Hypertension in Blacks: Unanswered Questions and Future Directions for the JHS (Jackson Heart Study)

Single nucleotide polymorphism-based biomarker in primary hypertension

Primary hypertension is a multiplex and multifactorial disease influenced by various strong components including genetics. Extensive research such as Genome-wide association studies and candidate gene studies have revealed various single nucleotide polymorphisms (SNPs) related to hypertension, providing insights into the genetic basis of the condition. This review summarizes the current status of SNP research in primary hypertension, including examples of hypertension-related SNPs, their location, function, and frequency in different populations. The potential clinical implications of SNP research for primary hypertension management are also discussed, including disease risk prediction, personalized medicine, mechanistic understanding, and lifestyle modifications. Furthermore, this review highlights emerging technologies and methodologies that have the potential to revolutionize the vast understanding of the basis of genetics in primary hypertension. Gene editing holds the potential to target and correct any kind of genetic mutations that contribute to the development of hypertension or modify genes involved in blood pressure regulation to prevent or treat the condition. Advances in computational biology and machine learning enable researchers to analyze large datasets and identify complex genetic interactions contributing to hypertension risk. In conclusion, SNP research in primary hypertension is rapidly evolving with emerging technologies and methodologies that have the potential to transform the knowledge about genetic basis related to the condition. These advances hold promise for personalized prevention and treatment strategies tailored to an individual's genetic profile ultimately improving patient outcomes and reducing healthcare costs.

Cumulative Systolic Blood Pressure and Incident Stroke Type Variation by Race and Ethnicity

Importance

Stroke risk varies by systolic blood pressure (SBP), race, and ethnicity. The association between cumulative mean SBP and incident stroke type is unclear, and whether this association differs by race and ethnicity remains unknown.

Objective

To examine the association between cumulative mean SBP and first incident stroke among 3 major stroke types-ischemic stroke (IS), intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH)-and explore how these associations vary by race and ethnicity.

Design, Setting, and Participants

Individual participant data from 6 US longitudinal cohorts (January 1, 1971, to December 31, 2019) were pooled. The analysis was performed from January 1, 2022, to January 2, 2024. The median follow-up was 21.6 (IQR, 13.6-31.8) years.

Exposure

Time-dependent cumulative mean SBP.

Main Outcomes and Measures

The primary outcome was time from baseline visit to first incident stroke. Secondary outcomes consisted of time to first incident IS, ICH, and SAH.

Results

Among 40 016 participants, 38 167 who were 18 years or older at baseline with no history of stroke and at least 1 SBP measurement before the first incident stroke were included in the analysis. Of these, 54.0% were women; 25.0% were Black, 8.9% were Hispanic of any race, and 66.2% were White. The mean (SD) age at baseline was 53.4 (17.0) years and the mean (SD) SBP at baseline was 136.9 (20.4) mm Hg. A 10-mm Hg higher cumulative mean SBP was associated with a higher risk of overall stroke (hazard ratio [HR], 1.20 [95% CI, 1.18-1.23]), IS (HR, 1.20 [95% CI, 1.17-1.22]), and ICH (HR, 1.31 [95% CI, 1.25-1.38]) but not SAH (HR, 1.13 [95% CI, 0.99-1.29]; P = .06). Compared with White participants, Black participants had a higher risk of IS (HR, 1.20 [95% CI, 1.09-1.33]) and ICH (HR, 1.67 [95% CI, 1.30-2.13]) and Hispanic participants of any race had a higher risk of SAH (HR, 3.81 [95% CI, 1.29-11.22]). There was no consistent evidence that race and ethnicity modified the association of cumulative mean SBP with first incident stroke and stroke type.

Conclusions and Relevance

The findings of this cohort study suggest that cumulative mean SBP was associated with incident stroke type, but the associations did not differ by race and ethnicity. Culturally informed stroke prevention programs should address modifiable risk factors such as SBP along with social determinants of health and structural inequities in society.

Racial and Ethnic Discrimination and Hypertension by Educational Attainment Among a Cohort of US Women

Importance

Although understudied, there are likely within-group differences among minoritized racial and ethnic groups in associations between racial and ethnic discrimination (RED) and hypertension risk, as minoritized individuals with higher educational attainment may more frequently encounter stress-inducing environments (eg, professional workplace settings, higher-income stores and neighborhoods) characterized by, for instance, exclusion and antagonism.

Objectives

To investigate educational attainment as a potential effect modifier of associations between RED and hypertension risk among US women; the study hypothesis was that the magnitude of associations would be stronger among participants with higher vs lower educational attainment.

Design, Setting, and Participants

This is a nested case-control study using Sister Study data collected at enrollment (2003-2009) and over follow-up visits until September 2019. Among eligible US Black or African American (hereafter Black), Latina, and non-Hispanic White women without prior hypertension diagnoses, incidence density sampling was performed to select self-reported hypertension cases that developed over a mean (SD) follow-up 11 (3) years. Data were analyzed August 2022 to February 2023.

Exposures

Participants reported lifetime everyday (eg, unfair treatment at a business) and major (eg, mistreatment by police) RED via a self-administered questionnaire.

Main Outcome and Measures

Adjusting for sociodemographic characteristics, conditional logistic regression was used to estimate odds ratios (ORs) and 95% CIs for associations between RED and hypertension by educational attainment category at baseline (college or higher, some college, and high school or less) within racial and ethnic groups.

Results

Among 5179 cases (338 [6.5%] Black; 200 [3.9%] Latina; and 4641 [89.6%] non-Hispanic White) and 10:1 race and ethnicity- and age-matched control participants with a mean (SD) age of 55 (9) years at enrollment, half (49.9%) of women reported attaining college or higher education, and Black women with college or greater education had the highest burden of RED (eg, 83% of case participants with college or higher education reported everyday RED compared with 64% of case participants with high school or less education). Everyday RED was associated with higher hypertension risk among Black women with college or higher education (OR, 1.56 [95% CI, 1.06-2.29]) but not among Black women with some college (OR, 0.72 [95% CI, 0.47-1.11]), with evidence of both multiplicative and additive interaction. Results for Black women with high school or less education suggested increased risk, but confidence intervals were wide, and the result was not statistically significant but may be clinically significant (OR, 1.89 [95% CI, 0.83-4.31]). Educational attainment was not a modifier among other racial and ethnic groups or for associations with major RED.

Conclusions and Relevance

In this nested case-control study of RED and hypertension risk, chronic or everyday RED-associated hypertension disproportionately affected Black women with the highest levels of educational attainment.

Race-based Versus Race-conscious Medicine in Obstetrics and Gynecology

Race is a social and power construct whose meaning has shifted over time. Racist beliefs in medicine fostered the continuation of these notions. In this commentary, we review race-based medicine versus race-conscious medicine. Race-conscious medicine emphasizes racism as a key determinant of illness and health. Racism in obstetrics and gynecology has deep roots in its history. The use of race in clinical decision-making tools, such as those that predict successful vaginal birth after cesarean delivery, should be eliminated. Research that explores the complexities of health disparities and their effects on clinical outcomes are pivotal to race-conscious approaches in medicine.

Evaluating novel approaches for estimating awake and sleep blood pressure: design of the Better BP Study - a randomised, crossover trial

INTRODUCTION

For many people, blood pressure (BP) levels differ when measured in a medical office versus outside of the office setting. Out-of-office BP has a stronger association with cardiovascular disease (CVD) events compared with BP measured in the office. Many BP guidelines recommend measuring BP outside of the office to confirm the levels obtained in the office. Ambulatory BP monitoring (ABPM) can assess out-of-office BP but is not available in many US practices and some individuals find it uncomfortable. The aims of the Better BP Study are to (1) test if unattended office BP is closer to awake BP on ABPM compared with attended office BP, (2) assess if sleep BP assessed by home BP monitoring (HBPM) agrees with sleep BP from a full night of ABPM and (3) compare the strengths of associations of unattended versus attended office BP, unattended office BP versus awake BP on ABPM and sleep BP on HBPM versus ABPM with markers of end-organ damage.

METHODS AND ANALYSIS

We are recruiting 630 adults not taking antihypertensive medication in Birmingham, Alabama, and New York, New York. Participants are having their office BP measured with (attended) and without (unattended) a technician present, in random order, using an automated oscillometric office BP device during each of two visits within one week. Following these visits, participants complete 24 hours of ABPM and one night of HBPM, in random order. Psychosocial factors, anthropometrics, left ventricular mass index and albumin-to-creatinine ratio are also being assessed.

ETHICS AND DISSEMINATION

This study was approved by the University of Alabama at Birmingham and the Columbia University Medical Center Institutional Review Boards. The study results will be disseminated at scientific conferences and published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT04307004.

Kidney-specific KO of the circadian clock protein PER1 alters renal Na+ handling, aldosterone levels, and kidney/adrenal gene expression

PERIOD 1 (PER1) is a circadian clock transcription factor that is regulated by aldosterone, a hormone that increases blood volume and Na+ retention to increase blood pressure. Male global Per1 knockout (KO) mice develop reduced night/day differences in Na+ excretion in response to a high-salt diet plus desoxycorticosterone pivalate treatment (HS + DOCP), a model of salt-sensitive hypertension. In addition, global Per1 KO mice exhibit higher aldosterone levels on a normal-salt diet. To determine the role of Per1 in the kidney, male kidney-specific Per1 KO (KS-Per1 KO) mice were generated using Ksp-cadherin Cre recombinase to remove exons 2-8 of Per1 in the distal nephron and collecting duct. Male KS-Per1 KO mice have increased Na+ retention but have normal diurnal differences in Na+ excretion in response to HS + DOCP. The increased Na+ retention is associated with altered expression of glucocorticoid and mineralocorticoid receptors, increased serum aldosterone, and increased medullary endothelin-1 compared with control mice. Adrenal gland gene expression analysis revealed that circadian clock and aldosterone synthesis genes have altered expression in KS-Per1 KO mice compared with control mice. These results emphasize the importance of the circadian clock not only in maintaining rhythms of physiological functions but also for adaptability in response to environmental cues, such as HS + DOCP, to maintain overall homeostasis. Given the prevalence of salt-sensitive hypertension in the general population, these findings have important implications for our understanding of how circadian clock proteins regulate homeostasis.NEW & NOTEWORTHY For the first time, we show that knockout of the circadian clock transcription factor PERIOD 1 using kidney-specific cadherin Cre results in increased renal Na+ reabsorption, increased aldosterone levels, and changes in gene expression in both the kidney and adrenal gland. Diurnal changes in renal Na+ excretion were not observed, demonstrating that the clock protein PER1 in the kidney is important for maintaining homeostasis and that this effect may be independent of time of day.

Association of Intensive Blood Pressure Control and Living Arrangement on Cardiovascular Outcomes by Race: Post Hoc Analysis of SPRINT Randomized Clinical Trial

IMPORTANCE

Living alone, a key proxy of social isolation, is a risk factor for cardiovascular disease. In addition, Black race is associated with less optimal blood pressure (BP) control than in other racial or ethnic groups. However, it is not clear whether living arrangement status modifies the beneficial effects of intensive BP control on reduction in cardiovascular events among Black individuals.

OBJECTIVE

To examine whether the association of intensive BP control with cardiovascular events differs by living arrangement among Black individuals and non-Black individuals (eg, individuals who identified as Alaskan Native, American Indian, Asian, Native Hawaiian, Pacific Islander, White, or other) in the Systolic Blood Pressure Intervention Trial (SPRINT).

DESIGN, SETTING, AND PARTICIPANTS

This secondary analysis incorporated data from SPRINT, a multicenter study of individuals with increased risk for cardiovascular disease and free of diabetes, enrolled at 102 clinical sites in the United States between November 2010 and March 2013. Race and living arrangement (ie, living alone or living with others) were self-reported. Data were collected between November 2010 and March 2013 and analyzed from January 2021 to October 2021.

EXPOSURES

The SPRINT participants were randomized to a systolic BP target of either less than 120 mm Hg (intensive treatment group) or less than 140 mm Hg (standard treatment group). Antihypertensive medications were adjusted to achieve the targets in each group.

MAIN OUTCOMES AND MEASURES

Cox proportional hazards model was used to investigate the association of intensive treatment with the incident composite cardiovascular outcome (by August 20, 2015) according to living arrangement among Black individuals and other individuals. Transportability formula was applied to generalize the SPRINT findings to hypothetical external populations by varying the proportion of Black race and living arrangement status.

RESULTS

Among the 9342 total participants, the mean (SD) age was 67.9 (9.4) years; 2793 participants [30%] were Black, 2714 [29%] lived alone, and 3320 participants (35.5%) were female. Over a median (IQR) follow-up of 3.22 (2.74-3.76) years, the primary composite cardiovascular outcome was observed in 67 of 1001 Black individuals living alone (6.7%), 76 of 1792 Black individuals living with others (4.2%), 108 of 1713 non-Black individuals living alone (6.3%), and 311 of 4836 non-Black individuals living with others (6.4%). The intensive treatment group showed a significantly lower rate of the composite cardiovascular outcome than the standard treatment group among Black individuals living with others (hazard ratio [HR], 0.53 [95% CI, 0.33-0.85]) but not among those living alone (HR, 1.07 [95% CI, 0.66-1.73]; P for interaction = .04). The association was observed among individuals who were not Black regardless of living arrangement status. Using transportability, we found a smaller or null association between intensive control and cardiovascular outcomes among hypothetical populations of 60% Black individuals or more and 60% or more of individuals living alone.

CONCLUSIONS AND RELEVANCE

Intensive BP control was associated with a lower rate of cardiovascular events among Black individuals living with others and individuals who were not Black but not among Black individuals living alone.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01206062.

Race and Modifiable Factors Influencing Cardiovascular Disease

A modern approach to mitigating the impact of cardiovascular disease on Americans demands not only an understanding of modifiable conditions that contribute to its development but also a greater appreciation of the heterogeneous distribution of these conditions based on race. As race is not a biological construct, further research is needed to fully elucidate the mechanisms that contribute to these differences. The consequences of the differential impact of modifiable risk factors on cardiovascular disease outcomes among black Americans compared with white Americans cannot be understated.

Approach to Hypertension in Adolescents and Young Adults

PURPOSE OF REVIEW

The prevalence of hypertension in adolescents and young adults has increased in part due to the obesity epidemic. The clinical impact and future cardiovascular risk of this underestimated public health problem is an evolving field.

RECENT FINDINGS

The development of hypertension is predicted by tracking of elevated blood pressure from childhood to adulthood. Young hypertensive individuals have lower awareness, slower diagnosis rates, and poorer blood pressure control than older patients. Increased awareness, appropriate screening, early identification, and individualized treatment approaches for elevated blood pressure could prevent development of hypertension in adulthood and cardiovascular events in later life. The optimal blood pressure management for young adults with a low 10-year risk of atherosclerotic cardiovascular disease of < 10% remains challenging due to lack of randomized controlled trials. Evidence-based recommendations are needed to implement appropriate measures for time of treatment initiation, preferred antihypertensive drug class to be used and optimal target blood pressure level from childhood through young adulthood.

Racial/Ethnic Disparities in Hypertension Prevalence, Awareness, Treatment, and Control in the United States, 2013 to 2018

[Figure: see text].

Comparing the associations of clinic vs. ambulatory blood pressure with subclinical organ damage in young healthy adults: the African-PREDICT study

Raised blood pressure (BP) causes pathophysiological cardiovascular changes resulting in target organ damage. Although ambulatory and central BP relate more strongly to outcomes than clinical brachial BP in the elderly population, it is unknown which measure of BP is most strongly associated with markers of organ damage in younger populations. We compared the strength of associations between different BPs and measures of subclinical organ damage and investigated whether ethnic differences exist between these associations. The design was a cross-sectional analysis of the African-PREDICT study, including young black and white men and women (aged 20-30, N = 1202). We obtained clinic, ambulatory, and central BP readings, as well as measures of subclinical organ damage: central retinal arteriolar equivalent (CRAE) from fundus images, echocardiography to determine left ventricular mass index (LVMi), carotid intima media thickness (CIMT), carotid-femoral pulse wave velocity (PWV), and albumin-to-creatinine ratio (ACR) determined from spot urine samples. Overall, weak correlations were evident between CIMT, ACR, and BP, whereas CRAE, LVMi, and PWV correlated strongly with BP. In the total group, clinic brachial BP had stronger associations with CRAE, LVMi, and PWV (all p < 0.001) than ambulatory and central BP. Although the ethnic groups showed similar correlations between CRAE, LVMi, CIMT, and the various BPs, PWV correlated more strongly with ambulatory systolic BP (p < 0.001) in white participants. In young healthy adults, clinic brachial BP correlated more strongly with measures of early target organ damage than central or ambulatory BP. No differences were observed between correlations of BP and measures of target organ damage in the two ethnic groups.

Twenty-four-hour versus clinic blood pressure levels as predictors of long-term cardiovascular and renal disease outcomes among African Americans

In Caucasian and Asian populations, evidence suggests that 24-h blood pressures (BP) are more predictive of long-term cardiovascular events than clinic BP. However, few long-term studies have evaluated the predictive value of 24-h BP phenotypes (24-h, daytime, nighttime) among African Americans (AA). The purpose of this study is to evaluate the added value of 24-h BP phenotypes compared to clinic BP in predicting the subsequent fatal and non-fatal cardiovascular/renal disease events in AA subjects. AA subjects (n = 270) were initially studied between 1994 and 2006 and standardized clinic BP measurements were obtained during screening procedures for a 3-day inpatient clinical study during which 24-h BP measurements were obtained. To assess the subsequent incidence of cardiovascular and renal disease events, follow-up information was obtained and confirmed by review of paper and electronic medical records between 2015 and 2017. During a mean follow-up of 14 ± 4 years, 50 subjects had one or more fatal or non-fatal cardiovascular/renal disease events. After adjustment for covariates, clinic systolic and diastolic BP were strongly associated with cardiovascular/renal disease events and all-cause mortality (p < 0.0001). Twenty-four-hour BP phenotypes conferred a small incremental advantage over clinic BP in predicting cardiovascular/renal events, which was limited to making a difference of one predicted event in 250-1,000 predictions depending on the 24-h BP phenotype. Nocturnal BP was no more predictive than the other 24-h BP phenotypes. In AA, 24-h BP monitoring provides limited added value as a predictor of cardiovascular/renal disease events. Larger studies are needed in AA to confirm these findings.

Periodontitis and Hypertension: Is the Association Causal?

High blood pressure (BP) and periodontitis are two highly prevalent conditions worldwide with a significant impact on cardiovascular disease (CVD) complications. Poor periodontal health is associated with increased prevalence of hypertension and may have an influence on BP control. Risk factors such as older age, male gender, non-Caucasian ethnicity, smoking, overweight/obesity, diabetes, low socioeconomic status, and poor education have been considered the common denominators underpinning this relationship. However, recent evidence indicates that the association between periodontitis and hypertension is independent of common risk factors and may in fact be causal in nature. Low-grade systemic inflammation and redox imbalance, in particular, represent the major underlying mechanisms in this relationship. Neutrophil dysfunction, imbalance in T cell subtypes, oral-gut dysbiosis, hyperexpression of proinflammatory genes, and increased sympathetic outflow are some of the pathogenetic events involved. In addition, novel findings indicate that common genetic bases might shape the immune profile towards this clinical phenotype, offering a rationale for potential therapeutic and prevention strategies of public health interest. This review summarizes recent advances, knowledge gaps and possible future directions in the field.

New research directions on disparities in obesity and type 2 diabetes

Obesity and type 2 diabetes disproportionately impact U.S. racial and ethnic minority communities and low-income populations. Improvements in implementing efficacious interventions to reduce the incidence of type 2 diabetes are underway (i.e., the National Diabetes Prevention Program), but challenges in effectively scaling-up successful interventions and reaching at-risk populations remain. In October 2017, the National Institutes of Health convened a workshop to understand how to (1) address socioeconomic and other environmental conditions that perpetuate disparities in the burden of obesity and type 2 diabetes; (2) design effective prevention and treatment strategies that are accessible, feasible, culturally relevant, and acceptable to diverse population groups; and (3) achieve sustainable health improvement approaches in communities with the greatest burden of these diseases. Common features of guiding frameworks to understand and address disparities and promote health equity were described. Promising research directions were identified in numerous areas, including study design, methodology, and core metrics; program implementation and scalability; the integration of medical care and social services; strategies to enhance patient empowerment; and understanding and addressing the impact of psychosocial stress on disease onset and progression in addition to factors that support resiliency and health.

Diagnostic Accuracy of Unattended Automated Office Blood Pressure Measurement in Screening for Hypertension in Kenya

Supplemental Digital Content is available in the text.

Despite increasing adoption of unattended automated office blood pressure (uAOBP) measurement for determining clinic blood pressure (BP), its diagnostic performance in screening for hypertension in low-income settings has not been determined. We determined the validity of uAOBP in screening for hypertension, using 24-hour ambulatory BP monitoring as the reference standard. We studied a random population sample of 982 Kenyan adults; mean age, 42 years; 60% women; 2% with diabetes mellitus; none taking antihypertensive medications. We calculated sensitivity using 3 different screen positivity cutoffs (≥130/80, ≥135/85, and ≥140/90 mm Hg) and other measures of validity/agreement. Mean 24-hour ambulatory BP monitoring systolic BP was similar to mean uAOBP systolic BP (mean difference, 0.6 mm Hg; 95% CI, −0.6 to 1.9), but the 95% limits of agreement were wide (−39 to 40 mm Hg). Overall discriminatory accuracy of uAOBP was the same (area under receiver operating characteristic curves, 0.66–0.68; 95% CI range, 0.64–0.71) irrespective of uAOBP cutoffs used. Sensitivity of uAOBP displayed an inverse association (P<0.001) with the cutoff selected, progressively decreasing from 67% (95% CI, 62–72) when using a cutoff of ≥130/80 mm Hg to 55% (95% CI, 49–60) at ≥135/85 mm Hg to 44% (95% CI, 39–49) at ≥140/90 mm Hg. Diagnostic performance was significantly better (P<0.001) in overweight and obese individuals (body mass index, >25 kg/m²). No differences in results were present in other subanalyses. uAOBP misclassifies significant proportions of individuals undergoing screening for hypertension in Kenya. Additional studies on how to improve screening strategies in this setting are needed.

Dietary Phosphorus and Ambulatory Blood Pressure in African Americans: The Jackson Heart Study

BACKGROUND

Higher dietary phosphorus is associated with left ventricular hypertrophy and mortality, which are blood pressure (BP)-related outcomes. For this reason, we hypothesized that dietary phosphorus may be associated with adverse clinic and ambulatory BP patterns.

METHODS

Our study included 973 African American adults enrolled in the Jackson Heart Study (2000-2004) with 24-hour ambulatory BP monitoring (ABPM) data at baseline. We quantified dietary phosphorus from a validated Food Frequency Questionnaire as follows: (i) absolute daily intake, (ii) ratio of phosphorus-to-protein intake, (iii) phosphorus density, and (iv) energy-adjusted phosphorus intake. Using multivariable linear regression, we determined associations between dietary phosphorus intake and systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse pressure in clinic and over daytime, nighttime, and 24-hour periods from ABPM. Extent of nocturnal BP dipping was also assessed. Using logistic regression, we modeled relationships between dietary phosphorus intake and clinically relevant qualitative BP phenotypes, such as masked, sustained, or white-coat hypertension and normotension.

RESULTS

There were no statistically significant associations between phosphorus intake and SBP or pulse pressure in adjusted models. Most metrics of higher phosphorus intake were associated with lower daytime, nighttime, and clinic DBP. Higher phosphorus intake was not associated with clinic or ABPM-defined hypertension overall, but most metrics of higher phosphorus intake were associated with lower odds of sustained hypertension compared to sustained normotension, white-coat hypertension, and masked hypertension. There were no associations between dietary phosphorus and nocturnal BP dipping.

CONCLUSIONS

These data do not support a role for higher phosphorus intake and higher BP in African Americans.

Renal Na-handling defect associated with PER1-dependent nondipping hypertension in male mice

Many physiological functions have a circadian rhythm, including blood pressure (BP). BP is highest during the active phase, whereas during the rest period, BP dips 10-20%. Patients that do not experience this dip at night are termed "nondippers." Nondipping hypertension is associated with increased risk of cardiovascular disease. The mechanisms underlying nondipping hypertension are not understood. Without the circadian clock gene Per1, C57BL/6J mice develop nondipping hypertension on a high-salt diet plus mineralocorticoid treatment (HS/DOCP). Our laboratory has shown that PER1 regulates expression of several genes related to sodium (Na) transport in the kidney, including epithelial Na channel (ENaC) and Na chloride cotransporter (NCC). Urinary Na excretion also demonstrates a circadian pattern with a peak during active periods. We hypothesized that PER1 contributes to circadian regulation of BP via a renal Na-handling-dependent mechanism. Na-handling genes from the distal nephron were inappropriately regulated in KO mice on HS/DOCP. Additionally, the night/day ratio of Na urinary excretion by Per1 KO mice is decreased compared with WT (4 × vs. 7×, P < 0.001, n = 6 per group). Distal nephron-specific Per1 KO mice also show an inappropriate increase in expression of Na transporter genes αENaC and NCC. These results support the hypothesis that PER1 mediates control of circadian BP rhythms via the regulation of distal nephron Na transport genes. These findings have implications for the understanding of the etiology of nondipping hypertension and the subsequent development of novel therapies for this dangerous pathophysiological condition.