Endocrine mechanisms of blood pressure rhythms

Effect of Acute Melatonin Injection on Metabolomic and Testicular Artery Hemodynamic Changes and Circulating Hormones in Shiba Goats under Sub-Tropical Environmental Conditions

The beneficial effects of melatonin were investigated to mitigate various detrimental effects and toxicity on reproductive performance. The present study aimed, for the first time, to explore the effect of intravenous melatonin injection on testicular artery hemodynamics (TH) and metabolomic changes, reproductive hormones in heat-stressed bucks. Ten bucks were randomly split into two groups (five each): (1) the melatonin group, treated with a single intravenous dose of melatonin solution containing 10 mg melatonin each, and (2) the control group, which was treated with 10 mL of the vehicle without melatonin. Changes in the TH at the level of the supra testicular artery (STA) were assessed by triplex ultrasonography just before (0 h) and at 0.5, 2, 7, 24, and 168 h after melatonin or vehicle administration. Doppler velocity parameters of peak systolic velocity (PSV; cm/s), end-diastolic velocity (EDV; cm/s), and time average maximum velocity (TAMAX; cm/s) were measured. Doppler indices (resistive index; RI and pulsatility index; PI), systole/diastole (S/D) ratio and total arterial blood flow volume (TABFV; ml/minute) were measured. Peripheral concentrations of FSH, LH, inhibin, melatonin, testosterone (T), estradiol (E2), and cortisol were measured just before injection (0 h) and at 0.5, 2, 7, and 24 h and daily up to day 7 post administration in both groups. Results revealed reductions in the RI values and increases in the TABFV in the melatonin group compared to the control one, especially 2 h after administration. Significant increases in concentrations of FSH, T, E2, and melatonin and decreases in cortisol and inhibin in the melatonin group compared to the control one. Plasma metabolomic analysis at 2 h indicated the up-regulation of L-glutamine, L-arginine, sorbitol, D-glucose, ascorbic acid, and ornithine and the down-regulation of D-xylose, D-arabitol, ribitol, and oleic acid in the melatonin versus the control group. In conclusion, acute administration of melatonin (10 mg IV) enhanced testicular artery blood flow and plasma reproductive hormones in the Shiba goat under heat-stress circumstances.

Changes in Circadian Variations in Blood Pressure, Pain Pressure Threshold and the Elasticity of Tissue after a Whole-Body Photobiomodulation Treatment in Patients with Fibromyalgia: A Tripled-Blinded Randomized Clinical Trial

This study analysed circadian variation changes in blood pressure (BP), the pain pressure threshold (PPT) and the elasticity of tissue in patients with fibromyalgia (FM) after a whole-body photobiomodulation (PBM) treatment. This was a tripled-blinded randomized clinical trial including forty participants with FM. Participants using validated self-measurement BP devices attained readings that were used to calculate the circadian variation. Additionally, a standard pressure algometer of 1cm2 was used to assess 13 tender points by exerting a pressure of up to 4 kg, and strain elastography assessed the elasticity of tissue. Circadian variations in BP showed significant differences after the PBM intervention (p = 0.036). When comparing PPT between groups, statistically significant differences were found in the occiput (p = 0.039), low cervical (p = 0.035), trapezius (p = 0.037), second rib (p < 0.001) and medial epicondyle points (p = 0.006). Furthermore, there were statistically significant differences in both the trapezius and the forearm at the distal dorsal third SEL values (p ≤ 0.001) when comparing groups. Whole-body PBM produces changes in circadian blood pressure, the pain pressure threshold and the elasticity of tissue after a treatment program was carried out. However, more studies are needed to corroborate our findings as well as to better understand the underlying mechanisms.

Effects of altered photoperiod due to COVID-19 lockdown on pregnant women and their fetuses

Maternal circadian rhythms provide highly important input into the entrainment and programming of fetal and newborn circadian rhythms. The light-dark cycle is an important regulator of the internal biological clock. Even though pregnant women spend a greater part of the day at home during the latter stages of pregnancy, natural light exposure is crucial for the fetus. The current recommended COVID-19 lockdown might dramatically alter normal environmental lighting conditions of pregnant women, resulting in exposure to extremely low levels of natural daylight and high-intensity artificial light sources during both day and night. This article summarizes the potential effects on pregnant woman and their fetuses due to prolonged exposure to altered photoperiod and as consequence altered circadian system, known as chronodisruption, that may result from the COVID-19 lockdown.

Prevalence of Poor Sleep Quality in Patients With Hypertension in China: A Meta-analysis of Comparative Studies and Epidemiological Surveys

OBJECTIVE

This meta-analysis examined the prevalence of poor sleep quality and its associated factors in patients with hypertension in China.

METHODS

Both English (PubMed, PsycINFO, EMBASE) and Chinese (Wan Fang Database and Chinese National Knowledge Infrastructure) databases were systematically and independently searched. The random-effects model was used to estimate the prevalence of poor sleep quality in Chinese patients with hypertension. The funnel plot and Egger's tests were used to assess publication bias.

RESULTS

The prevalence of poor sleep quality in 24 studies with 13,920 hypertensive patients was 52.5% (95% confidence interval [CI]: 46.1-58.9%). In contrast, the prevalence of poor sleep quality in six studies with 5,610 healthy control subjects was 32.5% (95% CI: 19.0-49.7%). In these studies, compared to healthy controls, the pooled odds ratio (OR) of poor sleep quality was 2.66 (95% CI: 1.80-3.93) for hypertensive patients. Subgroup and meta-regression analyses revealed that patients in hospitals were more likely to have poor sleep quality than patients in the community. Studies with smaller sample size, studies using convenience or consecutive sampling and those published in Chinese reported higher prevalence of poor sleep quality. Furthermore, poor sleep quality was more common in older and male hypertensive patients, while the proportion of poor sleep quality was negatively associated with survey year.

CONCLUSION

Appropriate strategies for screening, prevention, and treatment of poor sleep quality in this population should be developed.

A functional supervised learning approach to the study of blood pressure data

In this work, a functional supervised learning scheme is proposed for the classification of subjects into normotensive and hypertensive groups, using solely the 24-hour blood pressure data, relying on the concepts of Fréchet mean and Fréchet variance for appropriate deformable functional models for the blood pressure data. The schemes are trained on real clinical data, and their performance was assessed and found to be very satisfactory.

Wake-up stroke-Amendable for thrombolysis-like stroke with known onset time?

Patients suffering an acute ischemic stroke can be treated with intravenous thrombolysis in the absence of contraindications. A known onset time is a prerequisite as treatment, according to guidelines, has to be started within 4.5 hours. In patients awakening with a stroke, the last time they were seen without a neurological deficit is assumed to be the time of onset. Thus, despite of lack of contraindications on initial brain imaging, these patients are largely excluded from therapy. This review discusses the underlying pathophysiological, clinical, and radiological evidence surrounding wake-up stroke and its consequences for making treatment decisions.

Circadian behavior of adult mice exposed to stress and fluoxetine during development

INTRODUCTION

Women of child-bearing age are the population at greatest risk for depression. The stress experienced during pregnancy and the associated antidepressant treatments can both affect fetal development. Fluoxetine (FLX) is among the most common antidepressants used by pregnant women. We have previously demonstrated that perinatal exposure to FLX can alter expression of circadian rhythms in adulthood. Here, we examine the combined effects of maternal stress during pregnancy and perinatal exposure to the antidepressant FLX on the circadian behavior of mice as adults.

METHODS

Mouse dams were exposed to chronic unpredictable stress (embryonic (E) day 7 to E18), FLX (E15 to postnatal day 12), a combination of both stress and FLX, or were left untreated. At 2 months of age, male offspring were placed in recording chambers and circadian organization of wheel running rhythms and phase shifts to photic and non-photic stimuli were assessed.

RESULTS

Mice exposed to prenatal stress (PS) had smaller light-induced phase delays. Mice exposed to perinatal FLX required more days to re-entrainment to an 8-h phase advance of their light-dark cycle. Mice subjected to either perinatal FLX or to PS had larger light-induced phase advances and smaller phase advances to 8-OH-DPAT. FLX treatment partially reversed the effect of PS on phase shifts to late-night light exposure and to 8-OH-DPAT.

CONCLUSIONS

Our results suggest that, in mice, perinatal exposure to either FLX, or PS, or their combination, leads to discernible, persistent changes in their circadian systems as adults.

Circadian disruption: New clinical perspective of disease pathology and basis for chronotherapeutic intervention

Biological processes are organized in time as innate rhythms defined by the period (τ), phase (peak [Φ] and trough time), amplitude (A, peak-trough difference) and mean level. The human time structure in its entirety is comprised of ultradian (τ < 20 h), circadian (20 h > τ < 28 h) and infradian (τ > 28 h) bioperiodicities. The circadian time structure (CTS) of human beings, which is more complicated than in lower animals, is orchestrated and staged by a brain central multioscillator system that includes a prominent pacemaker - the suprachiasmatic nuclei of the hypothalamus. Additional pacemaker activities are provided by the pineal hormone melatonin, which circulates during the nighttime, and the left and right cerebral cortices. Under ordinary circumstances this system coordinates the τ and Φ of rhythms driven by subservient peripheral cell, tissue and organ clock networks. Cyclic environmental, feeding and social time cues synchronize the endogenous 24 h clocks and rhythms. Accordingly, processes and functions of the internal environment are integrated in time for maximum biological efficiency, and they are also organized and synchronized in time to the external environment to ensure optimal performance and response to challenge. Artificial light at night (ALAN) exposure can alter the CTS as can night work, which, like rapid transmeridian displacement by air travel, necessitates realignment of the Φ of the multitude of 24 h rhythms. In 2001, Stevens and Rea coined the phrase "circadian disruption" (CD) to label the CTS misalignment induced by ALAN and shift work (SW) as a potential pathologic mechanism of the increased risk for cancer and other medical conditions. Current concerns relating to the effects of ALAN exposure on the CTS motivated us to renew our long-standing interest in the possible role of CD in the etiopathology of common human diseases and patient care. A surprisingly large number of medical conditions involve CD: adrenal insufficiency; nocturia; sleep-time non-dipping and rising blood pressure 24 h patterns (nocturnal hypertension); delayed sleep phase syndrome, non-24 h sleep/wake disorder; recurrent hypersomnia; SW intolerance; delirium; peptic ulcer disease; kidney failure; depression; mania; bipolar disorder; Parkinson's disease; Smith-Magenis syndrome; fatal familial insomnia syndrome; autism spectrum disorder; asthma; byssinosis; cancers; hand, foot and mouth disease; post-operative state; and ICU outcome. Poorly conceived medical interventions, for example nighttime dosing of synthetic corticosteroids and certain β-antagonists and cyclic nocturnal enteral or parenteral nutrition, plus lifestyle habits, including atypical eating times and chronic alcohol consumption, also can be causal of CD. Just as surprisingly are the many proven chronotherapeutic strategies available today to manage the CD of several of these medical conditions. In clinical medicine, CD seems to be a common, yet mostly unrecognized, pathologic mechanism of human disease as are the many effective chronotherapeutic interventions to remedy it.

Intra-day variability of cystatin C, creatinine and estimated GFR in intensive care patients

BACKGROUND

Markers of renal function are widely used in intensive care and sudden changes are important indicators of acute kidney injury. The problem is to distinguish between disease progression/improvement from the natural variation in the patient. The aim of the present study was thus to study the normal intraday variation in ICU patients.

METHODS

We studied the intra-day variation of creatinine, cystatin C and estimated GFR based on these two markers in 28 clinically stable ICU patients.

RESULTS

The median diurnal coefficient of variation sCV) for creatinine was 3.70% (1.92-9.25%) while the median CV for cystatin C was 3.66% (1.36-8.11%). The corresponding CVs for the estimated GFRs were 2.00% (0.89-9.82%) for eGFRcreatinine and 4.60% (1.65-10.24%) for eGFRcystc.

CONCLUSIONS

The eGFRcreatinine values in individual patients were clearly higher than the eGFRcystc values. The median CV for creatinine, cystatin C and the eGFR measurements were below 5% which means that 95% of the test results will vary by <10% between sampling times in stable ICU patients. Differences >10% between sampling times are thus likely to be an indication of changes in biomarker levels due to the disease/treatment.

Chronotherapy with conventional blood pressure medications improves management of hypertension and reduces cardiovascular and stroke risks

Correlation between blood pressure (BP) and target organ damage, vascular risk and long-term patient prognosis is greater for measurements derived from around-the-clock ambulatory BP monitoring than in-clinic daytime ones. Numerous studies consistently substantiate the asleep BP mean is both an independent and a much better predictor of cardiovascular disease (CVD) risk than either the awake or 24 h means. Sleep-time hypertension is much more prevalent than suspected, not only in patients with sleep disorders, but also among those who are elderly or have type 2 diabetes, chronic kidney disease or resistant hypertension. Hence, cost-effective adequate control of sleep-time BP is of marked clinical relevance. Ingestion time, according to circadian rhythms, of hypertension medications of six different classes and their combinations significantly affects BP control, particularly sleep-time BP, and adverse effects. For example, because the high-amplitude circadian rhythm of the renin-angiotensin-aldosterone system activates during nighttime sleep, bedtime vs. morning ingestion of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers better reduces the asleep BP mean, with additional benefit, independent of medication terminal half-life, of converting the 24 h BP profile into more normal dipper patterning. The MAPEC (Monitorización Ambulatoria para Predicción de Eventos Cardiovasculares) study, first prospective randomized treatment-time investigation designed to test the worthiness of bedtime chronotherapy with ⩾1 conventional hypertension medications so as to specifically target attenuation of asleep BP, demonstrated, relative to conventional morning therapy, 61% reduction of total CVD events and 67% decrease of major CVD events, that is, CVD death, myocardial infarction, and ischemic and hemorrhagic stroke. The MAPEC study, along with other earlier conducted less refined trials, documents the asleep BP mean is the most significant prognostic marker of CVD morbidity and mortality; moreover, it substantiates attenuation of the asleep BP mean by a bedtime hypertension treatment strategy entailing the entire daily dose of ⩾1 hypertension medications significantly reduces CVD risk in both general and more vulnerable hypertensive patients, that is, those diagnosed with chronic kidney disease, diabetes and resistant hypertension.

Nocturnal light pollution and underexposure to daytime sunlight: Complementary mechanisms of circadian disruption and related diseases

Routine exposure to artificial light at night (ALAN) in work, home, and community settings is linked with increased risk of breast and prostate cancer (BC, PC) in normally sighted women and men, the hypothesized biological rhythm mechanisms being frequent nocturnal melatonin synthesis suppression, circadian time structure (CTS) desynchronization, and sleep/wake cycle disruption with sleep deprivation. ALAN-induced perturbation of the CTS melatonin synchronizer signal is communicated maternally at the very onset of life and after birth via breast or artificial formula feedings. Nighttime use of personal computers, mobile phones, electronic tablets, televisions, and the like--now epidemic in adolescents and adults and highly prevalent in pre-school and school-aged children--is a new source of ALAN. However, ALAN exposure occurs concomitantly with almost complete absence of daytime sunlight, whose blue-violet (446-484 nm λ) spectrum synchronizes the CTS and whose UV-B (290-315 nm λ) spectrum stimulates vitamin D synthesis. Under natural conditions and clear skies, day/night and annual cycles of UV-B irradiation drive corresponding periodicities in vitamin D synthesis and numerous bioprocesses regulated by active metabolites augment and strengthen the biological time structure. Vitamin D insufficiency and deficiency are widespread in children and adults in developed and developing countries as a consequence of inadequate sunlight exposure. Past epidemiologic studies have focused either on exposure to too little daytime UV-B or too much ALAN, respectively, on vitamin D deficiency/insufficiency or melatonin suppression in relation to risk of cancer and other, e.g., psychiatric, hypertensive, cardiac, and vascular, so-called, diseases of civilization. The observed elevated incidence of medical conditions the two are alleged to influence through many complementary bioprocesses of cells, tissues, and organs led us to examine effects of the totality of the artificial light environment in which humans reside today. Never have chronobiologic or epidemiologic investigations comprehensively researched the potentially deleterious consequences of the combination of suppressed vitamin D plus melatonin synthesis due to life in today's man-made artificial light environment, which in our opinion is long overdue.

Poor sleep quality associated with high risk of hypertension and elevated blood pressure in China: results from a large population-based study

Little information is available concerning the association between sleep quality and blood pressure (BP) in Chinese individuals. This study evaluated the association between sleep quality, as determined by the Pittsburgh sleep quality index (PSQI), and hypertension in a rural Chinese population. Using a multistage cluster and random sampling method, a representative sample of 9404 adults aged 20-93 years in northeastern China was selected from 2012 to 2013. Sleep quality was assessed by PSQI, and trained observers measured BP. A sleep disorder (SD) was diagnosed for any participant with a score of 6 or greater. Overall, 1218 male participants (25.53%) and 1261 female participants (27.22%) were defined as having SDs. Compared with the normal subjects, participants with hypertension had higher global PSQI scores and subscores in all elements. The odds ratios (ORs) of hypertension, systolic hypertension and diastolic hypertension among participants with SDs were 2.38 (95% confidence interval (CI): 2.13-2.65), 2.52 (95% CI: 2.26-2.80) and 1.93 (95% CI: 1.74-2.14) in contrast to the reference group, respectively. The risk for hypertension in poor sleepers with subscores over 0 in all of the elements was significantly increased, with ORs ranging from 1.16 (95% CI: 1.04-2.30) to 3.88 (95% CI: 1.24-12.16). The global PSQI score and its components were associated with hypertension and high BP.

Day-Night Variability of Hematoma Expansion in Patients with Spontaneous Intracerebral Hemorrhage

The levels of several coagulation factors, able to influence hemostatic balance, display circadian variations. We hypothesized that the onset and extent of hematoma expansion (HE) following intracerebral hemorrhage (ICH) also display diurnal patterns. We reviewed clinical, laboratory, and radiological data from 111 consecutive patients with spontaneous ICH who had baseline head computed tomography (CT) scans within 3 h of ICH onset and follow-up CT during the following 72 h. We defined any HE (AHE) as any increase in hematoma volume from baseline to follow-up CT and significant HE (SHE) as an absolute increase in hematoma volume >6 mL or relative increase >33%. We categorized the patients into 2 groups based on the timing of the initial CT scans—day group (from 0800 to 2000 h) and night group (from 2000 to 0800 h)—and performed logistic regression analyses. We also analyzed the differences in the rates of HE between the groups during six 4-h periods spanning 24 h, using χ2 tests. We found that the rates of AHE and SHE were higher in the day versus night group (75% vs. 48%; p = 0.009 for AHE and 47.6% vs. 25.9%; p = 0.047 for SHE). On multivariable logistic regression, day group assignment was independently associated with AHE (adjusted odds ratio = 3.53; p = 0.008) but not with SHE. Both AHE and SHE peaked in the early afternoon (1200-1600 h) and reached a nadir during the 2000 to 2400 h time period, and they were significantly different between the time periods (0000-0400, 0400-0800, 0800-1200, 1200-1600, 1600-2000, and 2000-2400 h); p = 0.002 and 0.029, respectively. These exploratory findings support the presence of a daily pattern in the occurrence of HE, with a higher risk during the day hours. Our results could have implications for future therapeutic efforts targeting HE in ICH and for the triage of ICH patients. They require further validation.

Relationship between self-reported sleep quality and metabolic syndrome in general population

BACKGROUND

To examine an association between self-reported sleep quality determined by Pittsburgh sleep quality index (PSQI) and metabolic syndrome.

METHODS

This study was designed as cross-sectional study. Participants were 1481 adults aged 20 years and above from general population (549 males and 932 females). We assessed the global sleep quality by PSQI. PSQI consists of 7 elements, i.e. subjective sleep quality, sleep latency (prolonged sleep onset time), sleep duration, habitual sleep efficiency (proportion of hours slept to hours spent in bed), sleep disturbance (interruption of sleep), use of sleep medication and daytime dysfunction (trouble staying awake while engaging in social activity). Any participants with score of 6 or more are diagnosed to have sleep disorder. We also assessed the above 7 elements, which consisted of a four-grade system (i.e. 0, 1, 2, 3). Metabolic syndrome consisted of abdominal obesity, hypertension, impaired glucose tolerance and dyslipidemia. Diagnosis of metabolic syndrome was done when the participants have abdominal obesity and meet two or more other components. All analyses were adjusted by age, drinking habit, smoking habit, working hours, exercise habit and depression.

RESULTS

Fifty-two male participants (9.5%) and 133 female (14.3%) scored 6 or more points in global PSQI score. The global PSQI score, sleep latency score and sleep disturbance score of participants with metabolic syndrome were higher level than those without the condition (p < 0.001, p = 0.009, p = 0.025 for male and p < 0.001, p < 0.001, p = 0.002 for females, respectively). The odds ratio of metabolic syndrome among participants with PSQI score of 6 or more points were 2.37 (95% confidence interval: 1.23-4.58) for males and 2.71 (1.45-5.07) for females in contrast to those with 5 or less points. The odds ratio of metabolic syndrome with sleep latency score of 2 was 2.65 (1.14-6.15) for male and 3.82 (1.81-8.09) for females in contrast with those of 0. The odds ratio of metabolic syndrome with sleep disturbance score of 1 was 1.76 (1.09-2.86) for males and 2.43 (1.26-4.69) for females in contrast with those of 0.

CONCLUSIONS

Global PSQI score and its components (especially, sleep latency and sleep disturbance) were associated with metabolic syndrome.

Comparison of ambulatory blood pressure parameters of hypertensive patients with and without chronic kidney disease

There is strong association between chronic kidney disease (CKD) and increased prevalence of hypertension, risk of end-organ damage, and cardiovascular disease (CVD). Non-dipping, as determined by ambulatory blood pressure (BP) monitoring (ABPM), is frequent in CKD and has also been consistently associated with increased CVD risk. The reported prevalence of non-dipping in CKD is highly variable, probably due to relatively small sample sizes, reliance only on a single, low-reproducibility, 24-h ABPM evaluation per participant, and definition of daytime and nighttime periods by arbitrary fixed clock-hour spans. Accordingly, we assessed the circadian BP pattern of patients with and without CKD by 48-h ABPM to increase reproducibility of the results. This cross-sectional study involved 10 271 hypertensive patients (5506 men/4765 women), 58.0 ± 14.2 (mean ± SD) yrs of age, enrolled in the Hygia Project. Among the participants, 3227 (1925 men/1302 women) had CKD. At the time of recruitment, 568/2234 patients with/without CKD were untreated for hypertension. Patients with than without CKD were more likely to be men and of older age, have diagnoses of obstructive sleep apnea, metabolic syndrome, diabetes, and/or obesity, plus have higher glucose, creatinine, uric acid, and triglyceride, but lower cholesterol, concentrations. In patients with CKD, ambulatory systolic BP (SBP) was significantly elevated (p < .001), mainly during the hours of nighttime sleep, independent of presence/absence of BP-lowering treatment. In patients without CKD, ambulatory diastolic BP (DBP), however, was significantly higher (p < .001), mainly during the daytime. Differing trends for SBP and DBP between groups resulted in large differences in ambulatory pulse pressure (PP), it being significantly greater (p < .001) for the entire 24 h in patients with CKD. Prevalence of non-dipping was significantly higher in patients with than without CKD (60.6% vs. 43.2%; p < .001). The largest difference between groups was in the prevalence of the riser BP pattern, i.e., asleep SBP mean > awake SBP mean (17.6% vs. 7.1% in patients with and without CKD, respectively; p < .001). The riser BP pattern significantly and progressively increased from 8.1% among those with stage 1 CKD to a very high 34.9% of those with stage 5 CKD. Elevated asleep SBP mean was the major basis for the diagnosis of hypertension and/or inadequate BP control among patients with CKD; thus, among the uncontrolled hypertensive patients with CKD, 90.7% had nocturnal hypertension. Our findings document significantly elevated prevalence of a blunted nocturnal BP decline in hypertensive patients with CKD. Most important, prevalence of the riser BP pattern, associated with highest CVD risk among all possible BP patterns, was 2.5-fold more prevalent in CKD, and up to 5-fold more prevalent in end-stage renal disease. Patients with CKD also presented significantly elevated ambulatory PP, reflecting increased arterial stiffness and enhanced CVD risk. Collectively, these findings indicate that CKD should be included among the clinical conditions for which ABPM is mandatory for proper diagnosis and CVD risk assessment, as well as a means to establish the best therapeutic scheme to increase CVD event-free survival.

Differences between men and women in ambulatory blood pressure thresholds for diagnosis of hypertension based on cardiovascular outcomes

Previous studies have reported sex differences in the pathophysiology of hypertension and responses to blood pressure (BP)-lowering medications. Moreover, men exhibit typically higher BP than women, the differences being greater for systolic (SBP) than diastolic (DBP) BP. These differences become apparent during adolescence and remain significant at least until 55-60 yrs of age. Despite such significant sex-related differences in BP regulation, the current recommended ambulatory BP monitoring (ABPM) thresholds for diagnosis of hypertension do not differentiate between men and women. We aimed to derive separate male and female diagnostic thresholds for the awake and asleep SBP and DBP means based upon cardiovascular disease (CVD) outcome. We prospectively studied 3344 subjects (1718 men/1626 women), 52.6 ± 14.5 yrs of age, during a median follow-up of 5.6 yrs. Those with hypertension at baseline were randomized to ingest all their prescribed hypertension medications upon awakening or the entire daily dose of ≥1 of them at bedtime. At baseline, BP was measured at 20-min intervals from 07:00 to 23:00 h and at 30-min intervals at night for 48 h, and physical activity was simultaneously monitored every minute by wrist actigraphy to accurately derive the awake and asleep BP means. Identical assessment was scheduled annually and more frequently (quarterly) if treatment adjustment was required. Cox regression analysis was used to derive outcome-based reference thresholds for ABPM in men and women. Men exhibited greater event rates than women of CVD death, myocardial infarction, angina pectoris, coronary revascularization, and heart failure; however, event rates of non-CVD death and cerebrovascular events were comparable. The relationship between progressively higher ambulatory BP and CVD risk increased more rapidly in women than men for awake SBP/DBP means ≥125/75 mm Hg and asleep means ≥110/70 mm Hg. The derived outcome-based reference thresholds for men were 135/85 mm Hg for the awake and 120/70 mm Hg for the asleep SBP/DBP means. In terms of CVD outcome, the equivalent cutoff threshold values for women were 125/80 mm Hg for the awake and 110/65 mm Hg for the asleep SBP/DBP means. Outcome-based reference thresholds for the diagnosis of hypertension were 10/5 mm Hg lower for ambulatory SBP/DBP in women than men. This marked sex difference indicates the need for revision of current guidelines that propose diagnostic thresholds for ambulatory BP without differentiation between men and women.

Administration-time-dependent effects of hypertension treatment on ambulatory blood pressure in patients with chronic kidney disease

Many published prospective trials have reported clinically meaningful morning-evening, treatment-time differences in the blood pressure (BP)-lowering efficacy, duration of action, and safety of most classes of hypertension medications. Most important, it was recently documented that routine ingestion of the full daily dose of ≥1 hypertension medications at bedtime, compared with ingestion of all of them upon awakening, significantly reduces cardiovascular disease (CVD) events. Nocturnal hypertension and non-dipping (<10% decline in the asleep relative to the awake BP mean), as determined by ambulatory BP monitoring (ABPM), are frequent in chronic kidney disease (CKD) and both are associated with increased CVD risk. Here, we investigated the influence of hypertension treatment time on the circadian BP pattern and degree of BP control of hypertensive patients with CKD evaluated by 48-h ABPM. This cross-sectional study evaluated 2659 such patients (1585 men/1074 women), 64.9 ± 13.2 (mean ± SD) yrs of age, enrolled in the Hygia Project, involving primary care centers of northwest Spain and designed to evaluate prospectively CVD risk by ABPM; 1446 were ingesting all BP-lowering medications upon awakening, whereas 1213 patients were ingesting ≥1 medications at bedtime. Among the latter, 359 patients were ingesting all medications at bedtime, whereas 854 were ingesting the full daily dose of some medications upon awakening and the others at bedtime. Those ingesting all medications upon awakening had significantly higher total cholesterol and low-density lipoprotein (LDL) cholesterol than those ingesting ≥1 medications at bedtime. Moreover, patients ingesting all medications at bedtime had the lowest fasting glucose, serum creatinine, and uric acid. Ingestion of ≥1 medications at bedtime was significantly associated with lower asleep systolic (SBP) and diastolic (DBP) BP means than treatment with all medications upon awakening. The sleep-time relative SBP decline was significantly attenuated in patients ingesting all medications upon awakening (p < .001). Thus, the prevalence of non-dipping was significantly higher when all hypertension medications were ingested upon awakening (68.3%) than when ≥1 of them was ingested at bedtime (54.2%; p < .001 between groups), and even further attenuated (47.9%) when all of them were ingested at bedtime (p < .001). Additionally, the prevalence of a riser BP pattern, associated with highest CVD risk, was much greater (21.5%) among patients ingesting all medications upon awakening, compared with those ingesting some (15.7%) or all medications at bedtime (10.6%; p < .001 between groups), independent of CKD severity (disease stage). The latter group also showed a significantly higher prevalence of properly controlled ambulatory BP (p < .001) that was achieved by a significantly lower number of hypertension medications (p < .001) compared with patients treated upon awakening. Our findings demonstrate significantly lower asleep SBP and DBP means and attenuated prevalence of a blunted nighttime BP decline, i.e., lower prevalence of markers of CVD risk, in patients with CKD ingesting hypertension medications at bedtime than in those ingesting all of them upon awakening. These collective findings indicate that bedtime hypertension treatment, in conjunction with proper patient evaluation by ABPM to corroborate the diagnosis of hypertension and avoid treatment-induced nocturnal hypotension, should be the preferred therapeutic scheme for CKD.

Administration-time differences in effects of hypertension medications on ambulatory blood pressure regulation

Specific features of the 24-h blood pressure (BP) pattern are linked to progressive injury of target tissues and risk of cardiovascular disease (CVD) events. Several studies have consistently shown an association between blunted asleep BP decline and risk of fatal and nonfatal CVD events. Thus, there is growing focus on ways to properly control BP during nighttime sleep as well as during daytime activity. One strategy, termed chronotherapy, entails the timing of hypertension medications to endogenous circadian rhythm determinants of the 24-h BP pattern. Significant and clinically meaningful treatment-time differences in the beneficial and/or adverse effects of at least six different classes of hypertension medications, and their combinations, are now known. Generally, calcium channel blockers (CCBs) are more effective with bedtime than morning dosing, and for dihydropyridine derivatives bedtime dosing significantly reduces risk of peripheral edema. The renin-angiotensin-aldosterone system is highly circadian rhythmic and activates during nighttime sleep. Accordingly, evening/bedtime ingestion of the angiotensin-converting enzyme inhibitors (ACEIs) benazepril, captopril, enalapril, lisinopril, perindopril, quinapril, ramipril, spirapril, trandolapril, and zofenopril exerts more marked effect on the asleep than awake systolic (SBP) and diastolic (DBP) BP means. Likewise, the bedtime, in comparison with morning, ingestion schedule of the angiotensin-II receptor blockers (ARBs irbesartan, olmesartan, telmisartan, and valsartan exerts greater therapeutic effect on asleep BP, plus significant increase in the sleep-time relative BP decline, with the additional benefit, independent of drug terminal half-life, of converting the 24-h BP profile into a more normal dipping pattern. This is the case also for the bedtime versus upon-awakening regimen of combination ARB-CCB, ACEI-CCB, and ARB-diuretic medications. The chronotherapy of conventional hypertension medications constitutes a new and cost-effective strategy for enhancing the control of daytime and nighttime SBP and DBP levels, normalizing the dipping status of their 24-h patterning, and potentially reducing the risk of CVD events and end-organ injury, for example, of the blood vessels and tissues of the heart, brain, kidney, and retina.

Dipper and non-dipper blood pressure 24-hour patterns: circadian rhythm-dependent physiologic and pathophysiologic mechanisms

Neuroendocrine mechanisms are major determinants of the normal 24-h blood pressure (BP) pattern. At the central level, integration of the major driving factors of this temporal variability is mediated by circadian rhythms of monoaminergic systems in conjunction with those of the hypothalamic-pituitary-adrenal, hypothalamic-pituitary-thyroid, opioid, renin-angiotensin-aldosterone, plus endothelial systems and specific vasoactive peptides. Humoral secretions are typically episodic, coupled either to sleep and/or the circadian endogenous (suprachiasmatic nucleus) central pacemaker clock, but exhibiting also weekly, monthly, seasonal, and annual periodicities. Sleep induction and arousal are influenced also by many hormones and chemical substances that exhibit 24-h variation, e.g., arginine vasopressin, vasoactive intestinal peptide, melatonin, somatotropin, insulin, steroids, serotonin, corticotropin-releasing factor, adrenocorticotropic hormone, thyrotropin-releasing hormone, endogenous opioids, and prostaglandin E2, all with established effects on the cardiovascular system. As a consequence, physical, mental, and pathologic stimuli that activate or inhibit neuroendocrine effectors of biological rhythmicity may also interfere with, or modify, the temporal BP structure. Moreover, immediate adjustment to exogenous components/environment demands by BP rhythms is modulated by the circadian-time-dependent responsiveness of biological oscillators and their neuroendocrine effectors. This knowledge contributes to a better understanding of the pathophysiology of abnormalities of the 24-h BP pattern and level and their correction through circadian rhythm-based chronotherapeutic strategies.

Twenty-four-hour patterns in occurrence and pathophysiology of acute cardiovascular events and ischemic heart disease

The scientific literature clearly establishes the occurrence of cardiovascular (CV) accidents and myocardial ischemic episodes is unevenly distributed during the 24 h. Such temporal patterns result from corresponding temporal variation in pathophysiologic mechanisms and cyclic environmental triggers that elicit the onset of clinical events. Moreover, both the pharmacokinetics and pharmacodynamics of many, though not all, CV medications have been shown to be influenced by the circadian time of their administration, even though further studies are necessary to better clarify the mechanisms of such influence on different drug classes, drug molecules, and pharmaceutical preparations. Twenty-four-hour rhythmic organization of CV functions is such that defense mechanisms against acute events are incapable of providing the same degree of protection during the day and night. Instead, temporal gates of excessive susceptibility exist, particularly in the morning and to a lesser extent evening (in diurnally active persons), to aggressive mechanisms through which overt clinical manifestations may be triggered. When peak levels of critical physiologic variables, such as blood pressure (BP), heart rate (HR), rate pressure product (systolic BP × HR, surrogate measure of myocardial oxygen demand), sympathetic activation, and plasma levels of endogenous vasoconstricting substances, are aligned together at the same circadian time, the risk of acute events becomes significantly elevated such that even relatively minor and usually harmless physical and mental stress and environmental phenomena can precipitate dramatic life-threatening clinical manifestations. Hence, the delivery of CV medications needs to be synchronized in time, i.e., circadian time, in proportion to need as determined by established temporal patterns in risk of CV events, and in a manner that averts or minimizes undesired side effects.

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.

Vitamin D and the prevention of hypertension and cardiovascular diseases: a review of the current evidence

Vitamin D plays an essential role in bone mineralization and calcium homeostasis. More recently, there has been growing evidence for a role of vitamin D in extraskeletal health, including beneficial effects in the cardiovascular system. Daylight exposure and vitamin D intake in many western populations are insufficient for maintaining an adequate vitamin D status. It is at present unclear whether vitamin D supplementation could improve cardiovascular health. This paper summarizes the evidence from observational studies and randomized-controlled trials on the relation of vitamin D with blood pressure (BP) and risk of cardiovascular diseases (CVDs). Epidemiological data suggest that optimal vitamin D status is important for CVD prevention, but results from different studies are conflicting and confounding cannot be ruled out. Randomized-controlled trials of vitamin D supplementation and BP have yielded inconsistent results, and trials that addressed the effect of vitamin D on CVDs are lacking. It is therefore premature to recommend supplemental vitamin D intake specifically for the prevention of hypertension or CVDs. Data from large, well-controlled clinical trials in this field with vitamin D supplements of sufficiently high doses are awaited to settle this issue.

Circadian Variation in Stroke Onset: Identical Temporal Pattern in Ischemic and Hemorrhagic Events

Stroke is the culmination of a heterogeneous group of cerebrovascular diseases that is manifested as ischemia or hemorrhage of one or more blood vessels of the brain. The occurrence of many acute cardiovascular events--such as myocardial infarction, sudden cardiac death, pulmonary embolism, critical limb ischemia, and aortic aneurysm rupture--exhibits prominent 24 h patterning, with a major morning peak and secondary early evening peak. The incidence of stroke exhibits the same 24 h pattern. Although ischemic and hemorrhagic strokes are different entities and are characterized by different pathophysiological mechanisms, they share an identical double-peak 24 h pattern. A constellation of endogenous circadian rhythms and exogenous cyclic factors are involved. The staging of the circadian rhythms in vascular tone, coagulative balance, and blood pressure plus temporal patterns in posture, physical activity, emotional stress, and medication effects play central and/or triggering roles. Features of the circadian rhythm of blood pressure, in terms of their chronic and acute effects on cerebral vessels, and of coagulation are especially important. Clinical medicine has been most concerned with the prevention of stroke in the morning, when population-based studies show it is of greatest risk during the 24 h; however, improved protection of at-risk patients against stroke in the early evening, the second most vulnerable time of cerebrovascular accidents, has received relatively little attention thus far.

Circadian variability of cystatin C, creatinine, and glomerular filtration rate (GFR) in healthy men during normal sleep and after an acute shift of sleep

The estimation of the glomerular filtration rate (GFR) is essential for the evaluation of patients with kidney disease and for the treatment of patients with medications that are eliminated by the kidneys. Plasma cystatin C has been shown in several studies to be superior to plasma creatinine for the estimation of GFR. However, there is limited information on the circadian variation of cystatin C and estimated GFR using cystatin C (eGFR(CystC)) or "The Modification of Diet in Renal Disease Study" (MDRD) (eGFR(MDRD)) equations. We studied the circadian variation of cystatin C and creatinine during night- and day-sleep conditions in seven healthy volunteers. Serum samples were collected every hour (48 samples per individual) to evaluate the effect of different sampling times on the test results. The median intra-individual coefficients of variations for the studied markers were 4.2% for creatinine, 4.7% for eGFR(MDRD), 5.5% for cystatin C, and 7.7% for eGFR(CystC). Neither cystatin C nor creatinine differed significantly between the night- and day-sleep conditions. Cystatin C differed significantly with time of day (p=.0003), but this was not the case for creatinine (p=.11). The circadian variation of cystatin C was minor. Small but significant increases in creatinine values and a decrease of eGFR(MDRD) were observed after food intake. Thus, cystatin C and creatinine sampling does not have to be restricted to specific times of the day.

Circadian variation of blood pressure: the basis for the chronotherapy of hypertension

Ambulatory blood pressure (BP) measurements present a close correlation with target organ damage and cardiovascular events, including myocardial infarction, stroke and cardiovascular mortality. With the use of this measurement technique, a significant circadian variation has been shown to characterize BP. This circadian BP variation, although affected by a variety of external factors, represents the influence of internal factors such as ethnicity, gender, autonomic nervous system tone, vasoactive hormones, and hematologic and renal variables. In most individuals, BP presents a morning increase, a small post-prandial valley, and a deeper descent during nocturnal rest. However, under certain pathophysiological conditions, the nocturnal BP decline may be reduced or even reversed. This cannot be determined by traditional clinical or home BP assessments. Subjects with a diminished nocturnal BP decline (non-dipper pattern) have a significantly worse prognosis than the ones with a normal dipper pattern. In particular, the non-dipper circadian BP pattern represents a risk factor for left ventricular hypertrophy, microalbuminuria, cerebrovascular disease, congestive heart failure, vascular dementia and myocardial infarction. The normalization of the circadian BP pattern to a dipper profile is a novel therapeutic goal, and accumulating medical evidence suggests this can delay the progression towards the renal and cardiovascular pathology known to be a consequence of the non-dipper BP pattern. The features of the circadian BP profile have direct implications for improving the drug-delivery of antihypertensive therapies as well as the qualification of patients for medication trials and assessment.

Characterization of the molecular clock in mouse peritoneal macrophages

Macrophages play essential roles in the innate immune system. In this study, we show that macrophage functions such as phagocytosis and cytokine/chemokine expressions display a circadian rhythm that is regulated by a molecular clock. Phagocytosis, a crucial early reaction by which macrophages protect their host against foreign particles, exhibited a circadian variation that peaks during the light period and bottoms during the dark period. These diurnal changes of phagocytosis activity in macrophages were induced without exogenous stimulants such as bacterial infection. The expression of the clock genes including brain and muscle Arnt-like protein-1 (BMAL1) exhibited robust circadian rhythms in macrophages. The expression patterns of the clock genes in macrophages were similar to those in the suprachiasmatic nucleus and other peripheral tissues. Among inflammation factors examined, the level of monocyte chemoattractant protein-1 (MCP-1/JE) mRNA exhibited most robust circadian oscillation. Expression of other cytokines such as IL-1beta, IL-6 and TNFalpha showed mild diurnal changes. Knockdown of the BMAL1 expression resulted in a decrease of the MCP-1/JE mRNA level in macrophages. BMAL1 increased significantly but weakly MCP-1/JE promoter activity. MCP-1/JE promoter activity is known to be regulated by nuclear factor-kappa B (NF-kappaB). NF-kappaB activity in BMAL1 knockdown macrophages was lower than that in control cells. Consequently, the circadian expression of MCP-1/JE in macrophages is regulated by BMAL1 through the activation of NF-kappaB. The results obtained in this study indicate that the innate immunoreactions involving macrophages are at least partly regulated by the autonomous clock machinery.

Role of sleep-wake cycle on blood pressure circadian rhythms and hypertension

Stages of different depth characterize the temporal organization of sleep. Each stage exerts an effect on blood pressure (BP) regulation and contributes to its 24-h variation. The main determinant of the circadian influences of sleep and wakefulness on BP is the daytime sympathetic and nighttime parasympathetic prevalence, but many other physiologic mechanisms known either to induce sleep or determine arousal may play an important role in the mediation of sleep influences on BP. Alteration of one or more of such mechanisms may be reflected in altered circadian BP rhythms. Sleep- and arousal-related mechanisms and phenomena that affect circadian BP rhythms include neurohumoral sleep factors (arginine vasopressin, vasoactive intestinal peptide, somatotropin, insulin, steroid hormones and metabolites, and serotonin among others) and waking factors (corticotropin-releasing factor, adrenocorticotropin, thyrotropin-releasing hormone, endogenous opioids, and prostaglandin (E(2))). Pathologic respiratory variations (sleep-disordered breathing) and insomnia are major causes of the sleep-related alteration of the circadian BP profile, including loss of the expected normal decline in BP by 10-20% from the daytime level. A great number of medical disorders can cause insomnia, but objective sleep studies have been performed only in a minority of them. Overall, the sleep-related pathophysiological mechanisms actually involved in causing altered circadian BP rhythms in different normotensive and hypertensive conditions are not completely understood. In any case, changes in the circadian BP rhythm are known to be strongly related to one's risk of cardiovascular morbidity and mortality, thus representing strong prognostic indicators worthy of further investigation.

Circadian rhythm in the cardiovascular system of domestic animals

Definition of the temporal characteristics of cardiovascular rhythms is of scientific interest. This article reviews the literature on the rhythmic pattern of some cardiovascular parameters in domestic animals, providing greater understanding of general chronobiological processes in mammals. The techniques of the chronophysiological studies have been applied in domestic species to determine the existence of periodicity in the cardiovascular functions. Detailed knowledge of these rhythms is useful for clinical, practical and pharmacological purposes and physical performances.

Circadian regulation of islet genes involved in insulin production and secretion

Both transcription factors albumin site d-binding protein (DBP) and thyrotroph embryonic factor (TEF) are elements of the "cell-clock". Their circadian accumulation in suprachiasmatic nucleus (SCN) and peripheral tissues such as liver, kidney and lung is thought to participate in controlling circadian regulation of downstream genes. TEF and DBP control elements have never been investigated in the insulin-secreting cells, but impairment of the circadian rhythm of the beta-cells might be involved in the development of diabetic state as type 2 diabetics have lost daily temporal variations of insulin secretion. We investigated the expression pattern of TEF and DBP in insulin-secreting cells. TEF and DBP transcripts are expressed at extremely high levels in human pancreatic islets compared to other tissues, suggesting a potentially important circadian regulation of these cells. Both TEF and DPB accumulate in a circadian way in insulin-secreting cells after a serum shock known to restore circadian rhythms in cultured cells. In addition, the expression of islet-specific genes involved in glucose sensing (glucose transporter 2 (Glut2), glucokinase), insulin production (insulin) and secretion (migration inhibitory factor (MIF), somatostatin and syntaxin 1A) were modulated in the same daily rhythm as well. The circadian deregulation of these genes could therefore participate in the diabetic state development.

An opioid basis for early-phase isoflurane-induced hypotension in rats

This study was conducted to more clearly delineate the possible role of endogenous opioid receptors and opioid peptides in general anesthesia-associated hypotension in rats. Exposure to 2% isoflurane in oxygen produced a triphasic change in mean arterial pressure (MAP), including an early phase in which MAP fell by -28.4 +/- 2.2%. The magnitude of this early-phase hypotension was attenuated in rats pretreated with intravenous (i.v.) mu-subtype-selective doses of either naloxone or methylnaloxone but not central doses of the selective mu-opioid antagonist beta-funaltrexamine. This early hypotensive phase was also reduced following i.v. pretreatment with antiserum against methionine-enkephalin but not beta-endorphin. These findings suggest that early-phase isoflurane-induced hypotension may be due to activation of peripheral mu-opioid receptors by an endogenous opioid peptide, possibly related to methionine-enkephalin.

Increases in amino-cupric-silver staining of the supraoptic nucleus after sleep deprivation

Sleep deprived rats undergo a predictable sequence of physiological changes, including changes in skin condition, increased energy expenditure, and altered thermoregulation. Amino-cupric-silver staining was used to identify sleep deprivation related changes in the brain. A significant increase in staining was observed in the supraoptic nucleus (SON) of the hypothalamus of rats with high sleep loss (>45 h) vs. their yoked controls. Follow-up experiments showed that staining was not significantly different in rats sleep deprived for less than 45 h, suggesting that injurious sleep deprivation-related processes occur above a threshold quantity of sleep loss. These anatomical changes suggest that the effects of sleep deprivation may be related to protein metabolism in certain brain regions.

The effects of endomorphin-1 on conditioned defeat in Syrian hamsters (Mesocricetus auratus)

The present study examined the effect of endomorphin-1 (EM1), an endogenous opioid with a high affinity for the mu opiate receptor, on conditioned defeat. Conditioned defeat is a phenomenon in which hamsters that have been defeated subsequently fail to exhibit normal territorial aggression and instead display submissive/defensive behaviors even when paired with a non-aggressive intruder. In experiment 1, animals were placed in the home cage of a larger resident for 15 min and were defeated. After 24 h, animals received a 3-microl injection of EM1 (0.0, 0.3, 3.0, or 10 nmol) into the left lateral cerebral ventricle 5 min before a smaller non-aggressive intruder was placed in the home cage of the experimental animal. In experiment 2, animals were infused with EM1 immediately after the initial defeat and were paired with a non-aggressive intruder 24 h later as in experiment 1. EM1 reduced the duration of submissive/defensive behavior in experiment 1 (P<0.05) but not in experiment 2 (P>0.05). These data support the hypothesis that the highly selective mu receptor agonist endomorphin-1 modulates the expression of conditioned defeat, but provides no support for the hypothesis that endomorphin-1 modulates the consolidation of conditioned defeat.

Adult men born in spring have lower blood pressure

OBJECTIVE

To determine whether there is a relationship between season of birth and adult blood pressure, as a possible early determinant of later blood pressure.

DESIGN

We studied 572 men, aged 45-64 years, whose blood pressure was measured in standardized manner as part of a nation-wide survey in Spain. To analyse the seasonal variation in blood pressure, a linear regression was performed, adjusting for age, height, body mass index, occupation and rural or urban residence.

RESULTS

We found seasonal variation in mean systolic blood pressure, with maxima in adults born in autumn and winter, and minima in those born in spring and summer. The greatest difference in systolic blood pressure occurred between adults born in spring (134.1 mmHg) and those born in autumn (140.3 mmHg). After adjustment, the difference in means between spring and autumn was 5.9 mmHg (95% confidence interval 0.7 to 11.1 mmHg, P = 0.03).

CONCLUSIONS

This study demonstrated differences in systolic blood pressures of adult men according to the season of their birth. Although this relationship is compatible with several hypotheses, the difference found between spring and autumn, partially independent of some other factors, might indicate that the extent of early exposure to sunlight is implicated in determining later blood pressure. This needs further investigation.

Restricted feeding uncouples circadian oscillators in peripheral tissues from the central pacemaker in the suprachiasmatic nucleus

In mammals, circadian oscillators exist not only in the suprachiasmatic nucleus, which harbors the central pacemaker, but also in most peripheral tissues. It is believed that the SCN clock entrains the phase of peripheral clocks via chemical cues, such as rhythmically secreted hormones. Here we show that temporal feeding restriction under light-dark or dark-dark conditions can change the phase of circadian gene expression in peripheral cell types by up to 12 h while leaving the phase of cyclic gene expression in the SCN unaffected. Hence, changes in metabolism can lead to an uncoupling of peripheral oscillators from the central pacemaker. Sudden large changes in feeding time, similar to abrupt changes in the photoperiod, reset the phase of rhythmic gene expression gradually and are thus likely to act through a clock-dependent mechanism. Food-induced phase resetting proceeds faster in liver than in kidney, heart, or pancreas, but after 1 wk of daytime feeding, the phases of circadian gene expression are similar in all examined peripheral tissues.

Circadian rhythm of plasma sodium is disrupted in spontaneously hypertensive rats fed a high-NaCl diet

High-NaCl diets elevate arterial pressure in NaCl-sensitive individuals, and increases in plasma sodium may trigger this effect. The present study tests the hypotheses that 1) plasma sodium displays a circadian rhythm in rats, 2) the plasma sodium rhythm is disturbed in spontaneously hypertensive rats (SHR), and 3) excess dietary NaCl elevates plasma sodium concentration in SHR. The results demonstrate that plasma sodium has a circadian rhythm that is inversely related to the circadian rhythm of arterial pressure. Although the plasma sodium rhythms of SHR and control rats are nearly identical, the plasma sodium concentrations are significantly higher in SHR throughout the 24-h cycle. Maintenance on a high-NaCl diet increases plasma sodium concentration similarly in both SHR and control rats, but it blunts the plasma sodium rhythm only in SHR. These results demonstrate that in rats, plasma sodium has a circadian rhythm and that high-NaCl diets increase plasma sodium concentration.