Salt, slavery and survival- hypertension in the African diaspora

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.

Promise of Physiological Profiling to Prevent Stroke in People of African Ancestry: Prototyping Ghana

PURPOSE OF REVIEW

Worldwide, compared to other racial/ethnic groups, individuals of African ancestry have an excessively higher burden of hypertension-related morbidities, especially stroke. Identifying modifiable biological targets that contribute to these disparities could improve global stroke outcomes. In this scoping review, we discuss how pathological perturbations in the renin-angiotensin-aldosterone pathways could be harnessed via physiological profiling for the purposes of improving blood pressure control for stroke prevention among people of African ancestry.

RECENT FINDINGS

Transcontinental comparative data from the USA and Ghana show that the prevalence of treatment-resistant hypertension among stroke survivors is 42.7% among indigenous Africans, 16.1% among African Americans, and 6.9% among non-Hispanic Whites, p < 0.0001. A multicenter clinical trial of patients without stroke in 3 African countries (Nigeria, Kenya, and South Africa) demonstrated that physiological profiling using plasma renin activity and aldosterone to individualize selection of antihypertensive medications compared with usual care resulted in better blood pressure control with fewer medications over 12 months. Among Ghanaian ischemic stroke survivors treated without renin-aldosterone profiling data, an analysis revealed that those with low renin phenotypes did not achieve any meaningful reduction in blood pressure over 12 months on 3-4 antihypertensive medications despite excellent adherence. For a polygenic condition such as hypertension, individualized therapy based on plasma renin-aldosterone-guided selection of therapy for uncontrolled BP following precision medicine principles may be a viable strategy for primary and secondary stroke prevention with the potential to reduce disparities in the poor outcomes of stroke disproportionately shared by individuals of African ancestry. A dedicated clinical trial to test this hypothesis is warranted.

Apparent Treatment-Resistant Hypertension Among Stroke Survivors: A Transcontinental Study Assessing Impact of Race and Geography

BACKGROUND

Race and geographic differences in the prevalence and predictors of hypertension in stroke survivors have been reported, but apparent treatment-resistant hypertension (aTRH) among stroke survivors by race (African ancestry vs. non-Hispanic Caucasians) and by geography (continental Africa vs. the United States) are under studied.

METHODS

This is a cross-sectional study using ethically approved stroke registries from the University of Florida and the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. Univariate and multivariate regression was used to evaluate for differences in prevalence of aTRH and associations with clinical covariates.

RESULTS

Harmonized data were available for 3,365 stroke survivors of which 943 (28.0%) were indigenous Africans, 558 (16.6%) African Americans, and 1,864 (55.4%) non-Hispanic Caucasians with median ages (interquartile range) of 59 (49-68), 61 (55-72), and 70 (62-78) years, P < 0.0001. The overall frequency of aTRH was 18.5% (95% confidence interval [CI]: 17.2%-19.8%) with 42.7% (95% CI: 39.6%-46.0%) among indigenous Africans, 16.1% (95% CI: 13.2%-19.5%) among African Americans, and 6.9% (95% CI: 5.8%-8.2%) among non-Hispanic Caucasians, P < 0.0001. Five factors associated with aTRH: age, adjusted odds ratio (95% CI) of 0.99 (0.98-0.99), female sex 0.70 (0.56-0.87), cigarette smoking 1.98 (1.36-2.90), intracerebral hemorrhage 1.98 (1.57-2.48), and Black race namely indigenous Africans 4.42 (3.41-5.73) and African Americans 2.44 (1.81-3.29).

CONCLUSIONS

Future studies are needed to investigate the contribution of socioeconomic disparities in the prevalence aTRH in those with African Ancestry to explore the long-term impact, and evaluate effective therapeutic interventions in this subpopulation.

Recent advances in preventing recurrent stroke

Since a 2017 update, there have been important advances in stroke prevention. These include new evidence about nutrition, antiplatelet therapy, anticoagulation, lipid-lowering therapy, hypertension control, pioglitazone, and carotid endarterectomy and stenting. Evidence regarding toxic metabolites produced by the intestinal microbiome from egg yolk and red meat has important dietary implications, particularly for patients with impaired renal function, including the elderly. They should avoid egg yolk and red meat and limit the intake of animal flesh. Higher doses of folic acid may be needed for patients with the T allele of MTHFR, so it may not be sufficient to give vitamin B12 (methylcobalamin) alone, even in countries with folate fortification. There is now good evidence that lipid-lowering therapy is even more beneficial in the elderly than in younger patients; we should be using lipid-lowering therapy more intensively, often/usually combining statins with ezetimibe. There is new evidence that lower systolic blood pressure targets are better for most patients, but a subgroup with stiff arteries, a wide pulse pressure, and a diastolic pressure of <60 would be more likely to be harmed than helped by aiming for a systolic target of <120 mmHg. There is a better understanding of how the pharmacological properties of direct-acting oral anticoagulants and the metabolism of antiplatelet agents should inform decisions about the use of these agents. Pioglitazone markedly reduces the risk of stroke, both in diabetics and prediabetics; it should be used more widely. It is now clear that carotid endarterectomy is safer than stenting and that the difference is strongly affected by age. Most patients, and in particular older patients, would be better served by endarterectomy than stenting.

Frequency and factors linked to refractory hypertension among stroke survivors in Ghana

BACKGROUND

Refractory hypertension (RfH) is a rare, severe phenotype of resistant hypertension, linked to higher risk of adverse cardiovascular outcomes. Little is known about the association of RfH with stroke type and subtype.

OBJECTIVE

To determine the prevalence and predictors of RfH among stroke survivors in Ghana.

METHODS

We interrogated the dataset of a prospectively collected registry of hypertensive patients seen between July 2015 and June 2019, at five hospitals in Ghana. We compared stroke survivors to stroke-free controls. Clinic-based blood pressure was measured using a standardized protocol and antihypertensive medications were assessed via review of medical records and inspection of pills. Refractory hypertension was defined as office BP ≥140/90 mmHg on ≥5 classes of antihypertensive medications. Multivariate logistic regression models were constructed to assess factors associated with RfH.

RESULTS

Of 3927 hypertensive patients (1169 stroke survivors, 2758 controls), 86 had RfH for an overall prevalence of 2.2% (95% CI: 1.8-2.7%). Among patients with RfH, 5.8% (4.5-7.3%) were stroke survivors vs. 0.7% (0.4-1.0%) were stroke-free (p < .0001). Adjusted odds ratio (95% CI) for factors associated with RfH were being male (1.81, 1.15-2.85), age < 60 years (2.64, 1.59-4.40), chronic kidney disease (2.09, 1.21-3.60), and known stroke (7.53, 4.35-13.04). RfH was associated with intracerebral hemorrhage, (11.43, 5.65-23.14), ischemic stroke (9.76, 5.47-17.42), lacunar stroke (13.58, 6.45-28.61), and non-lacunar ischemic stroke (3.67, 1.04-13.02).

CONCLUSION

Presence of RfH is significantly accentuated among stroke survivors. Intensified efforts are warranted to identify and aggressively address barriers to control in these patients to avert subsequent vascular events.

Clinical presentation and surgical outcomes in primary aldosteronism differ by race

BACKGROUND

Primary aldosteronism (PA) is the most common cause of secondary hypertension; early diagnosis and intervention correlate with outcomes. We hypothesized that race may influence clinical presentation and outcomes.

METHODS

We conducted a retrospective analysis of patients with PA (1997-2017) who underwent adrenal vein sampling (AVS). Patients were classified by self-reported race as black or non-black. Improvement was defined as postoperative decrease in mean arterial pressure (MAP), antihypertensive medications (AHM), or both.

RESULTS

Among patients undergoing AVS (n = 443), 287 underwent adrenalectomy. Black patients (28.2%) had higher body mass index (33.9 vs 31.8 kg/m² ; P = .01), longer median duration of hypertension (12 vs 10 years; P = .003), higher modified Elixhauser comorbidity index (2 vs 1; P = .004), and lower median income ($47 134 vs $78 280; P < .001). Black patients had similar aldosterone:renin ratios (150 vs 135.6 [ng/dL]/[ng·mL·^-1 hr^-1 ]; P = .23) compared to non-blacks. At long-term follow-up, black patients had a similar requirement for AHM (1 vs 0; P = .13) but higher MAP (100.6 vs 95.3 mm Hg; P = .004).

CONCLUSION

Black patients present with longer duration of hypertension and more comorbidities. They are equally likely to lateralize on AVS, suggesting similar disease phenotype. However, black patients demonstrate less improvement with adrenalectomy; this may reflect a delay in diagnosis or concomitant essential hypertension.

Resistant Hypertension: A Clinical Perspective

Resistant hypertension is a common clinical entity, defined as suboptimal blood pressure response to multiple therapies after excluding medication nonadherence and secondary forms of hypertension. Patients with resistant hypertension generally share several comorbidities. Resistant hypertension is more common in individuals of African descent. Blood pressure should be optimized using multiple strategies, including lifestyle changes and single-pill combination therapies, with the aim of reducing cardiovascular events while reducing side effects from using antihypertensive therapy. A renin/aldosterone-based diagnostic and treatment approach will help tailor therapy. The use of mineralocorticoid receptor antagonists or amiloride as appropriate is favored.

ARMC 5 Variants and Risk of Hypertension in Blacks: MH- GRID Study

Background We recently found that ARMC 5 variants may be associated with primary aldosteronism in blacks. We investigated a cohort from the MH - GRID (Minority Health Genomics and Translational Research Bio-Repository Database) and tested the association between ARMC 5 variants and blood pressure in black s. Methods and Results Whole exome sequencing data of 1377 black s were analyzed. Target single-variant and gene-based association analyses of hypertension were performed for ARMC 5, and replicated in a subset of 3015 individuals of African descent from the UK Biobank cohort. Sixteen rare variants were significantly associated with hypertension ( P=0.0402) in the gene-based (optimized sequenced kernel association test) analysis; the 16 and one other, rs116201073, together, showed a strong association ( P=0.0003) with blood pressure in this data set. The presence of the rs116201073 variant was associated with lower blood pressure. We then used human embryonic kidney 293 and adrenocortical H295R cells transfected with an ARMC 5 construct containing rs116201073 (c.*920T>C). The latter was common in both the discovery ( MH - GRID ) and replication ( UK Biobank) data and reached statistical significance ( P=0.044 [odds ratio, 0.7] and P=0.007 [odds ratio, 0.76], respectively). The allele carrying rs116201073 increased levels of ARMC5 mRNA , consistent with its protective effect in the epidemiological data. Conclusions ARMC 5 shows an association with hypertension in black s when rare variants within the gene are considered. We also identified a protective variant of the ARMC 5 gene with an effect on ARMC 5 expression confirmed in vitro. These results extend our previous report of ARMC 5's possible involvement in the determination of blood pressure in blacks.

Rates of abnormal aldosterone/renin ratio in African-origin compared to European-origin patients: A retrospective study

INTRODUCTION

The aldosterone/renin ratio is the initial screening test for primary hyperaldosteronism (PHA), but little data exists regarding ethnic variations in this.

METHODS

Following clinical observation of a high prevalence of abnormal aldosterone/renin ratio (ARR) in patients of African-origin, we retrospectively reviewed all ARR measurements in a single centre over 10 years. Rates of hypokalaemia, intraventricular septal thickness (IVS, by echocardiography) and adrenal imaging were recorded when available.

RESULTS

Aldosterone/renin ratio was available in 1473 patients, and abnormal in 374 (25.4%). Abnormal ARR was observed in 305/1349 (22.6%) of European-origin and 69/124 (55.6%) of African-origin patients (P < 0.001). Among those with abnormal ARR, hypokalaemia (<3.5 mmol/L) was documented on at least one occasion in 171/305 (56.1%) European-origin and 43/69 (62.3%) African-origin patients (P = 0.35). Median (range) IVS was 1.57 (0.78-2.80) cm in African-origin and 1.20 (0.69-2.18) cm in European-origin patients (P < 0.002); IVS did not correlate with aldosterone or ARR however. Adrenal adenoma was identified in 41/170 (24.1%) of European-origin and 4/29 (13.7%) African-origin patients (P = 0.15), while hyperplasia was identified in 35/170 (20.5%) of European and 8/29 (27.5%) African patients (P = 0.39).

CONCLUSION

In summary, ARR was abnormal in 55.6% of African-origin patients screened at an Irish hospital. Rates of hypokalaemia were similar between European-origin and African-origin patients. These findings have implications for the use of current screening guidelines for ARR in African-origin patients and also for the mechanistic role of aldosterone in hypertensive complications in African-origin patients.

Genetics of Hypertension in African Americans and Others of African Descent

Hypertension is the leading cause of cardiovascular disease in the United States, affecting up to one-third of adults. When compared to other ethnic or racial groups in the United States, African Americans and other people of African descent show a higher incidence of hypertension and its related comorbidities; however, the genetics of hypertension in these populations has not been studied adequately. Several genes have been identified to play a role in the genetics of hypertension. They include genes regulating the renin-aldosterone-angiotensin system (RAAS), such as Sodium Channel Epithelial 1 Beta Subunit (SCNN1B), Armadillo Repeat Containing 5 (ARMC5), G Protein-Coupled Receptor Kinase 4 (GRK4), and Calcium Voltage-Gated Channel Subunit Alpha1 D (CACNA1D). In this review, we focus on recent genetic findings available in the public domain for potential differences between African Americans and other populations. We also cover some recent and relevant discoveries in the field of low-renin hypertension from our laboratory at the National Institutes of Health. Understanding the different genetics of hypertension among various groups is essential for effective precision-guided medical therapy of high blood pressure.

Physiological Phenotyping for Personalized Therapy of Uncontrolled Hypertension in Africa

OBJECTIVES

African and African American hypertensives tend to retain salt and water, with lower levels of plasma renin and more resistant hypertension. We tested the hypothesis that physiological phenotyping with plasma renin and aldosterone would improve blood pressure control in uncontrolled hypertensives in Africa.

METHODS

Patients at hypertension clinics in Nigeria, Kenya, and South Africa with a systolic blood pressure >140 mm Hg or diastolic pressure > 90 mm Hg despite treatment were allocated to usual care (UC) vs. physiologically individualized care (PhysRx). Plasma renin activity and aldosterone were measured using ELISA kits. Patients were followed for 1 year; the primary outcome was the percentage of patients achieving blood pressure <140 mm Hg and diastolic <90 mm Hg.

RESULTS

Results are presented for the 94/105 participants who completed the study (42 UC, 52 PhysRx). Control of both systolic and diastolic pressures was obtained in 11.1% of UC vs. 50.0% of PhysRx (P = 0.0001). Systolic control was achieved in 13.9% of UC vs. 60.3% of PhysRx (P = 0.0001); diastolic control in 36.1% of UC vs. 67.2% of PhysRx, vs. (P = 0.003). Number of visits and total number of medications were not significantly different between treatment groups, but there were differences across the sites. There were important differences in prescription of amiloride as specified in the PhysRx algorithm.

CONCLUSIONS

Physiologically individualized therapy based on renin/aldosterone phenotyping significantly improved blood pressure control in a sample of African patients with uncontrolled hypertension. This approach should be tested in African American and other patients with resistant hypertension. Registered as ISRCTN69440037.

Recent advances in preventing stroke recurrence

Recent advances in secondary stroke prevention include new evidence in hypertension, nutrition, anticoagulation, antiplatelet therapy, intracranial stenosis, percutaneous closure of patent foramen ovale, and lipid-lowering therapy. Individualized therapy for hypertension based on phenotyping with plasma renin and aldosterone markedly improves blood pressure control in patients with resistant hypertension. A Mediterranean diet can reduce the risk of stroke by nearly half. The diagnosis and treatment of metabolic vitamin B12 deficiency, and B vitamins to lower homocysteine, can reduce the risk of stroke by approximately 30%. There are problems with clopidogrel that can be overcome by using ticagrelor, and new anticoagulant drugs markedly improve anticoagulation for stroke prevention, particularly in atrial fibrillation. There are pharmacokinetic problems with dabigatran that deserve attention. Intensive medical therapy is better than stenting for intracranial stenosis, and new therapies directed at proprotein convertase subtilisin–kexin type 9 (PCSK9) will revolutionize lipid-lowering therapy. In the past, it was estimated that rational therapy could reduce recurrent stroke by about 80%. With recent advances, we should be able to do even better.

High Frequency of Variants of Candidate Genes in Black Africans with Low Renin-Resistant Hypertension

OBJECTIVES

Black subjects tend to retain salt and water, be more sensitive to aldosterone, and have suppression of plasma renin activity. Variants of the renal sodium channel (ENaC, SCNN1B) account for approximately 6% of resistant hypertension (RHT) in Blacks; other candidate genes may be important.

METHODS

Six candidate genes associated with low renin-resistant hypertension were sequenced in Black Africans from clinics in Kenya and South Africa. CYP11B2 was sequenced if the aldosterone level was high (primary aldosteronism phenotype); SCNN1B, NEDD4L, GRK4, UMOD, and NPPA genes were sequenced if the aldosterone level was low (Liddle phenotype).

RESULTS

There were 14 nonsynonymous variants (NSVs) of CYP11B2: 3 previously described and associated with alterations in aldosterone synthase production (R87G, V386A, and G435S). Out of 14, 9 variants were found in all 9 patients sequenced. There were 4 NSV of GRK4 (R65L, A116T, A142V, V486A): at least one was found in all 9 patients; 3 were previously described and associated with hypertension. There were 3 NSV of SCNN1B (R206Q, G442V, and R563Q); 2 previously described and 1 associated with hypertension. NPPA was found to have 1 NSV (V32M), not previously described and NEDD4L did not have any variants. UMOD had 3 NSV: D25G, L180V, and T585I.

CONCLUSIONS

A phenotypic approach to investigating the genetic architecture of RHT uncovered a surprisingly high yield of variants in candidate genes. These preliminary findings suggest that this novel approach may assist in understanding the genetic architecture of RHT in Blacks and explain their two fold risk of stroke.

Illness Narratives of African Americans Living With Coronary Heart Disease: A Critical Interactionist Analysis

How African American men and women respond to and manage living with coronary heart disease (CHD) is not well understood despite the well-documented disproportionate burden of CHD and its complications among African Americans in the United States. Through a critical interactionist perspective, we explore illness experiences of African Americans living with CHD and describe a broad range of micro-, meso-, and macro-contextual factors that influence their illness experiences. For participants in this study, CHD has become a "Black disease" wherein certain bodies have become historically and racially marked; a conceptualization maintained and passed on by African Americans themselves. Such findings highlight that CHD is more than a "lifestyle disease" where high-risk behaviors and lack of healthy choices are ultimate culprits. Rather, CHD is perceived by African Americans who have it as yet another product of ongoing racial and socio-structural dynamics through which their health burdens are created, sustained, and reproduced.

End of Life in a Haitian American, Faith-Based Community: Caring for Family and Communal Unity

This article presents two models resulting from a grounded theory study of the end-of-life decision-making process for Haitian Americans. Successful access to this vulnerable population was achieved through the faith-based community. The first model describes this faith-based community of Haitian Americans. The second model describes the process used by families in this community who must make end-of-life healthcare decisions. Implications for nursing practice and caring science include a need to improve the congruence between the nursing care provided at this vulnerable time and the cultural values of a population.

Physiologic tailoring of treatment in resistant hypertension

Resistant hypertension is a major opportunity for prevention of cardiovascular disease. Despite widespread dissemination of consensus guidelines, most patients are uncontrolled with approaches that assume that all patients are the same.

Causes of resistant hypertension include 1) non-compliance 2) consumption of substances that aggravate hypertension (such as salt, alcohol, nonsteroidal anti-inflammatory drugs, licorice, decongestants) and 3) secondary hypertension.

Selecting the appropriate therapy for a patient depends on finding the cause of the hypertension. Once rare causes have been eliminated (such as pheochromocytoma, licorice, adult coarctation of the aorta), the cause will usually be found by intelligent interpretation (in the light of medications then being taken) of plasma renin and aldosterone.

If stimulated renin is low and the aldosterone is high, the problem is primary aldosteronism, and the best treatment is usually aldosterone antagonists (spironolactone or eplerenone; high-dose amiloride for men where eplerenone is not available). If the renin is high, with secondary hyperaldosteronism, the best treatment is angiotensin receptor blockers or aliskiren. If the renin and aldosterone are both low the problem is over-activity of renal sodium channels and the treatment is amiloride. This approach is particularly important in patients of African origin, who are more likely to have low-renin hypertension.

Human difference in the genomic era: Facilitating a socially responsible dialogue

Background

The study of human genetic variation has been advanced by research such as genome-wide association studies, which aim to identify variants associated with common, complex diseases and traits. Significant strides have already been made in gleaning information on susceptibility, treatment, and prevention of a number of disorders. However, as genetic researchers continue to uncover underlying differences between individuals, there is growing concern that observed population-level differences will be inappropriately generalized as inherent to particular racial or ethnic groups and potentially perpetuate negative stereotypes.

Discussion

We caution that imprecision of language when conveying research conclusions, compounded by the potential distortion of findings by the media, can lead to the stigmatization of racial and ethnic groups.

Summary

It is essential that the scientific community and with those reporting and disseminating research findings continue to foster a socially responsible dialogue about genetic variation and human difference.

Sodium, blood pressure, and ethnicity: what have we learned?

An enormous amount of research has yielded significant knowledge about ethnic differences in sodium homeostasis and blood pressure regulation. Consistent findings such as greater sodium-sensitivity, lower potassium excretion and high higher serum sodium levels in African Americans need further exploration to define more precise physiological mechanisms. The genetic alleles associated with sodium homeostasis in relation to blood pressure have accounted for only a small proportion of the variance in blood pressure. Several allelic variants differ in frequency among ethnic groups and heat-adapted genetic variants have a high prevalence in low latitudes and hot, wet climates which lends support to the "sodium retention" hypothesis. The blood pressure disparities between African Americans and whites may, in part, be due to different allelic frequencies of genes associated with sodium homeostasis. However, with advances in genomics, environmental factors tend to be neglected in research. Better measures of environmental stress have recently been developed by anthropologists and should be included in research designs by investigators in other disciplines. Public health efforts should encourage food producers to reduce sodium content of its products, and physicians should encourage patients to reduce consumption of high sodium packaged and fast foods.

A novel amiloride-sensitive h+ transport pathway mediates enhanced superoxide production in thick ascending limb of salt-sensitive rats, not na+/h+ exchange

It has been reported previously that H(+) efflux via the Na(+)/H(+) exchange stimulates NAD(P)H oxidase-dependent superoxide (O(2)(.-)) production in medullary thick ascending limb. We have demonstrated recently that N-methyl-amiloride-sensitive O(2)(.-) production is enhanced in the thick ascending limb of Dahl salt-sensitive (SS) rats, suggesting that H(+) efflux through Na(+)/H(+) exchangers may promote renal oxidative stress and the development of hypertension in these animals. In the current study we demonstrate, using selective and potent inhibitors, that inhibition of Na(+)/H(+) exchange does not mediate the ability of N-methyl-amiloride to inhibit thick ascending limb O(2)(.-) production. To determine the mechanism of action of N-methyl-amiloride, we examined H(+) efflux and O(2)(.-) production in SS and SS.13(BN) thick ascending limbs of prehypertensive, 0.4% NaCl-fed rats. Tissue strips containing the medullary thick ascending limb were isolated from male SS and salt-resistant consomic SS.13(BN) rats, loaded with either dihydroethedium or 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester, and imaged in a heated tissue bath. In Na(+)-replete media, activation of Na(+)/H(+) exchange using an NH(4)Cl prepulse did not stimulate thick ascending limb O(2)(.-) production. In Na(+)-free media containing BaCl(2) in which Na(+)/H(+) activity was inhibited, an NH(4)Cl prepulse stimulated O(2)(.-) production in medullary thick ascending limb renal tubular segments. This response was enhanced in medullary thick ascending limb of SS rats (slope Deltaethidium/Deltadihydroethedium=0.029+/-0.004) compared with SS.13(BN) rats (slope=0.010+/-0.004; P<0.04) and could be inhibited by N-methyl-amiloride (slope=0.005+/-0.002 and 0.006+/-0.002 for SS and SS.13(BN), respectively). We concluded that only H(+) efflux through a specific, as-yet-unidentified, amiloride-sensitive H(+) channel promotes O(2)(.-) production in the medullary thick ascending limb and that this channel is upregulated in SS rats.

Biobehavior of the human love of salt

We are beginning to understand why humans ingest so much salt. Here we address three issues: The first is whether our salt appetite is similar to that in animals, which we understand well. Our analysis suggests that this is doubtful, because of important differences between human and animal love of salt. The second issue then becomes how our predilection for salt is determined, for which we have a partial description, resting on development, conditioning, habit, and dietary culture. The last issue is the source of individual variation in salt avidity. We have partial answers to that too in the effects of perinatal sodium loss, sodium loss teaching us to seek salt, and gender. Other possibilities are suggested. From animal sodium appetite we humans may retain the lifelong enhancement of salt intake due to perinatal sodium loss, and a predisposition to learn the benefits of salt when in dire need. Nevertheless, human salt intake does not fit the biological model of a regulated sodium appetite. Indeed this archetypal 'wisdom of the body' fails us in all that has to do with behavioral regulation of this most basic need.

Opportunity Cost

Low-income rural southern African American women experience a high prevalence of morbidity and mortality from coronary heart disease (CHD) as well as other related cardiovascular (CV) diseases. Few models have taken into account the full impact of the contextual influences encountered on a daily basis by these women, and the effect of these influences on their CV health status. There are clearly demarcated examples of existing health disparities that occur in various ethnic/racial, underserved, and vulnerable populations. Yet, to date, there is no conceptual model that offers a plausible explanation as to why health disparities exist. Consequently, there is a lack of guidance as to where interventions should be focused for effective CV risk reduction. Because African American women continue to die at a disproportionately higher rate, and at earlier ages than do Caucasian women, it is imperative that new theoretical models capable of driving empirically based interventions be developed, tested, and implemented. One possible choice is the conceptual model proposed in this article. The model is based on the interrelationships between contextual risk factors, rational choice theory (RCT), and opportunity cost. Conceivably, this model may serve as a foundation to ground conceptual thought and drive theory-based interventions to reduce the health disparities in the CV health of low-income rural southern African American women. A model is presented in an attempt to provide guidance for advanced practice nurses who must struggle with addressing the critical need to reduce ethnic and race-associated CV health disparities.