The renin-angiotensin system in blacks: active, passive, or what?

Effect of Chronically Suppressed Plasma Angiotensin II on Regulation of the CYP4A/20-HETE Pathway in the Dahl Salt-Sensitive Rat

In Dahl salt-sensitive (SS) rats, impaired vascular relaxation can be restored by: (1) minipump infusion of a low (sub-pressor) dose of angiotensin II (ANG II) to restore physiological levels of plasma ANG II, (2) inhibition of 20-HETE production, and (3) introgression of a normally functioning renin allele from the Brown Norway rat (SS-13^BN consomic rat). Unlike SS rats, SS-13^BN rats have normal levels of ANG II on a normal-salt diet and suppressed ANG II on a high-salt (HS) diet. This study tested whether chronically low ANG II levels in SS rats upregulate cytochrome P450-4A (CYP4A) increasing the production of the vasoconstrictor 20-HETE. Although salt-induced suppression of ANG II levels increased reactive oxygen species (ROS) in basilar arteries from SS-13^BN rats in previous studies, this study showed no change in vascular 20-HETE levels in response to ANGII suppression. CYP4A inhibition significantly reduced vascular ROS levels and restored endothelium-dependent relaxation in response to acetylcholine in the middle cerebral artery (MCA) of SS rats and HS-fed SS-13^BN rats. These data demonstrate that both the renin-angiotensin system and the CYP4A/20-HETE pathway play a direct role in the vascular dysfunction of the Dahl SS rat but are independent of each other, even though they may both contribute to vascular dysfunction through ROS production.

Differential responses of resistance arterioles to elevated intraluminal pressure in blacks and whites

Black Americans have an earlier onset, higher average blood pressure, and higher rates of hypertension-related mortality and morbidity, compared to whites. The racial difference may be related to microvasculature, the major regulatory site of blood pressure. The goal of this study was to compare the response of resistance vessels to high intraluminal pressure between black and white participants. A total of 38 vessels were obtained from human fat samples [21 black, 17 white; mean age 32 ± 12 yr and body mass index (BMI) 26.9 ± 4.9; between-group P ≥ 0.05] and included in this study. Internal diameter was measured in response to the flow induced by various pressure gradients (Δ10, Δ20, Δ40, Δ60, and Δ100 cmH₂O), and flow-induced dilation (FID) was calculated before and after high intraluminal pressure (150 cmH₂O). Before high intraluminal pressure, FID was not different between blacks and whites (P = 0.112). After exposure to high intraluminal pressure, FID was reduced at every pressure gradient in vessels from blacks (P < 0.001), whereas FID did not change in white participants except at Δ100 cmH₂O. When incubated with the hydrogen peroxide (H₂O₂) scavenger polyethylene glycol-catalase (PEG-catalase), the FID response in vessels from black, but not white, individuals was significantly reduced and the magnitude was higher at normal pressure relative to high pressure. Our findings suggest that the vessels from self-identified black individuals are more susceptible to microvascular dysfunction following transient periods of high intraluminal pressure compared to whites and show greater dependence on H₂O₂ as a main contributor to FID at normal pressures.NEW & NOTEWORTHY Microvascular function regulates blood pressure and may contribute to racial differences in the incidence and prevalence of hypertension and other cardiovascular diseases. Here, we show that using an ex vivo model of resistance arterioles isolated from human gluteal fat tissue, flow-induced dilation is not different between black and white participants. However, when exposed to transient increases in intraluminal pressure, the flow-induced dilation in resistance arterioles from black participants demonstrated greater reductions relative to their white counterparts, indicating a higher sensitivity to pressure change in the microvasculature.

Differences in RAAS/vitamin D linked to genetics and socioeconomic factors could explain the higher mortality rate in African Americans with COVID-19

COVID-19 is said to be a pandemic that does not distinguish between skin color or ethnic origin. However, data in many parts of the world, especially in the United States, begin to show that there is a sector of society suffering a more significant impact from this pandemic. The Black population is more vulnerable than the White population to infection and death by COVID-19, with hypertension and diabetes mellitus as probable predisposing factors. Over time, multiple disparities have been observed between the health of Black and White populations, associated mainly with socioeconomic inequalities. However, some mechanisms and pathophysiological susceptibilities begin to be elucidated that are related directly to the higher prevalence of multiple diseases in the Black population, including infection and death by COVID-19. Plasma vitamin D levels and evolutionary adaptations of the renin-angiotensin-aldosterone system (RAAS) in Black people differ considerably from those of other races. The role of these factors in the development and progression of hypertension and multiple lung diseases, among them SARS-CoV-2 infection, is well established. In this sense, the present review attempts to elucidate the link between vitamin D and RAAS ethnic disparities and susceptibility to infection and death by COVID-19 in Black people, and suggests possible mechanisms for this susceptibility.

Managing hypertension in people of African origin with diabetes: Evaluation of adherence to NICE Guidelines

BACKGROUND

The pathophysiology of hypertension in people of African origin differs from other ethnicities. This effect may be exacerbated in people with type 2 diabetes mellitus (T2DM), hence control of hypertension is particularly important in this population.

AIMS

The primary aim was to evaluate the adherence to National Institute of Clinical Excellence (NICE) guidance (National Guidelines NG28) for hypertension management in African origin patients with T2DM.

METHODS

This study was done using electronic health records at a large primary care centre based in Birmingham, UK. Strict exclusion criteria were applied to identify individuals with T2DM, African origin patients and a diagnosis of hypertension. Retrospectively participants were identified, and NICE guideline adherence was assessed using descriptive statistics.

RESULTS

78 patients were included in the study of which 28 (36%) were on the NICE recommended combination of antihypertensives, suggesting poor adherence to the guidance in primary care prescribing. The blood pressure control of 35 (44.9%) patients was suboptimal, although this group received more frequent blood pressure monitoring. Microalbuminuria remains a problem in the suboptimal group.

CONCLUSION

This study provides insight into adherence to NICE guidance for managing hypertension in African origin patients with diabetes. Further work should be done to explore the effects of hypertension in this ethnic group and if there is a need for a more refined management guideline.

Sex-specific responses to mineralocorticoid receptor antagonism in hypertensive African American males and females

BACKGROUND

African Americans (AA) develop hypertension (HTN) at an earlier age, have a greater frequency and severity of HTN, and greater prevalence of uncontrolled HTN as compared to the white population. Mineralocorticoid antagonists have been shown to be very effective in treating uncontrolled HTN in both AA and white patients, but sex-specific responses are unclear.

METHODS

We evaluated the sex-specific impact of mineralocorticoid antagonism in an AA population. An AA cohort (n = 1483) from the Genetic Epidemiology Network of Arteriopathy study was stratified based on sex and whether they were taking spironolactone, a mineralocorticoid antagonist, in their antihypertensive regimen.

RESULTS

As compared to AA women not prescribed a mineralocorticoid antagonist, AA women taking spironolactone (n = 9) had lower systolic and diastolic blood pressure despite having a similar number of antihypertensive medications. The proportion of AA women with uncontrolled HTN was significantly less for patients taking spironolactone than for patients not prescribed spironolactone. Interestingly, none of these associations were found in the AA males or in white females.

CONCLUSIONS

Our data suggests that spironolactone is particularly effective in reducing blood pressure and controlling HTN in AA women. Further research into the impact of this therapy in this underserved and understudied minority is warranted.

Dysregulated aldosterone secretion in persons of African descent with endothelin-1 gene variants

Compared with persons of European descent (ED), persons of African descent (AD) have lower aldosterone (ALDO) levels, with the assumption being that the increased cardiovascular disease (CVD) risk associated with AD is not related to ALDO. However, the appropriateness of the ALDO levels for the volume status in AD is unclear. We hypothesized that, even though ALDO levels are lower in AD, they are inappropriately increased, and therefore, ALDO could mediate the increased CVD in AD. To test this hypothesis, we analyzed data from HyperPATH - 1,788 individuals from the total cohort and 765 restricted to ED-to-AD in a 2:1 match and genotyped for the endothelin-1 gene (EDN1). Linear regression analyses with adjustments were performed. In the total and restricted cohorts, PRA, ALDO, and urinary potassium levels were significantly lower in AD. However, in the AD group, greater ALDO dysregulation was present as evidenced by higher ALDO/plasma renin activity (PRA) ratios (ARR) and sodium-modulated ALDO suppression-to-stimulation indices. Furthermore, EDN1 minor allele carriers had significantly greater ARRs than noncarriers but only in the AD group. ARR levels were modulated by a significant interaction between EDN1 and AD. Thus, EDN1 variants may identify particularly susceptible ADs who will be responsive to treatment targeting ALDO-dependent pathways (e.g., mineralocorticoid-receptor antagonists).

Hypertension in African Americans

PURPOSE OF REVIEW

African Americans are over-burdened with hypertension resulting in excess morbidity and mortality. We highlight the health impact of hypertension in this population, review important observations regarding disease pathogenesis, and outline evidence-based treatment, current treatment guidelines, and management approaches.

RECENT FINDINGS

Hypertension accounts for 50% of the racial differences in mortality between Blacks and Whites in the USA. Genome-wide association studies have not clearly identified distinct genetic causes for the excess burden in this population as yet. Pathophysiology is complex likely involving interaction of genetic, biological, and social factors prevalent among African Americans. Non-pharmacologic and pharmacologic therapy is required and specific treatment guidelines for this population are varied. Combination therapy is most often necessary and single-pill formulations are most successful in achieving BP targets. Racial health disparities related to hypertension in African Americans are a serious public health concern that warrants greater attention. Multi-disciplinary research to understand the inter-relationship between biological and social factors is needed to guide successful treatments. Comprehensive care strategies are required to successfully address and eliminate the hypertension burden.

Evaluation of the angiotensin II receptor blocker azilsartan medoxomil in African‐American patients with hypertension

The efficacy and safety of azilsartan medoxomil (AZL‐M) were evaluated in African‐American patients with hypertension in a 6‐week, double‐blind, randomized, placebo‐controlled trial, for which the primary end point was change from baseline in 24‐hour mean systolic blood pressure (BP). There were 413 patients, with a mean age of 52 years, 57% women, and baseline 24‐hour BP of 146/91 mm Hg. Treatment differences in 24‐hour systolic BP between AZL‐M 40 mg and placebo (−5.0 mm Hg; 95% confidence interval, −8.0 to −2.0) and AZL‐M 80 mg and placebo (−7.8 mm Hg; 95% confidence interval, −10.7 to −4.9) were significant (P≤.001 vs placebo for both comparisons). Changes in the clinic BPs were similar to the ambulatory BP results. Incidence rates of adverse events were comparable among the treatment groups, including those of a serious nature. In African‐American patients with hypertension, AZL‐M significantly reduced ambulatory and clinic BPs in a dose‐dependent manner and was well tolerated.

Single-trait and multi-trait genome-wide association analyses identify novel loci for blood pressure in African-ancestry populations

Hypertension is a leading cause of global disease, mortality, and disability. While individuals of African descent suffer a disproportionate burden of hypertension and its complications, they have been underrepresented in genetic studies. To identify novel susceptibility loci for blood pressure and hypertension in people of African ancestry, we performed both single and multiple-trait genome-wide association analyses. We analyzed 21 genome-wide association studies comprised of 31,968 individuals of African ancestry, and validated our results with additional 54,395 individuals from multi-ethnic studies. These analyses identified nine loci with eleven independent variants which reached genome-wide significance (P < 1.25×10-8) for either systolic and diastolic blood pressure, hypertension, or for combined traits. Single-trait analyses identified two loci (TARID/TCF21 and LLPH/TMBIM4) and multiple-trait analyses identified one novel locus (FRMD3) for blood pressure. At these three loci, as well as at GRP20/CDH17, associated variants had alleles common only in African-ancestry populations. Functional annotation showed enrichment for genes expressed in immune and kidney cells, as well as in heart and vascular cells/tissues. Experiments driven by these findings and using angiotensin-II induced hypertension in mice showed altered kidney mRNA expression of six genes, suggesting their potential role in hypertension. Our study provides new evidence for genes related to hypertension susceptibility, and the need to study African-ancestry populations in order to identify biologic factors contributing to hypertension.

Renin angiotensin aldosterone system altered in resistant hypertension in Sub-Saharan African diabetes patients without evidence of primary hyperaldosteronism

BACKGROUND

The renin-angiotensin-aldosterone system may be altered in patients with resistant hypertension. This study aimed to evaluate the relation between renin-angiotensin-aldosterone system activity and resistant hypertension in Cameroonian diabetes patients with resistant hypertension.

METHODS

We carried out a case-control study including 19 diabetes patients with resistant hypertension and 19 diabetes patients with controlled hypertension matched to cases according to age, sex and duration of hypertension since diagnosis. After collection of data, fasting blood was collected for measurement of sodium, potassium, chloride, active renin and plasma aldosterone of which the aldosterone-renin ratio was derived to assess the activity of renin-angiotensin-aldosterone system. Then, each participant received 2000 ml infusion of saline solution after which plasma aldosterone was re-assayed.

RESULTS

Potassium levels were lower among cases compared to controls (mean: (4.10 ± 0.63 mmol/l vs. 4.47 ± 0.58 mmol/l), though nonsignificant (p = 0.065). Active renin, plasma aldosterone both before and after the dynamic test and aldosterone-renin ratio were comparable between cases and controls (all p values > 0.05). Plasma aldosterone significantly decreased after the dynamic test in both groups (p < 0.001), but no participant exhibited a post-test value>280 pmol/l. We found a significant negative correlation between potassium ion and plasma aldosterone (ρ = -0.324; p = 0.047), the other correlations being weak and unsignificant.

CONCLUSION

Although this study failed to show an association between RH and primary hyperaldosteronism in our context, there was a hyperactivity of renin-angiotensin-aldosterone system. Moreover, this study confirms the importance of potassium dosage when screening the renin-angiotensin-aldosterone system.

Hypertension Treatment in Blacks: Discussion of the U.S. Clinical Practice Guidelines

Blacks are especially susceptible to hypertension (HTN) and its associated organ damage leading to adverse cardiovascular, cerebrovascular and renal outcomes. Accordingly, HTN is particularly significant in contributing to the black-white racial differences in health outcomes in the US. As such, in order to address these health disparities, practical clinical practice guidelines (CPGs) on how to treat HTN, specifically in blacks, are needed. This review article is a timely addition to the literature because the most recent U.S. CPG more explicitly emphasizes race into the algorithmic management of HTN. However, recent clinical research cautions that use of race as a proxy to determine therapeutic response to pharmaceutical agents may be erroneous. This review will address the implications of the use of race in the hypertension CPGs. We will review the rationale behind the introduction of race into the U.S. CPG and the level of evidence that was available to justify this introduction. Finally, we will conclude with practical considerations in the treatment of HTN in blacks.

Elevated peripheral blood mononuclear cell-derived superoxide production in healthy young black men

Several studies have demonstrated that blacks exhibit elevations in systemic oxidative stress. However, the source(s) and mechanism(s) contributing to the elevation in oxidative stress remain unclear. Given that peripheral blood mononuclear cells (PBMCs) can be a major source of NADPH oxidase-derived superoxide production, we tested the hypothesis that young black men demonstrate greater superoxide production and NADPH oxidase expression in PBMCs compared with whites. PBMCs were freshly isolated from whole blood in young normotensive black (n = 18) and white (n = 16) men. Intracellular superoxide production in PBMCs was measured using dihydroethidium fluorescence, protein expression of NADPH oxidase subunits, gp91(phox) (membranous) and p47(phox) (cytosolic) in PBMCs were assessed using Western blot analysis, and plasma protein carbonyls were measured as a marker of systemic oxidative stress. Black men showed elevated intracellular superoxide production (4.3 ± 0.5 vs. 2.0 ± 0.6 relative fluorescence units; black men vs. white men, P < 0.05), increased protein expression for gp91(phox) and p47(phox) (e.g., p47(phox): 1.1 ± 0.2, black men vs. 0.4 ± 0.1, white men, P < 0.05) in PBMCs and higher circulating protein carbonyl levels (22 ± 4 vs. 14 ± 2 nmol/ml; black men vs. white men, P < 0.05). Interestingly, a positive family history of hypertension in black men did not further enhance PBMC-derived intracellular superoxide production or NADPH oxidase subunit protein expression. These findings indicate that black men exhibit greater resting PBMC-derived superoxide production and an upregulation of the NADPH oxidase pathway with a possible contribution to increases in systemic oxidative stress.

Dietary potassium intake and renal handling, and their impact on the cardiovascular health of normotensive afro-caribbeans

OBJECTIVE

Recent nutritional profiles of dietary intake have indicated a shift from the ancient diet to the Western diet. The ancient diet provided a high potassium and low sodium intake, which in turn leads to sodium conservation and potassium excretion. This change in the dietary intake is expected to affect potassium and sodium handling in the kidneys. Numerous studies have been done to emphasize the importance of sodium handling by the kidneys and its impact on cardiovascular health. This study will investigate potassium intake and handling, and its impact on the cardiovascular health of a sample of normotensive Afro-Caribbeans by the possible modulation of the renin angiotensin aldosterone system (RAAS).

METHODS

A sample of 51 normotensive Afro-Caribbean participants was recruited for the study. Participants were observed over a two-day period in which they were given a 24-hour ambulatory blood pressure monitor and a container to collect blood pressure data and a 24-hour urine sample. Anthropometric measurements were noted. Urinary electrolytes and supine plasma renin activity (PRA) were determined from the 24-hour urine collection and a blood sample. Dietary potassium intake was estimated based on dietary intake observations and calculated based on the urinary potassium excretion. SPSS version 19 was used to analyse the data to make inferences.

RESULTS

The daily potassium intake was observed to be 2.95 g/day and measured intake from the urinary potassium was between 4.95 and 7.32 g/day. Urinary potassium excretion was 3.66 (± 1.40) g/day. The urinary potassium excretion in the Afro-Caribbean sample in Barbados was higher than the other population samples. The averaged PRA of the participants (supine) was 0.778 (± 1.072) ng/mL/hour. The averaged nocturnal systolic blood pressure dip of the participants was 5.97 (± 4.324) %. There was no significant correlation between urinary potassium excretion, blood pressure, nocturnal systolic blood pressure dip and PRA.

CONCLUSIONS

The Afro-Caribbean sample has an inadequate daily potassium intake based on the observed intake and recommended values, with a high urinary excretion of the electrolyte compared to other values in the literature. This high potassium excretion could have been partly due to low plasma renin activity levels in the study participants. As a possible consequence, an increase in the nocturnal peripheral resistance is a likely cause for the diminished systolic dip. The lack of correlations between dietary potassium excretion and the blood pressure parameters does not allow any firm inference of the electrolyte's handling and its impact on cardiovascular health in the normotensive Afro-Caribbean participants. However, further research is needed to get a more accurate daily potassium intake value, and a more statistically robust sample to assess whether potassium handling and blood pressure would be affected by a change in potassium intake.

Race, plasma renin activity, and morning blood pressure surge--results from the Dietary Approaches to Stop Hypertension trial

BACKGROUND

The association of preawake (difference between pre- and postwaking blood pressure (BP)) and sleep-through surge (difference between sleeping nadir and postwaking BP) with cardiovascular events is unclear. Examination of factors associated with surge may provide novel insights. We examined the association of race, which associates with nocturnal dipping, and plasma renin activity (PRA) with preawake and sleep-through surge among individuals on a controlled diet.

METHODS

We performed a post hoc analysis of 323 subjects from the Dietary Approaches to Stop Hypertension trial who had available 24-hour BP data and who ingested a control diet during a 3-week run-in period. Linear regression models were fit to estimate the association of race and PRA with preawake and sleep-through surge.

RESULTS

Of the 323 individuals, 55% were black, 53% were men, and the average age was 45 years. After controlling for other factors, black race was associated with a 3.2mm Hg lower preawake and a 3.7mm Hg lower sleep-through surge compared with nonblacks. In nonblacks, higher PRA was associated with greater preawake surge only. There was no association of PRA with either preawake or sleep-through surge in blacks. Additional adjustment for dipping status resulted in attenuation of the race-surge associations.

CONCLUSIONS

Black race is associated with lower preawake and sleep-through surge compared with nonblacks, but the effect is partially attenuated by dipping status. Higher PRA appears to be associated with a higher preawake surge in nonblacks only. Further research should address if morning surge is definitively associated with clinical outcomes in racial subgroups, independent of dipping.

Plasma soluble (pro)renin receptor is independent of plasma renin, prorenin, and aldosterone concentrations but is affected by ethnicity

A soluble (pro)renin receptor (sPRR) circulates in plasma and is able to bind renin and prorenin. It is not known whether plasma sPRR concentrations vary with the activity of the renin-angiotensin system. We measured plasma sPRR, renin, prorenin, and aldosterone concentrations in 121 white and 9 black healthy subjects, 40 patients with diabetes mellitus, 41 hypertensive patients with or without renin-angiotensin system blockers, 9 patients with primary aldosteronism, and 10 patients with Gitelman syndrome. Median physiological plasma sPRR concentration was 23.5 ng/mL (interquartile range, 20.9-26.5) under usual uncontrolled sodium diet. sPRR concentration in healthy subjects, unlike renin and prorenin, did not display circadian variation or dependence on age, sex, posture, or hormonal status. sPRR concentrations were ≈25% lower in black than in white subjects, whereas renin concentrations were ≈40% lower. Patients with diabetes mellitus (average renin-high prorenin levels) and with hypertension only (average renin-average prorenin levels) had sPRR concentrations similar to healthy subjects. Renin-angiotensin system blockade was associated with increase of sPRR concentration by ≈12%. sPRR in patients with primary aldosteronism (low renin-low prorenin) and Gitelman syndrome (high renin-high prorenin) were similar and ≈10% higher than in healthy subjects. There was no correlation between sPRR and renin or prorenin. In conclusion, our results show that plasma sPRR concentrations are dependent on ethnicity and independent of renin, prorenin, and aldosterone concentrations in healthy subjects and in patients with contrasted degrees of renin-angiotensin system activity.

Vitamin D and the vascular sensitivity to angiotensin II in obese Caucasians with hypertension

Obesity and vitamin D deficiency have both been linked to augmented activity of the tissue renin-angiotensin system (RAS). We investigated whether obesity status influenced the relationship between 25-hydroxyvitamin D (25(OH)D) and vascular RAS activity. The levels of 25(OH)D were measured in hypertensive obese (n=39) and non-obese (n=58) Caucasian individuals. RAS activity was assessed by plasma renin activity, and evaluation of the vascular sensitivity to angiotensin II (AngII) using the mean arterial pressure (MAP) response to an infusion of AngII. Among obese subjects, 25(OH)D was an independent positive predictor of the MAP response to AngII (β=0.70, r=0.41, P<0.01); lower 25(OH)D concentrations were associated with a blunted MAP response to AngII. In contrast, 25(OH)D did not significantly predict the vascular sensitivity to AngII in non-obese subjects (β=0.10, r=0.07, P=0.62). A multivariable-adjusted interaction model confirmed that the positive relationship between 25(OH)D and the vascular sensitivity to AngII strengthened with obesity (P-interaction=0.03). These findings demonstrate a positive association between 25(OH)D and the vascular sensitivity to AngII in obese hypertensives, and further suggest that vascular RAS activity may progressively increase when 25(OH)D deficiency occurs in obesity. Future studies to evaluate the effect of vitamin D supplementation on vascular RAS activity in obesity are needed.

Serum aldosterone is associated with inflammation and aortic stiffness in normotensive overweight and obese young adults

Circulating aldosterone is increased in obesity and is associated with arterial stiffening in hypertensives and older adults. The aim of this article was to determine whether serum aldosterone is associated with pulse wave velocity (PWV), a measure of arterial stiffness, in normotensive overweight and obese adults aged 20-45 years (n = 344). Heart-femoral, femoral-ankle, and brachial-ankle PWV were measured. The sample was 77% female with mean body mass index 32.9 kg/m(2) (SD 3.9), median serum aldosterone 106.5 pg/mL (interquartile range 79.9, 155.5), and mean 24-hour urinary sodium excretion 185.9 mEq/day (SD 69.6). Higher serum aldosterone was not significantly correlated with any PWV measure in bivariate analysis. However, in multiple linear regression, adjusting for age, sex, race, height, heart rate, mean arterial pressure, and waist circumference, higher log aldosterone was associated with greater log heart-femoral PWV (β(se) = 0.042(0.021), P = .049). After adjusting for C-reactive protein, this association was no longer significant (β(se) = 0.035(0.021), P = .10). Circulating aldosterone may play an important role in vascular inflammation and aortic stiffening in normotensive overweight and obese adults.

25-Hydroxyvitamin D is associated with plasma renin activity and the pressor response to dietary sodium intake in Caucasians

INTRODUCTION

Concentrations of 1,25-hydroxyvitamin D have been positively associated with dietary sodium and salt sensitivity (SS) of blood pressure (BP), and inversely with plasma renin activity (PRA). We investigated the association between PRA and 25-hydroxyvitamin D (25OHD), the most clinically relevant vitamin D metabolite, and whether 25OHD associates with SS of BP in renin phenotypes of hypertension.

METHODS

We performed cross-sectional analyses on 223 Caucasian subjects with hypertension maintained in high and low dietary sodium balance. Subjects were distinguished as having low-renin (LR) or normal-renin (NR) hypertension. Multivariable linear regression was used to evaluate adjusted relationships.

RESULTS

Increasing 25OHD concentrations were inversely associated with PRA (p < 0.05) on both salt diets. Furthermore, 25OHD was associated with SS of BP in LR hypertension (b = 0.62, p = 0.04), but not in NR hypertension (b = 0.06, p = 0.59). In an adjusted multivariable interaction model, renin status (LR vs. NR) was a significant effect modifier of the relationship between 25OHD and SS of BP (p = 0.04).

CONCLUSIONS

Our findings suggest that 25OHD is inversely associated with PRA and positively associated with SS of BP in LR hypertension subjects. These results extend and support prior evidence indicating an interaction between dietary sodium, the RAS, and vitamin D that influences BP in hypertension.

Comparative efficacy and safety of combination aliskiren/amlodipine and amlodipine monotherapy in African Americans with stage 2 hypertension

Initial multiple drug therapy for hypertension achieves greater and quicker reductions and higher blood pressure (BP) control rates than monotherapy. This 8-week, prospective, multicenter, randomized, double-blind study compared the efficacy and safety of the initial combination of aliskiren/amlodipine with amlodipine monotherapy in African Americans with stage 2 hypertension. After a 1- to 4-week washout, patients received aliskiren/amlodipine 150/5 mg or amlodipine 5 mg for 1 week and then were force-titrated to aliskiren/amlodipine 300/10 mg or amlodipine 10 mg for 7 weeks. At week 8, greater reductions in mean sitting systolic BP were obtained with aliskiren/amlodipine (n = 220) than with amlodipine (n = 223) (least squares mean change [standard error of the mean], -34.1 [1.14] mm Hg vs -28.9 [1.12] mm Hg; P<.001). Ambulatory and central BP measures were consistent with clinic BP findings, although these were conducted in a small subset of patients (n = 94 in ambulatory BP monitoring substudy and n = 136 for central BP). More patients achieved goal BP (<140/90 mm Hg) with aliskiren/amlodipine than with amlodipine at week 8 (57.3% vs 48.0%; P = .051). Both treatment groups had similar adverse event rates (35.0% and 32.7%, respectively). The most common adverse events were peripheral edema (7.7% with aliskiren/amlodipine and 9.0% with amlodipine), headache, fatigue, and nausea. The combination of aliskiren/amlodipine reduced peripheral, ambulatory, and central BP more than amlodipine alone with similar tolerability in African Americans with stage 2 hypertension.

The influence of body mass index and renin-angiotensin-aldosterone system activity on the relationship between 25-hydroxyvitamin D and adiponectin in Caucasian men

OBJECTIVE

Previous studies have suggested that circulating adiponectin concentrations are associated positively with vitamin D and negatively with body mass index (BMI) but have not accounted for the influence of the renin-angiotensin-aldosterone system (RAAS) in this relationship. This is particularly relevant because increased RAAS activity is associated with obesity and is known to lower adiponectin levels. We evaluated the association between adiponectin and 25-hydroxyvitamin D (25(OH)D) after controlling RAAS activity with dietary sodium equilibration and also evaluated whether this relationship was influenced by BMI.

DESIGN

Cross-sectional study of 115 hypertensive Caucasian men from the Hypertensive Pathotype Consortium.

METHODS

To manipulate RAAS activity, all subjects underwent 1 week of high dietary sodium (HS) diet to suppress RAAS and 1 week of low dietary sodium (LS) diet to stimulate RAAS. Linear regression was used to evaluate the association between adiponectin and 25(OH)D, and the effect of BMI on this relationship, in each dietary condition.

RESULTS

Adiponectin was higher on HS, where circulating RAAS activity was low, when compared with LS (HS=2.9 versus LS=2.4 μg/ml, P<0.0001). 25(OH)D levels were positively associated with adiponectin, and BMI was a statistically significant effect modifier of the relationship between 25(OH)D and adiponectin on both diets (P interaction <0.01 between BMI and 25(OH)D).

CONCLUSIONS

Higher 25(OH)D concentrations were independently associated with higher adiponectin levels, particularly when BMI was high. Dietary sodium balance and circulating RAAS activity did not appear to affect this relationship. Future studies should explore whether vitamin D supplementation increases adiponectin levels in obesity.

The association of plasma resistin with dietary sodium manipulation, the renin-angiotensin-aldosterone system, and 25-hydroxyvitamin D3 in human hypertension

OBJECTIVE

Both resistin and vitamin D have been associated with the renin-angiotensin-aldosterone system (RAAS). We investigated the association between resistin and the RAAS, and resistin and vitamin D under controlled dietary sodium conditions.

DESIGN

Retrospective cross-sectional study of subjects from the HyperPATH Consortium, who were maintained in high dietary sodium (HS) and low dietary sodium (LS) balance for 1 week each.

PATIENTS

Caucasian subjects with hypertension (n=177).

MEASUREMENTS

25-Hydroxyvitamin D (25[OH]D) levels were used to assess vitamin D status. Plasma resistin and RAAS measures were evaluated on each dietary intervention.

RESULTS

Resistin levels were significantly higher in LS, where RAAS activity was high, when compared with HS balance, where RAAS activity was suppressed (6.36 vs 5.86 μg/l, P < 0.0001); however, resistin concentrations were not associated with plasma renin activity or serum aldosterone on either diet. 25(OH)D levels were positively and independently associated with resistin in both dietary conditions (HS: β=0.400, P-trend=0.027; LS: β=0.540, P-trend=0.014).

CONCLUSIONS

Dietary sodium loading reduced resistin levels, possibly by suppressing the RAAS; however, circulating RAAS components were not related to resistin concentrations within each specific dietary sodium condition. 25(OH)D was positively associated with resistin and may be involved in resistin regulation through an unknown mechanism. Further studies to understand resistin regulation in human hypertension better are warranted.

Pathogenesis and clinical physiology of hypertension

Significant advances have been made in understanding the pathogenesis and clinical physiology of primary hypertension. This article presents an overview of the physiology of normal blood pressure control and the pathophysiologic mechanisms that predispose individuals and populations to primary hypertension. The role of genetics, environment, and the gene-environment interaction is discussed. The spectrum of changes in physiologic states that result in chronic increases of arterial blood pressure are reviewed. The nature and characteristics of feedback loops and the primary modulating systems, the central and peripheral nervous systems, and circulating and tissue hormones are reviewed. The role of the endothelium of the artery and its production of endothelin, nitric oxide, angiotensin II, as well as other vasoactive substances in response to various stimuli, is also discussed. A unifying pathway for the development of hypertension and the practical implications for the prevention and control of hypertension are discussed.

Management of high blood pressure in Blacks: an update of the International Society on Hypertension in Blacks consensus statement

Since the first International Society on Hypertension in Blacks consensus statement on the "Management of High Blood Pressure in African American" in 2003, data from additional clinical trials have become available. We reviewed hypertension and cardiovascular disease prevention and treatment guidelines, pharmacological hypertension clinical end point trials, and blood pressure-lowering trials in blacks. Selected trials without significant black representation were considered. In this update, blacks with hypertension are divided into 2 risk strata, primary prevention, where elevated blood pressure without target organ damage, preclinical cardiovascular disease, or overt cardiovascular disease for whom blood pressure consistently <135/85 mm Hg is recommended, and secondary prevention, where elevated blood pressure with target organ damage, preclinical cardiovascular disease, and/or a history of cardiovascular disease, for whom blood pressure consistently <130/80 mm Hg is recommended. If blood pressure is ≤10 mm Hg above target levels, monotherapy with a diuretic or calcium channel blocker is preferred. When blood pressure is >15/10 mm Hg above target, 2-drug therapy is recommended, with either a calcium channel blocker plus a renin-angiotensin system blocker or, alternatively, in edematous and/or volume-overload states, with a thiazide diuretic plus a renin-angiotensin system blocker. Effective multidrug therapeutic combinations through 4 drugs are described. Comprehensive lifestyle modifications should be initiated in blacks when blood pressure is ≥115/75 mm Hg. The updated International Society on Hypertension in Blacks consensus statement on hypertension management in blacks lowers the minimum target blood pressure level for the lowest-risk blacks, emphasizes effective multidrug regimens, and de-emphasizes monotherapy.

Efficacy and safety of initial combination therapy with amlodipine/valsartan compared with amlodipine monotherapy in black patients with stage 2 hypertension: the EX-STAND study

The strategy of initiating hypertension treatment with combination versus single-drug therapy was formally tested in a prospective, double-blind, parallel-group trial in blacks with stage 2 hypertension (mean sitting systolic BP (MSSBP) >or=160 and <200 mm Hg). Participants were randomized equally to amlodipine/valsartan (A/V) (n=286) or amlodipine (A) monotherapy (n=286). After 2 weeks, there was forced titration of A/V 5/160 mg to A/V 10/160 mg and of A 5 to A 10 mg followed by 10 additional weeks of treatment. If SBP was >or=130 mm Hg at week 4, the protocol allowed optional titration of A/V to the 10/320 mg dose and, at week 8, hydrochlorothiazide 12.5 mg was optionally added to both A/V and A if SBP >or=130 mm Hg. Amlodipine/valsartan at week 8 lowered MSSBP last observation carried forward significantly>A (33.3 vs 26.6 mm Hg, P<0.0001). Lowering of MSSBP with A/V significantly exceeded that of A in several specified subgroups-the elderly (>or=65 years), isolated systolic hypertension, and those with body mass index (BMI) >or=30 kg/m(2). More patients treated with A/V than A achieved BP control (<140/90 mm Hg) both at weeks 8 (49.8 vs 30.2%; P<0.0001) and 12 (57.2 vs 35.9%; P<0.0001). Both treatment regimens were well tolerated. In conclusion, the strategy of initiating combination antihypertensive drug therapy in blacks with stage 2 hypertension with amlodipine /valsartan achieves greater and quicker reductions in BP as well as significantly higher BP control rates than starting treatment with amlodipine monotherapy.

High intraluminal pressure via H2O2 upregulates arteriolar constrictions to angiotensin II by increasing the functional availability of AT1 receptors

Previously, we found that high intraluminal pressure leads to production of reactive oxygen species (ROS) and also upregulates several components of the renin-angiotensin system in the wall of small arteries. We hypothesized that acute exposure of arterioles to high intraluminal pressure in vitro via increasing ROS production enhances the functional availability of type 1 angiotensin II (Ang II) receptors (AT1 receptors), resulting in sustained constrictions. In arterioles ( approximately 180 mum) isolated from rat skeletal muscle, Ang II elicited dose-dependent constrictions, which decreased significantly by the second application [maximum (max.): from 59% +/- 4% to 26% +/- 5% at 10(-8) M; P < 0.05] in the presence of 80 mmHg of intraluminal pressure. In contrast, if the arterioles were exposed to high intraluminal pressure (160 mmHg for 30 min), Ang II-induced constrictions remained substantial on the second application (max.: 51% +/- 3% at 10(-8) M). In the presence of Tiron and polyethylene glycol (PEG)-catalase, known to reduce the level of superoxide anion and hydrogen peroxide (H(2)O(2)), second applications of Ang II evoked similarly reduced constrictions, even after high-pressure exposure (29% +/- 4% at 10(-8) M). Furthermore, when arterioles were exposed to H(2)O(2) (for 30 min, 10(-7) M, at normal 80 mmHg pressure), Ang II-induced constrictions remained substantial on second applications (59% +/- 5% at 10(-8) M). These findings suggest that high pressure, likely via inducing H(2)O(2) production, increases the functional availability of AT1 receptors and thus enhances Ang II-induced arteriolar constrictions. We propose that in hypertension-regardless of etiology-high intraluminal pressure, via oxidative stress, enhances the functional availability of AT1 receptors augmenting Ang II-induced constrictions.

Racial differences in renal vascular response to angiotensin blockade with captopril or candesartan

OBJECTIVE

We compared the renal vascular response to captopril and candesartan among nondiabetic, normotensive black and white participants to explore angiotensin-converting enzyme-independent generation of angiotensin II.

METHODS

Thirteen black individuals and 10 white individuals in low-salt balance were given captopril and candesartan on sequential study days, and the renal plasma flow responses to these agents were measured.

RESULTS

Consistent with our prior observations, white individuals demonstrated a strong, significant correlation between responses to these drugs (r = 0.78, P = 0.008) and a significantly greater increase in the renal plasma flow in response to candesartan compared with captopril (104.2 +/- 26.8 versus 52.4 +/- 24.3 ml/min per 1.73 m; P = 0.03). In black participants, however, no correlation between responses to captopril and to candesartan was observed (r = 0.22, P = 0.47) and there was no difference in the renal plasma flow response between the two drugs (90.4 +/- 13.0 versus 80.4 +/- 15.3 ml/min per 1.73 m; P = 0.59). The difference in the response to the two drugs was significantly higher among white participants compared with black participants (P = 0.03).

CONCLUSION

We confirmed the contribution of an angiotensin-converting enzyme-independent pathway for angiotensin II generation in the kidneys of nondiabetic, normotensive white, but not black, individuals.

Renal and gastrointestinal potassium excretion in humans: new insight based on new data and review and analysis of published studies

OBJECTIVES

Little is known about the relationship between the renal and gastrointestinal excretion of potassium in humans. This information is important in light of strong associations of potassium intake with hypertension and occlusive stroke.

METHODS

We determined the relationship between fecal and urinary excretion of potassium under both fixed and variable potassium intakes using our unpublished archival data and published data of others. Twenty-five subjects were evaluated.

RESULTS

On a fixed, low oral potassium intake (61.2 +/- 4.7 mmol/day; mean +/- SD), there was an inverse relationship between fecal and urinary potassium excretion (r = -0.66, p = 0.040). In studies in which potassium intake varied between 61-135 mmol/day, fecal and urinary potassium excretions were positively correlated (r = 0.58, p = 0.024). Considerable within-and-between-subject variation was observed in the relationship between fecal and urinary potassium excretion.

CONCLUSIONS

Inter-individual variation in fecal potassium excretion may arise from both variation in dietary potassium intake and intrinsic individual differences in the renal versus gastrointestinal handling of potassium.

Aldosterone Synthase Promoter Polymorphism Predicts Outcome in African Americans With Heart Failure

OBJECTIVES

We sought to evaluate the effect of the aldosterone synthase promoter polymorphism on heart failure outcomes for subjects in the African American Heart Failure Trial (A-HeFT).

BACKGROUND

Genetic heterogeneity modulates clinical outcomes in subjects with heart failure (HF); however, little data exist in African American populations. A common polymorphism exists in the promoter region of the aldosterone synthase gene (CYP11B2) at position -344 (T/C). The -344C allele, associated with higher aldosterone synthase activity, has been linked to hypertension; however, its impact on outcomes in HF is unknown.

METHODS

A total of 354 subjects from A-HeFT participated in the GRAHF (Genetic Risk Assessment of Heart Failure in African Americans) substudy and were genotyped for the aldosterone synthase polymorphism. Patients were followed prospectively, and event-free survival (freedom from death and HF hospitalization) compared by CYP11B2 genotype.

RESULTS

Of the cohort, 218 patients were TT, 114 CT, and 22 patients were CC. Baseline etiology, blood pressure, and functional class were not significantly different among the 3 cohorts. The C allele was associated with significantly poorer HF hospitalization-free survival with the best survival among TT subjects, intermediate for heterozygotes, and the poorest for CC homozygotes (p = 0.018), and a higher rate of death (% death TT/TC/CC = 1.8/3.5/18.2, p = 0.001). The TT genotype, more prevalent in blacks, was associated with greater impact of fixed combination of isosorbide dinitrate and hydralazine on the primary composite end point (p = 0.01).

CONCLUSIONS

The aldosterone synthase promoter -344C allele linked to higher aldosterone levels is associated with poorer event-free survival in blacks with HF. The role of aldosterone receptor antagonists in diminishing this apparent genetic risk remains to be explored.

Update on disparities in the pathophysiology and management of hypertension: focus on African Americans

Hypertension treatment and control is of paramount importance in the prevention of premature cardiovascular disease. African Americans present a special challenge to the clinician due, in part, to their earlier age of onset,greater prevalence, and increased rates of untoward events. A review of the recent studies of genetic epidemiology has not revealed unique genotypes that explain human hypertension or the disparate impact suffered by African Americans. Moreover, a clear message has emerged that environmental factors predominate in their effect on cardiovascular risk and are mutable. These findings suggest that to have an immediate and substantial impact on the ethnic disparity of hypertension, resources and research should be directed toward social and behavioral factors. Prompt and aggressive control of blood pressure is an effective global strategy for cardiovascular risk reduction. In most cases, this approach requires multiple interventions including lifestyle modification and an antihypertensive regimen that is tailored to the individual under the current guidelines and not stipulated by race.

Racial and Ethnic Differences in Microalbuminuria Prevalence in a Diabetes Population: The Pathways Study

The objective of this study was to determine whether racial or ethnic differences in prevalence of diabetic microalbuminuria were observed in a large primary care population in which comparable access to health care exists. A cross-sectional analysis of survey and automated laboratory data 2969 primary care diabetic patients of a large regional health maintenance organization was conducted. Study data were analyzed for racial/ethnic differences in microalbuminuria (30 to 300 mg albumin/g creatinine) and macroalbuminuria (>300 mg albumin/g creatinine) prevalence among diabetes registry-identified patients who completed a survey that assessed demographics, diabetes care, and depression. Computerized pharmacy, hospital, and laboratory data were linked to survey data for analysis. Racial/ethnic differences in the odds of microalbuminuria and macroalbuminuria were assessed by unconditional logistic regression, stratified by the presence of hypertension. Among those tested, the unadjusted prevalence of micro- or macroalbuminuria was 30.9%, which was similar among the various racial/ethnic groups. Among those without hypertension, microalbuminuria was twofold greater (odds ratio [OR] 2.01; 95% confidence interval [CI] 1.14 to 3.53) and macroalbuminuria was threefold greater (OR 3.17; 95% CI 1.09 to 9.26) for Asians as compared with whites. Among those with hypertension, adjusted odds of microalbuminuria were greater for Hispanics (OR 3.82; 95% CI 1.16 to 12.57) than whites, whereas adjusted odds of macroalbuminuria were threefold greater for blacks (OR 3.32; 95% CI 1.26 to 8.76) than for whites. For most racial/ethnic minorities, hypertriglyceridemia was significantly associated with greater odds of micro- and macroalbuminuria. Among a large primary care population, racial/ethnic differences exist in the adjusted prevalence of microalbuminuria and macroalbuminuria depending on hypertension status. In this setting, racial/ethnic differences in early diabetic nephropathy were observed despite comparable access to diabetes care.

Sodium glomerulopathy: tubuloglomerular feedback and renal injury in African Americans

African Americans are prone to develop not only essential hypertension but also progressive renal injury. We present a simple model to explain salt-induced renal injury (sodium glomerulopathy) in African Americans, the central features of which are the tubuloglomerular feedback and the balance/imbalance between the vascular tones of the afferent and efferent glomerular arterioles. We propose that in African Americans, habitual consumption of high salt causes chronic intermittent tubular hyperperfusion of the macula densa, resulting in a rightward and upward resetting of the operating point for the tubuloglomerular feedback. The resetting of the operating point causes an imbalance between the vascular tones of the afferent/efferent arterioles, a rise in the glomerular capillary hydraulic pressure, and consequent hyperfiltration. Increased susceptibility to glomerular hyperfiltration of African Americans on a high salt intake may explain their proclivity to progressive renal injury associated with essential hypertension.