Renal responses to chronic cold exposure

Reduced hepatic bradykinin degradation accounts for cold-induced BAT thermogenesis and WAT browning in male mice

An important role for liver in the regulation of adipose tissue thermogenesis upon cold exposure has been suggested; however, the underlying mechanisms remain incompletely defined. Here, we identify elevated serum bradykinin levels in response to acute cold exposure in male mice. A bolus of anti-bradykinin antibodies reduces body temperature during acute cold exposure, whereas bradykinin has the opposite effect. We demonstrate that bradykinin induces brown adipose tissue thermogenesis and white adipose tissue browning, and bradykinin increases uncoupling protein 1 (UCP1) expression in adipose tissue. The bradykinin B2 receptor (B2R), adrenergic signaling and nitric oxide signaling are involved in regulating bradykinin-increased UCP1 expression. Moreover, acute cold exposure inhibits hepatic prolyl endopeptidase (PREP) activity, causing reduced liver bradykinin degradation and increased serum bradykinin levels. Finally, by blocking the breakdown of bradykinin, angiotensin-converting enzyme inhibitors (ACEIs) increase serum bradykinin levels and induce brown adipose tissue thermogenesis and white adipose tissue browning via B2R. Collectively, our data provide new insights into the mechanisms underlying organ crosstalk in whole-body physiology control during cold exposure and also suggest bradykinin as a possible anti-obesity target.

The hypokalaemia that came from the cold

While electrolyte disorders are common in nephrologists' clinical practice, hypothermia is a condition that nephrologists rarely encounter. Hypothermia can induce several pathophysiological effects on the human body, including hypokalaemia, which is reversible with rewarming. Despite growing evidence from animal research and human studies, the underlying mechanisms of hypothermia-induced hypokalaemia remain unclear. Boubes and colleagues recently presented a case series of hypokalaemia during hypothermia and rewarming, proposing a novel hypothesis for the underlying mechanisms. In this editorial, we review the current knowledge about hypothermia and associated electrolyte changes with insights into the effects of hypothermia on renal physiology.

Pre-hospital hypothermia is associated with transfusion risk after traumatic injury

OBJECTIVES

In traumatically injured patients, excessive blood loss necessitating the transfusion of red blood cell (RBC) units is common. Indicators of early RBC transfusion in the pre-hospital setting are needed. This study aims to evaluate the association between hypothermia (<36°C) and transfusion risk within the first 24 hours after arrival to hospital for a traumatic injury.

METHODS

We completed an audit of all traumatically injured patients who had emergent surgery at a single tertiary care center between 2010 and 2014. Using multivariable logistic regression analysis, we evaluated the association between pre-hospital hypothermia and transfusion of ≥1 unit of RBC within 24 hours of arrival to the trauma bay.

RESULTS

Of the 703 patients included to evaluate the association between hypothermia and RBC transfusion, 203 patients (29%) required a transfusion within 24 hours. After controlling for important confounding variables, including age, sex, coagulopathy (platelets and INR), hemoglobin, and vital signs (blood pressure and heart rate), hypothermia was associated with a 68% increased odds of transfusion in multivariable analysis (OR: 1.68; 95% CI: 1.11-2.56).

CONCLUSIONS

Hypothermia is strongly associated with RBC transfusion in a cohort of trauma patients requiring emergent surgery. This finding highlights the importance of early measures of temperature after traumatic injury and the need for intervention trials to determine if strategies to mitigate the risk of hypothermia will decrease the risk of transfusion and other morbidities.

AAV Delivery of Endothelin-1 shRNA Attenuates Cold-Induced Hypertension

Cold temperatures are associated with increased prevalence of hypertension. Cold exposure increases endothelin-1 (ET1) production. The purpose of this study is to determine whether upregulation of ET1 contributes to cold-induced hypertension (CIH). In vivo RNAi silencing of the ET1 gene was achieved by adeno-associated virus 2 (AAV2) delivery of ET1 short-hairpin small interfering RNA (ET1-shRNA). Four groups of male rats were used. Three groups were given AAV.ET1-shRNA, AAV.SC-shRNA (scrambled shRNA), and phosphate-buffered saline (PBS), respectively, before exposure to a moderately cold environment (6.7 ± 2°C), while the last group was given PBS and kept at room temperature (warm, 24 ± 2°C) and served as a control. We found that systolic blood pressure of the PBS-treated and SC-shRNA-treated groups increased significantly within 2 weeks of exposure to cold, reached a peak level (145 ± 4.8 mmHg) by 6 weeks, and remained elevated thereafter. By contrast, blood pressure of the ET1-shRNA-treated group did not increase, suggesting that silencing of ET1 prevented the development of CIH. Animals were euthanized after 10 weeks of exposure to cold. Cold exposure significantly increased the left ventricle (LV) surface area and LV weight in cold-exposed rats, suggesting LV hypertrophy. Superoxide production in the heart was increased by cold exposure. Interestingly, ET1-shRNA prevented cold-induced superoxide production and cardiac hypertrophy. ELISA assay indicated that ET1-shRNA abolished the cold-induced upregulation of ET1 levels, indicating effective silencing of ET1. In conclusion, upregulation of ET1 plays a critical role in the pathogenesis of CIH and cardiac hypertrophy. AAV delivery of ET1-shRNA is an effective therapeutic strategy for cold-related cardiovascular disease.

Accidental hypothermia in severe trauma

Hypothermia, along with acidosis and coagulopathy, is part of the lethal triad that worsen the prognosis of severe trauma patients. While accidental hypothermia is easy to identify by a simple measurement, it is no less pernicious if it is not detected or treated in the initial phase of patient care. It is a multifactorial process and is a factor of mortality in severe trauma cases. The consequences of hypothermia are many: it modifies myocardial contractions and may induce arrhythmias; it contributes to trauma-induced coagulopathy; from an immunological point of view, it diminishes inflammatory response and increases the chance of pneumonia in the patient; it inhibits the elimination of anaesthetic drugs and can complicate the calculation of dosing requirements; and it leads to an over-estimation of coagulation factor activities. This review will detail the pathophysiological consequences of hypothermia, as well as the most recent principle recommendations in dealing with it.

Urinary thrombomodulin and catecholamine levels are interrelated in healthy volunteers immersed in cold and warm water

Severe hypothermia has been shown to influence the levels of catecholamines and thrombomodulin, an endothelial protein essentially involved in the regulation of haemostasis and inflammation. A link between thrombomodulin and catecholamines during cold exposure has also been previously suggested. The aim of this study was to assess the influence of short-term cold exposure without hypothermia on catecholamines and the circulating and urinary thrombomodulin levels. Seven healthy male subjects were immersed in cold water (+10°C) for 10 minutes followed by a 20-minute immersion in +28°C water. Warm water immersion was performed separately for each subject (+30°C for 30 minutes). Thrombomodulin and catecholamine concentrations were measured from pre- and post-immersion (up to 23 hours) samples. In urine, the thrombomodulin level correlated strongly with adrenaline (ρ = 0.806) and noradrenaline (ρ = 0.760) levels. There were no significant differences in thrombomodulin levels between immersion temperatures. Post-immersion urinary thrombomodulin levels were significantly lower than the pre-immersion level at both immersion temperatures. Median concentrations of plasma noradrenaline and urinary adrenaline were higher after exposure to +10°C than to +30°C. Thus, further evidence of the association between thrombomodulin and catecholamines was gained in a physiologically relevant setting in humans. Additionally, it is evident that a short-term cold exposure was not able to elicit changes in the thrombomodulin levels in a follow-up period of up to 23 hours. These findings provide further understanding of the physiological responses to cold during immersion, and of the potential influence of stress on haemostatic and inflammatory responses.

Incidence of pregnancy-related discomforts and management approaches to relieve them among pregnant women

AIMS AND OBJECTIVES

To determine the incidence of pregnancy-related physical symptoms in healthy pregnant women and their management strategies.

BACKGROUND

In normal progression of pregnancy, many symptoms were experienced. Pregnancy-related physical symptoms may have a negative effect on pregnant women's quality of life. However, pregnant women avoid taking medications from the fear that the medication they use may have a harmful effect on the foetus. Therefore, they practise nonpharmacological methods to help them manage their pregnancy-related physical symptoms.

DESIGN

This study used a comparative and descriptive design.

METHODS

The study population comprised of pregnant women who were visiting for routine check-up and/or examination in the obstetrics gynaecology outpatient clinics of three hospitals in Erzurum, Turkey. The data were collected via a questionnaire including socio-demographic items and questions to identify the pregnancy-related physical symptoms that they experienced and their management strategies.

RESULTS

The top three most reported complaints were nausea-vomiting (87·8%), fatigue (77·9%) and breast pain-tenderness (76·2%) during the first trimester, whereas polyuria (79·9%, 88·4%), fatigue (75·6%, 88·4%) and heart burn (71·3%, 81·8%) during the second and third trimesters. Depending on the symptoms, the pregnant women either did nothing or took correct, incorrect or empirical actions to manage their problems. Data revealed that the major source of knowledge was based on their previous experience and that of close relatives. As their education level increased, the percentage of women taking scientifically proven action to correct the problem increased.

CONCLUSIONS

Various physical symptoms were experienced by women in each trimester of pregnancy. The majority of the women did not do anything to alleviate their physical symptoms.

RELEVANCE TO CLINICAL PRACTICE

Midwives and nurses should question the strategies used by pregnant women. In this way, the inappropriate and incorrect practices can be determined, and education on the appropriate practices can be provided.

Inhibition of phosphodiesterase-1 attenuates cold-induced pulmonary hypertension

Chronic exposure to cold caused pulmonary arterial hypertension (cold-induced pulmonary hypertension [CIPH]) and increased phosphodiesterase-1C (PDE-1C) expression in pulmonary arteries (PAs) in rats. The purpose of this study is to investigate a hypothesis that inhibition of PDE-1 would decrease inflammatory infiltrates and superoxide production leading to attenuation of CIPH. Three groups of male rats were exposed to moderate cold (5±1°C) continuously, whereas 3 groups were maintained at room temperature (23.5±1°C, warm; 6 rats/group). After 8-week exposure to cold, 3 groups in each temperature condition received continuous intravenous infusion of 8-isobutyl-methylxanthine (8-IBMX) (PDE-1 inhibitor), apocynin (NADPH oxidase inhibitor) or vehicle, respectively, for 1 week. Cold exposure significantly increased right-ventricular systolic pressure compared with warm groups (33.8±3.2 versus 18.6±0.3 mm Hg), indicating that animals developed CIPH. Notably, treatment with 8-IBMX significantly attenuated the cold-induced increase in right ventricular pressure (23.5±1.8 mm Hg). Cold exposure also caused right-ventricular hypertrophy, whereas 8-IBMX reversed cold-induced right ventricular hypertrophy. Cold exposure increased PDE-1C protein expression, macrophage infiltration, NADPH oxidase activity, and superoxide production in PAs and resulted in PA remodeling. 8-IBMX abolished cold-induced upregulation of PDE-1C in PAs. Interestingly, inhibition of PDE-1 eliminated cold-induced macrophage infiltration, NADPH oxidase activation, and superoxide production in PAs and reversed PA remodeling. Inhibition of NADPH oxidase by apocynin abolished cold-induced superoxide production and attenuated CIPH and PA remodeling. In conclusion, inhibition of PDE-1 attenuated CIPH and reversed cold-induced PA remodeling by suppressing macrophage infiltration and superoxide production, suggesting that upregulation of PDE-1C expression may be involved in the pathogenesis of CIPH.

Mild therapeutic hypothermia in cardiogenic shock syndrome

OBJECTIVE

Mortality in patients with cardiogenic shock after out-of-hospital cardiac arrest remains high despite advances in resuscitation and early revascularization strategies. Recent studies suggest a reduced mortality in survivors of cardiac arrest subjected to mild therapeutic hypothermia, but the underlying mechanisms are not yet clear. Because positive hemodynamic effects of mild therapeutic hypothermia have been suggested, we aimed at testing the hypothesis that patients in cardiogenic shock might benefit from mild therapeutic hypothermia.

METHODS

Hemodynamic effects of mild therapeutic hypothermia in 20 consecutive patients admitted in cardiogenic shock after successful resuscitation from out-of-hospital cardiac arrest were investigated. A historic normothermic control group was matched (one-to-one) by means of a propensity score. Patients were cooled to 33°C for 24 hrs using an endovascular cooling device and hemodynamic variables were continuously recorded by means of pulse contour analysis. Cardiac performance was determined by echocardiography.

RESULTS

Mild therapeutic hypothermia induced a significant decrease in heart rate from 74 to 64 beats per minute. Despite the reduction in heart rate, cardiac index remained unchanged under mild therapeutic hypothermia likely due to an increase in ejection fraction from 43 ± 4% to 55 ± 4%. Mean arterial pressure increased rapidly from 75 ± 2 mm Hg to 84 ± 3 mm Hg (p = .001) upon induction of hypothermia paralleled by an initial increase in systemic vascular resistance. Accordingly, patients with mild therapeutic hypothermia required lower cumulative doses of vasopressors and inotropes.

CONCLUSIONS

We conclude that in cardiogenic shock mild therapeutic hypothermia provides circulatory support and an increase in systemic vascular resistance that leads to reduced vasopressor use and may result in lower oxygen consumption. These findings suggest that mild therapeutic hypothermia could be a therapeutic option in hemodynamically unstable patients independent of cardiac arrest and further randomized clinical studies are needed.

Klotho gene delivery suppresses Nox2 expression and attenuates oxidative stress in rat aortic smooth muscle cells via the cAMP-PKA pathway

Klotho is a recently discovered anti-aging gene. The purpose of this study was to investigate whether klotho gene transfer attenuates superoxide production and oxidative stress in rat aorta smooth muscle (RASM) cells. RASM cells were transfected with AAV plasmids carrying mouse klotho full-length cDNA (mKL) or LacZ as a control. Klotho gene transfer increased klotho expression in RASM cells. Notably, klotho gene expression decreased Nox2 NADPH oxidase protein expression but did not affect Nox2 mRNA expression, suggesting that the inhibition may occur at the posttranscriptional level. Klotho gene transfer decreased intracellular superoxide production and oxidative stress in RASM cells. Klotho gene expression also significantly attenuated the angiotensin II (AngII)-induced superoxide production, oxidative damage, and apoptosis. Interestingly, klotho gene delivery dose dependently increased the intracellular cAMP level and PKA activity in RASM cells. Rp-cAMP, a competitive inhibitor of cAMP, abolished the klotho-induced increase in PKA activity, indicating that klotho activated PKA via cAMP. Notably, inhibition of cAMP-dependent PKA activity by RP-cAMP abolished klotho-induced inhibition of Nox2 protein expression, suggesting an important role of cAMP-dependent PKA in this process. This finding revealed a previously unidentified role of klotho in regulating Nox2 protein expression in RASM cells. Klotho not only downregulated Nox2 protein expression and intracellular superoxide production but also attenuated AngII-induced superoxide production, oxidative damage, and apoptosis. The klotho-induced suppression of Nox2 protein expression may be mediated by the cAMP-PKA pathway.

Klotho gene delivery suppresses Nox2 expression and attenuates oxidative stress in rat aortic smooth muscle cells via the cAMP-PKA pathway

Klotho is a recently discovered anti-aging gene. The purpose of this study was to investigate whether klotho gene transfer attenuates superoxide production and oxidative stress in rat aorta smooth muscle (RASM) cells. RASM cells were transfected with AAV plasmids carrying mouse klotho full-length cDNA (mKL) or LacZ as a control. Klotho gene transfer increased klotho expression in RASM cells. Notably, klotho gene expression decreased Nox2 NADPH oxidase protein expression but did not affect Nox2 mRNA expression, suggesting that the inhibition may occur at the posttranscriptional level. Klotho gene transfer decreased intracellular superoxide production and oxidative stress in RASM cells. Klotho gene expression also significantly attenuated the angiotensin II (AngII)-induced superoxide production, oxidative damage, and apoptosis. Interestingly, klotho gene delivery dose dependently increased the intracellular cAMP level and PKA activity in RASM cells. Rp-cAMP, a competitive inhibitor of cAMP, abolished the klotho-induced increase in PKA activity, indicating that klotho activated PKA via cAMP. Notably, inhibition of cAMP-dependent PKA activity by RP-cAMP abolished klotho-induced inhibition of Nox2 protein expression, suggesting an important role of cAMP-dependent PKA in this process. This finding revealed a previously unidentified role of klotho in regulating Nox2 protein expression in RASM cells. Klotho not only downregulated Nox2 protein expression and intracellular superoxide production but also attenuated AngII-induced superoxide production, oxidative damage, and apoptosis. The klotho-induced suppression of Nox2 protein expression may be mediated by the cAMP-PKA pathway.

Thyroid hormone induces artery smooth muscle cell proliferation: discovery of a new TRalpha1-Nox1 pathway

Thyroid hormone (T3) can stimulate protein synthesis and cell growth. NOX1 is a mitogenic oxidase. The aim of this study was to test a novel hypothesis that T3 induces artery smooth muscle cell proliferation by up-regulating NOX1. Immunofluoresence confocal microscopy was used to visualize the sub-cellular localization of NOX1 and TRα1 in rat aorta smooth muscle (RASM) cells. Optical sectioning showed that TRα1 and NOX1 co-localized around the nucleus. T3 promoted RASM cell proliferation as determined by the fact that T3 significantly increased the number of cytokinesis cells, proliferating cellular nuclear antigen (PCNA) and smooth muscle α-actin (SM α-actin). T3 increased NOX1 expression at both the transcription (mRNA) and translation (protein) levels as evaluated by RT-PCR and Western blot, respectively. T3 also significantly increased the intracellular ROS production based on the oxidation of 2’,7’-dichlorodihydrofluoresein (H₂DCF) to a fluorescent 2’,7’-dichlorofluoresein (DCF). RNAi silence of TRα1 or NOX1 abolished T3-induced intracellular ROS generation and PCNA and SM α-actin expression, indicating that TRα1 and NOX1 mediated T3-induced RASM cell proliferation. Notably, RNAi silence of TRα1 blocked the T3-induced increase in NOX1 expression, whereas silence of NOX1 did not affect TRα1 expression, disclosing a new pathway, i.e. T3-TRα1-NOX1-cell proliferation. TRα1 and NOX1 co-localized around the nucleus. T3 induced RASM cell proliferation by up-regulating NOX1 in a TRα1-dependent manner.

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

Mild to moderate hypothermia (32-35 degrees C) is the first treatment with proven efficacy for postischemic neurological injury. In recent years important insights have been gained into the mechanisms underlying hypothermia's protective effects; in addition, physiological and pathophysiological changes associated with cooling have become better understood.

OBJECTIVE

To discuss hypothermia's mechanisms of action, to review (patho)physiological changes associated with cooling, and to discuss potential side effects.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

A myriad of destructive processes unfold in injured tissue following ischemia-reperfusion. These include excitotoxicty, neuroinflammation, apoptosis, free radical production, seizure activity, blood-brain barrier disruption, blood vessel leakage, cerebral thermopooling, and numerous others. The severity of this destructive cascade determines whether injured cells will survive or die. Hypothermia can inhibit or mitigate all of these mechanisms, while stimulating protective systems such as early gene activation. Hypothermia is also effective in mitigating intracranial hypertension and reducing brain edema. Side effects include immunosuppression with increased infection risk, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy. Targeted interventions are required to effectively manage these side effects. Hypothermia does not decrease myocardial contractility or induce hypotension if hypovolemia is corrected, and preliminary evidence suggests that it can be safely used in patients with cardiac shock. Cardiac output will decrease due to hypothermia-induced bradycardia, but given that metabolic rate also decreases the balance between supply and demand, is usually maintained or improved. In contrast to deep hypothermia (<or=30 degrees C), moderate hypothermia does not induce arrhythmias; indeed, the evidence suggests that arrhythmias can be prevented and/or more easily treated under hypothermic conditions.

CONCLUSIONS

Therapeutic hypothermia is a highly promising treatment, but the potential side effects need to be properly managed particularly if prolonged treatment periods are required. Understanding the underlying mechanisms, awareness of physiological changes associated with cooling, and prevention of potential side effects are all key factors for its effective clinical usage.

Interindividual variability in plasma concentrations after systemic exposure of swine to dietary doxycycline supplied with and without paracetamol: a population pharmacokinetic approach

Anorexigenic substances released during infection may hinder the therapeutic efficacy of in-feed antibiotics. Paracetamol (acetaminophen; PARA) inhibits the anorexia of infection and seems to improve the clinical efficacy of doxycycline (DOX) against bacterial respiratory disease in swine herds. In order to verify whether PARA selectively stimulates intake of DOX-medicated feed in diseased pigs, we documented the pharmacokinetics (PK) of DOX when coadministered with PARA and examined the effect of in-feed PARA on the interindividual variability in plasma concentrations after systemic exposure to in-feed DOX in swine herds with respiratory disease. Systemic exposure to DOX was measured with the area under the curve (AUC) of its plasma concentrations over time. First, a rich-sampling PK study of in-feed and i.v. DOX (10 mg/kg of BW) and PARA (30 and 10 mg/kg of BW, respectively) was performed on 5 pigs. The PK profiles of in-feed DOX were used in mathematical simulations to determine 5 optimal sampling times for the farm-based population PK study. A randomized, blind, parallel PK study was performed in 2 herds with bacterial respiratory disease, where liquid feed was fortified with DOX alone (5 mg x kg of BW(-1) x meal(-1)) or combined with PARA (15 mg x kg of BW(-1) x meal(-1)). Medicated meals were given twice, 12 h apart, to group-housed growing pigs (n > 50 pigs x treatment(-1) x herd(-1), totaling 215 pigs). Plasma concentrations of DOX and PARA were measured with HPLC. At variance with our expectations, PARA decreased (P = 0.069) mean AUC of in-feed DOX and did not decrease its variability (P > 0.34). Mean AUC of DOX increased with feed intake and with initial exposure to DOX, and was greater in sick animals. Therefore, symptomatic PARA-induced improvement in bacterial respiratory disease control with DOX is more likely caused by its analgesic/antipyretic effects than by its orexigenic effect. Interindividual variation in the AUC of DOX was large in pigs given group medication, even when sufficient feeding space was allowed and the amount of feed offered was greater than their requirements. Therefore, future studies to improve the efficacy of group antibiotic therapy should focus on feeding behavior characteristics as well as biopharmaceutical properties of medicated feeds.

Genetic AVP deficiency abolishes cold-induced diuresis but does not attenuate cold-induced hypertension

Chronic cold exposure causes hypertension and diuresis. The aim of this study was to determine whether vasopressin (AVP) plays a role in cold-induced hypertension and diuresis. Two groups of Long-Evans (LE) and two groups of homozygous AVP-deficient Brattleboro (VD) rats were used. Blood pressure (BP) was not different among the four groups during a 2-wk control period at room temperature (25 degrees C, warm). After the control period, one LE group and one VD group were exposed to cold (5 degrees C); the remaining groups were kept at room temperature. BP and body weight were measured weekly during exposure to cold. Food intake, water intake, urine output, and urine osmolality were measured during weeks 1, 3, and 5 of cold exposure. At the end of week 5, all animals were killed and blood was collected for measurement of plasma AVP. Kidneys were removed for measurement of renal medulla V2 receptor mRNA and aquaporin-2 (AQP-2) protein expression. BP of LE and VD rats increased significantly by week 2 of cold exposure and reached a high level by week 5. BP elevations developed at approximately the same rate and to the same degree in LE and VD rats. AVP deficiency significantly increased urine output and solute-free water clearance and decreased urine osmolality. Chronic cold exposure increased urine output and solute-free water clearance and decreased urine osmolality in LE rats, indicating that cold exposure caused diuresis in LE rats. Cold exposure failed to affect these parameters in VD rats, suggesting that the AVP system is responsible for cold-induced diuresis. Cold exposure did not alter plasma AVP in LE rats. Renal medulla V2 receptor mRNA and AQP-2 protein expression levels were decreased significantly in the cold-exposed LE rats, suggesting that cold exposure inhibited renal V2 receptors and AVP-inducible AQP-2 water channels. We conclude that 1) AVP may not be involved in the pathogenesis of cold-induced hypertension, 2) the AVP system plays a critical role in cold-induced diuresis, and 3) cold-induced diuresis is due to suppression of renal V2 receptors and the associated AQP-2 water channels, rather than inhibition of AVP release.

Uric acid, evolution and primitive cultures

Hypertension is epidemic and currently affects 25% of the world's population and is a major cause of stroke, congestive heart failure, and end-stage renal disease. Interestingly, there is evidence that the increased frequency of hypertension is a recent event in human history and correlates with dietary changes associated with Westernization. In this article, we review the evidence that links uric acid to the cause and epidemiology of hypertension. Specifically, we review the evidence that the mutation of uricase that occurred in the Miocene that resulted in a higher serum uric acid in humans compared with most other mammals may have occurred as a means to increase blood pressure in early hominoids in response to a low-sodium and low-purine diet. We then review the evidence that the epidemic of hypertension that evolved with Westernization was associated with an increase in the intake of red meat with a marked increase in serum uric acid levels. Indeed, gout and hyperuricemia should be considered a part of the obesity, type 2 diabetes, and hypertension epidemic that is occurring worldwide. Although other mechanisms certainly contribute to the pathogenesis of hypertension, the possibility that serum uric acid level may have a major role is suggested by these studies.

Genetic AT1Areceptor deficiency attenuates cold-induced hypertension

The aim of this study was to test our hypotheses that AT1Areceptors play a role in the pathogenesis of cold-induced hypertension (CIH) and in the cold-induced increase in drinking responses to ANG II. Two groups of wild-type (WT) and two groups of AT1Areceptor gene knockout (AT1A-KO) mice were used (6/group). Blood pressures (BP) of the four groups were similar during the control period at room temperature (25°C). After the control period, one group of WT and one group of AT1A-KO mice were exposed to cold (5°C), while the remaining groups were kept at 25°C. BP of the cold-exposed WT group elevated significantly within 1 wk of exposure to cold and increased gradually to a maximum level by week 5. However, there was only a slight increase in BP of the cold-exposed AT1A-KO group. The maximal cold-induced increase in BP (ΔBP) is significantly less in AT1A-KO group (11 ± 3 mmHg) than in WT group (49 ± 6 mmHg), indicating that AT1Areceptor deficiency attenuates cold-induced elevation of BP. Interestingly, both WT and AT1A-KO mice developed cardiac and renal hypertrophy to the same extent. AT1A-KO caused a significant increase in urine and plasma levels of nitric oxide (NO), indicating that the renin-angiotensin system inhibits NO formation probably via AT1Areceptors. Cold exposure inhibited endothelial NO synthase protein expressions and decreased urine and plasma levels of NO, which may be mediated partially by AT1Areceptors. AT1A-KO completely abolished the cold-induced increase in drinking responses to ANG II. We conclude that 1) AT1Areceptors play an essential role in the pathogenesis of CIH but not cardiac hypertrophy; 2) the role of AT1Areceptors in CIH may be mediated partially by its inhibitory effect on the NO system; and 3) cold-induced increase in drinking response to ANG II is mediated by AT1Areceptors.