationship was evident between MBG excretion and LF HRV in multivariate adjusted regression analyses (Adj. R ²= 0.33; β = 0.11; P = 0.030). In men, MBG excretion associated positively with HF HRV in similar regression analyses (R ² = 0.36; β = 0.12; P = 0.034). Sex-specific results were corroborated only in blacks, namely, a positive association of MBG excretion with LF HRV in black women (R ² = 0.38; β = 0.13; P = 0.036), and negative association with HF HRV in black men (R ² = 0.40; β = 0.18; P = 0.045). No relationships were evident in white women (P = 0.58) or men (P = 0.27). Conclusion: Our findings in this human cohort support suggested mechanisms whereby MBG is elevated as a result of increased salt intake, including autonomic activity, previously demonstrated in Dahl salt-sensitive hypertension.

Large artery stiffness is associated with salt intake in young healthy black but not white adults: the African-PREDICT study

PURPOSE

There is global consensus on the benefits of reducing excessive salt intake. Indeed, lower salt intake associates with reduced arterial stiffness, a well-established predictor of cardiovascular risk, in older populations. Whether high habitual salt intake in healthy normotensive youth may already contribute to increased arterial stiffness is unknown. We, therefore, determined whether estimated salt intake is associated with large artery stiffness in young healthy black and white adults.

METHODS

We included 693 black and white adults (51% black; 42% men), aged 20-30 years. Participants were normotensive based on clinic blood pressure, and no previous diagnosed chronic illnesses. We measured carotid femoral pulse wave velocity (cfPWV) and determined estimated salt intake based on 24 h urinary sodium excretion.

RESULTS

We found estimated salt consumption of > 5 g/day in 47% of our population, whereas 21% consumed > 10 g/day. In multivariable-adjusted regression analyses a positive association existed between estimated salt intake and cfPWV in the total group (Adj. R² = 0.32; std. β = 0.10; p = 0.007), and black adults (Adj. R² = 0.37; std. β = 0.12; p = 0.029). This was independent of age, sex, mean arterial pressure, and other covariates. No association was evident in white individuals (p = 0.19).

CONCLUSION

Excessive salt intake is positively associated with large artery stiffness-independent of blood pressure-in young adults, especially in black individuals. Our results suggest a potential contributory role of salt consumption towards early vascular aging.

Hemodynamic responses to mental stress during salt loading

PURPOSE

The purpose was to examine whether prolonged moderate stress associated with a student exam would increase the blood pressure response to a salt load in young healthy normotensive individuals.

METHODS

Ten healthy young subjects were examined at two different occasions in random order (i) during preparation for a medical exam (prolonged stress) and (ii) outside the exam period (low stress). All subjects consumed a controlled diet for 3 days with low- or high-salt content in randomized order. The subjective stress was measured by Spielberger's State-Trait Anxiety Inventory-Scale, SCL Symptom Checklist for stress and the Visual Analogue Scale. On each level of stress, 24-h ambulatory blood pressure and cardiac output (CO) were measured. Furthermore, plasma norepinephrine (NE), epinephrine (E) and plasma renin activity (PRA) were measured.

RESULTS

Twenty-four-hour ABP, 24-h heart rate, CO as well as plasma levels of NE, E and PRA remained unchanged by changes in stress level. Day-night reduction in SAP was significantly larger during moderate stress and high-salt intake; however, no significant difference was observed during daytime and night-time. Individual increase in mental stress correlated significantly with an individual decrease in PRA (SCL-17, r = -0·80, P<0·05, STAIr = -0·64 P<0·05) during high-salt intake.

CONCLUSION

Moderate stress over a period of time in young healthy normotensive individuals does not lead to changes in 24-h ABP. However, the augmented reduction in day-to-night systolic blood pressure during high-salt intake and moderate stress may indicate that stress affects blood pressure regulation.

Outcomes with Angiotensin-converting Enzyme Inhibitors vs Other Antihypertensive Agents in Hypertensive Blacks

BACKGROUND

Angiotensin-converting enzyme inhibitors are used widely in the treatment of patients with hypertension. However, their efficacy in hypertensive blacks when compared with other antihypertensive agents is not well established.

METHODS

We performed a cohort study of patients using data from a clinical data warehouse of 434,646 patients from New York City's Health and Hospitals Corporation from January 2004 to December 2009. Patients were divided into the following comparison groups: angiotensin-converting enzyme inhibitors vs calcium channel blockers, angiotensin-converting enzyme inhibitors vs thiazide diuretics, and angiotensin-converting enzyme inhibitors vs β-blockers. The primary outcome was a composite of death, myocardial infarction, and stroke. Secondary outcomes included the individual components and heart failure.

RESULTS

In the propensity score-matched angiotensin-converting enzyme inhibitors vs calcium channel blocker comparison cohort (4506 blacks in each group), angiotensin-converting enzyme inhibitors were associated with a higher risk of primary outcome (hazard ratio [HR], 1.45; 95% confidence interval [CI], 1.19-1.77; P = .0003), myocardial infarction (HR, 3.40; 95% CI, 1.25-9.22; P = .02), stroke (HR, 1.82; 95% CI, 1.29-2.57; P = .001), and heart failure (HR, 1.77; 95% CI, 1.30-2.42; P = .0003) when compared with calcium channel blockers. For the angiotensin-converting enzyme inhibitors vs thiazide diuretics comparison (5337 blacks in each group), angiotensin-converting enzyme inhibitors were associated with a higher risk of primary outcome (HR, 1.65; 95% CI, 1.33-2.05; P < .0001), death (HR, 1.35; 95% CI, 1.03-1.76; P = .03), myocardial infarction (HR, 4.00; 95% CI, 1.34-11.96; P = .01), stroke (HR, 1.97; 95% CI, 1.34-2.92; P = .001), and heart failure (HR, 3.00; 95% CI, 1.99-4.54; P < .0001). For the angiotensin-converting enzyme inhibitors vs β-blocker comparison, the outcomes between the groups were not significantly different.

CONCLUSIONS

In a real-world cohort of hypertensive blacks, angiotensin-converting enzyme inhibitors were associated with a higher risk of cardiovascular events when compared with calcium channel blockers or thiazide diuretics.

Periodic limb movements during sleep and prevalent hypertension in the multi-ethnic study of atherosclerosis

Periodic limb movements during sleep (PLMS) are associated with immediate increases in blood pressure. Both PLMS and hypertension have different distributions across racial/ethnic groups. We sought to determine whether PLMS is associated with hypertension among various racial/ethnic groups. A total of 1740 men and women underwent measurement of blood pressure and polysomnography with quantification of PLMS. Hypertension was defined as systolic blood pressure (SBP) ≥140, diastolic BP ≥90, or taking antihypertensive medication. For those taking antihypertensives, an estimated pretreatment SBP value was derived based on observed SBP and medication type/dose. Measures of PLMS, PLMS index, and PLMS arousal index were the main explanatory variables. Hypertension and SBP were modeled with logistic and multivariable regression adjusted for age, sex, body mass index, cardiovascular risk factors, lifestyle/habitual factors, apnea-hypopnea index, and race/ethnicity. In the overall cohort, prevalent hypertension was modestly associated with PLMS index (10 U; odds ratio, 1.05; 95% confidence interval, 1.00-1.10) and PLMS arousal index (1 U; 1.05; 1.01-1.09) after adjusting for confounders. Association in the overall cohort was influenced by large effect sizes in blacks, in whom the odds of prevalent hypertension increased by 21% (1%-45%) for 10 U PLMS index increase and 20% (2%-42%) for 1-U PLMS arousal index increase. In blacks, every 1-U PLMS arousal index increase was associated with SBP 1.01 mm Hg higher (1.01; 0.04-1.98). Associations between PLMS and blood pressure outcomes were also suggested among Chinese-Americans but not in whites or Hispanics. In a multiethnic cohort of community-dwelling men and women, prevalent hypertension and SBP are associated with PLMS frequency in blacks.

Salt, fruit and vegetable consumption and blood pressure development: a longitudinal investigation in healthy children

Low salt intake and high fruit and vegetable intake (FVI) have been shown to reduce blood pressure (BP) in adults. Longitudinal data on the independent effect of both FVI and salt intake on BP in healthy normotensive children are not available yet. In the present study, we aimed to characterise the concomitant influence of salt intake and FVI on BP development throughout childhood and adolescence. We examined 435 healthy subjects, for whom at least three repeated measurements of BP had been taken and who had provided 24 h urine samples and 3 d weighed dietary records between 4 and 18 years of age. BP was measured using a mercury sphygmomanometer (Mercuro 300, WelchAllyn) and salt intake was determined based on 24 h Na excretion. The intra-individual change in salt intake was almost significantly associated with the change in systolic BP (SBP, P= 0·06) and marginally (P= 0·09) with that in diastolic BP (DBP) in puberty, but not in pre-puberty. A 1 g/d increase in salt intake was associated with a 0·2 mmHg increase in SBP. In pre-puberty, but not in puberty, differences in FVI between children predicted between-person variations in SBP and DBP (P= 0·03). Corresponding findings were obtained for 24 h K excretion (a urinary indicator for FVI). A 100 g/d lower FVI was related to a 0·4 mmHg higher BP value. In conclusion, in healthy children and adolescents with BP in the low-normal range, both salt intake and FVI may already start to influence BP, although at a small magnitude. The potential importance of establishing healthy eating habits in childhood for later BP development emphasises the role of higher FVI and lower salt intake in the prevention of hypertension in the long run.

High dietary cholecalciferol increases plasma 25-hydroxycholecalciferol concentration, but does not attenuate the hypertension of Dahl salt-sensitive rats fed a high salt diet

The Dahl salt-sensitive rat, a model for salt-induced hypertension, develops hypovitaminosis D during high salt intake, which is caused by loss of protein-bound vitamin D metabolites into urine. We tested the hypothesis that high dietary cholecalciferol (5- and 10-fold standard) would increase plasma 25-hydroxycholecalciferol (25-OHD(3)) concentration (indicator of vitamin D status) of salt-sensitive rats during high salt intake. Salt-sensitive rats were fed 0.3% salt (low salt, LS), 3% salt (HS), 3% salt and 7.5 microg cholecalciferol/d (HS-D5), or 3% salt and 15 microg cholecalciferol/d (HS-D10) and sacrificed at week 4. Plasma 25-OHD(3) concentrations of the two groups of HS-D rats were similar to that of LS rats and more than twice that of HS rats. Urinary cholecalciferol metabolite content of HS-D rats was more than seven times that of HS rats. Systolic blood pressures of the hypertensive HS and HS-D rats did not significantly differ, whereas LS rats were not hypertensive. We conclude that high dietary cholecalciferol increases plasma 25-OHD(3) concentration, but does not attenuate the hypertension of salt-sensitive rats during high salt intake. Low salt intake may be necessary to both maintain optimal vitamin D status and prevent hypertension in salt-sensitive individuals.

Dietary salt does not influence the disposition of verapamil enantiomers in relation to efflux transporter ABCB1 genetic polymorphism in healthy Korean subjects

To evaluate the effects of dietary salt on the stereoselective disposition of verapamil enantiomers in relation to the transporter ABCB1 2677GG/3435CC and 2677TT/3435TT haplotypes, ten healthy subjects were asked to take diets of three different salt levels for 7 days in a randomized, three-way crossover manner. The plasma concentrations of verapamil and norverapamil enantiomers were determined after a single oral dose of 240 mg verapamil on the last day of each phase. Pharmacokinetic parameters were calculated by non-compartmental analysis techniques and compared among the three different dietary salt phases. Compared with the medium salt diet, the high and low salt diets had no significant effect on the disposition of verapamil enantiomers. Moreover, the ABCB1 haplotypes did not alter the impact of dietary salt, although ABCB1 2677TT/3435TT subjects had slightly, but not significantly, higher C(max) and area under the curve (AUC) and lower T(max) for the verapamil enantiomers than did 2677GG/3435CC subjects in each salt phase.

Black and white female adolescents lose vitamin D metabolites into urine

BACKGROUND

The black American population has a higher prevalence of salt sensitivity compared with the white American population. Dahl salt-sensitive rats, models of salt-induced hypertension, excrete protein-bound vitamin D metabolites into urine, a process that is accelerated during high salt intake. We tested the hypothesis that urinary vitamin D metabolite content and 25-hydroxyvitamin D (25-OHD) binding activity of black female adolescents would be greater than that of white female adolescents.

METHODS

Female adolescents (11-15 years old, 11 black and 10 white) were fed low (1.3 g, 56 mmol/24 hours sodium) and high salt (3.86 g, 168 mmol/24 hours sodium) diets for 3 weeks in a randomized order cross-over study design.

RESULTS

White and black adolescents had similar mean urinary vitamin D metabolite content (low salt, black versus white: 50 +/- 10 versus 58 +/- 17 pmol/24 hours; high salt, black versus white: 47 +/- 7 versus 79 +/- 16 pmol/24 hours). Mean urinary 25-OHD binding activities of the black and white adolescents did not significantly differ. Urinary 25-OHD binding activity of 10/11 black adolescents and 7/10 white adolescents was greater at week 3 of high salt intake than at week 3 of low salt intake (r = 0.50, P = 0.002, n = 17). Plasma 24,25-dihydroxyvitamin D concentrations of the white female adolescents were significantly higher than that of the black female adolescents (P < 0.001).

CONCLUSION

Urinary loss of vitamin D metabolites may be one cause of low vitamin D status, in addition to low dietary intake and reduced skin synthesis.

Dietary sodium effects on heart rate variability in salt sensitivity of blood pressure

High dietary sodium intake is a risk factor for hypertension, and heart rate variability (HRV) is decreased in hypertension. Effects of dietary sodium intake on HRV of normotensive persons have not, however, been investigated to date. The present study examined effects of low and high sodium diets on blood pressure, heart rate, and HRV in 36 healthy, normotensive women, ages 40-70. Each was placed on a low sodium diet for 6 days followed by a high sodium diet for 6 days. The high salt diet increased mean systolic blood pressure, decreased heart rate, and increased high frequency HRV (HF). Cardiac vagal tone, estimated at baseline from heart period and a time domain estimate of respiratory sinus arrhythmia, was higher in salt-sensitive than salt-insensitive subjects. The finding of increased vagal tone in normotensive persons on high salt intake indicates that dietary sodium status should be considered in behavioral studies of HRV.

Dahl salt-sensitive rats develop hypovitaminosis D and hyperparathyroidism when fed a standard diet

The Dahl salt-sensitive rat (S), a model for salt-sensitive hypertension, excretes protein-bound 25-hydroxyvitamin D (25-OHD) into urine when fed a low salt diet. Urinary 25-OHD increases during high salt intake. We tested the hypothesis that continuous loss of 25-OHD into urine would result in low plasma 25-OHD concentration in mature S rats raised on a standard diet. Dahl S and salt-resistant (R) male rats were raised to maturity (12-month-old) on a commercial rat diet (1% salt) and switched to 0.3% (low) or 2% (high) salt diets 3 weeks before euthanasia. Urine (24 h) was collected at the end of the dietary treatments. Urinary 25-OHD and urinary 25-OHD binding activity of S rats were three times that of R rats, resulting in lower plasma 25-OHD and 24,25-dihydroxyvitamin D concentrations in S rats than in R rats (P < 0.001). Plasma parathyroid hormone concentrations of S rats were twice that of R rats. S rats fed 2% salt had higher plasma 1,25-dihydroxyvitamin D concentrations than those fed 0.3% salt (P = 0.002). S rats excreted more calcium into urine than R rats (P < 0.001) and did not exhibit the expected calciuric response to salt. Proteinuria of the S rats was three times that of the R rats, suggesting kidney damage in the S rats. Low plasma 25-OHD and 24,25-dihydroxyvitamin D and high plasma 1,25-dihydroxyvitamin D and PTH concentrations seen in the mature S rats have also been reported for elderly patients with low-renin (salt-induced) hypertension. An implication of this study is that low vitamin D status may occur with age in salt-sensitive individuals, even when salt intake is normal.

Salt and hypertension: a phylogenetic perspective

Our hunter-gatherer ancestors appeared to survive on little salt. When today's rural dwellers move to urban environments, they increase their salt intake and the salt-sensitive among them become prone to age-related increase in blood pressure and hypertension. This paper reviews our knowledge of the mechanisms of salt disposal and plasma volume regulation, salt consumption in human evolution, salt intake and prevalence of hypertension, and the results of interventions aimed at modulating both. Finally, it discusses current hypotheses on the mechanisms of selective pressure that may have favored the emergence of a salt-sensitive, hypertensive genotype. Similar to 'thrifty' genes, which supported energy savers in times of scarcity, but may now be causing obesity and type 2 diabetes, 'thirsty' genes, by acting on salt and water retention, might have helped individuals survive the challenge of volume-depleting illnesses, especially when combined with stress-inducing situations, but may now cause high BP and related damage in the post-reproductive age.

Influence of two doses of irbesartan on non-dipper circadian blood pressure rhythm in salt-sensitive black hypertensives under high salt diet

The authors examined whether the blockage of angiotensin II receptors by irbesartan (IRB) can reverse the "non-dipper" circadian rhythm of blood pressure (BP) to a "dipper" pattern in black salt-sensitive hypertensive patients submitted to a high-sodium loading. Twelve black salt-sensitive hypertensive patients (seven men; age, 35-58 years) on a high-sodium diet (300 mmol Na+ per day) were followed for 8 weeks. A placebo was given during the first 2 weeks, followed by 2 weeks on IRB 150 mg/d, 2 weeks on placebo, and 2 weeks on IRB 300 mg/d. On the last day of placebo, IRB 150 mg/d, and IRB 300 mg/d treatments, 24-hour BP and urinary 24-hour excretion of Na+ and potassium were measured. On placebo, ambulatory mean arterial pressure (MAP) was 112 mm Hg+/-2 (24 h), 112 mm Hg+/-2 (daytime), and 111 mm Hg+/-2 (nighttime), showing a clear circadian non-dipper profile. Versus placebo, IRB 150 mg/d reduced MAP by 4.2 mm Hg+/-1.1 (24 h), 2.6 mm Hg+/-0.8 (daytime) and 6.0 mm Hg+/-1.3 (nighttime; P<0.05 vs. placebo) and IRB 300 mg/d reduced MAP by 7.8 mm Hg+/-1.4 (24 h), 3.9 mm Hg+/-1.1 (daytime), and 11.8 mm Hg+/-2.1 mm Hg (all P<0.02 vs. placebo); nighttime/daytime MAP decrease was 0.7+/-0.8% on placebo, 3.5+/-2.1% on IRB 150 mg/d, and 7.0+/-1.2% on IRB 300 mg/d (P<0.02 for trend). Compared with placebo, IRB significantly increased serum potassium and plasma renin activity and reduced fractional excretion of potassium and plasma aldosterone levels in a dose-dependent manner. Body weight and urinary sodium excretion did not change throughout the study. It was concluded that the angiotensin receptor blocker IRB can reverse the BP non-dipper profile in salt-sensitive hypertensive patients on a high-salt diet, restoring nocturnal BP decline by a predominantly dose-dependent reduction of nighttime BP. Although the increment of potassium balance and reduction of aldosterone may account for this effect, it occurs independently of increased natriuresis. It is speculated that blunting of nighttime BP decrease in black salt-sensitive hypertensive patients may be related to a deficient suppression of the renin-angiotensin system during the night.

Dahl salt-sensitive rats excrete 25-hydroxyvitamin D into urine

The plasma 25-hydroxyvitamin D concentration of Dahl salt-sensitive rats (S) is markedly decreased in response to high sodium chloride (salt) intake. We tested the hypothesis that urinary excretion is a mechanism for the decrease. Female S rats excreted 0.26 +/- 0.04 nmol 25-hydroxyvitamin D/24 h at wk 2 of high salt (80 g/kg) intake, five times that of female salt-resistant (R) rats at wk 2 of high salt intake and nine times that of S rats at wk 2 of low salt (3 g/kg) intake. The 25-hydroxyvitamin D binding activity in 24-h urine of S rats was 79 +/- 11 pmol/h at wk 2 of high salt intake, two times that in urine of S rats at wk 2 of low salt intake and > 35 times that in urine of R rats at wk 2 of low or high salt intake. We conclude that markedly decreased plasma 25-hydroxyvitamin D concentrations of S rats during high salt intake result in part from excretion of protein-bound 25-hydroxyvitamin D. Low plasma 25-hydroxyvitamin D concentrations in humans may also result in part from salt sensitivity, which is prevalent in > 50% of the United States hypertensive population.

Plasma 24,25-dihydroxyvitamin D concentration of Dahl salt-sensitive rats decreases during high salt intake

Dahl salt-sensitive rats, but not salt-resistant rats, develop hypertension in response to high salt intake. We have previously shown an inverse relationship between plasma 25-hydroxyvitamin D (25-OHD) concentration and blood pressure of Dahl salt-sensitive rats during high salt intake. In this study, we report on the relationship between high salt intake and plasma 24,25-dihydroxyvitamin D (24,25-(OH)(2)D) concentration of Dahl salt-sensitive and salt-resistant rats. Rats were fed a high salt diet (8%) and sacrificed at day 2, 7, 14, 21, and 28. Plasma 24,25-(OH)(2)D concentrations of salt-sensitive rats were reduced to 50% of that at baseline at day 2-when blood pressure and plasma 25-OHD concentration were unchanged, but 25-OHD content in the kidney was 81% of that at baseline. Plasma 24,25-(OH)(2)D concentration was reduced further to 10% of that at baseline from day 7 to 14 of high salt intake, a reduction that was prevented in rats switched to a low salt (0.3%) diet at day 7. Exogenous 24,25-dihydroxycholecalciferol (24,25-(OH)(2)D(3)), administered at a level that increased plasma 24,25-(OH)(2)D concentration to five times normal, did not attenuate the salt-induced hypertension of salt-sensitive rats. Plasma 24,25-(OH)(2)D concentration of salt-resistant rats was gradually reduced to 50% of that at baseline at day 14 and returned to baseline value at day 28 of high salt intake. We conclude that the decrease in plasma 24,25-(OH)(2)D concentration in salt-sensitive rats during high salt intake is caused by decreased 25-OHD content in the kidney and also by another unidentified mechanism.

Enhanced affective startle modulation in salt-sensitive subjects

Salt-sensitive normotensive men exhibit an enhanced pressor response to mental stress. Although an enhanced pressor response is associated with higher affective startle modulation in men, an association between salt sensitivity of blood pressure and affective startle modulation has not been studied so far. We studied reactivity to mental stress and startle modulation in 14 salt-sensitive healthy white male students and 14 salt-resistant control subjects, who were well matched for age, body mass index, physical fitness, and family history of hypertension. Subjects performed a computerized information-processing task under time pressure (manometer test), while heart rate and blood pressure were continuously registered. In a separate session, subjects viewed a series of 42 pictures of the International Affective Picture System (IAPS), varying in pleasure and arousal, while acoustic startle probes were administered randomly, and electromyogram activity of the orbicular eye muscle was continuously recorded. Startle modulation was calculated as the difference between startle responses under negative and positive affective stimuli. In contrast to salt-resistant subjects, salt-sensitive subjects showed significantly enhanced startle amplitudes under negative stimuli and diminished amplitudes under positive stimuli. Thus, salt-sensitive subjects displayed a significantly higher startle modulation than did salt-resistant subjects (P<0.05). Subjective ratings of the presented IAPS pictures did not differ between the groups. The increased startle modulation of salt-sensitive subjects suggests an enhanced activity of the central nucleus of the amygdala. This enhanced central nervous responsiveness may contribute to higher sympathetic pressor reactivity and, thus, to the later development of hypertension in salt-sensitive individuals.

Hypertension in black patients: an emerging role of the endothelin system in salt-sensitive hypertension

The prevalence of essential hypertension in blacks is much higher than that in whites. In addition, the pathogenesis of hypertension appears to be different in black patients. For example, black patients present with a salt-sensitive hypertension characterized by low renin levels. Racial differences in renal physiology and socioeconomic factors have been suggested as possible causes of this difference, but reasons for this difference remain unclear. Endothelial cells are important in the regulation of vascular tonus and homeostasis, in part through the secretion of vasoactive substances. One of these factors, endothelin-1 (ET-1), is a 21 amino acid residue peptide with potent vasopressor actions. In addition to its contractile effects, it has been shown to stimulate mitogenesis in a number of cell types. Moreover, ET-1 displays modulatory effects on the endocrine system, including stimulation of angiotensin II and aldosterone production and inhibition of antidiuretic hormone in the kidney. Recent data from several laboratories indicate that ET-1 is overexpressed in the vasculature in several salt-sensitive models of experimental hypertension. Moreover, circulating plasma ET-1 levels are significantly increased in black hypertensives compared with white hypertensives. Thus, the ET system might be particularly important in the development or maintenance of hypertension in this population.

Deficiency of renal dopaminergic-dependent natriuretic response to acute sodium load in black salt-sensitive subjects in contrast to salt-resistant subjects

OBJECTIVE

To evaluate the involvement of the renal dopaminergic system in the natriuretic responses to acute saline load in salt-resistant (SR) and salt-sensitive (SS) black normotensive (NT) and hypertensive (HT) subjects.

DESIGN AND METHODS

We studied the relationship between the urinary excretion of dopa, dopamine (DA) and its metabolite DOPAC and the natriuretic responses to acute volume expansion (2 l NaCl 0.9% over 2 h) in 20 black NT subjects (12 SR and 8 SS) and 19 black HT subjects (10 SS and 9 SR). Subjects received a low salt (LS) diet (40 mmol sodium/day) for 1 week and a high salt (HS) diet (300 mmol sodium/day) for 1 week; the sequence of the dietary regimens was randomized. Comparisons were made between the results before the saline infusion (baseline) and the results 2 h after the infusion.

RESULTS

In all the groups saline infusion induced significant increases in urinary volume (ml/4 h) of two- to three-fold and in urinary sodium excretion (mmol/4 h) of three- to ten-fold; these increases were significantly greater during the HS diet than during the LS diet. Saline infusion significantly increased the mean arterial pressure (MAP) by 5 mmHg in HT-SS subjects and by 4-5 mmHg in NT-SS subjects, but the MAP did not changed in the NT-SR and HT-SR groups. Under the LS diet, saline infusion changed the DA excretion (in nmol/4 h) by -49+/-89 in HT-SS subjects, by 17+/-52 in NT-SS subjects, by 235+/-72 in HT-SR subjects and by 220+/-86 in NT-SR subjects (P < 0.05 between SR and SS subjects). The saline infusion-induced changes in DA excretion correlated significantly with the increases in urinary sodium excretion (r = 0.71, P < 0.01) in the NT-SR and HT-SR subjects under the LS diet, but not in the SR groups on the HS diet nor in the SS groups (HT and NT) on either diet. Saline infusion significantly reduced the DA/dopa ratio in SS (NT and HT) but not SR (NT and HT) subjects, whereas the DA/DOPAC (dihydroxyphenylacetic acid) ratios were similar in all the groups.

CONCLUSIONS

The urinary dopaminergic system may participate in the natriuretic responses to acute sodium load only in SR subjects (NT and HT) and only under LS diets, but not in SS subjects (NT and HT). This strongly suggests that black NT- and HT-SS subjects have an underlying impairment in the activity of the renal dopaminergic system which may be associated with a reduced decarboxylation of dopa into DA.

Blood pressure increase with impaired glucose tolerance in young adult american blacks

Hypertension and non-insulin-dependent diabetes mellitus are more prevalent in blacks than whites. The convergence of these 2 disorders augments the expression and severity of cardiovascular disease. The purpose of this study was to determine whether alterations in glucose metabolism are related to an increase in blood pressure (BP). This study was conducted on 304 nondiabetic blacks (mean age=32 years). Measurements in all subjects included BP, anthropometric measures, oral glucose tolerance test, insulin clamp to measure insulin sensitivity, and plasma lipids. The sample was stratified according to plasma glucose on oral glucose tolerance test to normal glucose tolerance (NGT), impaired glucose tolerance (IGT), and diabetes mellitus (DM). A 2-way ANOVA was performed to determine differences between the metabolic groups. With the use of American Diabetic Association criteria, 20.4% of the samples were classified as IGT and 5.9% were diabetic. A significant increase in BP existed from NGT to IGT to DM, which was stronger in women than men (systolic blood pressure in women: NGT=122, IGT=127, and DM=140 mm Hg, P<0.001) with a significant linear trend (P<0.001). With the use of body mass index as a covariate, the group difference in BP remained significant (P=0.006). Measures of insulin sensitivity demonstrated significant metabolic group differences (P<0.001) with a linear trend (P<0.001) of decreasing insulin sensitivity from NGT to DM. These results indicate that early alterations in glucose metabolism effects an upward shift in BP. The higher BP in IGT and DM may be due to vascular endothelial cell resistance to insulin action.

Acute hypotensive, natriuretic, and hormonal effects of nifedipine in salt-sensitive and salt-resistant black normotensive and hypertensive subjects

In a randomized double-blind study, we compared the short-term effects of nifedipine (10 mg 3x daily for 1 day) versus placebo on 24-h blood pressure, diuresis, natriuresis, urinary excretion of dopamine and metabolites, and on plasma renin activity (PRA) and plasma aldosterone levels in 18 black hypertensive (HT) patients [eight salt-resistant (HT-SR) and 10 salt-sensitive (HT-SS)], and in 20 black normotensive (NT) subjects (12 NT-SR and eight NT-SS) who were studied randomly with both a high- (HS) and a low-salt (LS) diet. In comparison to placebo, nifedipine significantly decreased 24-h mean BP in all groups either with HS or LS diets (all p<0.05). With HS, greater hypotensive effects were achieved in NT-SS (-10+/-2 mm Hg) versus NT-SR (-3+/-1 mm Hg; p<0.05) and in HT-SS (-18+/-2 mm Hg) versus HT-SR (-12+/-2 mm Hg; p<0.05). In NT-SS and HT-SS, nifedipine induced greater (p<0.05) BP decrease with HS (-10+/-2 and -18+/-2 mm Hg) than with LS (-4+/-1 and -9+/-1 mm Hg, respectively), whereas in NT-SR and HT-SR, the hypotensive effect did not differ between HS and LS. Nifedipine versus placebo significantly increased natriuresis and fractional excretion of sodium in all groups only with HS (p<0.05) but not with LS diets. Only in HT-SS were the hypotensive and natriuretic effects of nifedipine significantly correlated (r = -0.77; p<0.01). Nifedipine produced a similar increase of the urinary excretion of dopamine, L-DOPA, and of DOPAC in all subjects, which did not correlate with hypotensive and natriuretic effects. Nifedipine did not modify plasma levels of renin and of aldosterone except in NT-SS with HS, in whom nifedipine increased PRA levels (p <0.05). We conclude that although nifedipine reduces BP in all groups of NT and HT with LS and HS diets, the effect is greater in salt-sensitive subjects with HS. Although in HT-SS with HS, the short-term natriuretic response to nifedipine may contribute to its hypotensive effects, the diuretic-natriuretic effect of nifedipine is not necessary for the expression of its hypotensive effect. Moreover, it is unlikely that any short-term effects of nifedipine either on the renal dopaminergic system or on the secretion of aldosterone explain nifedipine short-term hypotensive and diuretic-natriuretic effects.

Cardiovascular complications in patients with primary aldosteronism

Primary aldosteronism (PA) is widely believed to be a relatively benign form of hypertension associated with a low incidence of vascular complications. However, several recent studies showed that cardiovascular complications were not rare in PA. PA is known as one of the most typical forms of sodium-sensitive hypertension. Recently, we found that the sodium sensitivity of blood pressure was a marker for greater risk for cardiovascular complications, especially stroke, in patients with essential hypertension. Therefore, we investigated cardiovascular complications in 58 patients with PA confirmed to be Conn's adenoma. Cardiovascular complications were found in 34% of 58 patients. Coronary artery disease was found in only one patient (1.7%), as angina pectoris. Stroke was found in nine patients (15.5%), four patients (6.9%) with cerebral infarctions and five patients (8.6%) with cerebral hemorrhages. Proteinuria and renal insufficiency were found in 14 (24.1%) and 4 (6.9%) patients, respectively. The incidence of cerebral infarction and renal insufficiency was greater in men than women. The prevalence of proteinuria was greater in patients with than without stroke (P = 0.03) among those aged older than 40 years. These results indicated that cardiovascular complications, especially stroke and proteinuria, were common in patients with PA, and proteinuria might be an indicator for stroke as target-organ damage.

Changes in the circadian rhythm of blood pressure in primary aldosteronism in response to dietary sodium restriction and adrenalectomy

OBJECTIVE

Recently, we found that sodium restriction restored the circadian rhythm of blood pressure from non-dippers to dippers in patients with a sodium-sensitive type of essential hypertension. In the present study, we investigated the effects of sodium restriction on the circadian blood pressure rhythm in patients with primary aldosteronism, a typical sodium-sensitive form of secondary hypertension.

DESIGN AND METHODS

We performed 24 h blood pressure monitoring in eight patients with primary aldosteronism due to unilateral adenoma (Conn's syndrome) during normal-sodium (7-12 g/day of NaCl) and low-sodium (1-3 g/day) diets, and after adrenalectomy.

RESULTS

Sodium restriction lowered the 24 h mean arterial pressure from 116+/-14 to 109+/-12 mmHg (P< 0.01). During a normal-sodium diet, there was no change in systolic, diastolic and mean arterial pressures during the night-time compared with the daytime. In contrast, during a low-sodium diet, all night-time pressure values were significantly lower than those in the daytime. After adrenalectomy, the night-time pressures in patients on a normal-sodium diet were lower than those of the daytime. The nocturnal mean arterial pressure fall was increased by sodium restriction and adrenalectomy.

CONCLUSIONS

These results indicate that the circadian rhythm of blood pressure was disturbed in patients with primary aldosteronism who maintained a relatively high sodium intake. Both adrenalectomy and sodium restriction restored a nocturnal dip in blood pressure in primary aldosteronism. Therefore, sodium restriction affects the circadian blood pressure rhythm in sodium-sensitive types of hypertension, not only in primary hypertension, but also in secondary hypertension.

Plasma 25-hydroxyvitamin D concentrations are inversely associated with blood pressure of Dahl salt-sensitive rats

Dietary salt is a contributing factor to the development of hypertension in individuals who are salt-sensitive. The vitamin D endocrine system has been reported to modulate vascular structure and function. Since elderly hypertensive females with low plasma renin activity, typical of salt-sensitivity, had significantly lower 25-hydroxyvitamin D concentrations compared with normotensive elderly and young females, we have used Dahl salt-sensitive and salt-resistant rats fed high (80 g/kg diet) and low (3 g/kg diet) salt diets as models to examine the relationship between salt-sensitivity and 25-hydroxyvitamin D, the precursor of the hormonal form of vitamin D, 1,25-dihydroxyvitamin D. Plasma 25-hydroxyvitamin D concentrations of salt-resistant rats were unaffected by a high salt diet, but plasma 25-hydroxyvitamin D concentrations of salt-sensitive rats were significantly reduced within three weeks to lower than 25%. There was a negative association between plasma 25-hydroxyvitamin D concentrations of salt-sensitive rats and the number of days that the rats were fed a high salt diet (r = -0.98, P < 0.02) and a positive association between blood pressure and the number of days that the rats were fed a high salt diet (r = 0.97, P < 0.05). An inverse relationship was found between plasma 25-hydroxyvitamin D concentrations and blood pressure (r = -0.99, P < 0.01). Spontaneously hypertensive rats did not have low plasma 25-hydroxyvitamin D concentrations, suggesting that reduction of plasma 25-hydroxyvitamin D concentration might be specific to salt-induced hypertension.

Psychophysiological reactivity of salt-sensitive normotensive subjects

OBJECTIVE

To evaluate the psychophysiological response to mental stress of young healthy salt-sensitive normotensive subjects.

METHODS

Thirty-two healthy volunteers who had previously been phenotyped for salt sensitivity were selected for the study. The 16 salt-sensitive and 16 salt-resistant subjects, who were matched for age, body mass index and family history of hypertension, underwent a mental stress test consisting of an information-processing task performed under time pressure (the Manometer test). During the experimental session the blood pressure, heart rate and pulse-wave velocity were registered continuously. Before and after the mental task subjects were instructed to complete several standardized psychological state and trait questionnaires.

RESULTS

Mental stress resulted in a greater rise in blood pressure (P < 0.05) and in pulse-wave velocity (P < 0.01) in salt-sensitive than in salt-resistant individuals. Salt-sensitive subjects also displayed significantly higher levels of anxiety (P < 0.01) and a lower level of control of anger (P < 0.01) than did salt-resistant subjects. Furthermore, the level of irritation of the salt-sensitive subjects was higher both before (P < 0.01) and after (P < 0.05) the stress test

CONCLUSIONS

An increased responsiveness of the blood pressure to mental stress and an increased level of irritation are associated with salt sensitivity in normotensive subjects. These findings are in line with the hypothesis that psychophysiological traits play a role in the development of salt-sensitive hypertension.

Reduced dietary potassium reversibly enhances vasopressor response to stress in African Americans

Acute vasopressor responses to stress are adrenergically mediated and hence potentially subject to differential modulation by dietary potassium and sodium. The greater vasopressor responsiveness in blacks compared with whites might then be consequent not only to a high dietary salt intake but also to a marginally reduced dietary potassium intake. Under controlled metabolic conditions, we compared acute vasopressor responses to cold and mental stress in black and white normotensive men during three successive dietary periods: (1) while dietary potassium was reduced (30 mmol K+/70 kg per day) and salt was restricted (10 to 14 days); (2) while salt was loaded (15 to 250 mmol Na+/70 kg per day) (7 days); and (3) while salt loading was continued and potassium was either supplemented (70 mmol K+/70 kg per day) (7 to 21 days) in 9 blacks and 6 whites or continued reduced (30 mmol K+/70 kg per day) (28 days) in 4 blacks (time controls). At the lower potassium intake, cold-induced increase in forearm vascular resistance in blacks was twice that in whites during both salt restriction and salt loading. Normalization of dietary potassium attenuated cold-induced increases in both forearm vascular resistance and systolic and diastolic blood pressures in blacks but only in systolic pressure in whites. In blacks but not in whites, normalization of dietary potassium attenuated mental stress-induced increases in systolic and diastolic pressures. In normotensive blacks but not whites, a marginally reduced dietary intake of potassium reversibly enhances adrenergically mediated vasopressor responsiveness to stress. That responsiveness so enhanced over time might contribute to the pathogenesis of hypertension in blacks.

Cardiovascular and plasma catecholamine response to static exercise in normotensive blacks and whites

OBJECTIVES

The objectives of the present study were (1) to evaluate the pressor response to an isometric handgrip exercise in normotensive black and white males; (2) to measure plasma catecholamine levels pre- and post-exercise, as an index of sympathetic nervous system activity; and (3) to quantify the pressor response to bolus intravenous injections of phenylephrine (an alpha-specific agonist).

METHODS

Cardiovascular and catecholamine responses to an isometric handgrip exercise (3 minutes at 30% MVC) were measured in 15 normotensive blacks and whites. In another phase of the study, pressor responses to bolus injections of phenylephrine were assessed to evaluate alpha-adrenergic sensitivity.

RESULTS

The blood pressure in the blacks increased from 119/69 to 160/120 mm HG during isometric exercise, while in the whites it increased from 118/67 to 153/110 mm HG. The blacks exhibited a greater diastolic blood pressure reactivity, as evidenced by a significant race x time interaction (p < 0.05). The heart rate responses were not significantly different between the two groups. The plasma levels of norepinephrine were similar at rest, but were 25% lower in the blacks than in the whites following isometric exercise (p < 0.01). Black subjects also demonstrated an increased pressor response to intravenous injections of phenylephrine at rest (p < 0.05).

CONCLUSIONS

The enhanced vascular sensitivity to norepinephrine may have contributed to the greater exercise pressor response in the blacks.

Heritability of salt sensitivity in black Americans

Salt sensitivity is defined as a change in blood pressure in response to changes in salt and water homeostasis. Found in 73% of hypertensive and 36% of normotensive blacks, it is generally considered a hallmark of hypertension in blacks. The higher prevalence of salt sensitivity in blacks compared with whites suggests a genetic influence on this trait, but there is little direct evidence of heritability. We determined the extent to which salt sensitivity is correlated in black families and estimated the heritability of this phenotype. Black families were recruited through a hypertensive proband. Both hypertensive and normotensive adults were phenotyped with respect to salt sensitivity with an intravenous sodium-loading, furosemide volume-depletion protocol. Salt sensitivity was defined as the difference between sodium-loaded and volume-depleted blood pressure. We enrolled 20 families, comprising 30 parent-offspring pairs and 115 adult sibling pairs. Age-adjusted familial correlations ranged from .33 to .44, .19 to .37, and .12 to .21 for mean arterial and systolic and diastolic pressure responses to the salt sensitivity maneuver, respectively. Corresponding heritability estimates were 0.26 to 0.84, 0.26 to 0.74, and 0.004 to 0.24, respectively. These data strongly suggest a heritable component of salt sensitivity.

Gender differences in insulin-induced free fatty acid suppression: studies in an African American population

This study of African Americans (AA) was designed to investigate gender differences in insulin-induced free fatty acid (FFA) suppression. Sixty AA (34 women, mean age 34 +/- 7.6 years, and 26 men, mean age 30 +/- 2.9 years) participated. All subjects had an oral glucose tolerance test (OGTT). Nineteen women and 18 men also underwent a euglycemic hyperinsulinemic clamp (IC) study. Plasma insulin and FFA concentrations were obtained during both tests at 0, 60, and 120 min. While there was no gender difference in body mass index (P = 0.21), women had greater percent body fat (P < 0.001) calculated by the Siri formula. There was no gender difference in fasting FFA levels, but during the OGTT, women compared to men had significantly greater FFA suppression. Both nonobese and obese women suppressed FFA concentration by 88%, and nonobese and obese men suppressed FFA concentration by 80 and 66% respectively. This gender difference in FFA suppression was significant (P = 0.001) and independent of obesity and insulin concentration. During the IC studies, there were no gender or obesity differences in FFA suppression, with women and men suppressing FFA levels by 87-89% (P = 0.7). Fasting insulin concentrations were higher in obese vs. nonobese (P = 0.03), but fasting FFA concentrations were not different (P = 0.15). For nonobese and obese females, fasting FFA levels were 0.55 +/- 0.24 and 0.44 +/- 0.26 mEq/L, respectively, and for nonobese and obese males, 0.45 +/- 0.2 and 0.35 +/- 0.18 mEq/L, respectively. In women, development of obesity may be enhanced by greater sensitivity to insulin-induced FFA suppression as measured during an OGTT. To detect gender differences in FFA metabolism, the OGTT is superior to the IC. The lack of elevation in fasting FFA levels in obese AA women and men has not been reported in other racial groups and may indicate a greater adipocyte sensitivity to insulin in AA.

Racial differences in the pathogenesis of hypertension

Hypertension occurs at an earlier age, is more prevalent, and is more often complicated by target organ damage in African-Americans than whites. Reasons for this increased severity of hypertension in African-Americans remain obscure. Based on studies recently completed in their laboratory, the authors propose that greater sympathetic reactivity to stress and a greater prevalence of NaCl sensitivity contribute to the earlier development of hypertension in African-Americans. Using microneurography to record muscle sympathetic nervous system activity, it was found that normotensive blacks manifest greater increases in sympathetic activity to cold stress than normotensive whites. If true of other types of stressors, greater sympathetic reactivity would predispose blacks to the development of hypertension. Using a telemetry-based monitoring system, the authors recently reported that both spontaneously hypertensive rats and normotensive Wistar-Kyoto rats manifest acute sensitivity to high dietary NaCl ingestion, but that the Wistar-Kyoto rats are able to compensate, thereby avoiding sustained increases in blood pressure. Based on these animal studies, it is proposed that elevated nocturnal pressures observed in blacks by other investigators may reflect the greater prevalence of NaCl sensitivity in the black population. As in animal models of NaCl-sensitive hypertension, blacks may retain ingested NaCl, resulting in sustained increases in blood pressure.

Insulin sensitivity, lipids, and blood pressure in young American blacks

The purpose of this study was to determine whether insulin resistance was linked with alterations in plasma lipids in adult young blacks with borderline hypertension. Ninety-four American blacks participated (46 men, 48 women, age range 28 to 33 years). Within this group of 94 subjects, there were 60 normotensive (Nt) subjects and 36 subjects with borderline hypertension (BHt), defined as blood pressure > 135/85 mm Hg. None of the subjects were diabetic or receiving antihypertension medication. All participants had blood pressure and anthropometric measurements, a fasting lipid profile, an oral glucose tolerance test, and a euglycemic hyper-insulinemic clamp. Insulin-stimulated glucose utilization (M), determined by insulin clamp, was significantly lower in the BHt subjects compared with the Nt subjects (men, Nt 6.91 +/- 0.62 versus BHt 5.54 +/- 0.65; women, Nt 5.97 +/- 0.47 versus BHt 3.79 +/- 0.38 mg.kg-1.min-1, P = .006). When M was corrected for adiposity and expressed in milligrams per kilogram of fat free mass (M'), the difference between Nt and BHt remained significant (P = .006). There was a significant correlation of M' with systolic blood pressure (r = .393, P < .0001), HDL-C (r = .382, P < .0001), triglyceride level (r = 308, P < .001), apolipoprotein A-I (r = .190, P = .033), and apolipoprotein B stepwise multiple linear regression analysis, HDL-C emerged as the most significant lipid component in the model for insulin resistance. These data suggest that in American blacks with mild hypertension, the risk for cardiovascular disease may be augmented in the presence of insulin resistance.

Parental history of hypertension, sodium loading, and cardiovascular response to stress

Parental history of hypertension, dietary sodium, and psychological stress have all been implicated in the development of essential hypertension and may interact in elevating disease risk. The mechanism by which this might occur is unclear, but it may be related to changes in the peripheral vasculature. The present study examined the effects of parental history and sodium on cardiovascular responses to an extended stressor. Eighteen normotensive offspring of hypertensives and 18 offspring of normotensives were exposed to a 1-hour shock-avoidance video-game procedure after 14 days of sodium loading (10 1-g tablets/day) and again after 14 days of placebo tablets. Order of sessions was counterbalanced between subjects in a double-blind design. In offspring of hypertensives, sodium loading elevated total peripheral resistance and norepinephrine responses to stress relative to placebo conditions and compared with offspring of normotensives. These increases were accompanied by decreases in stroke volume and cardiac output, which may explain the absence of familial differences in blood pressure responses to stress and sodium. Sodium loading had no effect on offspring of normotensives. The elevated resistance in offspring of hypertensives may suggest the initiation of pathological processes. The absence of sodium effects on resting values indicates the importance of research under conditions of stress.

Albuminuria in association with insulin and sodium-lithium countertransport in young African Americans with borderline hypertension

The purpose of this study was to determine whether early nephropathy, evidenced by urinary albumin excretion, can be detected in young African American subjects with only borderline hypertension, and whether there is a relationship of albuminuria with insulin resistance and with sodium-lithium countertransport activity. Clinically well young African American men and women including normotensive (blood pressure < 135/85 mm Hg, n = 41) and borderline hypertensive (blood pressure > or = 135/85 mm Hg, n = 26) individuals were studied. Each subject underwent an oral glucose tolerance test and euglycemic hyperinsulinemic clamp study. Albuminuria was measured on timed urine collections. Sodium-lithium countertransport activity was assayed in fresh red blood cells at 280 mmol/L Na+ for full saturation of external Na+ sites. The sum of insulin levels during glucose tolerance was significantly greater in the borderline hypertensive compared with the normotensive subjects (P = .014), and insulin-stimulated glucose utilization during the clamp was significantly lower in borderline hypertensive compared with normotensive subjects (P = .016). Albuminuria was greater in borderline hypertensive compared with normotensive subjects (P = .002). Albuminuria was significantly correlated with fasting plasma insulin concentration (r = .44, P < .002) and the sum of insulins during the glucose tolerance test (r = .45, P < .002). Sodium-lithium countertransport correlated with albuminuria (r = .31, P < .05) as well as significantly with insulin-stimulated glucose utilization during the clamp (r = .44, P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of individuals who excrete versus retain sodium under stress

To examine the role of stress on renal sodium excretion, we studied 27 normotensive and 21 hypertensive subjects. All subjects were placed on a standardized sodium diet. After water loading (2290 ml in 3 1/2 hr) they completed a 30 min baseline and a 30 min stress period (competitive videogame). Sixty-nine percent of the subjects increased ("excreters") and 31% decreased ("retainers") their sodium excretion under stress. In addition to increased potassium excretion (p < 0.006), excreters also manifested less of a stress associated increase in systolic (p = 0.055) and diastolic (p = 0.040) blood pressure and showed greater expression of anger (p < 0.02) than retainers. The same subjects were also studied to determin the effects of angiotensin converting enzyme inhibition (captopril 25 mg b.i.d.) on sodium excretion. On captopril, excreters now showed a retention of sodium (p < 0.001) and potassium (p < 0.01) under stress and no longer differed significantly in blood pressure reactivity. The results suggest that there are two different stress-related patterns of renal sodium excretion, that these patterns are related to blood pressure responses to stress, and may be related to anger expression. In addition, sodium excretion patterns under stress may be altered with certain type of antihypertensive medications.