Impaired atrial M(2)-cholinoceptor function in obesity-related hypertension

Body weight fluctuation is associated with rapid kidney function decline

OBJECTIVE

This study aimed to evaluate the effects of body weight fluctuations on kidney function deterioration in a prospective cohort of individuals with normal kidney function.

METHODS

Data were obtained from the Korean Genome and Epidemiology Study. Body weight fluctuations were determined using average successive variability (ASV), which was defined as the average absolute body weight change using repeated measurements for all participants. The decline of the estimated glomerular filtration rate (eGFR) over time was calculated using linear regression analysis of serial eGFR measurements for each patient. Rapid eGFR decline was defined as an average eGFR decline > 3 mL/min/1.73 m² per year.

RESULTS

A total of 6,790 participants were analyzed. During a median follow-up of 11.7 years, rapid eGFR decline was observed in 913 (13.4%) participants. When the participants were categorized into tertiles according to ASV, rapid eGFR decline was more prevalent in the highest ASV tertile group than in the lowest. Analyses using multiple logistic regression models revealed that the risk of rapid eGFR decline was increased in the highest ASV tertile group compared with the lowest (odds ratio: 1.66).

CONCLUSIONS

Body weight fluctuations were significantly associated with an increased risk of rapid kidney function decline in participants with normal kidney function.

Validation of obesity coding among newly treated nonvalvular atrial fibrillation patients using an integrated electronic medical record and claims database

Objective: To evaluate the validity of diagnosis codes for identifying obesity and morbid obesity among newly treated nonvalvular atrial fibrillation (NVAF) patients.Methods: An integrated electronic medical record (EMR) and claims database (1 January 2013-31 March 2018) was used. Adult patients with ≥1 claim for an oral anticoagulant (OAC) from 1 January 2014-30 September 2017 were identified (index date). Patients were required to have ≥1 atrial fibrillation diagnosis, no OAC use or valvular disease during the 12 months before index date, ≥12 months of continuous enrollment before and ≥6 months after index date, and ≥1 BMI measurement 6 months before or after index date. Patients with BMI ≥30 kg/m² and BMI ≥40 kg/m² were classified as obese and morbidly obese, respectively. Sensitivity, specificity and positive predictive value (PPV) were calculated to assess the validity of diagnosis codes for obesity and morbid obesity.Results: A total of 7501 patients met all selection criteria. Forty-six percent of patients had BMI ≥ 30 kg/m², of whom about one-quarter had a BMI ≥ 40 kg/m². Twenty-five percent and 10% of patients had a diagnosis code for obesity or morbid obesity, respectively. Sensitivity, specificity and PPV for obesity diagnosis codes were 48.67% (95% CI: 47.00%-50.35%), 95.24% (94.54%-95.88%) and 89.78% (88.32%-91.12%), respectively, and 62.75% (59.30%-66.11%), 96.46% (95.99%-96.89%) and 67.93% (64.43%-71.29%) for morbid obesity diagnosis codes, respectively.Conclusion: Among newly treated NVAF patients, obesity diagnosis codes had high PPV, high specificity and modest sensitivity. Morbid obesity diagnosis codes also had high specificity, but modest PPV and sensitivity. These findings have implications for case selection and control for obesity as a confounder in studies using a claims database.

Body mass index, abdominal fatness, fat mass and the risk of atrial fibrillation: a systematic review and dose-response meta-analysis of prospective studies

Different adiposity measures have been associated with increased risk of atrial fibrillation, however, results have previously only been summarized for BMI. We therefore conducted a systematic review and meta-analysis of prospective studies to clarify the association between different adiposity measures and risk of atrial fibrillation. PubMed and Embase databases were searched up to October 24th 2016. Summary relative risks (RRs) were calculated using random effects models. Twenty-nine unique prospective studies (32 publications) were included. Twenty-five studies (83,006 cases, 2,405,381 participants) were included in the analysis of BMI and atrial fibrillation. The summary RR was 1.28 (95% confidence interval: 1.20-1.38, I² = 97%) per 5 unit increment in BMI, 1.18 (95% CI: 1.12-1.25, I² = 73%, n = 5) and 1.32 (95% CI: 1.16-1.51, I² = 91%, n = 3) per 10 cm increase in waist and hip circumference, respectively, 1.09 (95% CI: 1.02-1.16, I² = 44%, n = 4) per 0.1 unit increase in waist-to-hip ratio, 1.09 (95% CI: 1.02-1.16, I² = 94%, n = 4) per 5 kg increase in fat mass, 1.10 (95% CI: 0.92-1.33, I² = 90%, n = 3) per 10% increase in fat percentage, 1.10 (95% CI: 1.08-1.13, I² = 74%, n = 10) per 5 kg increase in weight, and 1.08 (95% CI: 0.97-1.19, I² = 86%, n = 2) per 5% increase in weight gain. The association between BMI and atrial fibrillation was nonlinear, p _nonlinearity < 0.0001, with a stronger association at higher BMI levels, however, increased risk was observed even at a BMI of 22-24 compared to 20. In conclusion, general and abdominal adiposity and higher body fat mass increase the risk of atrial fibrillation.

The State of the Art: Atrial Fibrillation Epidemiology, Prevention, and Treatment

As the most common sustained arrhythmia in adults, atrial fibrillation (AF) is an established and growing epidemic. To provide optimal patient care, it is important for clinicians to be aware of AF's epidemiological trends, methods of risk reduction, and the various available treatment modalities. Our understanding of AF's pathophysiology has advanced, and with this new understanding has come advancements in prevention strategies as well as pharmacological and nonpharmacological treatment options. Following PubMed and MEDLINE searches for AF risk factors, epidemiology, and therapies, we reviewed relevant articles (and bibliographies of those articles) published from 2000 to 2016. This "state-of-the-art" review provides a comprehensive update on the understanding of AF in the world today, contemporary therapeutic options, and directions of ongoing and future study.

Incidence, Predictors, and Impact of Postoperative Atrial Fibrillation after Coronary Artery Bypass Grafting in Military Veterans

Little is known about the frequency and clinical implications of postoperative atrial fibrillation in military veterans who undergo coronary artery bypass grafting (CABG). We examined long-term survival data, clinical outcomes, and associated risk factors in this population. We retrospectively reviewed baseline, intraoperative, and postoperative data from 1,248 consecutive patients with similar baseline risk profiles who underwent primary isolated CABG at a Veterans Affairs hospital from October 2006 through March 2013. Multivariable logistic regression identified predictors of postoperative atrial fibrillation. Kaplan-Meier analysis was used to evaluate long-term survival (the primary outcome measure), morbidity, and length of hospital stay. Postoperative atrial fibrillation occurred in 215 patients (17.2%). Independent predictors of this sequela were age ≥65 years (odds ratios [95% confidence intervals], 1.7 [1.3-2.4] for patients of age 65-75 yr and 2.6 [1.4-4.8] for patients >75 yr) and body mass index ≥30 kg/m² (2.0 [1.2-3.2]). Length of stay was longer for patients with postoperative atrial fibrillation than for those without (12.7 ± 6.6 vs 10.3 ± 8.9 d; P ≤0.0001), and the respective 30-day mortality rate was higher (1.9% vs 0.4%; P=0.014). Seven-year survival rates did not differ significantly. Older and obese patients are particularly at risk of postoperative atrial fibrillation after CABG. Patients who develop the sequela have longer hospital stays than, but similar long-term survival rates to, patients who do not.

Review Of Obesity And Atrial Fibrillation: Exploring The Paradox

There is a well established association between obesity and atrial fibrillation (AF). Nevertheless, the effects of obesity in the outcomes of patients with AF has not been investigated since a few years before. In this regard, several studies have demonstrated a better clinical prognosis of AF in overweight and obese populations. In the present manuscrit, we aimed to explore the main articles in which the "obesity paradox in AF" was found.

Specific role of dietary fat in modifying cardiovascular and locomotor activity 24-h rhythms

Meal-fed conscious rabbits normally exhibit postprandial elevation in blood pressure, heart rate (HR) and locomotor activity, which is abolished by consumption of a high-fat diet (HFD). Here, we assessed whether the cardiovascular changes are attributable to the increased caloric intake due to greater fat content or to hyperphagia. Rabbits were meal-fed during the baseline period then maintained on either an ad libitum normal fat diet (NFD) or ad libitum HFD for 2 weeks. Blood pressure, HR and locomotor activity were measured daily by radio-telemetry alongside food intake and body weight. Caloric intake in rabbits given a NFD ad libitum rose 50% from baseline but there were no changes in cardiovascular parameters. By contrast, HR increased by 10% on the first day of the ad libitum HFD (p < 0.001) prior to any change in body weight while blood pressure increased 7% after 4 d (p < 0.01) and remained elevated. Baseline 24-h patterns of blood pressure and HR were closely associated with mealtime, characterised by afternoon peaks and morning troughs. When the NFD was changed from meal-fed to ad libitum, blood pressure and HR did not change but afternoon activity levels decreased (p < 0.05). By contrast, after 13 d ad libitum HFD, morning HR, blood pressure and activity increased by 20%, 8% and 71%, respectively. Increased caloric intake specifically from fat, but not as a result of hyperphagia, appears to directly modulate cardiovascular homeostasis and circadian patterns, independent of white adipose tissue accumulation.

A body shape index and heart rate variability in healthy indians with low body mass index

Background. One third of Indian population is said to be suffering from chronic energy deficiency (CED), with increased risk of developing chronic diseases. A new anthropometric measure called A Body Shape Index (ABSI) is said to be a better index in predicting risks for premature mortality. ABSI is also in part said to be a surrogate of visceral fat. Objective. The present study aimed to explore the association between indices of HRV (heart rate variability), BMI, WC, and ABSI in healthy Indian males with low BMI (BMI < 18.5 kg/m²) and to compare with normal BMI group (BMI 18.5 to 24.9 kg/m²). Methodology. ABSI and BMI were derived from anthropometric parameters, namely, height, weight, and waist circumference in 178 males aged 18 to 78 years. Subjects were categorized into two groups based on their BMI. Results and Conclusions. Power spectral analysis of HRV demonstrated a significant negative correlation between Log HF (high frequency) and ABSI in both low BMI [−24.2 (9.4), P < 0.05] and normal BMI group [−23.41 (10.1), P < 0.05] even after controlling for age. Thus even with slight increase in BMI among low BMI individuals, there could be a greater risk of cardiovascular morbidity and mortality.

Obesity, physical activity, and their interaction in incident atrial fibrillation in postmenopausal women

Background

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with increased risk of stroke and death. Obesity is an independent risk factor for AF, but modifiers of this risk are not well known. We studied the roles of obesity, physical activity, and their interaction in conferring risk of incident AF.

Methods and Results

The Women's Health Initiative (WHI) Observational Study was a prospective observational study of 93 676 postmenopausal women followed for an average of 11.5 years. Incident AF was identified using WHI‐ascertained hospitalization records and diagnostic codes from Medicare claims. A multivariate Cox's hazard regression model adjusted for demographic and clinical risk factors was used to evaluate the interaction between obesity and physical activity and its association with incident AF. After exclusion of women with prevalent AF, incomplete data, or underweight body mass index (BMI), 9792 of the remaining 81 317 women developed AF. Women were, on average, 63.4 years old, 7.8% were African American, and 3.6% were Hispanic. Increased BMI (hazard ratio [HR], 1.12 per 5‐kg/m² increase; 95% confidence interval [CI], 1.10 to 1.14) and reduced physical activity (>9 vs. 0 metabolic equivalent task hours per week; HR, 0.90; 95% CI, 0.85 to 0.96) were independently associated with higher rates of AF after multivariate adjustment. Higher levels of physical activity reduced the AF risk conferred by obesity (interaction P=0.033).

Conclusions

Greater physical activity is associated with lower rates of incident AF and modifies the association between obesity and incident AF.

Weight cycling during growth and beyond as a risk factor for later cardiovascular diseases: the 'repeated overshoot' theory

In people trying to lose weight, there are often repeated cycles of weight loss and regain. Weight cycling is, however, not limited to obese adults but affects people of normal weight, particularly young women, who are unhappy with their appearance. Furthermore, the onset of a pattern of weight cycling is shifting towards younger ages, owing to the increasing prevalence of overweight and obesity in children and adolescents, and the pressure from the media and society for a slim image even for normal weight children. Although there is still controversy whether weight cycling promotes body fat accumulation and obesity, there is mounting evidence from large population studies for increased cardiovascular risks in response to a behavior of weight cycling. Potential mechanisms by which weight cycling contributes to cardiovascular morbidity include hypertension, visceral fat accumulation, changes in adipose tissue fatty acid composition, insulin resistance and dyslipidemia. Moreover, fluctuations in blood pressure, heart rate, sympathetic activity, glomerular filtration rate, blood glucose and lipids that may occur during weight cycling--with overshoots above normal values during weight regain periods--put an additional load on the cardiovascular system, and may be easily overlooked if humans or animals are studied during a state of relatively stable weight. Overshoot of those risks factors, when repeated over time, will stress the cardiovascular system and probably contribute to the overall cardiovascular morbidity of weight cycling.

Influence of obesity on outcomes in atrial fibrillation: yet another obesity paradox

BACKGROUND

Obese patients have favorable outcomes in congestive heart failure, hypertension, peripheral vascular disease, and coronary artery disease. Obesity also has been linked with increased incidence of atrial fibrillation, but its influence on outcomes in atrial fibrillation patients has not been investigated. The objective of this research is to investigate the effect of obesity on outcomes in atrial fibrillation.

METHODS

The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study was one of the largest multicenter trials of atrial fibrillation, with 4060 patients. Subjects were randomized to rate versus rhythm-control strategy. We performed a post hoc analysis of the National Heart, Lung and Blood Institute limited access dataset of atrial fibrillation patients who had body mass index (BMI) data available in the AFFIRM study. BMI data were not available on 1542 patients. Patients with BMI >or=18.5 were split into normal (18.5-25), overweight (25-30), and obese (>30) categories as per BMI (kg/m(2)). Multivariate Cox proportional hazards regression was used on the eligible 2492 patients. End points were all-cause mortality and cardiovascular mortality.

RESULTS

Over three fourths of all patients in our cohort were overweight or obese. There were 304 deaths (103 among normal weight, 108 among overweight, and 93 among obese) and 148 cardiovascular deaths (54 among normal weight, 41 among overweight, and 53 among obese) over a mean period of 3 years of patient follow-up. On multivariate analysis, overweight (hazard ratio [HR] 0.64; 95% confidence interval [CI], 0.48-0.84; P=.001) and obese (HR 0.80; 95% CI, 0.68-0.93; P=.005) categories were associated with lower all-cause mortality as compared with normal weight. Overweight (HR 0.40; 95% CI, 0.26-0.60; P <.001) and obese patients (HR 0.77; 95% CI, 0.62-0.95; P=.01) also had lower cardiovascular mortality as compared with the normal weight patients.

CONCLUSIONS

Although in prior studies, obesity has been associated with increased risk of atrial fibrillation, an obesity paradox exists for outcomes in atrial fibrillation. Obese patients with atrial fibrillation appear to have better long-term outcomes than nonobese patients.

Pressed for time: the circadian clock and hypertension

Hypertension is a major risk factor for cardiovascular disease and death. The "silent" rise of blood pressure that occurs over time is largely asymptomatic. However, its impact is deafening-causing and exacerbating cardiovascular disease, end-organ damage, and death. The present article addresses recent observations from human and animal studies that provide new insights into how the circadian clock regulates blood pressure, contributes to hypertension, and ultimately evolves vascular disease. Further, the molecular components of the circadian clock and their relationship with locomotor activity, metabolic control, fluid balance, and vascular resistance are discussed with an emphasis on how these novel, circadian clock-controlled mechanisms contribute to hypertension.

Comparison of outcome in catheter ablation of atrial fibrillation in patients with versus without the metabolic syndrome

Previous studies have reported that metabolic syndrome (MS) is associated with the development of atrial fibrillation (AF). However, its impact on the atrial substrate properties and catheter ablation in patients with AF is still unclear. This study consisted of 282 patients with AF (216 with paroxysmal AF and 66 with nonparoxysmal AF) who underwent catheter ablation using a 3-dimensional mapping system (NavX). Detailed AF mapping (frequency analysis and complex fractionated electrographic mapping) was performed in 59 patients. The patients were classified on the basis of MS, which was defined according to the guidelines of the National Cholesterol Education Program Adult Treatment Panel III. Patients with MS had larger left atrial sizes, shorter fractionated intervals, and higher dominant frequencies compared with those without it. Higher incidences of complex fractionated atrial electrographic sites located in the left atrial appendage base, coronary sinus, and crista terminalis regions were found in patients with MS. Patients with MS had a higher incidence of recurrent AF compared with those without MS (55% vs 24%, p <0.001). A higher incidence of recurrent AF from non-pulmonary vein origins was observed in patients with MS compared with those without it (45% vs 20%, p = 0.037). In conclusion, MS is associated with larger left atrial size and an arrhythmogenic substrate, which may increase the risk for recurrence after the ablation of AF. Close follow-up with good control of any metabolic disturbances may be needed in patients with MS to improve their outcomes after AF ablation.

Body mass index, obstructive sleep apnea, and outcomes of catheter ablation of atrial fibrillation

BACKGROUND

Obesity and obstructive sleep apnea (OSA) are associated with atrial fibrillation (AF). The effects of a large body mass index (BMI) and OSA on the results of radiofrequency catheter ablation (RFA) of AF are unclear.

OBJECTIVE

To evaluate the effect of BMI and OSA on the efficacy of RFA for AF.

METHODS

RFA was performed in 324 consecutive patients (mean age = 57 +/- 11 years) with paroxysmal (234) or chronic (90) AF. OSA was diagnosed by polysomnography in 32 of 324 patients (10%) prior to ablation. Among the 324 patients, 18% had a normal BMI (<25 kg/m(2)), 39% were overweight (BMI >/= 25 kg/m(2) and <30 kg/m(2)), and 43% were obese (>or=30 kg/m(2)). RFA was performed to eliminate complex fractionated atrial electrograms (CFAE) in the pulmonary vein antrum and left atrium.

RESULTS

At 7 +/- 4 months after a single ablation procedure, 63% of patients without OSA and 41% with OSA were free from recurrent AF without antiarrhythmic drug therapy (P = 0.02). Multivariate analysis including variables of age, gender, type and duration of AF, OSA, BMI, left atrial size, ejection fraction, and hypertension demonstrated that OSA was the strongest predictor of recurrent AF (OR = 3.04, 95% CI: 1.11-8.32, P = 0.03). There was no association between BMI and freedom from recurrent AF. A serious complication occurred in 3 of 324 patients, with no relationship to BMI.

CONCLUSIONS

OSA is a predictor of recurrent AF after RFA independent of its association with BMI and left atrial size. Obesity does not appear to affect outcomes after radiofrequency catheter ablation of AF.

Severe obesity and P-wave dispersion: the effect of surgically induced weight loss

BACKGROUND

Recent data have shown that obesity is an important potential risk factor for atrial fibrillation (AF). The mechanism of development of AF in obesity patients is still unclear and may be related to atrial refractoriness heterogeneity. The aim of our study was to determine the influence of bariatric surgery with a consequent substantial weight loss on P-wave dispersion in morbidly obese population.

METHODS

We enrolled in this study 40 severe obese patients, and 40 age-matched non-obese healthy subjects were also recruited as controls. All subjects underwent conventional 12-lead electrocardiography for the analysis of P-wave dispersion. All subjects underwent bariatric surgery and were resubmitted to electrocardiography, biochemical, and anthropometric examination within 12 months after intervention.

RESULTS

Severe obese patients had greater values in P-wave duration and dispersion than the normal weight controls. Bariatric surgery reduced significantly P-wave dispersion. There was a significant correlation between decrease of atrial refractoriness heterogeneity and bariatric-surgery-induced weight loss.

CONCLUSIONS

In severe obese patients, surgically induced weight loss reduction is associated with significant decreased in P-wave dispersion. The reduction of the atrial refractoriness heterogeneity may be of clinical significance by reducing the risk of atrial fibrillation in morbidly obese subjects.

Dietary Effects of Structured Lipids and Phytosteryl Esters on Cardiovascular Function in Spontaneously Hypertensive Rats

This study examined the dietary effects of sesame oil (SO)-based structured lipids (SL) and phytosteryl esters (PE) on cardiovascular function in conscious spontaneously hypertensive rats (SHR) fed high-fat (HF) diets (20% w/w fat). The dietary groups were as follows: normal diet (4.5% w/w fat), SO, SO fortified with PE (SOP), SL, and SL fortified with PE (SLP). Mean arterial blood pressures were similar in all groups, whereas resting heart rates (HR) were higher in all HF-fed groups. The pressor responses to the alpha1-adrenoceptor agonist, phenylephrine (5 microg/kg), were similar in all groups. However, the pressor responses to phenylephrine (10 microg/kg) were diminished in SO- or SL-fed SHR, whereas they were not diminished in SOP- or SLP-fed SHR. The depressor responses elicited by the nitric oxide (NO) donor, sodium nitroprusside (5 and 10 microg/kg), were not diminished in HF-fed rats. Baroreflex-mediated changes in HR were variously decreased in the HF-fed groups, and this decrease tended to be greater in SOP and SLP than in SO and SL groups. The depressor and tachycardic responses elicited by the beta-adrenoceptor agonist, isoproterenol, were equivalent in all groups. The depressor responses elicited by the endothelium-dependent agonist, acetylcholine (0.1 microg/kg), and the hypertension elicited by the NO synthesis inhibitor, NG-nitro-L-arginine methylester (25 micromol/kg), were similar in all groups. These findings demonstrate that (1) HF diets increase resting HR and impair baroreflex function in SHR, whereas they do not obviously affect endothelium-dependent vasodilation, and (2) fortification with PE may be deleterious to cardiovascular function (eg, baroreflex activity) in SHR.

In vivo pharmacodynamic interactions between two drugs used in orthostatic hypotension ? midodrine and dihydroergotamine

A combination of midodrine and dihydroergotamine (DHE) is frequently used clinically in patients suffering from severe orthostatic hypotension (OH). Whereas midodrine acts as a selective, peripheral alpha1-receptor agonist, DHE displays complex pharmacology and can behave as an alpha-adrenergic receptor agonist or antagonist. Surprisingly, the consequences of such a combination on blood pressure have never been investigated. The present study was performed in order to evaluate the pressor effects induced by the administration of both midodrine and DHE in old conscious dogs (n = 6) in experimental condition reproducing autonomic failure-related baroreflex dysfunction (atropine 0.1 mg/kg). For this purpose, we first studied the relative potency and intrinsic activity of each agonist and noradrenaline (NA) for the alpha1-adrenergic receptor. The orders of potency obtained in our study were 0.35, 11 and 400 microg/kg for NA, DHE and midodrine, and intrinsic activity: NA > midodrine > DHE. These results strongly suggest that DHE really acts in vivo as an alpha1-adrenoceptor partial agonist. Afterwards, the pressor effects of coadministration of midodrine (0.4 mg/kg) and DHE (15 microg/kg) were investigated: in one setting, midodrine was first administered, followed by DHE; in another, DHE was first administered, followed by midodrine. Our results show that in conscious dogs, the combination of midodrine and DHE leads to near-complete abolition of the pressor effect induced by the first administered drug. This in vivo proof of such antagonistic effects on blood pressure could explain clinical observations of worsening of OH in humans administered midodrine plus DHE. Although in vivo results obtained in conscious healthy dogs need to be experimentally and clinically confirmed in humans suffering from OH, these results strongly suggest that a midodrine-DHE combined treatment should be avoided in clinical practice.

Increased monoamine oxidase and semicarbazide-sensitive amine oxidase activities in white adipose tissue of obese dogs fed a high-fat diet

Adipocytes express two types of amine oxidases: the cell surface semicarbazide-sensitive amine oxidase (SSAO) and the mitochondrial monoamine oxidase (MAO). In human abdominal subcutaneous adipose tissue, it has been reported that SSAO substrates stimulate glucose transport and inhibit lipolysis while MAO activity is decreased in obese patients when compared to age-matched controls. However, no information has been reported on visceral WAT. To further investigate the obesity-induced regulations of MAO and SSAO in white adipose tissue (WAT) from different anatomical locations, enzyme activities and mRNA abundance have been determined on tissue biopsies from control and high-fat fed dogs, an obesity model already described to be associated with arterial hypertension and hyperinsulinemia. MAO activity was increased in the enlarged omental WAT of diet-induced obese dogs, but not in their mesenteric WAT, another intra-abdominal fat depot. Subcutaneous WAT did not exhibit any change in MAO activity, as did the richest MAO-containing tissue: liver. Similarly, SSAO was increased in omental WAT of diet-induced obese dogs, but was not modified in other WAT and in aorta. The increase in SSAO activity observed in omental WAT likely results from an increased expression of the AOC3 gene since mRNA abundance and maximal benzylamine oxidation velocity were increased. Finally, plasma SSAO was decreased in obese dogs. Although the observed regulations differ from those found in subcutaneous WAT of obese patients, this canine model shows a tissue- and site-specific regulation of peripheral MAO and SSAO in obesity.

Epidemiology of atrial fibrillation: a current perspective

The prevalence of atrial fibrillation (AF) increases with age. Recent population-based data indicate a trend of increasing incidence and prevalence of AF that is incompletely explained by an aging population. A recent population study estimated that the number of Americans afflicted by AF will increase from the current 2.3 million to more than 10 million by 2050. Novel risk factors--obesity and sleep apnea--may partially account for the current AF epidemic. Ethnic differences in the epidemiology of AF have been suggested but not clearly elucidated by population-based studies. The heritability of AF in the general population is strongly supported by population-based data. Genetic epidemiological studies on AF can potentially yield important mechanistic insights that may ultimately lead to novel preventative and therapeutic strategies.

Impaired endothelium-dependent vasodilation in normotensive and normoglycemic obese adult humans

Acetylcholine (ACh)-mediated endothelium-dependent vasodilation has been shown to be impaired in obese adults. However, the mechanisms responsible for this impairment are not clear. We determined whether the blunted forearm vasodilator response to acetylcholine with obesity is due, at least in part, to reduced muscarinic receptor responsiveness. Twenty-eight sedentary middle-aged adults were studied: 14 normal weight (BMI, 23.6 +/- 0.5 kg/m) and 14 obese (32.2 +/- 0.9 kg/m). Forearm blood flow (FBF) was determined in response to intraarterial infusion of acetylcholine (8-128 microg/min) and sodium nitroprusside (SNP: 2.0-8.0 microg/min). Regardless of the dose, forearm blood flow responses to acetylcholine were 25% (P < 0.01) lower in the obese (from 4.2 +/- 0.3 to 12.0 +/- 0.8 mL/100 mL tissue/min) compared with normal weight (4.4 +/- 0.3 to 16.9 +/- 1.0 mL/100 mL tissue/min) adults. Of note, forearm blood flow responses to acetylcholine plateaued at doses higher than 32 microg/min in both groups, no further increase in forearm blood flow was observed at either 64 or 128 microg/min. EC50 for acetylcholine-stimulated vasodilation was not different between the obese (7.8 +/- 0.8 microg/min) and normal weight (7.8 +/- 0.6 microg/min) adults. There were no group differences in the vasodilator response to sodium nitroprusside. These results indicate that the obesity-related impairment in acetylcholine-mediated vasodilation in the human forearm is not due to reduced muscarinic receptor responsiveness or sensitivity.

Is reduced baroreflex gain a component of the metabolic syndrome? Insights from the LINOSA study

OBJECTIVE

To assess the relationship between insulin resistance and baroreflex gain (BRS) in the context of the metabolic syndrome.

DESIGN

Observational population study.

PATIENTS

We studied the healthy population of a small Mediterranean island (Linosa, about 0.5 square miles, 450 inhabitants) where genetic, psychosocial and behavioral bias is likely to be minimal for historical and social reasons.

MEASURES

Baroreflex gain (BRS, by the frequency domain alpha index) and indices of autonomic regulation of the sino-atrial (SA) node derived from spectral analysis of RR interval variability were obtained, together with metabolic and behavioral indicators in the 144 participating subjects (age range 20-82 years). Carotid artery thickness (CCA) was also obtained with computer-aided ultrasound techniques. Insulin resistance was estimated by the homeostasis model assessment (HOMA), and subjects divided in tertiles accordingly.

RESULTS

BRS appeared to be reduced progressively with increasing levels of HOMA (respectively, 21.0 +/- 2.6, 17.7 +/- 1.7, 15.7 +/- 1.9 ms/mmHg, P < 0.03), while spectral indices of autonomic SA regulation appeared to be only insignificantly affected. Conversely, CCA was significantly increased with increasing HOMA (P < 0.024). Furthermore, BRS appeared to be significantly correlated with various elements of the metabolic syndrome, with CCA and abdominal obesity showing the strongest link.

CONCLUSIONS

In an otherwise healthy population, BRS, but not spectrally derived indices of SA node autonomic regulation, are progressively reduced with increasing severity of insulin resistance, possibly as a consequence of attendant carotid artery thickening.

Interrelationships Between the Autonomic Nervous System and Atrial Fibrillation

Mechanisms responsible for atrial fibrillation are not completely understood but the autonomic nervous system is a potentially potent modulator of the initiation, maintenance, termination and ventricular rate determination of atrial fibrillation. Complex interactions exist between the parasympathetic and sympathetic nervous systems on the central, ganglionic, peripheral, tissue, cellular and subcellular levels that could be responsible for alterations in conduction and refractoriness properties of the heart as well as the presence and type of triggered activity, all of which could contribute to atrial fibrillation. These dynamic inter-relationships may also be altered dependent upon other neurohumoral modulators and cardiac mechanical effects from ventricular dysfunction and congestive heart failure. The clinical implications regarding the effects of the autonomic nervous system in atrial fibrillation are widespread. The effects of modulating ganglionic input into the atria may alter the presence or absence of atrial fibrillation as has been highlighted from ablation investigations. This article reviews what is known regarding the inter-relationships between the autonomic nervous system and atrial fibrillation and provides state of the art information at all levels of autonomic interactions.

Mechanism of Fatty Acids Induced Suppression of Cardiovascular Reflexes in Rats

A blunted baroreflex sensitivity (BRS), impaired heart rate variability (HRV), and high plasma nonesterified fatty acids (NEFA) are predictors of adverse cardiovascular outcomes. We tested the hypothesis that elevation of NEFA negatively impacts the cardiac baroreflex response and undertook spectral analyses and molecular studies to delineate the mechanism of action. We used two interventions to elevate serum NEFA: 1) overnight fasting (n = 7) and 2) i.v. infusion of 1.2 ml/kg intralipid 20% + heparin (I/H) over 10 min (n = 9) in conscious unrestrained male rats. Elevated NEFA caused by fasting complemented by I/H infusion were associated with a concentration-dependent reduction in spontaneous BRS measured by spectral analysis [low-frequency alpha and high-frequency alpha (HFalpha) indices] and sequence method and HRV measured by frequency domain as power of RR interval (RRI) spectra (low-frequency RRI and high-frequency RRI) and by time domain as standard deviation of beat-to-beat interval and root mean square of successive differences along with increase in blood pressure variability measured as standard deviation of mean arterial pressure and power of systolic arterial pressure spectra (low-frequency systolic arterial pressure). Because elevated NEFA suppressed the vagal component of the baroreflex response (HFalpha), we tested the hypothesis that NEFA-evoked sequestration of myocardial muscarinic receptor (M2-mAChR) contributes to the reduced BRS. High NEFA level was accompanied by increased caveolar sequestration of cardiac M2-mAChRs without changing M2-mAChR protein expression. We report the first detailed analyses of NEFA's effect on the cardiac baroreflex and show that increased caveolar sequestration of cardiac M2-mAChRs constitutes a cellular mechanism for elevated NEFA-related deleterious cardiovascular outcomes.

Insulin downregulates M(2)-muscarinic receptors in adult rat atrial cardiomyocytes: a link between obesity and cardiovascular complications

OBJECTIVE

To determine whether decreased cardiac parasympathetic activity observed in obesity is due to insulin-induced alterations in cardiac M(2)-muscarinic receptors and/or adenylyl cyclase activity.

DESIGN AND METHODS

After incubation with increasing concentrations of insulin, adult rat atrial cardiomyocytes were assayed for M(2)-muscarinic receptor binding density and affinity, and for M(2)R mRNA expression using RT-PCR analysis. Forskolin-stimulated adenylyl cyclase activity and its inhibition by carbachol were also assayed, as was endothelial nitric oxide synthase mRNA expression. The effects of insulin on M(2)-muscarinic receptor density and mRNA expression levels were analyzed using the insulin signaling inhibitors rapamycin, wortmanin and PD 098059.

RESULTS

Insulin induces a concentration- and time-dependent decrease in expression of the M(2)R mRNA, and in [(3)H]N-methylscopolamine binding by the receptor. These effects on the M(2)R mRNA levels and on [(3)H]N-methylscopolamine binding were prevented by PD 98059, but not by wortmanin or rapamycin. Basal and forskolin-induced cAMP production did not differ, but the inhibition of forskolin-simulated enzyme activity by carbachol was blunted by insulin. No change in the mRNA levels for endothelial nitric oxide synthase was observed.

CONCLUSION

In rat atrial cardiomyocytes, insulin markedly alters both the M(2)-muscarinic receptor density, and its mRNA expression through transcriptional regulation and adenylyl cyclase activity. These data suggest that the obesity-associated decrease in cardiac parasympathetic tone may be related to hyperinsulinemia, which could directly contribute to cardiovascular morbidity in obese patients.

Uncomplicated human obesity is associated with a specific cardiac transcriptome: involvement of the Wnt pathway

A dramatic increase in obesity prevalence and cardiovascular morbidity is expected for the coming years. However, with relevance to the heart, little is known about the specific contribution of obesity on associated morbidity. Consequently, global analysis of gene regulations in human heart was undertaken to monitor molecular regulations related to obesity or to obesity-related hypertension. Transcriptome analysis using cDNA arrays was performed in right appendage biopsies from obese patients (n=5), from patients with arterial hypertension with (n=5) or without obesity (n=5), and from 5 leans. All biopsies came from patients that had cardiac surgery and coronary bypass. Statistical analysis of the data revealed 2686 differentially expressed genes out of 11,500 when compared with lean tissues. Differential expression was verified by real-time PCR in 84% of 50 randomly chosen genes. Among genes encountered, 397 were specifically regulated in obese, 1,299 in non-obese hypertensive, and 355 in obese hypertensive patients, respectively, whereas an additional set of 153 genes was differentially expressed in all these situations. Ontology analysis, hierarchical clustering, and molecular pathway analysis indicated that the heart molecular picture of obesity differs clearly from that observed for obesity-related hypertension or arterial hypertension. Clearly, the Wnt pathway known to be involved in cardiac hypertrophy mechanisms, showed opposite regulation in obese heart compared with hypertensive heart and potentially prevented the development of cardiac remodeling in obese patients. All over, this work shows that uncomplicated obesity has a strong impact on cardiac gene expression, which could be considered as precursor signs for future cardiac disease and also demonstrates that obesity-related hypertension generates a heart-molecular-distinct phenotype that cannot be predicted by a simple sum of the impact of obesity and arterial hypertension on gene expression.

Adrenomedullin upregulates M2-muscarinic receptors in cardiomyocytes from P19 cell line

1. The effects of AM on expression of muscarinic (M) receptors from P19-derived cardiomyocytes were examined. 2. RT-PCR experiments revealed expression of M(1)-M(4) receptor genes. Immuno-histochemistry indicated that M(2) expression is restricted to contractile cells. Carbachol inhibition of isoprenaline-induced increase in beating rate was prevented by atropine and methoctramine (pA(2): 8.1). Inhibition of [(3)H]-NMS binding by atropine (pK(i): -8.4+/-0.2) and methoctramine (pK(i): -8.3+/-0.2) suggests that M(2) is the functional expressed isoform. 3. [(3)H]-NMS binding and semiquantitative RT-PCR studies showed a dome shaped time course of M(2) expression with a maximum at 7 days of differentiation followed by a progressive decline. 4. AM concentration-dependently upregulated M(2) receptor mRNA during late differentiation stages in P19 cells but also in rat atrial cardiomyocytes. This effect was potentiated by factor H. AM (100 nM) plus factor H (50 nM) treatment of P19 cells for 24 h significantly increased [(3)H]-NMS-specific binding (B(max): 81+/-7 vs 31+/-6 fmol mg(-1) prot). The effect of AM on mRNA levels was prevented by AM receptor antagonist AM(22-52) (1 micro M) but not by CGRP antagonist, CGRP(8-37) (1 micro M). 5. The mRNA levels encoding CRLR receptor declined with culture duration, whereas those encoding L1/G10D receptor remained stable. 6. Our findings demonstrate that AM regulates M(2) receptors expression in cardiomyocytes probably through a mechanism involving L1/G10D receptors. The 'in vivo' significance of this phenomenon remains to be demonstrated.

Alpha2 -adrenoceptor function in arterial hypertension associated with obesity in dogs fed a high-fat diet

OBJECTIVE

To investigate the status of alpha2-adrenoceptors in a model of obesity-related arterial hypertension.

DESIGN

A parallel study in dogs randomly assigned to a high-fat diet (HFD group, n = 6) or normal canine food (controls, n = 6) for 9 weeks.

METHODS

Postsynaptic vascular alpha2-adrenoceptors were assessed through analysis of dose-pressor responses to clonidine [2.5, 5.0 and 15.0 microg/kg intravenously (i.v.)] after muscarinic, beta- and alpha1-adrenergic receptor blockade. Presynaptic and central alpha2-adrenoceptors were studied through measurement of changes in plasma concentrations of catecholamine induced by yohimbine (0.05 mg/kg i.v.). The number of platelet alpha2-adrenoceptors (expressed as fmol/mg protein) and the percentage in a state of high affinity were measured using [3H]RX821002.

RESULTS

Clonidine, when administered to dogs that were under autonomic blockade, elicited a dose-dependent increase in blood pressure. The doses of clonidine required to induce a 50% maximum increase in systolic and diastolic blood pressures remained unchanged after 9 weeks of a high-fat diet (systolic: 6.0 +/- 0.3 microg/kg at baseline and 5.6 +/- 0.2 microg/kg after 9 weeks; diastolic: 4.2 +/- 0.2 microg/kg at baseline and 3.9 +/- 0.2 microg/kg after 9 weeks). After 9 weeks of the regimen, plasma concentrations of noradrenaline were significantly greater in the HFD group than in controls (337 +/- 22 pg/ml compared with 212 +/- 37 pg/ml). The increment in plasma concentrations of noradrenaline elicited by yohimbine after 9 weeks was smaller in the HFD group than in controls (93 +/- 44% compared with 181 +/- 46%; P = 0.024). In the HFD group, the number of platelet alpha2-adrenoceptors and the percentage that were in a state of high affinity were significantly lower after 9 weeks, compared with baseline (number: 239 +/- 21 fmol/mg protein at baseline and 95 +/- 7 fmol/mg protein after 9 weeks; high-affinity: 30 +/- 3% at baseline and 21 +/- 4% after 9 weeks; P < 0.05).

CONCLUSIONS

These results suggest that presynaptic or central alpha2-adrenoceptor function, or both, is specifically impaired after 9 weeks of a high-fat diet. These modifications may account for the development of arterial hypertension in this model.

Ophidian envenomation strategies and the role of purines

Snake envenomation employs three well integrated strategies: prey immobilization via hypotension, prey immobilization via paralysis, and prey digestion. Purines (adenosine, guanosine and inosine) evidently play a central role in the envenomation strategies of most advanced snakes. Purines constitute the perfect multifunctional toxins, participating simultaneously in all three envenomation strategies. Because they are endogenous regulatory compounds in all vertebrates, it is impossible for any prey organism to develop resistance to them. Purine generation from endogenous precursors in the prey explains the presence of many hitherto unexplained enzyme activities in snake venoms: 5'-nucleotidase, endonucleases (including ribonuclease), phosphodiesterase, ATPase, ADPase, phosphomonoesterase, and NADase. Phospholipases A(2), cytotoxins, myotoxins, and heparinase also participate in purine liberation, in addition to their better known functions. Adenosine contributes to prey immobilization by activation of neuronal adenosine A(1) receptors, suppressing acetylcholine release from motor neurons and excitatory neurotransmitters from central sites. It also exacerbates venom-induced hypotension by activating A(2) receptors in the vasculature. Adenosine and inosine both activate mast cell A(3) receptors, liberating vasoactive substances and increasing vascular permeability. Guanosine probably contributes to hypotension, by augmenting vascular endothelial cGMP levels via an unknown mechanism. Novel functions are suggested for toxins that act upon blood coagulation factors, including nitric oxide production, using the prey's carboxypeptidases. Leucine aminopeptidase may link venom hemorrhagic metalloproteases and endogenous chymotrypsin-like proteases with venom L-amino acid oxidase (LAO), accelerating the latter. The primary function of LAO is probably to promote prey hypotension by activating soluble guanylate cyclase in the presence of superoxide dismutase. LAO's apoptotic activity, too slow to be relevant to prey capture, is undoubtedly secondary and probably serves principally a digestive function. It is concluded that the principal function of L-type Ca(2+) channel antagonists and muscarinic toxins, in Dendroaspis venoms, and acetylcholinesterase in other elapid venoms, is to promote hypotension. Venom dipeptidyl peptidase IV-like enzymes probably also contribute to hypotension by destroying vasoconstrictive peptides such as Peptide YY, neuropeptide Y and substance P. Purines apparently bind to other toxins which then serve as molecular chaperones to deposit the bound purines at specific subsets of purine receptors. The assignment of pharmacological activities such as transient neurotransmitter suppression, histamine release and antinociception, to a variety of proteinaceous toxins, is probably erroneous. Such effects are probably due instead to purines bound to these toxins, and/or to free venom purines.

Reduced cardiovagal baroreflex gain in visceral obesity: implications for the metabolic syndrome

The influence of excess total and abdominal adiposity on cardiovagal baroreflex gain remains unclear. We tested the hypotheses that cardiovagal baroreflex gain would be reduced in men with 1) higher [higher fat (HF), mass >20 kg, n = 11] compared with lower [lower fat (LF), mass <20 kg, n = 10] levels of total body and abdominal fat and 2) higher abdominal visceral fat (HAVF; n = 10) compared with total body weight- and subcutaneous fat-matched peers with lower abdominal visceral fat (LAVF; n = 7) levels. To accomplish this, we measured cardiovagal baroreflex gain (modified Oxford technique), body composition (dual energy X-ray absorptiometry), and abdominal visceral and subcutaneous fat (computed tomography) in sedentary men (age, 18-40 yr; body mass index, <34.9 kg/m(2)) across a wide range of adiposity. Cardiovagal baroreflex gain was significantly lower in HF compared with LF (14.3 +/- 2.8 vs. 21.4 +/- 2.8 ms/mmHg, respectively). In addition, cardiovagal baroreflex gain was lower in HAVF compared with LAVF (13.0 +/- 2.0 vs. 21.4 +/- 3.6 ms/mmHg, P < 0.05). Therefore, the results of the present study indicate that cardiovagal baroreflex gain is reduced in men with elevated total body and abdominal fat mass. The reduced cardiovagal baroreflex gain in these individuals appears to be linked to their higher level of abdominal visceral fat. Importantly, reduced cardiovagal baroreflex gain may contribute to the increased risk of cardiovascular disease observed in men with the metabolic syndrome.