The Relationship between Cold Exposure and Hypertension

Angiotensin II participates in mitochondrial thermogenic functions via the activation of glycolysis in chemically induced human brown adipocytes

Brown adipocytes are potential therapeutic targets for the prevention of obesity-associated metabolic diseases because they consume circulating glucose and fatty acids for heat production. Angiotensin II (Ang II) peptide is involved in the pathogenesis of obesity- and cold-induced hypertension; however, the mechanism underlying the direct effects of Ang II on human brown adipocytes remains unclear. Our transcriptome analysis of chemical compound-induced brown adipocytes (ciBAs) showed that the Ang II type 1 receptor (AGTR1), but not AGTR2 and MAS1 receptors, was expressed. The Ang II/AGTR1 axis downregulated the expression of mitochondrial uncoupling protein 1 (UCP1). The simultaneous treatment with β-adrenergic receptor agonists and Ang II attenuated UCP1 expression, triglyceride lipolysis, and cAMP levels, although cAMP response element-binding protein (CREB) phosphorylation was enhanced by Ang II mainly through the protein kinase C pathway. Despite reduced lipolysis, both coupled and uncoupled mitochondrial respiration was enhanced in Ang II-treated ciBAs. Instead, glycolysis and glucose uptake were robustly activated upon treatment with Ang II without a comprehensive transcriptional change in glucose metabolic genes. Elevated mitochondrial energy status induced by Ang II was likely associated with UCP1 repression. Our findings suggest that the Ang II/AGTR1 axis participates in mitochondrial thermogenic functions via glycolysis.

Cold exposure, gut microbiota, and hypertension: A mechanistic study

Cold exposure has been recognized as an important risk factor for hypertension, and altered gut microbiota has been reported to be associated with hypertension. We hypothesized that there is a plausible relationship between gut microbiota and cold-induced hypertension (CIH). Therefore, we explored the potential link between the gut microbiota and its metabolites with CIH. Male Sprague-Dawley (SD) rats were randomly divided into the normal temperature group (NT, 20 ± 2 °C) and the cold exposure group (CE, 4 ± 1 °C), and faecal bacteria cross-transplantation was performed after six weeks. We analyzed the gut microbiota of rats using the 16S rDNA sequence and measured the blood pressure of rats and the content of short-chain fatty acids in rat faeces. After six weeks of cold exposure, the CIH rat model was successfully established. The cold exposure reduced the diversity of the gut microbiota, increased the abundance of potentially pathogenic and conditionally pathogenic bacteria (e.g., Quinella, Rothia, and Senegalimassilia genera), and reduced the abundance of beneficial bacteria (e.g., Lactobacillus genus) and butyric acid-producing bacteria (e.g., Lachnospiraceae UCG-008 and Ruminococcaceae UCG-013 genera). Faecal bacteria cross-transplantation altered gut microbiota composition and regulated blood pressure levels. The NT group rats transplanted with CIH rats' faecal bacteria were enriched with certain conditional pathogenic bacteria such as Prevotellaceae UCG-003 genus. The CIH rats transplanted with faecal bacteria from the NT group rats were enriched with beneficial bacteria such as Bacteroides genus. In addition, we found a significant reduction in butyric acid levels in CIH rats, which may be related to the increase in blood pressure. In conclusion, CIH is associated with altered gut microbiota and reduced butyric acid. Our findings provide novel insights for the prevention and treatment of CIH by modulating the gut microbiota through supplementation of beneficial bacteria/butyrate.

Occupational exposure to noise and cold environment and the risk of death due to myocardial infarction and stroke

Purpose

The present study examined a possible association between occupational exposure to noise, working and living in cold conditions, and the risk of mortality in myocardial infarction and stroke.

Methods

The present cohort study consists of 194,501 workers in the Swedish construction industry that participated in health examinations between 1971 and 1993. Noise exposure was defined on a job-exposure matrix based on a survey of the working conditions carried out during the mid 1970s. All workers were categorised into three main regions of Sweden, differing in temperature: Reference (Götaland), colder (Svealand), and coldest (Norrland). Relative risks (RR) were analysed by negative binomial regression adjusting for age, BMI, and smoking habits.

Results

Moderate and high noise exposure was associated with increased risk of myocardial infarction (RR 1.10–1.13 with 95% CI over unit) and stroke mortality (RR 1.15 to 1.19 with 95% CI over unit). There was an increased risk for myocardial infarction (RR 1.10, 95% CI 1.01–1.20), but not for stroke mortality (RR 1.09, 95% CI 0.94–1.25) associated with living and working in the coldest region. There was an interaction on the risk of myocardial infarction mortality between different regions and noise exposure (p = 0.016), but not for stroke mortality (p = 0.88).

Conclusions

The study indicates an interaction between working at hazardous noise levels and living and working in cold conditions for increased mortality in myocardial infarction.

Electronic supplementary material

The online version of this article (10.1007/s00420-019-01513-5) contains supplementary material, which is available to authorized users.

TRPM8 and RAAS-mediated hypertension is critical for cold-induced immunosuppression in mice

Mechanisms underlying cold-induced immunosuppression remain unclear. Here we found that cold exposure leads to transient receptor potential melastatin 8 (TRPM8)-dependent, renin–angiotensin–aldosterone system (RAAS)-mediated hypertension, which subsequently induces small molecule and fluid extravasation, increases plasma Ig levels, and elicits immunosuppression. An effect is similar to the clinically-used immunosuppressive treatments of intravenous immunoglobulin (IVIg) against various inflammatory diseases, such as immune thrombocytopenia (ITP). Essential roles of TRPM8 and Ig in cold-induced immunosuppression are supported by the cold-mediated amelioration of ITP and the cold-mediated suppression of bacterial clearance, which were observed in wild-type mice but not in Ig- and TRPM8-deficient mutants. Treatment with antihypertensive drugs aliskiren and losartan drastically reversed high plasma Ig levels and ameliorated cold-induced immunosuppression, indicating the involvement of the RAAS and hypertension. These results indicated that the natively increased plasma Ig level is associated with immunosuppression during periods of cold exposure, and antihypertensive drugs can be useful to manage cold-induced immunosuppression.

Changes in the peripheral blood flow in legs in response to the cold: own studies using plethysmography

The thermal environment in the workplace is an important factor which affects workers' health. During 2011 in Poland, 14,781 workers were exposed to a cold working environment, i.e., 3.8% of persons employed in hazardous work conditions. The aim of this study was to determine the cardiovascular response to continuous (4 °C for 60 min) and intermittent (10 min at 4 °C and 10 min at room temperature alternately) exposure to the cold in 30 healthy men aged 20-27 years. Peripheral blood flow was assessed with impedance plethysmography. Heart rate and arterial blood pressure were monitored with the Holter system. Having assessed the results, it is difficult to say which kind of exposure has a more severe impact on the cardiovascular system. Longer observation and a more detailed analysis would be necessary (e.g., Doppler echocardiography).

Aortic Hemodynamics and Arterial Stiffness Responses to Muscle Metaboreflex Activation With Concurrent Cold Pressor Test

BACKGROUND

Overweight/obese young men have increased sympatho-excitation to cold and pain stress-induced by the cold pressor test (CPT) that may lead to abnormal hemodynamic responses. Concurrent CPT and exercise may augment the sympathetic-induced increases in aortic blood pressure (BP), pressure wave reflection (augmentation index, AIx), and arterial stiffness (pulse wave velocity, PWV). Since obesity is related with hypertension and sympathetic activity, we evaluated the aortic hemodynamic and PWV responses to muscle metaboreflex activation imposed by postexercise muscle ischemia (PEMI) concurrent with CPT in overweight/obese men.

METHODS

In 16 healthy (body mass index >25 and <40kg/m(2)) men (24±2 years), heart rate (HR), brachial BP, aortic BP, augmented pressure (AP), AIx, AIx adjusted to 75 beats/min (AIx@75), reflection time (Tr), first (P1) and second systolic peak (P2, wave reflection magnitude), and PWV (brachial-ankle PWV, baPWV) were evaluated at baseline, during isometric-handgrip exercise (IHG), and PEMI with (PEMI + CPT) and without CPT.

RESULTS

During IHG, brachial BP, aortic BP, AP, AIx, AIx@75, P1, and P2 increased ( P < 0.01) while Tr decreased ( P < 0.05) compared with baseline. During PEMI, all hemodynamic parameters remained elevated ( P < 0.05) and baPWV increased (P < 0.05) while Tr and HR returned to baseline. Compared with PEMI, the increases in HR, brachial BP, aortic BP, AIx@75, P1, P2, and baPWV were greater ( P < 0.05) during PEMI + CPT. During PEMI + CPT, Tr remained lower ( P < 0.05) than baseline.

CONCLUSIONS

Cold exposure with concurrent metaboreflex activation induces a significant increase in aortic hemodynamics and arterial stiffness, which may explain the high risk of adverse cardiovascular events during physiological stress.

CLINICAL TRIALS REGISTRATION

Trial Number NCT02104375.

Prevalence of hypertension and associated risk factors in Chinese Jing compared with Mulao populations

OBJECTIVE

*These authors contributed equally to this work. At present, they work at the Hezhou People's Hospital, Hezhou, China.To retrospectively compare differences in the prevalence of hypertension and associated risk factors between the Chinese Jing and Mulao populations.

METHODS

Subjects of Jing and Mulao ethnicities were surveyed using stratified randomized sampling. Demography, diet and lifestyle data were collected using standardized questionnaires. Several anthropometric parameters, blood pressure (BP) levels and serum lipid concentrations were obtained.

RESULTS

Data from 915 Jing and 911 Mulao subjects aged ≥ 35 years were included. Diastolic BP levels and prevalence of hypertension were lower, but prevalence of isolated systolic hypertension was higher, in the Jing compared with the Mulao population. Prevalence of hypertension in the age 60-69 years, body mass index (BMI) > 24 kg/m(2), and smoker subgroups was lower in the Jing compared with the Mulao populations. Prevalence of hypertension correlated with age, cigarette smoking, triglyceride level, waist circumference, sodium intake and total dietary fibre in the Jing population; hypertension prevalence also correlated with age, triglyceride level, BMI, total fat, sodium intake and total dietary fibre in the Mulao population (unconditional logistic regression analyses).

CONCLUSIONS

Prevalence of hypertension and associated risk factors were different between the two ethnic minorities, which might result from the combined effects of differences in their geographic, dietary, lifestyle, and genetic backgrounds.

Environmental temperature impact on bone and cartilage growth

Environmental temperature can have a surprising impact on extremity growth in homeotherms, but the underlying mechanisms have remained elusive for over a century. Limbs of animals raised at warm ambient temperature are significantly and permanently longer than those of littermates housed at cooler temperature. These remarkably consistent lab results closely resemble the ecogeographical tenet described by Allen's "extremity size rule," that appendage length correlates with temperature and latitude. This phenotypic growth plasticity could have adaptive significance for thermal physiology. Shortened extremities help retain body heat in cold environments by decreasing surface area for potential heat loss. Homeotherms have evolved complex mechanisms to maintain tightly regulated internal temperatures in challenging environments, including "facultative extremity heterothermy" in which limb temperatures can parallel ambient. Environmental modulation of tissue temperature can have direct and immediate consequences on cell proliferation, metabolism, matrix production, and mineralization in cartilage. Temperature can also indirectly influence cartilage growth by modulating circulating levels and delivery routes of essential hormones and paracrine regulators. Using an integrated approach, this article synthesizes classic studies with new data that shed light on the basis and significance of this enigmatic growth phenomenon and its relevance for treating human bone elongation disorders. Discussion centers on the vasculature as a gateway to understanding the complex interconnection between direct (local) and indirect (systemic) mechanisms of temperature-enhanced bone lengthening. Recent advances in imaging modalities that enable the dynamic study of cartilage growth plates in vivo will be key to elucidating fundamental physiological mechanisms of long bone growth regulation.

Cold pressor response in high landers versus low landers

BACKGROUND

Native high landers face two main environmental challenges i.e. hypobaric hypoxia and low ambient temperatures. Both factors contribute to increased sympathetic stimulation and increased blood pressure. Despite these challenges, subjects living at high altitude have lower systolic and diastolic pressures as compared to subjects living in plains. Present study investigated cold pressor test (CPT) which is a potential predictor of future hypertension in high landers and low landers Materials and Methods: Vascular reactivity in terms of changes in systolic and diastolic blood pressure and heart rate in response to cold pressor test has been compared in high lander (n=45) and low lander (n=46) population.

RESULTS

Systolic and diastolic blood pressure changes and heart rate changes with cold pressor test are lower in high landers as compared to low landers. Females in both the groups in general exhibited greater cold pressor response than males.

CONCLUSION

Hypo-reactive cold pressor test is due to higher parasympathetic tone and lower sympathetic tone. Decreased cold pressor response in high landers reflects another adaptive modulation of sympatho-vagal activity that enables them to stay in hypobaric atmosphere and lower temperatures without undue autonomic stress.

Impact of acute whole-body cold exposure with concurrent isometric handgrip exercise on aortic pressure waveform characteristics

PURPOSE

Adverse cardiovascular events are more prevalent during winter and in people that exercise/work in cold temperatures. Since pulse wave analysis indices, aortic systolic blood pressure (ASBP), augmentation index (AIx), and wasted left ventricular pressure energy (ΔE w), are stronger predictors of cardiovascular events and myocardial performance than brachial blood pressure (BP), we sought to evaluate the aortic hemodynamic responses during cold exposure with concurrent isometric handgrip exercise (IHG).

METHODS

In a crossover randomized fashion, 20 healthy normotensive men (22.1 ± 2 years) were evaluated, by means of radial applanation tonometry, inside an environmental chamber in the supine position at cold (4 °C) and temperate (24 °C) conditions. Following a 30-min equilibration period, measurements were performed during pre-exercise baseline (REST), in the last 90 s of a 3-min IHG at 30% maximal voluntary contraction, and 3 min immediately after the finalization of IHG bout (recovery, REC).

RESULTS

At REST, brachial systolic BP (BSBP) (12 ± 2 mmHg; P < 0.01), ASBP (14 ± 3 mmHg; P < 0.01), AIx (11 ± 3%; P < 0.05), and ΔE w (737 ± 128 dynes s/cm(2); P < 0.01) were higher in 4 °C compared to 24 °C trial. Compared to REST, IHG significantly increased (P < 0.01) BSBP, ASBP, AIx, and ΔEw, while BSBP and ASBP remained elevated during REC (P < 0.01). Compared to REST and temperate, AIx (11 ± 3%) and ΔE w (793 ± 145 dynes s/cm(2); P < 0.01) were higher during IHG and cold, while BSBP and ASBP were elevated during REC and cold. AIx and ΔE w returned to REST values in both trials, but AIx (11 ± 4%; P < 0.05) and ΔE w (656 ± 132 dynes s/cm(2); P < 0.05) were higher in the cold.

CONCLUSIONS

Cold exposure with concurrent IHG induces a significant increase in aortic hemodynamic markers, which may evoke adverse cardiovascular events.

Analysis of differentially expressed genes in cold-exposed mice to investigate the potential causes of cold-induced hypertension

Cold exposure is considered to be an important contributing factor to the high morbidity of hypertension. In order to elucidate the cause and mechanism of cold-induced hypertension (CIH), gene expression analysis was performed on microarray data for two groups of cold-exposed mice (4°C for 1 week and 4°C for 5 weeks, three replicates per group) and their respective control groups maintained at 30°C. Analysis results indicated that the differentially expressed genes with the most significance were associated with adaptive thermogenesis, fatty acid metabolism and energy metabolism. The expected marked increase in metabolism during cold exposure caused tissue hypoxia. Genes involved in the hypoxia-inducible factor signaling pathway were activated. In addition, genes associated with oxidative stress were significantly upregulated, including superoxide dismutase 2 (SOD2) and epoxide hydrolase 2 (EPHX2). The majority of genes involved in inflammation-associated pathways were shown to be downregulated in the 4°C 5-week group. Therefore, the results of the present study indicate that tissue hypoxia and increased oxidative stress may play important roles in the process of CIH.

Socioeconomic and behavioural risk factors for adverse winter health and social outcomes in economically developed countries: a systematic review of quantitative observational studies

BACKGROUND

Mortality and morbidity rates are often highest during the winter period, particularly in countries with milder climates. A growing body of research has identified potential socioeconomic, housing and behavioural mediators of cold weather-related adverse health and social outcomes, but an inclusive systematic review of this literature has yet to be performed.

METHODS

A systematic review, with narrative synthesis, of observational research published in English between 2001 and 2011, which quantified associations between socioeconomic, housing or behavioural factors and cold weather-related adverse health or social outcomes.

RESULTS

Thirty-three studies met the inclusion criteria. Average study quality was not high. Most studies failed to control for all relevant confounding factors, or to conduct research over a long enough period to ascertain causality. Low income, housing conditions and composite fuel poverty measures were most consistently associated with cold weather-related adverse health or social outcomes.

CONCLUSIONS

This review identified socioeconomic, housing and behavioural factors associated with a range of cold weather-related adverse health or social outcomes. Only tentative conclusions can be drawn due to the limitations of existing research. More robust studies are needed to address the methodological issues identified and uncover causal associations. A review of qualitative and intervention studies would help to inform policies to reduce the adverse health and social impacts of cold weather.

The effects of short term L-citrulline supplementation on wave reflection responses to cold exposure with concurrent isometric exercise

BACKGROUND

Supplementation with L-citrulline (L-cit) has shown attenuating effects on blood pressure (BP) and pulse-wave-reflection responses (augmentation index (AIx)) to local exposure to cold, but the potential cardioprotective effects of L-cit during whole-body cold exposure with concurrent exercise are poorly understood. We hypothesized that L-cit would attenuate the BP and AIx responses to cold exposure and isometric handgrip (IHG) exercise.

METHODS

Sixteen healthy males with a mean age of 23±3 years volunteered for a study of the effect of L-cit on the BP and AIx responses to cold exposure and IHG exercise. Experiments were conducted inside an environmental chamber in cold conditions (4 ºC). Radial waveforms were obtained in duplicates and averaged through applanation tonometry. After 5 minutes of measurements made at rest in the supine position (RES), after the finalization of the exercise about the subjects were evaluated in non exercise condition that were basically the same as the RES. After initial measurements in cold conditions, subjects were randomized to receive either a placebo (Maltodextrin, PL) or L-cit (100mg/kg) for 14 days, followed by a 14-day washout period and then a 14-day regimen of the other agent. Subjects were re-evaluated after each treatment period.

RESULTS

At RES, there was a significant treatment-by-time interaction for brachial systolic BP (BSBP; P < 0.01), aortic systolic BP (ASBP; P < 0.01), and AIx (P < 0.05), such that L-cit decreased BSBP (-11±2mm Hg; P < 0.01), ASBP (-10±2mm Hg; P < 0.05), and AIx (-2±2%; P < 0.05) as compared with their respective values before the intervention. During IHG, BSBP, ASBP, and AIx were increased (P < 0.05) as compared with their values at RES, but these responses were unaffected by either of the study treatments.

CONCLUSIONS

L-citrulline may be a feasible adjuvant treatment for decrease the BP and AIx responses induced by cold. Further research is warranted to evaluate the impact of cold exposure and exercise on cardiovascular risk in clinical populations.

Cardiac overexpression of metallothionein rescues cold exposure-induced myocardial contractile dysfunction through attenuation of cardiac fibrosis despite cardiomyocyte mechanical anomalies

Cold exposure is associated with an increased prevalence of cardiovascular disease although the mechanism is unknown. Metallothionein, a heavy-metal-scavenging antioxidant, protects against cardiac anomalies. This study was designed to examine the impact of metallothionein on cold exposure-induced myocardial dysfunction, intracellular Ca(2+) derangement, fibrosis, endoplasmic reticulum (ER) stress, and apoptosis. Echocardiography, cardiomyocyte function, and Masson trichrome staining were evaluated in Friend virus B (FVB) and cardiac-specific metallothionein transgenic mice after cold exposure (3 months, 4 °C). Cold exposure increased plasma levels of norepinephrine, endothelin-1, and TGF-β; reduced plasma NO levels and cardiac antioxidant capacity; enlarged ventricular end-systolic diameter; compromised fractional shortening; promoted reactive oxygen species (ROS) production and apoptosis; and suppressed the ER stress markers Bip, calregulin, and phospho-eIF2α, accompanied by cardiac fibrosis and elevated levels of matrix metalloproteinases and Smad-2/3 in FVB mice. Cold exposure-induced echocardiographic, histological, ER stress, ROS, apoptotic, and fibrotic signaling changes (but not plasma markers) were greatly improved by metallothionein. In vitro metallothionein induction by zinc chloride ablated H(2)O(2)- but not TGF-β-induced cell proliferation in fibroblasts. In summary, our data suggest that metallothionein protects against cold exposure-induced cardiac anomalies possibly through attenuation of myocardial fibrosis.

Changes in blood pressure with compensatory heart rate decrease and in the level of aerobic capacity in response to repeated whole-body cryostimulation in normotensive, young and physically active men

OBJECTIVE

In Poland and all over the world, whole-body cryostimulation is becoming more and more popular in the treatment of different diseases and in sport. However, changes that occur in the human body subjected to cryogenic temperatures are still not completely understood. Therefore, the aim of this study was to evaluate changes in blood circulation and aerobic capacity induced by repeated exposure to whole-body cryostimulation of young and clinically healthy male subjects.

MATERIAL AND METHODS

The study included 25 young men, aged 21 ± 0.9 years, average body weight 74.65 ± 6.98 kg and height 179.5 ± 5.12 cm. The participants were exposed to extremely low temperatures in a cryogenic chamber once a day for 15 days. Each session lasted 3 min at -130°C and was preceded by 30-second, adaptation in a vestibule at -60°C. Blood pressure and heart rate were measured before entering the chamber, immediately after exiting and 10 min later. We also calculated pulse pressure and the mean arterial blood pressure. Before and after the treatment the maximal oxygen uptake was measured.

RESULTS

Our results showed a significant increase in systolic blood pressure after each cryostimulation (by an average of 19 mmHg) and an increase in diastolic blood pressure only after the first cryostimulation (by 6 mm Hg). The increase in systolic blood pressure was accompanied by a significant decrease in heart rate (by about 7 bpm). No adaptation changes were observed after 15 treatments. There were no changes in aerobic capacity after 15 sessions of WBC, however we observed a significant decrease in RBC and hemoglobin concentration.

CONCLUSION

Due to the increase in systolic blood pressure after WBC, this kind of physiotherapy treatment is not recommended for people with advanced or not pharmacologically controlled hypertension.

Heart rate variability in occupational health --a systematic review

This systematic review evaluates and summarizes the evidence of association between work-related factors and heart rate variability (HRV) in workers. We reviewed English articles indexed in MEDLINE under the key words: work, worker, occupational, industrial, and heart rate variability. Studies were included if one or more of the dependent variables was one of the time- or frequency-domain indexes of HRV [standard deviation of all normal-to-normal (NN) intervals (SDNN), mean of the 5-min standard deviations of NN intervals calculated over several hours (SDNN index), the root mean squared differences of successive NN intervals (RMSSD), integrated spectral powers of high (HF, > 0.15 Hz) and low frequency (LF, 0.04-0.15 Hz) HRV, and the LF/HF ratio] as recommended by the European Society of Cardiology and the North American Society of Pacing Electrophysiology. Physical and chemical work environments (i.e. exposure to occupational toxicants and hazardous environments), psychosocial workload (i.e. job stressors), and working time (i.e. shift work) had been examined and identified as having associations with low HF power. These findings may indicate that research into parasympathetic nervous system activity should be focused to protect cardiovascular health at work. We also propose the use of very low and ultralow frequency HRV components in autonomic research for workers' health.

Health problems in cold work

Cold in- and outdoor work can result in different adverse effects on human health. Health problems decrease performance and work productivity and increase the occurrence of accidents and injuries. Serious health problems can also result in absence from work due to sick leave or hospitalization. At its worst, work in cold conditions could be associated with deaths due to cold-related accidents or a sudden health event. Musculoskeletal complaints, like pain, aches etc. are common in indoor cold work. Breathing cold air while working may lead to respiratory symptoms, which can decrease performance in cold. The symptoms are usually worsened by exercise and ageing, being more common in persons having a respiratory disease. Cardiovascular complaints and related performance decrements could be especially pronounced during work in cold weather and involving physical exercise, especially among those with an underlying cardiovascular disease. The article also reviews the current information related to diabetes, skin disorders and diseases, as well as cold injuries and accidents occurring in cold work. Increasing awareness and identifying workplace- and individual-related cold risks is the first step in proper cold risk management. Following this, the susceptible population groups need customized advice on proper prevention and protection in cold work.

Modification of atrial natriuretic peptide system in cold-induced hypertensive rats

Cold exposure induces hypertension and cardiac hypertrophy via sympathetic activation. The sympathetic nervous system is fundamentally important for the regulation of cardiac atrial natriuretic peptide (ANP) secretion. The present study aimed to define changes in ANP level with renal functions during cold exposure of rats. We also measured the direct effects of adrenergic stimulation on ANP secretion in cold-induced hypertensive rat atria. Sustained elevation of blood pressure and tachycardia were observed by 2-wk cold exposure. Cold exposure increased urine volume, UNaV, UKV and positive water balance. Atrial ANP content, its mRNA level, and plasma ANP concentration increased. Plasma norepinephrine level was increased but both alpha(1A)- and beta(1)-adrenoceptor (AR) mRNA levels in atrium were decreased. In isolated perfused atria from cold-exposed rats, basal ANP secretion increased and pulse pressure decreased. Phenylephrine (alpha(1)-AR agonist)-induced stimulation of ANP secretion, and isoproterenol (beta-AR agonist)-induced suppression of ANP secretion were significantly attenuated. These results suggest that an increased plasma and atrial ANP level by cold exposure may be a compensatory response to changes in hemodynamics and body fluid balance. The phenylephrine- and isoproterenol-induced attenuation of ANP secretion in cold-exposed rat atria may be due to the downregulation of alpha(1A)- and beta(1)-adrenoceptors mRNA levels.

Associations between environmental exposures and serum concentrations of Clara cell protein among elderly men in Oslo, Norway

Cardiopulmonary morbidity and mortality is associated with several environmental exposures. Mechanistically, pathophysiological changes in the cardiopulmonary system may lead to the induction of inflammatory responses. In the present study we explored associations between environmental exposures and serum concentrations of lung Clara cell protein 16kDa, a biomarker that has recently been used to assess the integrity of the lung epithelium. Serum Clara cell protein concentrations were associated with both number of cigarettes smoked per day and number of pack-years of smoking. There was no evidence of an association between long-term exposure to ambient air pollution, as assessed at each participant's home address, and serum concentrations of CC16. However, short-term variations in both ambient air pollution and temperature were associated with increases in serum Clara cell concentrations. All findings were robust when other factors were adjusted for. These findings suggest that acute environmental exposures may compromise the integrity of the lung epithelium and lead to increased epithelial barrier permeability in the lungs of elderly men.

RNAi inhibition of mineralocorticoid receptors prevents the development of cold-induced hypertension

The objective was to determine whether the mineralocorticoid receptor (MR) plays a role in the initiation and development of cold-induced hypertension (CIH) by testing the hypothesis that the RNA interference (RNAi) inhibition of the MR attenuates CIH. The recombinant adeno-associated virus (AAV) carrying a short-hairpin small-interference RNA for MR (MRshRNA) or a scrambled sequence (ControlshRNA) was constructed. Six groups of albino mice were used (6 mice/group). Three groups were exposed to cold (6.7°C), whereas the remaining three groups were kept at room temperature (RT; warm) as controls. In each temperature condition, three groups received an intravenous injection of MRshRNA, ControlshRNA, or virus-free PBS, respectively, before exposure to cold. The viral complexes (0.35 × 1011 particles/mouse, 0.5 ml) or PBS (0.5 ml) was delivered into the circulation via the tail vein. The blood pressure (BP) of the mice treated with ControlshRNA or PBS increased significantly during exposure to cold, whereas the BP of the cold-exposed MRshRNA-treated mice did not increase and remained at the level of the control group kept at RT. Thus AAV delivery of MRshRNA prevented the initiation of CIH. MRshRNA significantly attenuated cardiac and renal hypertrophy. MRshRNA decreased the cold-induced increase in MR protein expression to the control level in the hypothalamus, kidneys, and heart, indicating an effective prevention of the cold-induced upregulation of MR. RNAi inhibition of MR resulted in significant decreases in the plasma level of norepinephrine, plasma renin activity, and plasma level of aldosterone in cold-exposed mice. MR played a critical role in the initiation and development of CIH. AAV delivery of MRshRNA may serve as a new approach for the prevention of cold-induced hypertension.

Effects of alcohol consumption and other lifestyle behaviors on blood pressure for the middle-aged and elderly in the Guangxi Hei Yi Zhuang and Han populations

Han is the largest group and Zhuang is the largest minority among the 56 ethnic groups in China. Geographically and linguistically, Zhuang can be classified into 43 ethnic subgroups, in which Hei Yi Zhuang is proved to be the most conservative subgroup. Little is known about the relationship between alcohol consumption and blood pressure levels in this population. Therefore, the present study was undertaken to compare the effects of alcohol consumption and other lifestyle behaviors on blood pressure levels for the middle-aged and elderly in the Guangxi Hei Yi Zhuang and Han populations. A total of 657 subjects of Hei Yi Zhuang aged 40 and older were surveyed by a stratified randomized cluster sampling. Information on demography, diet, and other lifestyle factors was collected by standard questionnaires. Anthropometric parameters and serum lipid levels were also obtained in all subjects. The results were compared with those in 520 participants of Han Chinese from the same region. The levels of systolic blood pressure and pulse pressure in Hei Yi Zhuang were higher than those in Han (P < .01-.001). Hypertension was positively correlated with sex (male), age, physical activity, alcohol consumption, serum triglyceride levels, and total energy, total fat, and salt intakes, and negatively associated with educational level in Hei Yi Zhuang (P < .05-.001), whereas positively correlated with sex (male), age, physical activity, alcohol consumption, body mass index, waist circumference, serum total cholesterol levels, and total energy, total fat, and salt intakes, and negatively associated with educational level in Han (P < .05-.001). The difference in blood pressure levels between the two ethnic groups might result from different dietary habit, lifestyle, sodium intake, educational level, physical activity, and even genetic factors.

Effects of Demographic Characteristics, Health-Related Behaviors and Lifestyle Factors on the Prevalence of Hypertension for the Middle-Aged and Elderly in the Guangxi Hei Yi Zhuang and Han Populations

BACKGROUND/AIMS

Hei Yi (meaning black worship and black dress) Zhuang is the most conservative group among the 43 ethnic subgroups of Zhuang in China due to its unique culture and customs. The prevalence of hypertension in this population has not been well defined. Therefore, the present study was undertaken to compare the effects of the demographic characteristics, health-related behaviors and lifestyle factors on the prevalence of hypertension in the middle-aged and elderly of the Guangxi Hei Yi Zhuang and Han populations.

METHODS

A total of 657 people of Hei Yi Zhuang aged 40 and over were randomly selected from 7 villages in Napo County of China. Information on the demographic characteristics, health-related behaviors and lifestyle factors was collected by questionnaire. Blood pressure, height, weight, waist circumference, serum lipid and apolipoprotein levels were measured, and body mass index (BMI) was calculated as a measure of weight relative to height. The results were compared with those of 520 Han who live in the same district.

RESULTS

The prevalence of hypertension and isolated systolic hypertension in Hei Yi Zhuang was significantly higher than in Han (32.9 vs. 24.6%, p < 0.01, and 16.7 vs. 5.2%, p < 0.001, respectively). The systolic blood pressure levels and pulse pressure in Hei Yi Zhuang were also significantly higher than in Han (129 +/- 20.1 vs. 125.8 +/- 17.4 mm Hg, p < 0.01, and 51.5 +/- 16.1 vs. 47.1 +/- 12.0 mm Hg, p < 0.01, respectively). The prevalence of hypertension was positively correlated with triglycerides, male, age, and alcohol consumption in Hei Yi Zhuang, whereas it was positively correlated with total cholesterol, male, age, alcohol consumption and BMI in Han. The rates of awareness, treatment and control in Hei Yi Zhuang and Han are 7.9 vs. 19.5%, 4.2 vs. 13.3% and 1.4 vs. 9.4% (p < 0.01 for all), respectively.

CONCLUSION

The current study reveals a significant difference in the prevalence of hypertension, blood pressure levels, and the relative factors between the Hei Yi Zhuang and Han ethnic groups, which may have been due to differences in geographical characteristics, lifestyle, sodium intake, education levels, and even genetic factors.

Physiological reaction to work in cold microclimate

OBJECTIVES

In Poland, occupational exposure to cold microclimate is quite common (5.1 workers/1000 occupationally active people). Reports on health effects of this exposure are rather scarce. The aim of the study was to evaluate the physiological reaction in workers occupationally exposed to cold microclimate.

MATERIALS AND METHODS

Examinations were performed in a group of 102 workers (41 women and 61 men) employed at cold storage units. The mean age in the group was 39.1 +/- 9.9 years and the duration of employment under conditions of cold environment was over 12 years. The study population was divided into four groups, according to microclimate conditions (group I, ambient temperature -26 degrees C; group II, 10-14 degrees C; group III, 18-20 degrees C, control group; and group IV, 0-10 degress C). The workers underwent the following procedures: general medical examinations, cold pressor test, ambulatory blood pressure monitoring, and heart rate variability (HRV) analysis (time- and frequency-domain parameters).

RESULTS

The results were adjusted for confounding factors (age, smoking and drinking habits). The analysis of HRV parameters did not reveal any significant differences between the study groups. However, systolic and diastolic blood pressure (BP) in the daytime and at night was significantly higher in group IV compared to group II. Mean heart rate (HR) in the daytime and at night and the BP and HR day/night ratio did not differ between the groups. The analysis of BP by gender revealed that in women, systolic BP during the day and at night was significantly higher in group IV than in group II. In the group of workers with hypertension (18 men and 5 women), men reacted to the cold pressor test either by increased or decreased BP while all the women reacted by the increased BP.

CONCLUSIONS

Our findings indicated that in workers exposed to cold microclimate, the physiological reaction was dependent on gender and ambient temperature. Women seemed to be more sensitive to cold stress than men. However, this finding must be further investigated.

Associations between environmental exposure and blood pressure among participants in the Oslo Health Study (HUBRO)

BACKGROUND

It is well known that environmental conditions are related to the risk of developing cardiovascular diseases and events. However, the mechanisms behind these relations are not well understood. One mechanism could be elevation of blood pressure. In this study we assessed associations between blood pressure and environmental conditions among citizens in Oslo, Norway.

MATERIALS AND METHODS

We used the Oslo Health Study (HUBRO), a population based study of 18,770 Oslo citizens, to assess associations between blood pressure and environmental conditions including season, smoking, outdoor temperature and air pollution.

RESULTS

Blood pressure was higher in the winter season, but the association disappeared when we adjusted for temperature. A 10 degrees C reduction in outdoor temperature, the day blood pressure was measured was related to an increase in blood pressure for both men [SBP: 1.5 mmHg (95% CI, 0.6-2.3); DBP: 1.3 mmHg (95% CI, 0.1-1.8)] and women [SBP: 2.4 mmHg (95% CI, 1.6-3.2); DBP: 1.8 mmHg (95% CI, 1.3-2.3)]. No convincing relation was found between indicators of air pollution exposure and blood pressure.

CONCLUSION

Several environmental conditions were related to blood pressure, and have similar associations with cardiovascular diseases or mortality. This could indicate that some of the effect these exposures have on the cardiovascular system is by increasing blood pressure.

Effects of chronic cold exposure on the endothelin system

Cold temperatures have adverse effects on the human cardiovascular system. Endothelin (ET)-1 is a potent vasoconstrictor. We hypothesized that cold exposure increases ET-1 production and upregulates ET type A (ETA) receptors. The aim of this study was to determine the effect of cold exposure on regulation of the ET system. Four groups of rats (6–7 rats/group) were used: three groups were exposed to moderate cold (6.7 ± 2°C) for 1, 3, and 5 wk, respectively, and the remaining group was maintained at room temperature (25°C) and served as control. Cold exposure significantly increased ET-1 levels in the heart, mesenteric arteries, renal cortex, and renal medulla. Cold exposure increased ETA receptor protein expression in the heart and renal cortex. ET type B (ETB) receptor expression, however, was decreased significantly in the heart and renal medulla of cold-exposed rats. Cold exposure significantly increased the ratio of ETA to ETB receptors in the heart. An additional four groups of rats (3 rats/group) were used to localize changes in ETA and ETB receptors at 1, 3, and 5 wk of cold exposure. Immunohistochemical analysis showed an increase in ETA, but a decrease in ETB, receptor immunoreactivity in cardiomyocytes of cold-exposed rats. Increased ETA receptor immunoreactivity was also found in vascular smooth muscle cells of cold-exposed rats. Cold exposure increased ETA receptor immunoreactivity in tubule epithelial cells in the renal cortex but decreased ETB receptor immunoreactivity in tubule epithelial cells in the renal medulla. Therefore, cold exposure increased ET-1 production, upregulated ETA receptors, and downregulated ETB receptors.

AAV delivery of mineralocorticoid receptor shRNA prevents progression of cold-induced hypertension and attenuates renal damage

The aim of this study was to determine the effect of RNA interference inhibition of mineralocorticoid receptor (MR) on cold-induced hypertension (CIH) and renal damage. Recombinant adeno-associated virus (AAV) carrying short hairpin small interference (si)RNA for MR (AAV.MR-shRNA) was constructed and tested for the ability to inhibit renal MR and to control CIH. Three groups of rats with CIH received AAV.MR-shRNA (1.25 x 10(9) particles/rat, intravenous), AAV carrying scrambled shRNA (AAV.Control-shRNA) (1.25 x 10(9) particles/rat, intravenous) and phosphate buffer solution (PBS), respectively. All rats were kept in a cold chamber (6.7 degrees C) throughout the experiment. Adeno-associated virus delivery of MR-shRNA prevented progression of CIH. Blood pressure (BP) of the AAV.MR-shRNA-treated group did not increase and remained at 145+/-3 mm Hg, whereas BP of the AAV.Control-shRNA-treated and PBS-treated group increased to 167+/-4 and 161+/-3 mm Hg, respectively, at 3 weeks after gene delivery. Thus, the antihypertensive effect of a single injection of AAV.MR-shRNA lasted for at least 3 weeks (length of the study). Adeno-associated virus carrying short hairpin siRNA for MR significantly increased urinary sodium excretion and decreased proteinuria. It also decreased serum creatinine and blood urea nitrogen, suggesting enhanced renal function. Both Western blot and immunohistochemical analysis showed that MR expression was decreased significantly in the kidney in the AAV.MR-shRNA-treated rats, confirming that renal MR is effectively inhibited by AAV.MR-shRNA. Adeno-associated virus carrying short hairpin siRNA for MR also significantly attenuated renal hypertrophy. In addition, AAV delivery of MR-shRNA prevented atrophy and dilation of renal tubules and abolished tubular deposition of proteinaceous material seen in CIH rats.

CONCLUSIONS

(1) AAV delivery of MR-shRNA effectively silenced MR in vivo. (2) RNA interference inhibition of MR may open a new avenue for the long-term control of hypertension and renal damage.

The thermoregulatory-vascular remodeling hypothesis: an explanation for essential hypertension

The supposition that temperature homeostasis has precedence over blood pressure homeostasis, that vascular remodeling ensues, that hypertension is the consequence and that sodium chloride ingestion sets the sequence in motion, constitutes the thermoregulatory-vascular remodeling hypothesis. Because the cardiovascular system plays a role in both temperature and blood pressure regulation, the ingestion of sodium chloride creates conflict between temperature homeostasis and blood pressure homeostasis. Vasodilatation would lower the blood pressure following the ingestion of sodium chloride, but increased blood flow to the cutaneous circulation would increase heat loss and decrease core body temperature. Regional vasodilatation that does not involve the cutaneous circulation could lower the blood pressure without lowering the core temperature, but if temperature homeostasis has precedence over blood pressure homeostasis, and if regional vasodilatation incompletely restores blood pressure homeostasis, then elevations in blood pressure may persist following the ingestion of sodium chloride. The kidneys gradually excrete the excess sodium chloride, thereby normalizing the blood pressure, but prolonged elevations in blood pressure lead to vascular remodeling, sustained increases in peripheral resistance, and a higher baseline blood pressure. Following countless sodium chloride ingestions, essential hypertension develops. The thermoregulatory-vascular remodeling hypothesis predicts that antihypertensive medications that are vasodilators will accelerate heat loss due to increased blood flow to the cutaneous circulation. As a result, either core body temperature will decrease or there will be a compensatory increase in the metabolic rate. This prediction could be tested experimentally. The main clinical implication of the thermoregulatory-vascular remodeling hypothesis is that avoiding the ingestion of sodium chloride is the key to preventing essential hypertension.

Prevalence, Awareness, Treatment, Control and Risk Factors of Hypertension in the Guangxi Hei Yi Zhuang and Han Populations

Han is the largest nationality and Zhuang is the largest minority among the 56 nationalities in China. Geographically and linguistically, Zhuang can be classified into 43 ethnic subgroups, with the Hei Yi Zhuang Chinese, who live in Napo County bordering northeast Vietnam and comprise a population of 51,655, having the most conservative culture and customs (Hei Yi means "black-clothing" and the Hei Yi Zhuang revere and wear the color black). The determinants of hypertension and its risk factors in this population have not been well-defined. To obtain some of this information, a cross-sectional study of hypertension was carried out in 1,166 Hei Yi Zhuang Chinese (aged 7-84; mean, 44.00+/-17.54 years) and 1,018 Han Chinese controls (42.95+/-17.11; range, 6-89 years) in the same area. Information on demographic characteristics, health-related behaviors and lifestyle factors was collected by questionnaire. The overall prevalence rates of hypertension and isolated systolic hypertension in Hei Yi Zhuang were higher than those in Han (23.2% vs. 16.0% and 11.5% vs. 3.7%; p<0.001 for each). The levels of systolic blood pressure and pulse pressure in Hei Yi Zhuang were also higher than those in Han (p<0.001 for each). The prevalence of hypertension was positively correlated with triglycerides, male gender, and age in Hei Yi Zhuang, whereas it was positively correlated with total cholesterol, male gender, age, and alcohol consumption in Han. The rates of awareness, treatment and control in Hei Yi Zhuang were lower than those in Han (8.5% vs. 20.9%, 4.4% vs. 15.3%, and 1.9% vs. 10.4%; p<0.001 for each), which may have been due to unique geographical characteristics, unwholesome lifestyles, greater sodium intake, lower education levels, and genetic risk factors in the former group.