Racial differences in aldosterone excretion and plasma aldosterone concentrations in children

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

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

Elevated Blood Pressure and Aldosterone Dysregulation in Young Black Women Versus White Women on Controlled Sodium Diets

CONTEXT

Black women have a higher prevalence of hypertension as compared to White women. Differences in dietary sodium intake have been implicated as a contributing factor for the disparities in hypertension.

OBJECTIVE

Our objective was to understand whether young Black women would have higher systolic blood pressure (SBP) than White women even on controlled sodium diets and to determine whether SBP differences were due to differences in dietary sodium intake and/or aldosterone regulation.

DESIGN

The analyses included 525 hypertensive and normotensive women (ages 18-71) from the International Hypertensive Pathotype consortium, who were maintained on liberal sodium (LIB; >200 mEq sodium/day) and restricted sodium (RES; 10 mEq sodium/day) diets.

RESULTS

Multivariate regression analyses (adjusted for age, race, study site, body mass index) found that Black women (ages 18-50) had significantly higher SBP than White women on both sodium diets: +8.7 ± 2.7 mmHg (P-value = .002) on a LIB diet and +8.5 ± 2.5 mmHg (P-value = .001) on a RES diet. Even among 18- to 35-year-olds-who were normotensive and nonobese-Black women had higher SBP: +7.9 ± 2.4 mmHg (P-value = .001) on a LIB diet and +7.6 ± 2.7 mmHg (P-value = .005) on a RES diet. Younger Black women also had higher plasma aldosterone concentration to plasma renin activity ratio (ARR) on both LIB and RES diets as well as a higher sodium-modulated aldosterone suppression-stimulation index-an indicator of aldosterone dysregulation. In younger Black women-but not in White women-there was a significant association between SBP and ARR on both LIB and RES diets.

CONCLUSION

Young Black women had increased SBP and ARR as compared to White women on LIB and RES diets, which offers insights into the possible mechanisms for the increased hypertension and cardiovascular disease risk in an at-risk and understudied population.

Aldosterone Antagonism Is More Effective at Reducing Blood Pressure and Excessive Renal ENaC Activity in AngII-Infused Female Rats Than in Males

BACKGROUND

AngII (angiotensin II)-dependent hypertension causes comparable elevations of blood pressure (BP), aldosterone levels, and renal ENaC (epithelial Na+ channel) activity in male and female rodents. Mineralocorticoid receptor (MR) antagonism has a limited antihypertensive effect associated with insufficient suppression of renal ENaC in male rodents with AngII-hypertension. While MR blockade effectively reduces BP in female mice with salt-sensitive and leptin-induced hypertension, MR antagonism has not been studied in female rodents with AngII-hypertension. We hypothesize that overstimulation of renal MR signaling drives redundant ENaC-mediated Na+ reabsorption and BP increase in female rats with AngII-hypertension.

METHODS

We employ a combination of physiological, pharmacological, biochemical, and biophysical approaches to compare the effect of MR inhibitors on BP and ENaC activity in AngII-infused male and female Sprague Dawley rats.

RESULTS

MR blockade markedly attenuates AngII-hypertension in female rats but has only a marginal effect in males. Spironolactone increases urinary sodium excretion and urinary sodium-to-potassium ratio in AngII-infused female, but not male, rats. The expression of renal MR and HSD11β2 (11β-hydroxysteroid dehydrogenase type 2) that determines the availability of MR to aldosterone is significantly higher in AngII-infused female rats than in males. ENaC activity is ≈2× lower in spironolactone-treated AngII-infused female rats than in males. Reduced ENaC activity in AngII-infused female rats on spironolactone correlates with increased interaction with ubiquitin ligase Nedd4-2 (neural precursor cell expressed developmentally down-regulated protein 4-2), targeting ENaC for degradation.

CONCLUSIONS

MR-ENaC axis is the primary determinant of excessive renal sodium reabsorption and an attractive antihypertensive target in female rats with AngII-hypertension, but not in males.

Associations of renal sinus fat with blood pressure and ectopic fat in a diverse cohort of adults

Background

Renal sinus fat (RSF) is an ectopic fat depot shown to be associated with visceral adiposity and hypertension in predominantly white populations. The purpose of this analysis is to investigate RSF and associations between RSF and blood pressure in a cohort of African American (AA) and European American (EA) adults. A secondary purpose was to explore risk factors associated with RSF.

Methods

Participants were 116 A A and EA adult men and women. Ectopic fat depots were assessed with MRI: RSF, intraabdominal adipose tissue (IAAT), intermuscular adipose tissue (IMAT), perimuscular adipose tissue (PMAT), and liver fat. Cardiovascular measures included diastolic blood pressure (DBP), systolic blood pressure (SBP), pulse pressure, mean arterial pressure, and flow mediated dilation. Matsuda index was calculated for insulin sensitivity. Pearson correlations were used to investigate associations of RSF with cardiovascular measures. Multiple linear regression was used to evaluate contributions of RSF on SBP and DBP and to explore factors associated with RSF.

Results

No difference was observed in RSF between AA and EA participants. RSF was positively associated with DBP in AA participants, but this was not independent of age and sex. Age, male sex, and total body fat were positively associated with RSF in AA participants. Insulin sensitivity was inversely and IAAT and PMAT were positively associated with RSF in EA participants.

Conclusions

Differential associations of RSF with age, insulin sensitivity, and adipose depots among AA and EA adults suggest unique pathophysiological mechanisms influence RSF deposition, which may contribute to chronic disease etiology and progression.

Vitamin D and risk of hypertension among Black women

Evidence of an association between plasma 25-hydroxyvitamin D [25(OH)D] levels and risk of hypertension, predominantly from studies of White individuals, suggests an inverse relationship. Limited data are available on Black individuals, who are more likely to have vitamin D deficiency. In the Black Women's Health Study (BWHS), a prospective study of 59 000 self-identified Black women from across the US, we assessed levels of a validated predicted vitamin D score in relation to incident hypertension. We followed 42 239 participants who were free of cardiovascular disease and cancer from 1995 to 2019, during which time 19 505 incident cases of hypertension were identified. Cox proportional hazards model were used to calculate multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of predicted vitamin D with the risk of incident hypertension. In age-adjusted analyses, there was a strong inverse dose-response association between predicted vitamin D score and hypertension risk, with an HR of .66 (95% CI: .63-.68, p trend < .0001) for the highest quartile of predicted vitamin D relative to the lowest. After control for potential confounders including body mass index, physical activity, and cigarette smoking, the HR was attenuated to .91 (95% CI: .87-.95, p trend = .002). In this prospective cohort study of Black women, predicted vitamin D score was weakly inversely associated with the incidence of hypertension. This observed association may reflect an inability to fully control for confounding factors.

Dysnatremias, Mortality, and Kidney Failure in CKD: Findings From the Chronic Renal Insufficiency Cohort (CRIC) Study

Rationale & Objective

Dysnatremias have been associated with an increased risk of mortality in the chronic kidney disease (CKD) population. Our objective is to identify the prevalence of and risk factors associated with dysnatremias in a CKD population and assess the association of dysnatremias with kidney failure and mortality among patients with CKD enrolled in the Chronic Renal Insufficiency Cohort Study.

Study Design

Analysis of prospective cohort study.

Setting & Participants

Adult patients aged 21-74 years with CKD from the Chronic Renal Insufficiency Cohort study.

Predictors

Baseline and time-dependent hyponatremia and hypernatremia.

Outcomes

All-cause mortality and kidney failure.

Analytical Approach

Baseline characteristics were compared using χ2 tests for categorical variables, analysis of variance for age, and Kruskal-Wallis tests for laboratory variables. Cox proportional hazards models and competing risk models were used to evaluate the association between baseline sodium level and overall mortality.

Results

Of a total of 5,444 patients with CKD, 486 (9%) had hyponatremia and 53 (1%) had hypernatremia. Altogether, 1,508 patients died and 1,206 reached kidney failure. In adjusted Cox models, time-dependent dysnatremias were strongly associated with mortality for both hyponatremia (HR, 1.38; 95% CI, 1.16-1.64) and hypernatremia (HR, 1.54; 95% CI, 1.04-2.29). Factors associated with hyponatremia included female sex, diabetes, and hypertension. Regardless of age, time-dependent hypernatremia was associated with an increased risk of kidney failure (HR, 1.64; 95% CI, 1.06-2.53). Baseline and time-dependent hyponatremia were associated with an increased risk of kidney failure in patients younger than 65 (baseline hyponatremia HR, 1.30; 95% CI, 1.03-1.64 and time-dependent hyponatremia HR, 1.36; 95% CI, 1.09-1.70) but not among patients aged >65 years.

Limitations

Inability to establish causality and lack of generalizability to hospitalized patients.

Conclusions

Dysnatremias are prevalent among ambulatory CKD patients and are associated with mortality and kidney failure. Time-dependent dysnatremias were significantly associated with mortality in patients with CKD. Time-dependent hypernatremia was associated with progression to kidney failure. Baseline and time-dependent hyponatremia were associated with an increased risk of progression to kidney failure in those younger than 65 years.

Streamlined variational inference for higher level group-specific curve models

A two-level group-specific curve model is such that the mean response of each member of a group is a separate smooth function of a predictor of interest. The three-level extension is such that one grouping variable is nested within another one, and higher level extensions are analogous. Streamlined variational inference for higher level group-specific curve models is a challenging problem. We confront it by systematically working through two-level and then three-level cases and making use of the higher level sparse matrix infrastructure laid down in Nolan and Wand (2019). A motivation is analysis of data from ultrasound technology for which three-level group-specific curve models are appropriate. Whilst extension to the number of levels exceeding three is not covered explicitly, the pattern established by our systematic approach sheds light on what is required for even higher level group-specific curve models.

Combined associations of 25-hydroxivitamin D and parathyroid hormone with diabetes risk and associated comorbidities among U.S. white and black women

Background/objectives

There is evidence of black–white differences in vitamin D status and cardiometabolic health. This study aimed to further evaluate the joint associations of 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) with risks of diabetes and related cardiometabolic comorbidities among white and black women.

Subjects/methods

We cross-sectionally and prospectively analyzed data from 1850 black and 3000 white postmenopausal women without cardiovascular disease or dialysis at baseline from the Women’s Health Initiative—Observational Study. Weighted Cox proportional hazards analyses and weighted logistic regression models were used to examine the joint associations of 25(OH)D and PTH with incident diabetes and prevalence of other diabetes-related cardiometabolic comorbidities (including CKD, hypertension, or obesity).

Results

We identified 3322 cases of obesity (n = 1629), hypertension (n = 2759), or CKD (n = 318) at baseline and 453 incident cases of diabetes during 11 years of follow-up. Cross-sectionally, lower 25(OH)D and higher PTH were independently associated with higher prevalence of hypertension [odds ratio (OR) = 0.79; 95% confidence interval (CI): 0.72–0.87 and OR = 1.55; 95% CI: 1.39–1.73] among white women only. When stratified by diabetes status, compared to women with 25(OH)D ≥50 nmol/L and PTH ≤6.89 pmol/L (65 pg/mL), women who did not have diabetes with vitamin D deficiency (<50 nmol/L) and PTH excess (>6.89 pmol/L) had higher prevalence of CKD, hypertension, or obesity (OR = 4.23; 95% CI: 2.90–6.18) than women who had diabetes (OR = 1.89; 95% CI: 0.96–3.71). Prospectively, lower 25(OH)D was associated with lower diabetes incidence [hazard ratio (HR) = 0.73; 95% CI: 0.62–0.86] in white women. Jointly, compared to the group with 25(OH)D ≥50 nmol/L and PTH ≤6.89 pmol/L, white women with 25(OH)D deficiency (<50 nmol/L) had elevated risk for diabetes, regardless of PTH levels.

Conclusions

Low 25(OH)D and high PTH were jointly associated with increased risk of diabetes among white women only. Their joint associations with high prevalence of CKD, hypertension, and obesity were more pronounced among women without diabetes.

Aldosterone sensitivity: an opportunity to explore the pathogenesis of hypertension

Aldosterone sensitivity is defined as an outcome variable for a given circulating level of aldosterone. In basic and translational studies, aldosterone sensitivity has been measured in differential tissue responses, e.g., lower urine sodium and higher urine potassium, as an index of the renal response; in clinical studies, aldosterone sensitivity has been measured in differential blood pressure responses. The concept of aldosterone sensitivity disrupts the conventional wisdom of the renin-angiotensin-aldosterone system and has the potential to uncover novel mechanisms of hypertension. Here, we review basic and translational science studies that uncovered differential renal responses to aldosterone and connect this earlier work to more recent observational studies and randomized trials that have demonstrated differential blood pressure responses for a given level of aldosterone in healthy and hypertensive persons. Black race and older age are associated with higher aldosterone sensitivity and blood pressure. We also discuss gaps in the field and how future basic and clinical studies might inform mechanisms of differential sensitivity.

Racial Differences in Diuretic Efficiency, Plasma Renin, and Rehospitalization in Subjects With Acute Heart Failure

BACKGROUND

Black patients have higher rates of hospitalization for acute heart failure than other race/ethnic groups. We sought to determine whether diuretic efficiency is associated with racial differences in risk for rehospitalization after acute heart failure.

METHODS

A post hoc analysis was performed on 721 subjects (age, 68±13 years; 22% black) enrolled in 3 acute heart failure clinical trials: ROSE-AHF (Renal Optimization Strategies Evaluation in Acute Heart Failure), DOSE-AHF (Diuretic Optimization Strategy Evaluation in Acute Decompensated Heart Failure), and CARRESS-HF (Cardiorenal Rescue Study in Acute Decompensated Heart Failure). Repeated-measures ANOVA was used to test for a race×time effect on measures of decongestion. Diuretic efficiency was calculated as net fluid balance per total furosemide equivalents. In a subset of subjects, Cox regression was used to examine the association between race and rehospitalization according to plasma renin activity (PRA).

RESULTS

Compared with nonblack patients, black patients were younger and more likely to have nonischemic heart failure. During the first 72 to 96 hours, there was greater fluid loss (P=0.001), decrease in NT-proBNP (N-terminal pro-B-type natriuretic peptide; P=0.002), and lower levels of PRA (P<0.0001) in black patients. Diuretic efficiency was higher in black than in nonblack patients (403 [interquartile range, 221-795] versus 325 [interquartile range, 154-698]; P=0.014). However, adjustment for baseline PRA attenuated the association between black race and diuretic efficiency. Over a median follow-up of 68 (interquartile range, 56-177) days, there was an increased risk of all-cause and heart failure-specific rehospitalization in nonblack patients with increasing levels of PRA, while the risk of rehospitalization was relatively constant across levels of PRA in black patients.

CONCLUSIONS

Higher diuretic efficiency in black patients with acute heart failure may be related to racial differences in activity of the renin-angiotensin-aldosterone system.

Racial and Ethnic Differences in Mortality Associated with Serum Potassium in Incident Peritoneal Dialysis Patients

BACKGROUND

Abnormalities in serum potassium are risk factors for sudden cardiac death and arrhythmias among dialysis patients. Although a previous study in hemodialysis patients has shown that race/ethnicity may impact the relationship between serum potassium and mortality, the relationship remains unclear among peritoneal dialysis (PD) patients where the dynamics of serum potassium is more stable.

METHODS

Among 17,664 patients who started PD between January 1, 2007 and December 31, 2011 in a large US dialysis organization, we evaluated the association of serum potassium levels with all-cause and arrhythmia-related deaths across race/ethnicity using time-dependent Cox models with adjustments for demographics. We also used restricted cubic spline functions for serum potassium levels to explore non-linear associations.

RESULTS

Baseline serum potassium levels were the highest among Hispanics (4.2 ± 0.7 mEq/L) and lowest among non-Hispanic blacks (4.0 ± 0.7 mEq/L). Among 2,949 deaths during the follow-up of median 2.2 (interquartile ranges 1.3-3.2) years, 683 (23%) were arrhythmia-related deaths. Overall, both hyperkalemia and hypokalemia (i.e., serum potassium levels >5.0 and <3.5 mEq/L, respectively) were associated with higher all-cause and arrhythmia-related mortality. In a stratified analysis according to race/ethnicity, the association of hypokalemia with all-cause and arrhythmia-related mortality was consistent with an attenuation for arrhythmia-related mortality in non-Hispanic blacks. Hyperkalemia was associated with all-cause and arrhythmia-related mortality in non-Hispanic whites and non-Hispanic blacks, but no association was observed in Hispanics.

CONCLUSION

Among incident PD patients, hypokalemia was consistently associated with all-cause and arrhythmia-related deaths irrespective of race/ethnicity. However, while hyperkalemia was associated with both death outcomes in non-Hispanic blacks and whites, it was not associated with either death outcome in Hispanic patients. Further studies are needed to demonstrate whether different strategies should be followed for the management of serum potassium levels according to race/ethnicity.

Thick Ascending Limb Sodium Transport in the Pathogenesis of Hypertension

The thick ascending limb plays a key role in maintaining water and electrolyte balance. The importance of this segment in regulating blood pressure is evidenced by the effect of loop diuretics or local genetic defects on this parameter. Hormones and factors produced by thick ascending limbs have both autocrine and paracrine effects, which can extend prohypertensive signaling to other structures of the nephron. In this review, we discuss the role of the thick ascending limb in the development of hypertension, not as a sole participant, but one that works within the rich biological context of the renal medulla. We first provide an overview of the basic physiology of the segment and the anatomical considerations necessary to understand its relationship with other renal structures. We explore the physiopathological changes in thick ascending limbs occurring in both genetic and induced animal models of hypertension. We then discuss the racial differences and genetic defects that affect blood pressure in humans through changes in thick ascending limb transport rates. Throughout the text, we scrutinize methodologies and discuss the limitations of research techniques that, when overlooked, can lead investigators to make erroneous conclusions. Thus, in addition to advancing an understanding of the basic mechanisms of physiology, the ultimate goal of this work is to understand our research tools, to make better use of them, and to contextualize research data. Future advances in renal hypertension research will require not only collection of new experimental data, but also integration of our current knowledge.

Age-Related Blood Pressure Sensitivity to Aldosterone in Blacks and Whites

Aldosterone sensitivity, defined as the magnitude of the association of plasma aldosterone concentration with blood pressure (BP), seems to be a function of plasma volume. It increases as plasma renin activity decreases, and it is more significant in blacks but less so in whites. Age is a strong determinant of BP, and an increase in aldosterone sensitivity could contribute to the increase in BP. In the present study, we tested the hypothesis that aldosterone sensitivity increases with age. We used observational data collected from normotensive blacks and whites enrolled in a prospective cohort study. They were studied as children (248 blacks/357 whites) and again as young adults (74 blacks/125 whites) over an age range of 7 to 39 years. A varying-coefficient regression analysis was used to explore the influences of aldosterone on systolic BP. After controlling for body mass index, race, and sex, both plasma renin activity and plasma aldosterone concentration were lower in blacks, and their levels declined with age (P<0.001). In blacks, plasma aldosterone concentration decreased 0.25 ng/dL per year; in whites, plasma aldosterone concentration decreased 0.18 per year. Aldosterone's effect on BP, characterized by a smooth function of age, intensified as age increased, especially in blacks (P<0.01), suggesting an increased aldosterone sensitivity with age. In comparison to blacks, age-related changes in aldosterone sensitivity in whites were not statistically significant. These findings extend the rationale for targeting aldosterone in the treatment of hypertension, especially in blacks.

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).

Race, obesity, and the renin-angiotensin-aldosterone system: treatment response in children with primary hypertension

BACKGROUND

Pediatric primary hypertension (HTN) is increasingly recognized, but the effect of patient characteristics such as obesity and race on treatment outcomes is not well described. The renin-angiotensin-aldosterone system (RAAS) may also contribute to HTN. We hypothesized patient parameters of these factors, including baseline RAAS, influence blood pressure (BP) response to pharmacological treatment in HTN.

METHODS

This was a retrospective cohort of 102 consecutive patients with HTN. Primary outcomes were changes per year in systolic and diastolic BP (SBP, DBP). Secondary outcome was change per year in left ventricular mass index (LVMI). We evaluated whether baseline plasma renin activity (PRA), aldosterone, renin-to-aldosterone ratio, overweight/obesity, race, initial drug choice, and multidrug therapy were associated with the outcomes using general linear regression models adjusted for confounding variables.

RESULTS

Racially diverse (43% Hispanic, 28% black, 25% white) and predominantly overweight/obese (75%) patients were studied. Median length of follow-up was 14.5 months. Higher baseline aldosterone was associated with decreased SBP (-1.03 mmHg/year), DBP (-0.95 mmHg/year), and DBP z score (-0.07/year) during the study period. Higher baseline PRA was associated with decreased SBP z score (-0.04/year) and LVMI (-2.89 g/m^2.7/year). Stratified analyses revealed the relationships between baseline aldosterone and PRA, and annual reductions in outcomes were strengthened in nonobese and white patients.

CONCLUSIONS

Pretreatment aldosterone and PRA predicted short-term follow-up BP and LVMI, especially in nonobese and white patients. The RAAS profile could guide treatment of HTN and suggests consideration of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers as first-line treatment options.

Aldosterone, Renin, Cardiovascular Events, and All-Cause Mortality Among African Americans: The Jackson Heart Study

OBJECTIVES

This study examined the association of aldosterone and plasma renin activity (PRA) with incident cardiovascular disease (CVD), using a composite endpoint of coronary heart disease, stroke, and/or heart failure and mortality among African Americans in the Jackson Heart Study.

BACKGROUND

There is a paucity of data for the association of aldosterone and PRA with incident CVD or all-cause mortality among community-dwelling African Americans.

METHODS

A total of 4,985 African American adults, 21 to 94 years of age, were followed for 12 years. Aldosterone, PRA, and cardiovascular risk factors were collected at baseline (from 2000 to 2004). Incident events included coronary heart disease and stroke (assessed from 2000 to 2011) and heart failure (assessed from 2005 to 2011). Cox models were used to estimate hazard ratios (HRs) for incident CVD and mortality, adjusting for age, sex, education, occupation, current smoking, physical activity, dietary intake, and body mass index.

RESULTS

Among 4,160 participants without prevalent CVD over a median follow-up of 7 years, there were 322 incident CVD cases. In adjusted analyses, each 1-U SD increase in log-aldosterone and log-PRA were associated with HR of 1.26 (95% confidence intervals [CI]: 1.14 to 1.40) and 1.16 (95% CI: 1.02 to 1.33) for incident CVD, respectively. Over a median of 8 years, 513 deaths occurred among 4,985 participants. In adjusted analyses, each 1-U SD increase in log-aldosterone and log-PRA were associated with HRs of 1.13 (95% CI: 1.04 to 1.23) and 1.12 (95% CI: 1.01 to 1.24) for mortality, respectively.

CONCLUSIONS

Elevated aldosterone and PRA may play a significant role in the development of CVD and all-cause mortality among African Americans.

Varying Influences of Aldosterone on the Plasma Potassium Concentration in Blacks and Whites

BACKGROUND

Aldosterone acts to restrain the extracellular potassium (K+) concentration. Blacks have on average lower plasma aldosterone concentrations (PACs) than Whites. Whether this ethnic difference is associated with similar changes in the concentration of K+ is unclear.

METHODS

Subjects were Blacks and Whites from an observational study of blood pressure regulation. PAC was known to be significantly lower in Blacks than Whites. We sought to test the hypothesis that the concentration of K+ remains constant despite variability in PAC. Initial enrollment took place in childhood in 1986. Some of the original enrollees were studied again in adulthood: 160 healthy Blacks and 271 healthy Whites (ages 5 to 39 years; all were studied as children and as adults).

RESULTS

Plasma renin activity [a biomarker of angiotensin II and, more proximally, extracellular fluid volume (ECFV)] and PAC were lower in Blacks (P < 0.0354 and P < 0.001, respectively, for all ages). At the same time no ethnic difference in levels of K+ was observed regardless of age. Plasma K+ concentration and PAC associated differently based on ethnicity: PAC increased in Blacks by 1.5-2.0 and in Whites by 2.3-3.0 ng/dl per mmol/l increase in K+ (P < 0.001).

CONCLUSIONS

Lower aldosterone levels in Blacks did not translate into higher K+ concentrations. We speculate that reaching the right concentration of K+ was an endpoint of aldosterone production in the presence of varying levels of ECFV and angiotensin II.

Plasma potassium, diuretic use and risk of developing chronic kidney disease in a predominantly White population

Objective

Both hypokalemia and hyperkalemia are associated with disease progression in patients with chronic kidney disease (CKD). It is unclear whether similar associations are present in the general population. Our aim was to examine the association of plasma potassium with risk of developing CKD and the role of diuretics in this association in a population-based cohort.

Research design and methods

We studied 5,130 subjects free of CKD at baseline of the Prevention of Renal and Vascular End-Stage Disease (PREVEND) study, a prospective, population-based cohort of Dutch men and women aged 28–75 years. Hypokalemia was defined as plasma potassium <3.5 mmol/L, and hyperkalemia as plasma potassium ≥5.0 mmol/L. Risk of CKD was defined as de novo development of eGFR <60 ml/min/1.73m² and/or albuminuria >30 mg/24h.

Results

Mean baseline plasma potassium was 4.4±0.3 mmol/L. The prevalences of hypokalemia and hyperkalemia were 0.5% and 3.8%, respectively; 3.0% of the subjects used diuretics. During a median follow-up of 10.3 years (interquartile range: 6.3–11.4 years), 753 subjects developed CKD. The potassium-CKD association was modified by diuretic use (P_interaction = 0.02). Both hypokalemia without (HR, 7.74, 95% CI, 3.43–17.48) or with diuretic use (HR, 4.32, 95% CI, 1.77–10.51) were associated with an increased CKD risk as compared to plasma potassium 4.0–4.4 mmol/L without diuretic use. Plasma potassium concentrations ≥3.5 mmol/L were associated with an increased CKD risk among subjects using diuretics (P_trend = 0.01) but not among subjects not using diuretics (P_trend = 0.74).

Conclusion

In this population-based cohort, hypokalemia was associated with an increased CKD risk, regardless of diuretic use. In the absence of hypokalemia, plasma potassium was not associated with an increased CKD risk, except among subjects using diuretics.

Model selection in multivariate semiparametric regression

Variable selection in semiparametric mixed models for longitudinal data remains a challenge, especially in the presence of multiple correlated outcomes. In this paper, we propose a model selection procedure that simultaneously selects fixed and random effects using a maximum penalized likelihood method with the adaptive least absolute shrinkage and selection operator penalty. Through random effects selection, we determine the correlation structure among multiple outcomes and therefore address whether a joint model is necessary. Additionally, we include a bivariate nonparametric component, as approximated by tensor product splines, to accommodate the joint nonlinear effects of two independent variables. We use an adaptive group least absolute shrinkage and selection operator to determine whether the bivariate nonparametric component can be reduced to additive components. To implement the selection and estimation method, we develop a two-stage expectation-maximization procedure. The operating characteristics of the proposed method are assessed through simulation studies. Finally, the method is illustrated in a clinical study of blood pressure development in children.

Body Mass Index Predicts 24-Hour Urinary Aldosterone Levels in Patients With Resistant Hypertension

Prospective studies indicate that hyperaldosteronism is found in 20% of patients with resistant hypertension. A small number of observational studies in normotensive and hypertensive patients suggest a correlation between aldosterone levels and obesity while others could not confirm these findings. The correlation between aldosterone levels and body mass index (BMI) in patients with resistant hypertension has not been previously investigated. Our objective was to determine whether BMI is positively correlated with plasma aldosterone concentration, plasma renin activity, aldosterone:renin ratio, and 24-hour urinary aldosterone in black and white patients. We performed a cross-sectional analysis of a large diverse cohort (n=2170) with resistant hypertension. The relationship between plasma aldosterone concentration, plasma renin activity, aldosterone:renin ratio, 24-hour urinary aldosterone, and BMI was investigated for the entire cohort, by sex and race (65.3% white, 40.3% men). We demonstrate that plasma aldosterone concentration and aldosterone:renin ratio were significantly correlated to BMI (P<0.0001) across the first 3 quartiles, but not from the 3rd to 4th quartile of BMI. Plasma renin activity was not correlated with BMI. Twenty-four-hour urinary aldosterone was positively correlated across all quartiles of BMI for the cohort (P<0.0001) and when analyzed by sex (men P<0.0001; women P=0.0013) and race (P<0.05), and stronger for men compared with women (r=0.19, P<0.001 versus r=0.05, P=0.431, P=0.028) regardless of race. In both black and white patients, aldosterone levels were positively correlated to increasing BMI, with the correlation being more pronounced in black and white men. These findings suggest that obesity, particularly the abdominal obesity typical of men, contributes to excess aldosterone in patients with resistant hypertension.

Urinary potassium excretion and risk of cardiovascular events

BACKGROUND

Observational studies on dietary potassium and risk of cardiovascular disease (CVD) have reported weak-to-modest inverse associations. Long-term prospective studies with multiple 24-h urinary samples for accurate estimation of habitual potassium intake, however, are scarce.

OBJECTIVE

We examined the association between urinary potassium excretion and risk of blood pressure-related cardiovascular outcomes.

DESIGN

We studied 7795 subjects free of cardiovascular events at baseline in the Prevention of Renal and Vascular End-stage Disease study, a prospective, observational cohort with oversampling of subjects with albuminuria at baseline. Main cardiovascular outcomes were CVD [including ischemic heart disease (IHD), stroke, and vascular interventions], IHD, stroke, and new-onset heart failure (HF). Potassium excretion was measured in two 24-h urine specimens at the start of the study (1997-1998) and midway through follow-up (2001-2003).

RESULTS

Baseline median urinary potassium excretion was 70 mmol/24 h (IQR: 56-84 mmol/24 h). During a median follow-up of 10.5 y (IQR: 9.9-10.8 y), a total of 641 CVD, 465 IHD, 172 stroke, and 265 HF events occurred. After adjustment for age and sex, inverse associations were observed between potassium excretion and risk [HR per each 26-mmol/24-h (1-g/d) increase; 95% CI] of CVD (0.87; 0.78, 0.97) and IHD (0.86; 0.75, 0.97), as well as nonsignificant inverse associations for risk of stroke (0.85; 0.68, 1.06) and HF (0.94; 0.80, 1.10). After further adjustment for body mass index, smoking, alcohol consumption, education, and urinary sodium and magnesium excretion, urinary potassium excretion was not statistically significantly associated with risk (multivariable-adjusted HR per 1-g/d increment; 95% CI) of CVD (0.96; 0.85, 1.09), IHD (0.90; 0.81, 1.04), stroke (1.09; 0.86, 1.39), or HF (0.99; 0.83, 1.18). No associations were observed between the sodium-to-potassium excretion ratio and risk of CVD, IHD, stroke, or HF.

CONCLUSION

In this cohort with oversampling of subjects with albuminuria at baseline, urinary potassium excretion was not independently associated with a lower risk of cardiovascular events.

Pathophysiology, diagnosis, and treatment of mineralocorticoid disorders

The renin-angiotensin-aldosterone system (RAAS) is a major regulator of blood pressure control, fluid, and electrolyte balance in humans. Chronic activation of mineralocorticoid production leads to dysregulation of the cardiovascular system and to hypertension. The key mineralocorticoid is aldosterone. Hyperaldosteronism causes sodium and fluid retention in the kidney. Combined with the actions of angiotensin II, chronic elevation in aldosterone leads to detrimental effects in the vasculature, heart, and brain. The adverse effects of excess aldosterone are heavily dependent on increased dietary salt intake as has been demonstrated in animal models and in humans. Hypertension develops due to complex genetic influences combined with environmental factors. In the last two decades, primary aldosteronism has been found to occur in 5% to 13% of subjects with hypertension. In addition, patients with hyperaldosteronism have more end organ manifestations such as left ventricular hypertrophy and have significant cardiovascular complications including higher rates of heart failure and atrial fibrillation compared to similarly matched patients with essential hypertension. The pathophysiology, diagnosis, and treatment of primary aldosteronism will be extensively reviewed. There are many pitfalls in the diagnosis and confirmation of the disorder that will be discussed. Other rare forms of hyper- and hypo-aldosteronism and unusual disorders of hypertension will also be reviewed in this article.

Associations between menarche-related genetic variants and pubertal growth in male and female adolescents

PURPOSE

Previous studies have identified novel genetic variants associated with age at menarche in females of European descent. The pubertal growth effects of these variants have not been carefully evaluated in non-European descent groups. We aimed to examine the effects of 31 newly identified menarche-related single-nucleotide polymorphisms (SNPs) on growth outcomes in African-American (AA) and European-American (EA) children in a prospective cohort.

METHODS

We analyzed longitudinal data collected from 263 AAs and 338 EAs enrolled between ages 5 and 17 years; the subjects were followed semiannually for an average of 6 years. The associations between the SNPs and growth-related outcomes, including weight, height, and body mass index (BMI), were examined using mixed-effect models.

RESULTS

Longitudinal analyses revealed that 4 (near or in genes VGLL3, PEX2, CA10, and SKOR2) of the 14 menarche-only-related SNPs were associated with changes in weight and BMI in EA and AA (p ≤ .0032), but none of them was associated with changes in height. Of the eight menarche-timing and BMI-related SNPs, none was associated with changes in height, but three (in or near genes NEGR1, ETV5, and FTO) were associated with more rapid increases in weight and/or BMI in EA (p ≤ .0059). Among the nine menarche-timing and height-related SNPs, four (in or near genes ZBTB38, LOC728666, TBX2, and CABLES) were associated with changes in weight or height in EA and AA (p ≤ .0042).

CONCLUSIONS

Genetic variants related to age at menarche were found to be associated with various growth parameters in healthy adolescents. The identified associations were often race and sex specific.

Urinary potassium excretion and risk of developing hypertension: the prevention of renal and vascular end-stage disease study

Previous prospective cohort studies on the association between potassium intake and risk of hypertension have almost exclusively relied on self-reported dietary data, whereas repeated 24-hour urine excretions, as estimate of dietary uptake, may provide a more objective and quantitative estimate of this association. Risk of hypertension (defined as blood pressure ≥140/90 mm Hg or initiation of blood pressure-lowering drugs) was prospectively studied in 5511 normotensive subjects aged 28 to 75 years not using blood pressure-lowering drugs at baseline of the Prevention of Renal and Vascular End-Stage Disease (PREVEND) study. Potassium excretion was measured in two 24-hour urine specimens at baseline (1997-1998) and midway during follow-up (2001-2003). Baseline median potassium excretion was 70 mmol/24 h (interquartile range, 57-85 mmol/24 h), which corresponds to a dietary potassium intake of ≈91 mmol/24 h. During a median follow-up of 7.6 years (interquartile range, 5.0-9.3 years), 1172 subjects developed hypertension. The lowest sex-specific tertile of potassium excretion (men: <68 mmol/24 h; women: <58 mmol/24 h) had an increased risk of hypertension after multivariable adjustment (hazard ratio, 1.20; 95% confidence interval, 1.05-1.37), compared with the upper 2 tertiles (Pnonlinearity=0.008). The proportion of hypertension attributable to low potassium excretion was 6.2% (95% confidence interval, 1.7%-10.9%). No association was found between the sodium to potassium excretion ratio and risk of hypertension after multivariable adjustment. Low urinary potassium excretion was associated with an increased risk of developing hypertension. Dietary strategies to increase potassium intake to the recommended level of 90 mmol/d may have the potential to reduce the incidence of hypertension.

Association of renin and aldosterone with ethnicity and blood pressure: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Although variations in plasma renin activity (PRA) and aldosterone have been examined in whites and blacks, the association of these hormones with blood pressure in multiethnic populations has not been described.

METHODS

We measured PRA and aldosterone in 1,021 participants in the Multi-Ethnic Study of Atherosclerosis not taking antihypertensives and examined the association between ethnicity and PRA/aldosterone and the association between PRA/aldosterone with systolic blood pressure (SBP).

RESULTS

Average age was 62 (SD = 9) years, and 49% of participants were women. Median PRA was 0.51 (interquartile range (IQR) = 0.29-0.87) ng/ml/hour, and median aldosterone was 12.6 (IQR = 9.1-17.1) ng/dl. After age and sex adjustment, compared with whites, blacks had 28% lower PRA and 17.4% lower aldosterone, and Hispanics had 20.1% higher PRA but similar aldosterone levels. After multivariable adjustment, compared with whites, only Hispanic ethnicity independently associated with higher PRA (0.18ng/ml/hour; 95% confidence interval (CI) = 0.06-0.31). Blacks had lower aldosterone (-1.7ng/dl; 95% CI = -3.2 to -0.2) compared with whites. After multivariable adjustment, PRA was associated with lower SBP in whites (-3.2mm Hg; 95% CI = -5.2 to -1.2 per standardized unit PRA), Chinese (-3.5mm Hg; 95% CI = -6.2 to -0.80 per standardized unit), and Hispanics (-2.3mm Hg; 95% CI = -4.1 to -0.6 per standardized unit) but not blacks. Aldosterone was associated with higher SBP only in Hispanics (2.5mm Hg; 95% CI = 0.4-4.5 per SD).

CONCLUSIONS

Compared with whites, blacks have lower aldosterone and Hispanics have higher PRA. Aldosterone had significant associations with higher SBP in Hispanics compared with other groups, a finding that may suggest a different mechanism of hypertension.

Racial differences in sensitivity of blood pressure to aldosterone

Blacks in comparison with whites are at risk for a more serious form of hypertension with high rates of complications. Greater sodium retention is thought to underlie the blood pressure (BP)-determining physiology of blacks, but specific mechanisms have not been identified. In a prospective observational study of BP, 226 black children and 314 white children (mean age, 10.6 years) were enrolled initially. Assessments were repeated in 85 blacks and 136 whites after reaching adulthood (mean age, 31 years). The relationship of BP to plasma aldosterone concentration in the context of the prevailing level of plasma renin activity was studied in blacks and whites. In a secondary interventional study, 9-α fludrocortisone was administered for 2 weeks to healthy adult blacks and whites to simulate hyperaldosteronism. BP responses in the 2 race groups were then compared. Although black children had lower levels of plasma renin activity and plasma aldosterone, their BP was positively associated with the plasma aldosterone concentration, an effect that increased as plasma renin activity decreased (P=0.004). Data from black adults yielded similar results. No similar relationship was observed in whites. In the interventional study, 9-α fludrocortisone increased BP in blacks but not in whites. In conclusion, aldosterone sensitivity is a significant determinant of BP in young blacks. Although its role in establishing the risk of hypertension is not known, it could be as relevant as the actual level of aldosterone.

Adiposity has unique influence on the renin-aldosterone axis and blood pressure in black children

OBJECTIVE

To comparatively examine the effects of adiposity on the levels of plasma renin activity (PRA), plasma aldosterone concentration (PAC), and aldosterone-renin ratio (ARR) in young black and white children.

STUDY DESIGN

We prospectively assessed 248 black and 345 white children and adolescents. A novel analytical technique was used to assess the concurrent influences of age and body mass index (BMI) on PRA, PAC, and ARR. The estimated effects were depicted by colored contour plots.

RESULTS

In contrast to whites, blacks had lower PRA (2.76 vs 3.36 ng/mL/h; P < .001) and lower PAC (9.01 vs 14.59 ng/dL; P < .001). In blacks, BMI was negatively associated with PRA (P = .001), consistent with an association with a more expanded plasma volume; there was no association with PAC. In whites, BMI was positively associated with PAC (P = .005); we did not detect a BMI-PRA association. The effects of BMI on ARR were directionally similar in the two race groups but more pronounced in blacks. Mean systolic blood pressure was greater in blacks with lower PRA (P < .01), higher PAC (P = .015), and higher ARR (P = .49).

CONCLUSIONS

An increase in adiposity was associated with a suppressed PRA in blacks and an increase in PAC in whites. The unique relationship between adiposity and renin-aldosterone axis in blacks suggests the possible existence of a population-specific mechanism characterized by volume expansion, which could in turn enhance the influences of adiposity on blood pressure in black children and adolescents.

A consideration of genetic mechanisms behind the development of hypertension in blacks

Hypertension is a more serious disease in blacks. The determinants of the blood pressure (BP) may be uniquely different from those in whites. The characteristic low-renin, salt-sensitive hypertension of blacks is consistent with the kidney reabsorbing additional sodium (Na), which leads to an expanded plasma volume that drives the BP. Mechanisms considered are genetically based. These include: (1) the intra-renal renin-angiotensin system (RAS), one based on molecular variations in angiotensinogen; (2) the Na, K, 2Cl cotransporter (NKCC2) and its regulators in the thick ascending limb, which are associated with a variety of phenotypes consistent with a more active cotransporter in blacks; and (3) the genes for MYH9 and APOL 1, which have been associated with kidney disease in blacks. To achieve a state of hypertension, an increase in Na uptake in proximal nephron regions may require a distal nephron that does not fully adjust due to less than adequate suppression of aldosterone production.

Gastrointestinal and renal excretion of potassium in African-Americans and White Americans

OBJECTIVE

Several studies have confirmed the remarkable observation that cumulative urinary potassium (K(+)) excretion is less in African-Americans than White Americans even when identical amounts of potassium are provided in the diet. This study was designed to examine whether this decrease in urinary potassium could be compensatory to an increase in gastrointestinal excretion of potassium in African-Americans.

METHODS

Twenty-three young, healthy, normotensive participants of both sexes and races were placed on a fixed diet of 100 mEq per day of K(+) and 180 mEq per day of sodium (Na(+)) for 9 days. All urine and stool were collected daily and analyzed for electrolytes. Blood was obtained for determination of electrolytes, blood urea nitrogen (BUN), creatinine, glucose, insulin, renin, and aldosterone at the beginning and at the end of the study period.

RESULTS

Cumulative urinary excretion of K(+) was significantly less in African-Americans (609 ± 31 mEq) compared with White Americans (713 ± 22 mEq, P = 0.015). There was no significant racial difference, however, in the cumulative gastrointestinal excretion of K (105 ± 11 versus 95 ± 9 mEq, P = 0.28) in African-Americans versus White Americans, respectively.

CONCLUSION

The racial difference in urinary K(+) handling manifested by decreased excretion of K(+) in African-Americans cannot be attributed to an increase in net gastrointestinal excretion of this cation.

HSD11B2 CA-repeat and sodium balance

Type 2 11β-hydroxysteroid dehydrogenase encoded by the HSD11B2 gene converts cortisol to inactive cortisone and thus protects the mineralocorticoid receptor from cortisol exposure. Impaired activity of this enzyme leads to mineralocorticoid excess, suggesting HSD11B2 as a candidate locus for patients at risk of developing low renin or salt-sensitive essential hypertension. In the present study, we searched for frequent polymorphisms in 155 Japanese subjects but detected none in the proximal promoter or coding regions of HSD11B2. Following this result, we genotyped a highly polymorphic CA-repeat polymorphism within the first intron in 848 normotensive and 430 hypertensive Japanese patients, and we then analyzed its association with disease and clinical parameters. We confirmed 12 alleles (12, 15-25 CA repeats) in the population and found no significant difference in the distribution of the allele length between normotensive and hypertensive patients. In 174 normal subjects without medication, urinary cortisol excretion was higher in subjects with more CA repeats in the shorter allele, but the ratio of urinary cortisone to cortisol, a reliable marker of renal HSD11B2 activity, did not differ. However, longer CA-repeat length was positively correlated with 24-h urinary sodium excretion, fractional sodium excretion and potassium clearance, and this observation was confirmed when the longer CA-repeat length was dichotomized. Thus, HSD11B2 CA-repeat genotype is not associated with hypertension itself, but with renal sodium excretion, probably through salt intake/appetite.

Intensified effect of adiposity on blood pressure in overweight and obese children

In children, blood pressure (BP) and risk for hypertension are proportional to degree of adiposity. Whether the relationship to BP is similar over the full range of adiposity is less clear. Subjects from a cohort study (n=1111; 50% male and 42% black) contributed 9102 semiannual BP and height/weight assessments. The mean enrollment age was 10.2 years, and mean follow-up was 4.5 years. Adiposity was expressed as body mass index percentile, which accounted for effects of age and sex. The following observations were made. The effect of relative adiposity on BP was minimal until the body mass index percentile reached 85, beginning of the overweight category, at which point the effect of adiposity on BP increased by 4-fold. Similarly intensified adiposity effects on BP were observed in children aged ≤10, 11 to 14 years, and ≥15 years. Serum levels of the adipose tissue-derived hormone, leptin, together with heart rate, showed an almost identically patterned relation to BP to that of body mass index percentile and BP, thus implicating a possible mediating role for leptin. In conclusion, there is a marked intensification of the influence of adiposity on BP when children reach the categories of overweight and obese. Among the possible pathways, leptin may be a potentially important mediator acting through the sympathetic nervous system (reflected in heart rate). The findings have relevance to interventions designed to prevent or treat adiposity-related increases in BP and to the analytic approaches used in epidemiological studies.

Racial differences in potassium homeostasis in response to differences in dietary sodium in girls

BACKGROUND

Racial differences in the renal disposition of potassium may be related to mechanisms for the greater susceptibility to hypertension in blacks than in whites.

OBJECTIVE

Our objective was to study the racial differences in the renin-angiotensin-aldosterone system and in potassium balance in black and white girls consuming a controlled diet that was low in potassium with 2 amounts of sodium intake (low compared with high).

DESIGN

The studies reported here were performed in 40 black and 28 white girls, aged 11-15 y, under highly controlled metabolic conditions. The studies comprised 2 sessions of 20-d metabolic balance sessions, at 2 amounts of dietary sodium intake (58 and 170 mmol . L(-1) . d(-1)), in a crossover design and with a constant dietary potassium intake of 50 mmol . L(-1) . d(-1). Repeated-measures analysis of variance was used to test for racial differences in potassium output and retention by sodium intakes.

RESULTS

Thirty black and 20 white girls completed the study. Urinary potassium excretion was lower in blacks than in whites, regardless of sodium intake (P < 0.05), with no differences in fecal or sweat potassium excretion. Cumulative potassium retention was significantly higher in blacks while consuming the low sodium diet. Plasma aldosterone concentrations after upright posture were significantly lower in blacks than in whites but were similar when supine, as were urinary aldosterone excretion rates. On week 3, blood pressure, body weight, urinary volume, creatinine, and serum sodium and potassium were similar.

CONCLUSION

The well-known racial difference in urinary potassium excretion appears to be at least in part due to greater renal retention of potassium in black girls.

Glomerular hyperfiltration and increased proximal sodium reabsorption in subjects with type 2 diabetes or impaired fasting glucose in a population of the African region

BACKGROUND. Glomerular hyperfiltration (GHF) is a well-recognized early renal alteration in diabetic patients. As the prevalence of GHF is largely unknown in populations in the African region with respect to normal fasting glucose (NFG), impaired fasting glucose (IFG) and type 2 diabetes [diabetes mellitus (DM)], we conducted a cross-sectional study in the Seychelles islands among families including at least one member with hypertension. METHODS. The glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and proximal tubular sodium reabsorption were measured using inulin, p-aminohippurate (PAH) and endogenous lithium clearance, respectively. Twenty-four-hour urine was collected on the preceding day. RESULTS. Of the 363 participants (mean age 44.7 years), 6.6% had IFG, 9.9% had DM and 63.3% had hypertension. The prevalence of GHF, defined as a GFR >140 ml/min, was 17.2%, 29.2% and 52.8% in NFG, IFG and DM, respectively (P trend <0.001). Compared to NFG, the adjusted odds ratio for GHF was 1.99 [95% confidence interval (CI) 0.73-5.44] for IFG and 5.88 (2.39-14.45) for DM. Lithium clearance and fractional excretion of lithium were lower in DM and IFG than NFG (P < 0.001). CONCLUSION. In this population of African descent, subjects with impaired fasting glucose or type 2 diabetes had a high prevalence of GHF and enhanced proximal sodium reabsorption. These findings provide further insight on the elevated incidence of nephropathy reported among African diabetic individuals.

How to treat hypertension in blacks: review of the evidence

Presentation, response to therapy, and clinical outcome differ according to race for patients with hypertension. Black patients have a higher prevalence and earlier onset of hypertension than other ethnic groups, with poorer prognosis than white patients. Blacks are more likely to be salt-sensitive, and to have a low plasma renin activity than are whites. They are at much greater risk of developing cardiovascular and renal complications. Despite many advances in the understanding and treatment of cardiovascular diseases, black patients continue to have increased morbidity and mortality from the end-organ complications of hypertension. The explanations for these observations remain incompletely understood, but genetic differences, added to socio-economic and environmental factors, have been proposed to explain this disparity. The first therapeutic approach is to decrease salt and increase potassium intakes. Diuretics (thiazides and potassium-sparing agents) and calcium channel blockers constitute the first antihypertensive drug choices. The angiotensin-converting-enzyme inhibitors, the angiotensin II receptor blockers and beta-blockers appear to be less effective in blacks with regard to uncomplicated hypertension, especially in older people, but addition of a small dose of diuretic improves their efficacy. These combinations are preferred among patients with chronic kidney disease or heart failure. The goal for blood pressure target is the same in blacks as it is in whites, being a blood pressure of less than 140/90 mmHg in uncomplicated hypertension and less than 130/80 mmHg in patients with diabetes mellitus or chronic kidney disease.

Blood aldosterone-to-renin ratio, ambulatory blood pressure, and left ventricular mass in children

OBJECTIVE

To assess the blood aldosterone-to-renin ratio (ARR) and its relationship to ambulatory blood pressure (ABP) and left ventricular mass (LVM) in children.

STUDY DESIGN

A cross-sectional clinical study was conducted in 102 children (71.6% African American; 62.7% male) ranging in age from 7 to 18 years (mean, 13.6 years; median, 14 years). ABP (24-hour monitoring) was expressed as blood pressure index (BPI; mean blood pressure/95th percentile by sex and height). LVM was measured by echocardiography and expressed as an index (LVMI = g/height [m](2.7)). Regression analyses were used to estimate associations.

RESULTS

African-American children had significantly lower serum aldosterone concentration and plasma renin activity compared with European-American children (aldosterone: 5.9 ng/dL vs 11.4 ng/dL, P < .0001; renin: 1.6 ng/mL/hour vs 2.8 ng/mL/hour, P = .01). However, ARR was not significantly different by race. ARR was not associated with 24-hour ABP but was significantly associated with LVMI (beta = 0.4 g/m(2.7); P = .02) after adjustment for the ratio of 24-hour urine Na to creatinine excretion, body mass index z- score, and ABP index.

CONCLUSIONS

The data indicated a significant association between ARR and LVMI, but not ABP, in children, suggesting early cardiac remodeling associated with a high ARR.

Association of the calcium-sensing receptor gene with blood pressure and urinary calcium in African-Americans

CONTEXT

Calcium binding to the Ca-sensing receptor (CASR) expressed in thick ascending limb inhibits the Na,K,2Cl cotransporter, which decreases sodium reabsorption and secondarily decreases Ca reabsorption. CASR gene variants could influence blood pressure (BP) by affecting Na retention.

OBJECTIVE

The objective of the study was to determine whether variations in CASR associated with BP in African-Americans, an ethnic group at high risk for hypertension.

DESIGN

Population- and family-based association studies of single-nucleotide polymorphisms (SNPs) in CASR with BP measured over the age range 5.6-25 yr (14 biannual visits per subject on average) were carried out. In a cross-sectional study where urinary Ca excretion had been measured, Ca excretion was used as an additional phenotype of CASR influence on Na,K,2Cl cotransporter activity.

PARTICIPANTS

Subjects were normotensive. In the longitudinal study, there were 223 subjects (mean age 14 yr) and 123 families (one or both parents provided a DNA sample); in the cross-sectional study, there were 106 subjects (mean age 23 yr) and 88 families.

RESULTS

Three SNPs in linkage disequilibrium associated with systolic BP at P < 0.005 (the significance threshold corrected for multiple comparisons) in the population-based longitudinal study. In the cross-sectional study, SNPs contained in the same linkage disequilibrium block associated with urinary Ca excretion in both population- and family-based association studies.

CONCLUSION

The findings suggest that in African-Americans, functional heterogeneity of the CASR in thick ascending limb may influence BP.

Aldosterone and alterations of hypertension-related vascular function in African Americans

BACKGROUND

African Americans have a high prevalence of hypertension and hypertension-related vascular disease. We previously reported that plasma aldosterone concentrations are relatively high in hypertensive African Americans. This study evaluates the hypothesis that hypertension and hypertension-related alterations of peripheral vascular and renal vascular function are associated with aldosterone.

METHODS

Twenty four-hour blood pressures, cardiac output, renal blood flow (RBF), plasma renin activity (PRA), and plasma aldosterone were measured in hypertensive and normotensive African Americans. Hemodynamic measurements were repeated in response to graded infusions of norepinephrine (NE).

RESULTS

Ambulatory blood pressures in hypertensives and normotensives were 142 +/- 1/86 +/- 1 and 117 +/- 1/70 +/- 1 mm Hg, respectively. Cardiac index (CI) was lower (P < 0.01), peripheral vascular resistance was higher (P < 0.0001), arterial compliance was lower (P < 0.0001), RBF was lower (P = 0.04), and renal vascular resistance (RVR) was higher (P < 0.0001) in the hypertensives. Overall, blood pressures were positively correlated with peripheral vascular resistance (P < 0.0001) and inversely correlated with vascular compliance (P < 0.0001). In response to NE, hypertensives had greater increases of systolic blood pressure (P < 0.004) and pulse pressure (P < 0.005). PRA was lower (P < 0.0001) and plasma aldosterone was higher (P < 0.0001) in the hypertensives. Overall, blood pressures and pulse pressure were correlated with aldosterone (P < or = 0.01). Vascular compliance, RVR, and the increment of RVR in response to NE were also correlated with aldosterone (P < or = 0.03).

CONCLUSIONS

Aldosterone may contribute to hypertension and to hypertension-related alterations of peripheral vascular and renal vascular function in African Americans.

Ethnic Differences in Renal Responses to Furosemide

Blacks have a greater tendency to retain Na than whites. The present study sought evidence for ethnic differences in parameters reflective of Na uptake by the Na,K,2Cl cotransporter in the thick ascending limb, namely, the urine concentration and urinary excretion of certain cations before and after furosemide administration (40 mg IV). Subjects were healthy (ages 18 to 36 years). During the preceding overnight period, urine volume was lower, and osmolality was higher in blacks than in whites, an ethnic difference that disappeared when water intake was restricted to infused normal saline (60 mL/h). Plasma vasopressin levels were higher in black males than in other sex/ethnic groups. Baseline urinary excretion rates of K, Ca, and Mg were significantly lower in blacks than in whites. After furosemide (0 to 1 hour), K and Ca excretion rates increased, but the proportionate ethnic difference decreased from 44% to 22% and from 22% to 10%, respectively, consistent with blacks having more basal Na,K,2Cl cotransporter activity to inhibit. During a later postfurosemide period (1 to 5 hours), urinary concentrations of Ca and Mg recovered more slowly in blacks, consistent with greater reuptake in the thick ascending limb. In summary, there were distinct ethnic differences in renal handling of Ca and Mg basally and in response to furosemide that were consistent with a more active Na,K,2Cl cotransporter in the thick ascending limb in blacks. An increase in vasopressin levels appeared to explain greater urine concentrations in black males but not black females.

Differential aerobic exercise-induced changes in plasma aldosterone between African Americans and Caucasians

Aldosterone influences the kidney's regulation of blood pressure (BP), but aldosterone can contribute to the pathogenesis of hypertension. Blood pressure is reduced with aerobic exercise training (AEX), but the extent to which plasma aldosterone (PA) levels change is unclear. The purpose of this study was to determine whether 6 months of AEX changed PA levels, 24 h sodium (Na(+)) excretion and BP in prehypertensive and hypertensive subjects and whether these changes differed according to ethnicity. The study was performed in the Kinesiology Department at the University of Maryland, College Park, and 35 (22 Caucasian; 13 African American) sedentary prehypertensive and hypertensive subjects completed 6 months of AEX. Blood samples were collected under fasting and supine conditions, and PA was measured by radioimmunoassay. In total population aerobic exercise training increased maximal oxygen consumption (24 +/- 0.8 versus 28 +/- 1 ml kg(-1) min(-1), P < 0.001) and decreased PA levels (97 +/- 11 versus 72 +/- 6 pg ml(-1), P = 0.01), body mass index (28 +/- 0.5 versus 28 +/- 0.5 kg m(-2), P = 0.004) and weight (85 +/- 2 versus 83 +/- 2 kg, P = 0.003). Aerobic exercise training decreased PA levels (from 119 +/- 16 to 81 +/- 7 pg ml(-1), P = 0.02) in the Caucasians but there was no change in BP or Na(+) excretion. African American participants had no significant changes in PA levels, BP and Na(+) excretion. Plasma aldosterone levels were 47% lower at baseline (P = 0.01) and 30% lower after AEX (P = 0.04) in African American participants compared with Caucasians. Baseline (P = 0.08) and final PA levels (P = 0.17) did not differ between the two groups after accounting for baseline and final intra-abdominal fat, respectively. The reduction in PA levels with AEX appeared to be driven by the change in PA levels in Caucasian participants. Fat distribution contributed to the ethnic differences in PA levels.

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.

Central Role for ENaC in Development of Hypertension

Na(+) reabsorption by the epithelial Na(+) channel (ENaC) in cortical collecting duct provides the final renal adjustment to Na(+) balance, there being no further downstream Na(+) transport system. This fact coupled with the responsiveness of ENaC to aldosterone, which conveys stimulation inversely proportional to the state of Na(+) balance, places ENaC in a pivotal position to influence the risk for hypertension. Although several molecular variants of ENaC subunits have been identified, there has been no consistent demonstration of an association of any of the variants with hypertension. More compelling is the notion that ENaC activity does not fully adjust to an increase in Na(+) reabsorption occurring elsewhere in the nephron, there being overstimulation by inappropriately elevated aldosterone levels. Additional evidence that the maintenance of hypertension can be dependent on ENaC is derived from the observed responses to the treatment of hypertensive individuals with inhibitors of ENaC. Described is a clinical trial in which black hypertensive individuals who did not fully respond to more traditional therapy were given amiloride, spironolactone, a combination of the two drugs, or placebo. Treatment with either of the active inhibitors of ENaC resulted in a substantial improvement in BP. In conclusion, evidence to date is supportive of the concept that an increase in Na(+) transport by ENaC may be a common and requisite component of salt-dependent forms of hypertension.

The cardiovascular implications of hypokalemia

The role of potassium in the progression of cardiovascular disease is complex and controversial. Animal and human data suggest that increases in dietary potassium, decreases in urinary potassium loss, or increases in serum potassium levels through other mechanisms have benefits in several disease states. These include the treatment of hypertension, stroke prevention, arrhythmia prevention, and treatment of congestive heart failure. Recently, the discovery that aldosterone antagonists not only decrease sodium reabsorption and decrease potassium secretion in the nephron, but also decrease pathological injury of such nonepithelial tissues as the myocardium and endothelium, has generated great controversy regarding the actual mechanisms of benefit of these agents. We review the available data and draw conclusions about the relative benefits of modulating potassium balance versus nonrenal effects of aldosterone blockade in patients with cardiovascular disease.