Nighttime blood pressure and nocturnal dipping are associated with daytime urinary sodium excretion in African subjects

Duration until nighttime blood pressure fall indicates excess sodium retention

Impaired renal sodium excretion causes sodium retention, which prevents the nocturnal dip in blood pressure (BP); thus, high BP persists until excess sodium is excreted. The authors defined "dipping time" (DT) as the duration until the nocturnal BP falls below 90% of the daytime average. Diuretic (e.g., hydrochlorothiazide [HCTZ]) and angiotensin receptor blocker (ARB) are able to eliminate sodium retention and restore the non-dipper BP rhythm. Reanalysis of two previous studies demonstrate that HCTZ and ARB shortened the DT. Shortening DT correlated directly with the increase in daytime urinary sodium excretion (Study 2). DT can be used as a preliminary indicator of sodium retention.

Short-term increase in particulate matter blunts nocturnal blood pressure dipping and daytime urinary sodium excretion

Short-term exposure to ambient particulate matter with aerodynamic diameters<10 µm were found to be positively associated with blood pressure. Yet, little information exists regarding the association between particles and circadian rhythm of blood pressure. Hence, we analyzed the association of exposure to particulate matter with aerodynamic diameters<10 µm on the day of examination and ≤7 days before with ambulatory blood pressure and with sodium excretion in 359 adults from the general population using multiple linear regression. After controlling for potential confounders, a 10-µg/m3 increase in particulate matter with aerodynamic diameters<10 µm levels was associated with nighttime systolic blood pressure (β=1.32 mm Hg 95% CI, 0.06-2.58 mm Hg at lag 0; P=0.04), nighttime diastolic blood pressure (0.72 mm Hg 95% CI, 0.03-1.42 mm Hg at lag 2; P=0.04), nocturnal systolic blood pressure dipping (-0.96 mm Hg 95% CI, -1.89 to -0.03 mm Hg at lag 0; P=0.044), and daytime urinary sodium excretion (-0.05 log-mmol/min 95% CI, -0.10 to -0.01 log-mmol/min at lag 0; P=0.027) but not with nighttime sodium excretion. The associations with blood pressure rapidly diminished with increasing lag days, and the associations with daytime sodium excretion were maximal with particulate matter with aerodynamic diameters<10 µm in exposures 2 to 5 days before. The associations of short-term increases in particulate matter with aerodynamic diameters<10 µm with higher nighttime blood pressure and blunted systolic blood pressure dipping were preceded by associations with reduced ability of the kidney to excrete sodium during daytime. The underlying mechanism linking air pollution to increased cardiovascular risk may include disturbed circadian rhythms of renal sodium handling and blood pressure.

Correlation between sodium and potassium excretion in 24- and 12-h urine samples

Low-sodium and high-potassium diets have been recommended as an adjunct to prevention and treatment of hypertension. Analysis of these nutrients in 24-h urine has been considered the reference method to estimate daily intake of these minerals. However, 24-h urine collection is difficult in epidemiological studies, since urine must be collected and stored in job environments. Therefore, strategies for shorter durations of urine collection at home have been proposed. We have previously reported that collecting urine during a 12-h period (overnight) is more feasible and that creatinine clearance correlated strongly with that detected in 24-h samples. In the present study, we collected urine for 24 h divided into two 12-h periods (from 7:00 am to 7:00 pm and from 7:00 pm to 7:00 am next day). A sample of 109 apparently healthy volunteers aged 30 to 74 years of both genders working in a University institution was investigated. Subjects with previous myocardial infarction, stroke, renal insufficiency, and pregnant women were not included. Significant (P < 0.001) Spearman correlation coefficients (r_s) were found between the total amount of sodium and potassium excreted in the urine collected at night and in the 24-h period (r_s = 0.76 and 0.74, respectively). Additionally, the 12-h sodium and potassium excretions (means ± SD, 95% confidence interval) corresponded to 47.3 ± 11.2%, 95%CI = 45.3-49.3, and 39.3 ± 4.6%, 95%CI = 37.3-41.3, respectively, of the 24-h excretion of these ions. Therefore, these findings support the assumption that 12-h urine collected at night can be used as a reliable tool to estimate 24-h intake/excretion of sodium and potassium.

Declining stroke and myocardial infarction mortality between 1989 and 2010 in a country of the african region

BACKGROUND AND PURPOSE

In low- and middle-income countries, the total burden of cardiovascular diseases is expected to increase due to demographic and epidemiological transitions. However, data on cause-specific mortality are lacking in sub-Saharan Africa. Seychelles is one of the few countries in the region where all deaths are registered and medically certified. In this study, we examine trends in mortality for stroke and myocardial infarction (MI) between 1989 and 2010.

METHODS

Based on vital statistics, we ascertained stroke and MI as the cause of death if appearing in any of the 4 fields for immediate, intermediate, underlying, and contributory causes in death certificates.

RESULTS

Mortality rates (per 100 000, age-standardized to World Health Organization standard population) decreased from 1669/710 (men/women) in 1989 to 1991 to 1113/535 in 2008-10 for all causes, from 250/140 to 141/86 for stroke, and from 117/51 to 59/24 for MI, corresponding to proportionate decreases of 33%/25% for all-cause mortality, 44%/39% for stroke, and 50%/53% for MI over 22 years. The absolute number of stroke and MI deaths did not increase over time. In 2008 to 2010, the median age of death was 65/78 years (men/women) for all causes, 68/78 for stroke, and 66/73 for MI.

CONCLUSIONS

Between 1989 and 2010, age-standardized stroke and MI mortality decreased markedly and more rapidly than all-cause mortality. The absolute number of cardiovascular disease deaths did not increase over time because the impact of population aging was fully compensated by the decline in cardiovascular disease mortality. Stroke mortality remained high, emphasizing the need to strengthen cardiovascular disease prevention and control.

Role of the renal circadian timing system in maintaining water and electrolytes homeostasis

Many basic physiological functions exhibit circadian rhythmicity. These functional rhythms are driven, in part, by the circadian clock, an ubiquitous molecular mechanism allowing cells and tissues to anticipate regular environmental events and to prepare for them. This mechanism has been shown to play a particularly important role in maintaining stability (homeostasis) of internal conditions. Because the homeostatic equilibrium is continuously challenged by environmental changes, the role of the circadian clock is thought to consist in the anticipative adjustment of homeostatic pathways in relation with the 24h environmental cycle. The kidney is the principal organ responsible for the regulation of the composition and volume of extracellular fluids (ECF). Several major parameters of kidney function, including renal plasma flow (RPF), glomerular filtration rate (GFR) and tubular reabsorption and secretion have been shown to exhibit strong circadian oscillations. Recent evidence suggest that the circadian clock can be involved in generation of these rhythms through external circadian time cues (e.g. humoral factors, activity and body temperature rhythms) or, trough the intrinsic renal circadian clock. Here, we discuss the role of renal circadian mechanisms in maintaining homeostasis of water and three major ions, namely, Na(+), K(+) and Cl(-).

Blood glucose and nocturnal blood pressure in African and Caucasian men: The SABPA study

AIM

To investigate the relationship between nocturnal blood pressure and chronically elevated blood glucose to determine if these elevated blood glucose concentrations contribute to a non-dipping blood pressure, especially in high-risk groups such as Africans.

METHODS

Nocturnal blood pressures and blood glucose levels of 41 non-dipping African and 28 non-dipping Caucasian men were investigated. Ambulatory systolic (SBP) and diastolic blood pressure (DBP) were measured and blood collected in sodium fluoride tubes from the antebrachial vein to determine serum glucose and glycosylated hemoglobin A1c (HbA1c) percentage. The estimated average glucose (eAG) was determined from HbA1c percentage with a regression formula.

RESULTS

The African non-dippers had higher blood pressures (p<0.001) and elevated HbA1c (p=0.037) and eAG (p=0.041) levels compared to the Caucasians. In single, partial and multiple regression analyses nighttime (00:00-04:00) SBP correlated positively with HbA1c (p=0.069) and eAG (p<0.001) in the African men. No correlations were found in the Caucasian men. Sensitivity analysis confirmed that the association between nighttime SBP (00:00-04:00) and eAG was independent of carotid intima-media thickness in the African men (R(2)=0.617; β=0.438; p=0.008).

CONCLUSION

The blunted nocturnal decline in SBP during the early morning hours is associated with chronically elevated blood glucose in non-dipper African men.

Short-term reproducibility of ambulatory blood pressure monitoring in autosomal dominant polycystic kidney disease

BACKGROUND AND OBJECTIVES

Nondipping, defined as a less than 10% decline in Night:Day (N:D) ratio of blood pressure using 24 h ambulatory blood pressure monitoring, is associated with poor cardiovascular outcomes. However, its reproducibility has been questioned in autosomal dominant polycystic kidney disease.

MATERIALS AND METHODS

Twenty-five of 29 recruited hypertensive or prehypertensive patients with autosomal dominant polycystic kidney disease completed ambulatory blood pressure monitoring on two occasions, 7-15 days apart, on a stable antihypertensive regimen. Daytime and night-time were defined as 6:00-21:59 h and 22:00-5:59 h, respectively. Correlation and concordance coefficients for systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate were determined based on N:D and Asleep:Awake (A:A) ratios. Consistency of dipping was assessed by using Cohen's Kappa statistics.

RESULTS

Mean (±standard deviation) for age, estimated glomerular filtration rate, differences in daytime and night-time SBP and DBP were 43.12 years (8.55 years), 63.1 ml/min (20.5 ml/min), 11.74 mmHg (8.2 mmHg), and 10.82 mmHg (6.4 mmHg), respectively. Seventeen of 25 (68%) and 18 of 25 (72%) participants maintained the same dipping category based on D:N or A:A separation. Cohen's Kappa was 0.34 for D:N ratio and 0.38 for A:A ratio. Correlation and concordance coefficients were 0.89 and 0.88 for daytime SBP, 0.91 and 0.91 for daytime DBP, 0.79 and 0.78 for night-time SBP, 0.81 and 0.80 for night-time DBP, 0.58 and 0.56 for N:D ratio of SBP, and 0.56 and 0.53 for N:D ratio of DBP. Coefficients for A:A ratio were almost identical to N:D values except for A:A ratios of SBP (0.69 and 0.67) and DBP (0.48 and 0.45).

CONCLUSION

Repeated measures of SBP and DBP, 7-15 days apart, are highly correlative and concordant in the studied population, but nondipping, even though predominant, was found to be modestly reproducible.

Circadian rhythms in urinary functions: possible roles of circadian clocks?

Circadian clocks are the endogenous oscillators that harmonize a variety of physiological processes within the body. Although many urinary functions exhibit clear daily or circadian variation in diurnal humans and nocturnal rodents, the precise mechanisms of these variations are as yet unclear. In this review, we briefly introduce circadian clocks and their organization in mammals. We then summarize known daily or circadian variations in urinary function. Importantly, recent findings by others as well as results obtained by us suggest an active role of circadian clock genes in various urinary functions. Finally, we discuss possible research avenues for the circadian control of urinary function.

Circadian rhythms and cardiovascular health

The functional organization of the cardiovascular system shows clear circadian rhythmicity. These and other circadian rhythms at all levels of organization are orchestrated by a central biological clock, the suprachiasmatic nuclei of the hypothalamus. Preservation of the normal circadian time structure from the level of the cardiomyocyte to the organ system appears to be essential for cardiovascular health and cardiovascular disease prevention. Myocardial ischemia, acute myocardial infarct, and sudden cardiac death are much greater in incidence than expected in the morning. Moreover, supraventricular and ventricular cardiac arrhythmias of various types show specific day-night patterns, with atrial arrhythmias--premature beats, tachycardias, atrial fibrillation, and flutter - generally being of higher frequency during the day than night--and ventricular fibrillation and ventricular premature beats more common, respectively, in the morning and during the daytime activity than sleep span. Furthermore, different circadian patterns of blood pressure are found in arterial hypertension, in relation to different cardiovascular morbidity and mortality risk. Such temporal patterns result from circadian periodicity in pathophysiological mechanisms that give rise to predictable-in-time differences in susceptibility-resistance to cyclic environmental stressors that trigger these clinical events. Circadian rhythms also may affect the pharmacokinetics and pharmacodynamics of cardiovascular and other medications. Knowledge of 24-h patterns in the risk of cardiac arrhythmias and cardiovascular disease morbidity and mortality plus circadian rhythm-dependencies of underlying pathophysiologic mechanisms suggests the requirement for preventive and therapeutic interventions is not the same throughout the day and night, and should be tailored accordingly to improve outcomes.

Prognostic value of isolated nocturnal hypertension on ambulatory measurement in 8711 individuals from 10 populations

BACKGROUND

We and other investigators previously reported that isolated nocturnal hypertension on ambulatory measurement (INH) clustered with cardiovascular risk factors and was associated with intermediate target organ damage. We investigated whether INH might also predict hard cardiovascular endpoints.

METHODS AND RESULTS

We monitored blood pressure (BP) throughout the day and followed health outcomes in 8711 individuals randomly recruited from 10 populations (mean age 54.8 years, 47.0% women). Of these, 577 untreated individuals had INH (daytime BP <135/85 mmHg and night-time BP ≥120/70 mmHg) and 994 untreated individuals had isolated daytime hypertension on ambulatory measurement (IDH; daytime BP ≥135/85 mmHg and night-time BP <120/70 mmHg). During follow-up (median 10.7 years), 1284 deaths (501 cardiovascular) occurred and 1109 participants experienced a fatal or nonfatal cardiovascular event. In multivariable-adjusted analyses, compared with normotension (n = 3837), INH was associated with a higher risk of total mortality (hazard ratio 1.29, P = 0.045) and all cardiovascular events (hazard ratio 1.38, P = 0.037). IDH was associated with increases in all cardiovascular events (hazard ratio 1.46, P = 0.0019) and cardiac endpoints (hazard ratio 1.53, P = 0.0061). Of 577 patients with INH, 457 were normotensive (<140/90 mmHg) on office BP measurement. Hazard ratios associated with INH with additional adjustment for office BP were 1.31 (P = 0.039) and 1.38 (P = 0.044) for total mortality and all cardiovascular events, respectively. After exclusion of patients with office hypertension, these hazard ratios were 1.17 (P = 0.31) and 1.48 (P = 0.034).

CONCLUSION

INH predicts cardiovascular outcome in patients who are normotensive on office or on ambulatory daytime BP measurement.

Comparison of the efficacy and safety of single-pill fixed-dose combinations of losartan/hydrochlorothiazide and valsartan/hydrochlorothiazide in patients with hypertension (SALT-VAT study)

OBJECTIVE

We analyzed the efficacy and safety of Preminent(®) [losartan (50 mg/day)/HCTZ (12.5 mg/day)] compared to CodioMD(®) [valsartan (80 mg/day)/HCTZ (6.25 mg/day)].

METHODS

In this study, 31 hypertensive patients after receiving 3 months of Preminent(®) (Stage A) were enrolled. We applied a changeover with switching from Preminent(®) to CodioMD(®) (Stage B). We then applied another changeover with switching from CodioMD(®) to Preminent(®) after 3 months (Stage C).

RESULTS

Average values of 24-h blood pressure (BP), daytime BP and nighttime BP using ambulatory BP monitoring (ABPM) significantly increased from Stage A to B [4/3 mmHg, 5/3 mmHg and 3/3 mmHg, respectively]. Average values of 24-h BP, morning BP, daytime BP, nighttime BP significantly decreased from the end of Stage B to C [-5/-5 mmHg, -4/-6 mmHg, -5/-5 mmHg and -6/-4 mmHg, respectively]. Interestingly, the serum levels of uric acid and the urinary albumin/creatinine ratio showed a significant increase after the change to CodioMD(®). Since these adverse effects did not disappear after the return to Preminent(®) at the end of Stage C, we performed an additional 3-month follow-up (extended stage). These adverse effects finally disappeared at the end of this extended stage.

CONCLUSION

Single-pill fixed-dose combination therapy using Preminent(®) showed significant 24-h BP-lowering effects and was safe when compared with CodioMD(®).

Vasopressin V2 receptors, ENaC, and sodium reabsorption: a risk factor for hypertension?

Excessive sodium reabsorption by the kidney has long been known to participate in the pathogenesis of some forms of hypertension. In the kidney, the final control of NaCl reabsorption takes place in the distal nephron through the amiloride-sensitive epithelial sodium channel (ENaC). Liddle's syndrome, an inherited form of hypertension due to gain-of-function mutations in the genes coding for ENaC subunits, has demonstrated the key role of this channel in the sodium balance. Although aldosterone is classically thought to be the main hormone regulating ENaC activity, several studies in animal models and in humans highlight the important effect of vasopressin on ENaC regulation and sodium transport. This review summarizes the effect of vasopressin V2 receptor stimulation on ENaC activity and sodium excretion in vivo. Moreover, we report the experimental and clinical data demonstrating the role of renal ENaC in water conservation at the expense of a reduced ability to excrete sodium. Acute administration of the selective V2 receptor agonist dDAVP not only increases urine osmolality and reduces urine flow rate but also reduces sodium excretion in rats and humans. Chronic V2 receptor stimulation increases blood pressure in rats, and a significant correlation was found between blood pressure and urine concentration in healthy humans. This led us to discuss how excessive vasopressin-dependent ENaC stimulation could be a risk factor for sodium retention and resulting increase in blood pressure.

Circadian regulation of renal function

Urinary excretion of water and all major electrolytes exhibit robust circadian oscillations. The 24-h periodicity has been well documented for several important determinants of urine formation, including renal blood flow, glomerular filtration, tubular reabsorption, and tubular secretion. Disturbance of the renal circadian rhythms is increasingly recognized as a risk factor for hypertension, polyuria, and other diseases and may contribute to renal fibrosis. The origin of these rhythms has been attributed to the reactive response of the kidney to circadian changes in volume and/or in the composition of extracellular fluids that are entrained by rest/activity and feeding/fasting cycles. However, numerous studies have shown that most of the renal excretory rhythms persist for long periods of time, even in the absence of periodic environmental cues. These observations led to the hypothesis of the existence of a self-sustained mechanism, enabling the kidney to anticipate various predictable circadian challenges to homeostasis. The molecular basis of this mechanism remained unknown until the recent discovery of the mammalian circadian clock made of a system of autoregulatory transcriptional/translational feedback loops, which have been found in all tissues studied, including the kidney. Here, we present a review of the growing evidence showing the involvement of the molecular clock in the generation of renal excretory rhythms.

Genetic influences on daytime and night-time blood pressure: similarities and differences

OBJECTIVE

To examine whether the genetic influences on blood pressure (BP) during night-time are different from those during daytime and the extent to which they depend on ethnicity or sex.

METHODS

Ambulatory BP was measured in 240 European-American and 190 African-American twins (mean +/- SD age, 17.2 +/- 3.4). Individuals with night-time BP falls more than 10% of the daytime values were defined as dippers. A bivariate analysis of the daytime and the night-time BP levels, as well as a liability-threshold model of dippers vs. nondippers were used.

RESULTS

Bivariate model fitting showed no ethnic or sex differences for any of the measures, with heritabilities of 0.70 and 0.68 for SBP and 0.70 and 0.64 for DBP at daytime and at night-time. The genetic influences on daytime and night-time were not significantly different for SBP or DBP. The bivariate analysis also indicated that about 56 and 33% of the heritabilities of night-time SBP and DBP could be attributed to genes that also influenced daytime levels. The specific heritabilities due to genetic effects only influencing night-time values were 0.30 for SBP and 0.43 for DBP. The heritabilities of systolic and diastolic dipping were 0.59 and 0.81, respectively.

CONCLUSION

Independent of ethnicity and sex, an overlap exists between genes that influence daytime and night-time BP, as well as a significant genetic component that is specific to the night-time BP. These findings suggest that different genes or sets of genes contribute to BP regulation at daytime and night-time.

Do restless legs syndrome (RLS) and periodic limb movements of sleep (PLMS) play a role in nocturnal hypertension and increased cardiovascular risk of renally impaired patients?

Hypertension can cause or promote renal failure and is related to cardiovascular mortality, the major cause of death in patients with renal impairment. Changes in the circadian BP pattern, particularly the blunting or reversal of the nocturnal decline in BP, are common in chronic renal failure. These changes in turn are among the major determinants of left ventricular hypertrophy. Using a chronobiological approach, it is possible to obtain better insight into the reciprocal relationship between hypertension, renal disease, and increased cardiovascular risk of renal patients. Disruption of the normal circadian rhythm of rest/activity may be hypothesized to underlie the high cardiovascular morbidity and mortality of such patients. Epidemiological studies reveal that hemodialysis patients experience poor subjective sleep quality and insomnia and, in comparison to healthy persons, are more likely to show shorter sleep duration and lower sleep efficiency. Sleep apnea may be present and is usually investigated in these patients; however, the prevalence of restless legs syndrome (RLS), which is high in dialysis patients and which has been associated with increased risk for cardiovascular disease in the general population, could also play a role in the pathogenesis of sleep-time hypertension in renal patients. Careful assessment of sleep quality, in particular, diagnostic screening for RLS and periodic limb movements (PLM) in renal patients, is highly recommended. In renal failure, attention to sleep quality and related perturbations of the sleep/wake cycle may help prevent the occurrence and progression of cardiovascular disease.

Nocturnal dosing and chronic kidney disease progression: new insights

PURPOSE OF REVIEW

Several studies have identified the presence of altered diurnal blood pressure patterns, specifically elevated nighttime blood pressure in patients with chronic kidney disease. The lack of nocturnal decline in blood pressure is associated with markers of hypertensive target organ damage and predictive of long-term clinical outcomes. The purpose of this review is to summarize the literature in this area and explore the potential for use of nighttime blood pressure for improving risk stratification and as a therapeutic target.

RECENT FINDINGS

The mechanisms of persistent elevation of blood pressure at night in chronic kidney disease are likely to be multifactorial, including altered sodium handling and sympathetic activation among others. Elevated nocturnal blood pressures have been shown to be associated with increased adverse clinical outcomes. Recent studies demonstrate that it is feasible to lower nocturnal blood pressure by modifying the time of administration of antihypertensive medications.

SUMMARY

Currently, clinical blood pressure measurements are assessed and targeted for drug therapy. This article shows the importance of measuring ambulatory blood pressures, specifically nocturnal blood pressures to improve risk stratification. More research needs to be done to identify interventions that lower nighttime blood pressure, and test their efficacy in improving clinical outcomes.

Association between white-coat effect and blunted dipping of nocturnal blood pressure

BACKGROUND

In this study, we assessed whether the white-coat effect (difference between office and daytime blood pressure (BP)) is associated with nondipping (absence of BP decrease at night).

METHODS

Data were available in 371 individuals of African descent from 74 families selected from a population-based hypertension register in the Seychelles Islands and in 295 Caucasian individuals randomly selected from a population-based study in Switzerland. We used standard multiple linear regression in the Swiss data and generalized estimating equations to account for familial correlations in the Seychelles data.

RESULTS

The prevalence of systolic and diastolic nondipping (<10% nocturnal BP decrease) and white-coat hypertension (WCH) was respectively 51, 46, and 4% in blacks and 33, 37, and 7% in whites. When white coat effect and nocturnal dipping were taken as continuous variables (mm Hg), systolic (SBP) and diastolic BP (DBP) dipping were associated inversely and independently with white-coat effect (P < 0.05) in both populations. Analogously, the difference between office and daytime heart rate was inversely associated with the difference between daytime and night-time heart rate in the two populations. These results did not change after adjustment for potential confounders.

CONCLUSIONS

The white-coat effect is associated with BP nondipping. The similar associations between office-daytime values and daytime-night-time values for both BP and heart rate suggest that the sympathetic nervous system might play a role. Our findings also further stress the interest, for clinicians, of assessing the presence of a white-coat effect as a means to further identify patients at increased cardiovascular risk and guide treatment accordingly.

Molecular clock is involved in predictive circadian adjustment of renal function

Renal excretion of water and major electrolytes exhibits a significant circadian rhythm. This functional periodicity is believed to result, at least in part, from circadian changes in secretion/reabsorption capacities of the distal nephron and collecting ducts. Here, we studied the molecular mechanisms underlying circadian rhythms in the distal nephron segments, i.e., distal convoluted tubule (DCT) and connecting tubule (CNT) and the cortical collecting duct (CCD). Temporal expression analysis performed on microdissected mouse DCT/CNT or CCD revealed a marked circadian rhythmicity in the expression of a large number of genes crucially involved in various homeostatic functions of the kidney. This analysis also revealed that both DCT/CNT and CCD possess an intrinsic circadian timing system characterized by robust oscillations in the expression of circadian core clock genes (clock, bma11, npas2, per, cry, nr1d1) and clock-controlled Par bZip transcriptional factors dbp, hlf, and tef. The clock knockout mice or mice devoid of dbp/hlf/tef (triple knockout) exhibit significant changes in renal expression of several key regulators of water or sodium balance (vasopressin V2 receptor, aquaporin-2, aquaporin-4, alphaENaC). Functionally, the loss of clock leads to a complex phenotype characterized by partial diabetes insipidus, dysregulation of sodium excretion rhythms, and a significant decrease in blood pressure. Collectively, this study uncovers a major role of molecular clock in renal function.

Can nocturnal hypertension predict cardiovascular risk?

Nocturnal hypertension and non-dipping of blood pressure during sleep are distinct entities that often occur together and are regarded as important harbingers of poor cardiovascular prognosis. This review addresses several aspects related to these blood pressure abnormalities including definitions, diagnostic limitations, pathogenesis and associated patient profiles, prognostic significance, and therapeutic strategies. Taken together, persistent nocturnal hypertension and non-dipping blood pressure pattern, perhaps secondary to abnormal renal sodium handling and/or altered nocturnal sympathovagal balance, are strongly associated with deaths, cardiovascular events, and progressive loss of renal function, independent of daytime and 24-hour blood pressure. Several pharmacological and non-pharmacological approaches may restore nocturnal blood pressure and circadian blood pressure rhythm to normal; however, whether this translates to a clinically meaningful reduction in unfavorable cardiovascular and renal consequences remains to be seen.

Disparate estimates of hypertension control from ambulatory and clinic blood pressure measurements in hypertensive kidney disease

Ambulatory blood pressure (ABP) monitoring provides unique information about day-night patterns of blood pressure (BP). The objectives of this article were to describe ABP patterns in African Americans with hypertensive kidney disease, to examine the joint distribution of clinic BP and ABP, and to determine associations of hypertensive target organ damage with clinic BP and ABP. This study is a cross-sectional analysis of baseline data from the African American Study of Kidney Disease Cohort Study. Masked hypertension was defined by elevated daytime (>or= 135/85 mm Hg) or elevated nighttime (>or= 120/70 mm Hg) ABP in those with controlled clinic BP (<140/90 mm Hg); nondipping was defined by a Collapse

Key Words Collapse

MESH Headings

• Adolescent
• Adult
• Black or African American/ethnology
• Aged
• Ambulatory Care Facilities
• Blood Pressure/physiology
• Blood Pressure Monitoring, Ambulatory
• Circadian Rhythm/physiology
• Cohort Studies
• Cross-Sectional Studies
• Female
• Humans
• Hypertension, Renal/ethnology
• Hypertension, Renal/physiopathology
• Kidney/physiopathology
• Kidney Diseases/ethnology
• Kidney Diseases/physiopathology
• Male
• Middle Aged
• Prevalence
• Reproducibility of Results
• Severity of Illness Index
• Young Adult

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Grants

• P20-RR11145 NCRR NIH HHS
• M01 RR00827 NCRR NIH HHS
• 5M01 RR-00071 NCRR NIH HHS
• 2P20 RR11104 NCRR NIH HHS

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Affiliation(s)

Velvie Pogue Division of Nephrology, Department of Medicine, Columbia University Medical Center, Harlem Hospital Center, New York, NY 10037, USA.
Mahboob Rahman
Michael Lipkowitz
Robert Toto
Edgar Miller
Marquetta Faulkner
Stephen Rostand
Leena Hiremath
Mohammed Sika
Cynthia Kendrick
Bo Hu
Tom Greene
Lawrence Appel
Robert A Phillips

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Patients with renal dysfunction require a longer duration until blood pressure dips during the night

We have postulated that the diminished renal capacity to excrete sodium causes nocturnal blood pressure (BP) elevation, which enhances pressure natriuresis in compensation for impaired daytime natriuresis. If such a mechanism holds, high BP during sleep at night may continue until excess sodium is sufficiently excreted into urine. This study examined whether the duration, defined as "dipping time," until nocturnal mean arterial pressure began to fall to <90% of daytime average became longer as renal function deteriorated. Ambulatory BP measurements and urinary sodium excretion rates were evaluated for daytime and nighttime to estimate their circadian rhythms in 65 subjects with chronic kidney disease. Dipping time showed an inverse relationship with creatinine clearance (C(cr); rho=-0.61; P<0.0001) and positive relationships with night/day ratios of mean arterial pressure (rho=0.84; P<0.0001) and natriuresis (rho=0.61; P<0.0001), both of which were also inversely correlated with C(cr) (mean arterial pressure: r=-0.58, P<0.0001; natriuresis: r=-0.69, P<0.0001). When divided into tertiles by C(cr) (mL/min), hazard ratios of nocturnal BP dip adjusted for age, gender, and body mass index were 0.37 (95% CI: 0.17 to 0.79; P=0.01) for the second tertile (C(cr): 50 to 90) and 0.20 (95% CI: 0.08 to 0.55; P=0.002) for the third tertile (C(cr): 5 to 41) compared with the first tertile (C(cr): 91 to 164). These findings demonstrate that patients with renal dysfunction require a longer duration until BP falls during the night. The prolonged duration until BP dip during sleep seems an essential component of the nondipper pattern of the circadian BP rhythm.