Leptin interacts with heart rate but not sympathetic nerve traffic in healthy male subjects

The Prevalence of Bradycardia 12 Years After Roux-en-Y Gastric Bypass for Severe Obesity

PURPOSE

The aim was to describe the frequency of bradycardia 12 years after Roux-en-Y gastric bypass (RYGB), relations to weight loss, patient characteristics, and the clinical impact.

MATERIALS AND METHODS

The BAROPS study is a prospective observational study of patients who had follow-up > 10 years after RYGB. Patients with heart rate (HR) ≤ 50 bpm were compared to patients with HR > 50 bpm.

RESULTS

After a mean observation period of 12 years, 32 of 546 patients (6%) had a HR ≤ 50 with a mean HR of 47.0 (2.8) bpm. The comparator group (192 patients) had a mean HR of 66.4 (10.2) bpm (p < 0.001). A higher proportion of the bradycardic vs. non-bradycardic patients (18.8% vs. 7.8% at baseline (p = 0.05) and 18.8% vs. 5.2% at end of study (p = 0.006)) used beta-blockers. Both groups had a significant reduction in heart rate from pre-surgery to end of observation. Percent total weight loss from baseline was negatively related to heart rate (p < 0.001), and smoking was positively related to heart rate (p = 0.014). Change in BMI from pre-surgery (p < 0.001) and hypertension at pre-surgery (p = 0.006) were significant predictors of change in heart rate. The only predictor of HR ≤ 50 was the use of beta-blockers (p = 0.010). There were no difference in bradycardia-related symptoms.

CONCLUSION

Six percent of patients had HR ≤ 50 bpm 12 years after RYGB, but there was no increased bradycardia-related symptoms in these patients. RYGB induced a significant reduction in HR, and heart rate and changes in heart rate 12 years after RYGB were related to the amount of weight loss.

Endothelial leptin receptor is dispensable for leptin-induced sympatho-activation and hypertension in male mice

Leptin plays a crucial role in blood pressure (BP) regulation, notably in the context of obesity through central sympatho-mediated pressor effects. Leptin also relaxes arteries via endothelial (EC) leptin receptor (LepREC)-mediated increases in nitric oxide (NO) bioavailability. Herein, we investigated whether leptin-mediated increases in NO bioavailability represent a buffering mechanism against leptin-induced sympatho-activation. We tested the direct contribution of LepREC to BP regulation in physiological conditions and in response to chronic leptin infusion using mice deficient in LepREC. LepREC deficiency did not alter baseline metabolic profile nor leptin-induced reduction in adiposity and increases in energy expenditure. LepREC-/- mice demonstrated no increase in baseline BP and heart rate (HR) (MAP: LepREC+/+:94.7 ± 1.6, LepREC-/-:95.1 ± 1.8 mmHg; HR:LepREC+/+:492.4 ± 11.7, LepREC-/-:509.5 ± 13.4 bpm) nor in response to leptin (MAP, LepREC+/+:101.1 ± 1.7, LepREC-/-:101.7 ± 1.8 mmHg; HR, LepREC+/+:535.6 ± 11.1, LepREC-/-:539.3 ± 14.2 bpm). Moreover, baseline neurogenic control of BP and HR was preserved in LepREC-/- mice as well as leptin-mediated increases in sympathetic control of BP and HR and decreases in vagal tone. Remarkably, LepREC deficiency did not alter endothelium-dependent relaxation in resistance vessels, nor NO contribution to vasodilatation. Lastly, leptin induced similar increases in adrenergic contractility in mesenteric arteries from both LepREC+/+ and LepREC-/- mice. Collectively, these results demonstrate that the NO buffering effects of leptin are absent in resistance arteries and do not contribute to BP regulation. We provide further evidence that leptin-mediated hypertension involves increased vascular sympatho-activation and extend these findings by demonstrating for the first time that increased cardiac sympatho-activation and reduced vagal tone also contribute to leptin-mediated hypertension.

Asymptomatic Sinus Bradycardia Post-Bariatric Surgery: A Case Report

Bradyarrhythmia as a result of significant weight loss post-bariatric surgery is slowly gaining recognition in few case reports and even fewer studies. However, awareness of its diagnosis and management amongst physicians remains modest. We report a case of asymptomatic sinus bradycardia in a 41-year-old woman who shed 19.5 kg/m2 in 4 months following bariatric surgery. The pathophysiology, diagnostics and management of post-bariatric surgery sinus bradycardia is briefly discussed.

Hypertensive Heart Disease and Obesity: A Review

Metabolic syndrome is an increasingly prevalent constellation of disease processes among the global population. Hypertension and obesity are among the contributing etiologies, and obesity increases the likelihood of hypertensive heart disease by creating a proinflammatory state, as well as increasing sympathetic tone and formation of reactive oxygen species. Hypertensive heart disease is characterized by myocardial fibrosis, which portends higher risk of developing reduced ejection fraction, diastolic dysfunction, ischemia, and arrhythmias, making early diagnosis and treatment essential to the prevention of cardiac events.

Sympathetic Neural Overdrive in the Obese and Overweight State

Nerve traffic recordings (muscle sympathetic nerve traffic [MSNA]) have shown that sympathetic activation may occur in obesity. However, the small sample size of the available studies, presence of comorbidities, heterogeneity of the subjects examined represented major weaknesses not allowing to draw definite conclusions. This is the case for the overweight state. The present meta-analysis evaluated 1438 obese or overweight subjects recruited in 45 microneurographic studies. The analysis was primarily based on MSNA quantification in obesity and overweight, excluding as concomitant conditions hypertension, metabolic syndrome, and other comorbidities. Assessment was extended to the relationships of MSNA with other neuroadrenergic markers, such as plasma norepinephrine and heart rate, anthropometric variables, as body mass index, waist-to-hip ratio, presence/absence of obstructive sleep apnea, and metabolic profile. Compared with normoweights MSNA was significantly greater in overweight and more in obese individuals (37.0±4.1 versus 43.2±3.5 and 50.4±5.0 burts/100 heartbeats, P<0.01). This was the case even in the absence of obstructive sleep apnea. MSNA was significantly directly related to body mass index and waist-to-hip ratio ( r=0.41 and r=0.64, P<0.04 and <0.01, respectively), clinic blood pressure ( r=0.68, P<0.01), total cholesterol, LDL (low-density lipoprotein) cholesterol, and triglycerides ( r=0.91, r=0.94, and r=0.80, respectively, P<0.01) but unrelated to plasma insulin, glucose, and homeostatic model assessment for insulin resistance. No significant correlation was found between MSNA, heart rate, and norepinephrine. Thus, obesity and overweight are characterized by sympathetic overactivity which mirrors the severity of the clinical condition and reflects metabolic alterations, with the exclusion of glucose/insulin profile. Neither heart rate nor norepinephrine appear to represent faithful markers of the muscle sympathetic overdrive.

Delayed Chronotropic Response due to Autonomic Imbalance Presenting as Dyspnea on Early Exertion: A Complication of Bariatric Surgery

Bariatric surgery has shown promising outcomes in improving overall morbidity and mortality in morbidly obese patients. Cardiovascular risk reduction from weight loss is well known in the literature. However, little is highlighted about the cardiovascular complications of massive and rapid weight loss associated with bariatric surgery. These complications result mainly from autonomic imbalance manifesting as increased parasympathetic tone and a decrease in sympathetic response. This imbalance is a consequence of hormonal changes associated with massive weight loss. We present a unique case which is a demonstration of the aforementioned changes. Our patient presented with dyspnea during an early phase of exercise with the resolution of symptoms with the continuation of exercise.

Clinical utility of sympathetic blockade in cardiovascular disease management

INTRODUCTION

A dysregulated sympathetic nervous system is a major factor in the development and progression of cardiovascular disease; thus, understanding the mechanism and function of the sympathetic nervous system and appropriately regulating sympathetic activity to treat various cardiovascular diseases are crucial. Areas covered: This review focused on previous studies in managing hypertension, atrial fibrillation, coronary artery disease, heart failure, and perioperative management with sympathetic blockade. We reviewed both pharmacological and non-pharmacological management. Expert commentary: Chronic sympathetic nervous system activation is related to several cardiovascular diseases mediated by various pathways. Advancement in measuring sympathetic activity makes visualizing noninvasively and evaluating the activation level even in single fibers possible. Evidence suggests that sympathetic blockade still has a role in managing hypertension and controlling the heart rate in atrial fibrillation. For ischemic heart disease, beta-adrenergic receptor antagonists have been considered a milestone drug to control symptoms and prevent long-term adverse effects, although its clinical implication has become less potent in the era of successful revascularization. Owing to pathologic involvement of sympathetic nervous system activation in heart failure progression, sympathetic blockade has proved its value in improving the clinical course of patients with heart failure.

Role of leptin in energy expenditure: the hypothalamic perspective

The adipocyte-derived hormone leptin is a peripheral signal that informs the brain about the metabolic status of an organism. Although traditionally viewed as an appetite-suppressing hormone, studies in the past decade have highlighted the role of leptin in energy expenditure. Leptin has been shown to increase energy expenditure in particular through its effects on the cardiovascular system and brown adipose tissue (BAT) thermogenesis via the hypothalamus. The current review summarizes the role of leptin signaling in various hypothalamic nuclei and its effects on the sympathetic nervous system to influence blood pressure, heart rate, and BAT thermogenesis. Specifically, the role of leptin signaling on three different hypothalamic nuclei, the dorsomedial hypothalamus, the ventromedial hypothalamus, and the arcuate nucleus, is reviewed. It is known that all of these brain regions influence the sympathetic nervous system activity and thereby regulate BAT thermogenesis and the cardiovascular system. Thus the current work focuses on how leptin signaling in specific neuronal populations within these hypothalamic nuclei influences certain aspects of energy expenditure.

Increased body fat is associated with potentiation of blood pressure response to hypoxia in healthy men: relations with insulin and leptin

Background

Increased peripheral chemosensitivity (PChS) has been proposed as mechanism underlying obesity-related sympathoactivation, with insulin and/or leptin as possible mediators. However, human data on PChS in obesity are scarce. Therefore, we explored this issue in a sample of 41 healthy men aged 30–59 years, divided according to body fat percentage (fat %) into two groups: <25 and ≥25 %.

Methods

PChS was assessed using transient hypoxia method [respiratory (PChS-MV), heart rate (PChS-HR), and blood pressure (PChS-SBP) responses were calculated]. Baroreflex sensitivity (BRS-Seq) was assessed using sequence method. Fasting plasma insulin and leptin levels were measured. Homeostatic model assessment (HOMA) was used to assess insulin sensitivity/resistance.

Results

Individuals with ≥25 % body fat demonstrated increased PChS-SBP (p < 0.01), but unchanged PChS-MV and PChS-HR (both p > 0.4). PChS-SBP was related positively with anthropometric characteristics (e.g. waist circumference, fat %), plasma insulin and HOMA (all p < 0.05), and negatively with BRS-Seq (p = 0.001), but not with plasma leptin (p = 0.27).

Conclusions

In healthy men, overweight/obesity is accompanied by augmented blood pressure response from peripheral chemoreceptors, while respiratory and heart rate responses remain unaltered. Hyperinsulinaemia and insulin resistance (but not hyperleptinaemia) are associated with augmented pressure response from chemoreceptors.

Electronic supplementary material

The online version of this article (doi:10.1007/s10286-015-0338-2) contains supplementary material, which is available to authorized users.

A woman who lost weight at the cost of her heartbeat

With increasing prevalence of obesity worldwide, the number of patients undergoing bariatric surgery is also rising. Although the incidence of adverse outcomes associated with bariatric surgery has reduced, the physiological compensatory changes occurring after weight loss can lead to some unavoidable outcomes. One such condition is sinus bradycardia. The pathophysiology behind this is well studied but there is little awareness about this outcome. Sinus bradycardia in this clinical setting is generally asymptomatic and does not require any treatment. Extensive cardiac workup and unnecessary treatment can be avoided by increasing awareness among healthcare providers.

Asymptomatic sinus bradycardia following bariatric surgery

Approximately 121,000 bariatric surgical procedures are performed annually, and salutary effects include a reduction in cardiovascular morbidity and mortality, risk factor modification, and improvement in sympathovagal tone. There are anecdotal accounts of unexplained sinus bradycardia (SB) after significant weight loss but no systematic studies have been conducted. The purpose of this study was to determine the frequency of incident SB, its timing, and association with weight loss, clinical characteristics, and predictors. We evaluated various clinical characteristics including resting heart rate, blood pressure, body mass index (BMI), heart rate reserve (HRR), basal metabolic rate, and exercise regimen in 151 consecutive patients who underwent bariatric surgery. Multiple logistic regression analysis was performed to determine predictors of SB. Twenty-five of 137 patients (18%) experienced postoperative SB. Patients with SB had significantly greater reduction in BMI than those without bradycardia (35 ± 9.6% and 25.7 ± 13%, respectively, p = 0.002). HRR was significantly greater in patients with SB (116 ± 14 beats/min) compared with those without bradycardia (105 ± 14 beats/min, p = 0.007). Multiple logistic regression analysis revealed that the odds of developing SB were 1.96 and 1.91 and associated with the percent decrease in BMI (95% confidence interval 1.3 to 3.0, p = 0.002) or increase in HRR (95% confidence interval 1.28 to 2.85, p = 0.002), respectively. In conclusion, SB occurred 14 ± 11 months postoperatively and its predictors were the percent reduction in BMI or increase in HRR.

Relationship of muscle sympathetic nerve activity to insulin sensitivity

PURPOSE

An association between insulin resistance and activation of the sympathetic nervous system has been reported in previous studies. However, potential interactions between insulin sensitivity and sympathetic neural mechanisms in healthy people remain poorly understood. We conducted a study to determine the relationship between sympathetic activity and insulin resistance in young, healthy humans.

METHODS

Thirty-seven healthy adults (18-35 years, BMI <28 kg m(-2)) were studied. Resting muscle sympathetic nerve activity (MSNA) was measured with microneurography and insulin sensitivity of glucose and free fatty acid metabolism was measured during a hyperinsulinemic-euglycemic clamp with two levels of insulin.

RESULTS

During lower doses of insulin, we found a small association between lower insulin sensitivity and higher MSNA (P < 0.05) but age was a cofactor in this relationship. Overall, we found no difference in insulin sensitivity between groups of low and high MSNA, but when women were analyzed separately, insulin sensitivity was lower in the high MSNA group compared with the low MSNA group of women.

CONCLUSIONS

These data suggest that MSNA and insulin sensitivity are only weakly associated with young healthy individuals and that age and sex may be important modifiers of this relationship.

Selective leptin resistance revisited

In addition to effects on appetite and metabolism, leptin influences many neuroendocrine and physiological systems, including the sympathetic nervous system. Building on my Carl Ludwig Lecture of the American Physiological Society, I review the sympathetic and cardiovascular actions of leptin. The review focuses on a critical analysis of the concept of selective leptin resistance (SLR) and the role of leptin in the pathogenesis of obesity-induced hypertension in both experimental animals and humans. We introduced the concept of SLR in 2002 to explain how leptin might increase blood pressure (BP) in obese states, such as diet-induced obesity (DIO), that are accompanied by partial leptin resistance. This concept, analogous to selective insulin resistance in the metabolic syndrome, holds that in several genetic and acquired models of obesity, there is preservation of the renal sympathetic and pressor actions of leptin despite attenuation of the appetite and weight-reducing actions. Two potential overlapping mechanisms of SLR are reviewed: 1) differential leptin molecular signaling pathways that mediate selective as opposed to universal leptin action and 2) brain site-specific leptin action and resistance. Although the phenomenon of SLR in DIO has so far focused on preservation of sympathetic and BP actions of leptin, consideration should be given to the possibility that this concept may extend to preservation of other actions of leptin. Finally, I review perplexing data on the effects of leptin on sympathetic activity and BP in humans and its role in human obesity-induced hypertension.

Influence of heart rate at rest for predicting the metabolic syndrome in older Chinese adults

The aim of this study was to examine the relationship between seated resting heart rate and the metabolic syndrome (MetS) among older residents of Guangzhou, South China. A total of 30,519 older participants (≥50 years) from the Guangzhou Biobank Cohort Study were stratified into quartiles based on seated resting heart rate. The associations between each quartile and the MetS were assessed using multivariable logistic regression. A total of 6,907 (22.8 %) individuals were diagnosed as having the MetS, which was significantly associated with increasing heart rate quartiles (P < 0.001). Participants in the uppermost quartile (mean resting heart rate 91 ± 8 beats/min) of this cardiovascular proxy had an almost twofold increased adjusted risk (odds ratio (95 % CI) = 1.94 (1.79, 2.11), P < 0.001) for the MetS, as compared to those in the lowest quartile (mean resting heart rate, 63 ± 4 beats/min). Heart rate, which is an inexpensive and simple clinical measure, was independently associated with the MetS in older Chinese adults. We hope these observations will spur further studies to examine the usefulness of resting heart rate as a means of risk stratification in such populations, for which targeted interventions should be implemented.

Risk of elevated resting heart rate on the development of type 2 diabetes in patients with clinically manifest vascular diseases

OBJECTIVE

Sympathetic nerve activation is causally related to insulin resistance as both a cause and a consequence. Resting heart rate (RHR) reflects sympathetic nerve activity. We investigated the effect of RHR on the incidence of type 2 diabetes mellitus (T2DM) in patients with clinically manifest vascular diseases.

DESIGN

Data were used from the second manifestations of arterial disease (SMART) study: a prospective cohort study of patients with clinically manifest vascular diseases (n=3646).

METHODS

RHR was obtained using an electrocardiogram. Patients were followed up for incident type 2 diabetes (n=289) during a median period of 5.5 (interquartile range 3.2-8.4) years. The relation between RHR and incident T2DM was estimated by Cox proportional hazard analysis. As age was an effect modifier (P=0.048), analyses were stratified for age.

RESULTS

Patients in quartile 4 (Q4) of RHR had a 65% increased risk of T2DM compared with those in Q1 (reference; hazard ratios (HR), 1.65; 95% confidence interval (95% CI), 1.15-2.36) adjusted for age, gender, smoking, estimated glomerular filtration rate, systolic blood pressure, location of vascular disease, and antihypertensive medication. Every 10 beats per minute (bpm) increase in RHR increased the risk for T2DM with 10% (HR, 1.10; 95% CI, 1.00-1.21) in the total population. This risk was particularly high in subjects aged 55-63 years (per 10 bpm: HR, 1.22; 95% CI, 1.04-1.43) and was independent of the location of vascular disease and beta-blocker use.

CONCLUSIONS

Increased RHR, an indicator of sympathetic nerve activity, is associated with an increased risk for T2DM in patients with manifest vascular diseases, particularly in middle-aged patients.

Increased visceral adipose tissue is associated with increased resting heart rate in patients with manifest vascular disease

Abdominal obesity is characterized by sympathetic nerve activation (SNA), probably mediated by elevated insulin and leptin levels. Resting heart rate (RHR) is a marker of sympathetic tone, and independently associated with cardiovascular events and death in various populations. We investigated and quantified the relation between visceral adipose tissue (VAT) and RHR in patients with vascular disease. In 3,723 patients with manifest vascular disease, visceral and subcutaneous fat tissue was measured with ultrasonography. RHR was obtained from an electrocardiogram (ECG). The association between quartiles of VAT and RHR was quantified using linear regression analysis with adjustments for potential confounding factors. Separate analyses were performed for men and women and for location of vascular disease. Visceral fat was categorized into sex-pooled quartiles (Q) ranging from 2.7-8.0 cm in Q1 (reference) to 9.4-20.6 cm in Q4. High visceral fat thickness was associated with increased RHR, in men (Q4 vs. Q1, β = 4.36; 95% confidence interval (CI) = 3.11-5.61) and women (β = 1.48; 95% CI = -0.70 to 3.66), after full adjustment. Waist circumference and BMI had a significant relation with RHR in men (β = 3.51; 95% CI = 2.21-4.81 and β = 2.80; 95% CI = 1.51-4.08, respectively) but these relations were smaller and not significant in women (β = 0.71; 95% CI = -1.44 to 2.85 and β = 0.24; 95% CI = -1.90 to 2.37, respectively). There was no relation between subcutaneous fat and RHR in men and women. The relation between visceral fat and RHR was similar in patients with different locations of vascular diseases. Increased visceral fat is associated with increased RHR in male and female patients with vascular disease, independent of the location.

Obesity and adipokines: effects on sympathetic overactivity

Excess body weight is a major risk factor for cardiovascular disease, increasing the risk of hypertension, hyperglycaemia and dyslipidaemia, recognized as the metabolic syndrome. Adipose tissue acts as an endocrine organ by producing various signalling cytokines called adipokines (including leptin, free fatty acids, tumour necrosis factor-α, interleukin-6, C-reactive protein, angiotensinogen and adiponectin). A chronic dysregulation of certain adipokines can have deleterious effects on insulin signalling. Chronic sympathetic overactivity is also known to be present in central obesity, and recent findings demonstrate the consequence of an elevated sympathetic outflow to organs such as the heart, kidneys and blood vessels. Chronic sympathetic nervous system overactivity can also contribute to a further decline of insulin sensitivity, creating a vicious cycle that may contribute to the development of the metabolic syndrome and hypertension. The cause of this overactivity is not clear, but may be driven by certain adipokines. The purpose of this review is to summarize how obesity, notably central or visceral as observed in the metabolic syndrome, leads to adipokine expression contributing to changes in insulin sensitivity and overactivity of the sympathetic nervous system.

Influence of resting energy expenditure on blood pressure is independent of body mass and a marker of sympathetic tone

Two recent examinations reported a strong association between blood pressure (BP) and resting energy expenditure (REE), independent of body mass and body composition. Both reports postulate that neurohumoral processes that contribute to variation in REE may partly mediate the body mass effect on BP. Therefore, we examined the relationship of REE and BP in 108 asymptomatic women (a) to confirm previous findings in a novel population and (b) to examine the impact of a marker of sympathetic tone on this relationship, as this was indicated as a potentially salient intermediary in previous reports. All testing was performed during a 4-day admission to the General Clinical Research Center. Resting energy expenditure was measured by indirect calorimetry, body composition was determined by dual-energy x-ray absorptiometry, and 24-hour fractionated urinary norepinephrine was determined by high-performance liquid chromatography. Multiple linear regression revealed REE as a significant predictor of systolic BP (β = 0.30, P = .04), independent of race (β = 0. 28, P = .01), age (β = -0.02, P = .80), height (β = -0.38, P = .08), fat mass (β = 0.22, P = .20), fat-free mass (β = 0.08, P = .65), and 24-hour fractionated urinary norepinephrine (β = 0.06, P = .57); and the same model using diastolic BP as the dependent variable approached significance (β = 0.24, P = .09). This study affirms previous findings that REE may be a potential mediator in resting BP, independent of many well-cited factors and, additionally, a marker of sympathetic tone.

Hemodynamics and metabolism at low versus moderate altitudes

Despite the higher prevalence of diabetes and hypertension in populations residing at moderate altitudes, mortality in these populations is lower than in populations residing at low altitudes. To examine whether metabolic and hemodynamic differences can explain this apparent paradox, we performed a cross-sectional study of a general population sample recruited in the Canary Islands, Spain (n=6729). We recorded altitude of residence, age, heart rate, blood pressure, body mass index, social class, physical activity, energy intake, alcohol intake, smoking habit, prevalence of type 2 diabetes mellitus and hypertension. In a subsample (n=903), we recorded serum concentration of cholesterol, triglycerides, glucose, C peptide, leptin, soluble leptin receptor (sObR), C-reactive protein, resistin, soluble CD40 ligand (sCD40L), and paraoxonase activity (PON), and we estimated insulin resistance and free leptin index. We found an inverse association between altitude and heart rate (p<0.001), leptin (p<0.001), free leptin index (p<0.001), resistin (p<0.001), and sCD40L (p<0.05) and a direct association between altitude and hypertension (odds ratio=1.29 for altitude >600 m; 95% confidence interval=1.03-1.62), glycemia (p<0.05), C peptide (p<0.001), insulin resistance (p<0.001), sObR (p<0.05), and PON (p<0.05). When social class was included in the multivariate model, the association with PON was no longer significant. In conclusion, individuals residing at moderate altitudes have a lower heart rate and lower serum concentration of total leptin, free leptin, and sCD40L. These differences may partially explain the lower mortality in these populations.

Assessment of sympathetic cardiovascular drive in human hypertension: achievements and perspectives

Methodological refinements in the assessment of human sympathetic cardiovascular drive have allowed throughout the years to better define the role of the sympathetic nervous system in the pathophysiology of hypertension. Earlier studies have provided evidence that indirect markers of adrenergic drive, such as plasma or urinary norepinephrine as well as heart rate, often display an increase in the hypertensive state. Direct recording of efferent postganglionic muscle sympathetic nerve traffic via microneurography and regional norepinephrine spillover technique have conclusively documented the occurrence of an adrenergic overdrive in hypertension, showing that the sympathetic activation is directly related to the severity of the hypertensive state and is widespread to different cardiovascular districts. The present review will focus on some major features of the "neuroadrenergic hypothesis of hypertension." In particular it will examine the mechanisms responsible for the adrenergic overdrive, the relationships between the sympathetic activation and the metabolic disarray of frequent detection in the hypertensive state, and the participation of neuroadrenergic factors at the development of the hypertension-related target organ damage. Further issues addressed will be the contribution of the hyperadrenergic state to the different patterns of the 24-hour blood pressure profile as well as to the day/night blood pressure variability described in the hypertensive state and the behavior of the sympathetic function in the hypertensive states complicated by the presence of other cardiovascular or metabolic disease. Finally, the clinical and therapeutic implications of the neuroadrenergic abnormalities occurring in hypertension, as well as the areas worthy of future research, will be highlighted.

Urinary potassium is a clinically useful test to detect a poor quality diet

Poor eating habits, a strong predictor of health outcomes, are not objectively assessed in routine clinical practice. In this study, we evaluated the use of urinary potassium (K(+)) as a means to identify people consuming a poor quality diet. Consecutive patients with kidney stones (n = 220), aged 18-50 y, from a population-based lithotripsy unit, collected a single 24-h urine sample to assess urinary K(+). They also completed a FFQ to derive the recommended foods score (RFS), an index of overall diet quality, and had their blood pressure, heart rate, weight, and height measured. Urinary K(+) was related positively with the intake of recommended food items, including vegetables, fruit, whole grains, low-fat dairy products, fish and poultry, and wine and negatively to those not recommended by current dietary guidelines, including red meat, fast food, and high-energy drinks. Urinary K(+) was also correlated with the RFS (r = 0.226; P < 0.001). Using a receiver operating characteristic curve, K(+) excretion values below the gender-specific median (men, 60 mmol/d; women, 41 mmol/d) were identified as the optimal cutoff values for a poor quality diet, indicated by the RFS. Higher urinary K(+) was inversely related to adjusted BMI (P-trend = 0.03), diastolic blood pressure (P-trend = 0.04) and heart rate (P-trend = 0.006), after controlling for potential confounders. Urinary K(+) provides a summary measure of diet quality, is significantly related to BMI, blood pressure, and heart rate, and may be useful clinically to detect poor dietary habits and monitor response to dietary interventions.

Renin-angiotensin system, natriuretic peptides, obesity, metabolic syndrome, and hypertension: an integrated view in humans

The obesity pandemic is closely related to hypertension and metabolic syndrome. Visceral adipose tissue plays a key role in the metabolic and cardiovascular complications of being overweight. The pathophysiological link between visceral adiposity and cardiometabolic complications focuses on insulin sensitivity, sympathetic nervous system, renin-angiotensin-aldosterone system (RAAS) and, only recently, on cardiac natriuretic peptide system (CNPS). RAAS and CNPS are endogenous antagonistic systems on sodium balance, cardiovascular system, and metabolism. The circulating RAAS is dysregulated in obese patients, and adipose tissue has a full local renin-angiotensin system that is active at local and systemic level. Adipocyte biology and metabolism are influenced by local renin-angiotensin system, with angiotensin II acting as a 'growth factor' for adipocytes. CNPS induces natriuresis and diuresis, reduces blood pressure, and, moreover, has powerful lipolytic and lipomobilizing activity in humans but not in rodents. In obesity, lower plasmatic natriuretic peptides levels with increasing BMI, waist circumference, and metabolic syndrome have been documented. Thus, reduced CNPS effects coupled with increased RAAS activity have a central role in obesity and its deadly complications. We propose herein an integrated view of the dysregulation of these two antagonistic systems in human obesity complicated with hypertension, metabolic syndrome, and increased cardiovascular risk.

Gender differences in sympathetic nervous activity: influence of body mass and blood pressure

BACKGROUND

Obesity and high blood pressure (BP) commonly coexist in patients, and both conditions are associated with elevated sympathetic nervous activity. We tested whether the sympathetic nervous system was differently affected in men and women by the body mass index (BMI), BP, leptin and weight loss.

METHODS

We measured muscle sympathetic nerve activity (MSNA, microneurography), BP and plasma leptin concentrations in 167 age-matched normotensive and hypertensive men and women divided into three subgroups: lean, BMI < 25 kg/m; overweight, BMI > or = 25 and < 30 kg/m; and obese, BMI > or = 30 kg/m. These measurements were repeated in a subgroup of 19 obese subjects who underwent a 12-week diet.

RESULTS

Women with hypertension had increased MSNA compared with their normotensive counterparts (37 +/- 2 versus 25 +/- 2 bursts/min, analysis of variance, P < 0.001) and MSNA was significantly related to BP (P < 0.05, r = 0.236) but not to BMI. MSNA in men with hypertension was no different from that in normotensive subjects (33 +/- 2 versus 30 +/- 2 bursts/min), but MSNA was significantly related to BMI (P < 0.05, r = 0.249). Diet resulted in the same degree of weight loss in men and women, but induced a decrease in MSNA only in men (43 +/- 3 to 34 +/- 3 bursts/min, P < 0.01). The plasma leptin concentration was higher in women than in men, and for both groups it was related to BMI not BP (r = 0.497, P < 0.001 in women and r = 0.483, P < 0.001 in men).

CONCLUSION

These data demonstrate a gender difference in the regulation of the sympathetic nervous system, in which MSNA mainly relates to BP in women and to BMI in men.

The effect of red wine on plasma leptin levels and vasoactive factors from adipose tissue: A randomized crossover trial

AIMS

It has been reported that alcohol has multiple effects on appetite. To elucidate potential mechanisms we measured the levels of plasma leptin and the vasoactive factors after red wine intake.

METHODS

We conducted a randomized crossover trial to study the effect of red wine on the levels of leptin, TNF-alpha, TGF- beta(1), IL-6, ICAM-1, and VCAM-1 in healthy, non-smoking individuals. The subjects were randomized to drinking one glass of red wine (150 ml, 15 g alcohol) every day ('wine period') or to undergo a period of total abstention from alcohol ('abstention period'). After 3 weeks they switched the intervention group. Eighty-seven volunteers completed the study (mean age 50 years).

RESULTS

After 3 weeks' daily intake of red wine, plasma leptin was significantly increased (from 6308 pg/ml to 7402 pg/ml, P = 0.05). There was a marked gender difference, as leptin levels increased only in females (P = 0.012). When calculated as leptin/body mass index (BMI) ratio, the trend and results were similar. Red wine consumption had no significant effect on other vasoactive factors measured in this study.

CONCLUSION

Red wine increases levels of the appetite-regulating hormone leptin in females, but not in males. Whether red wine has an effect on appetite-regulation in its own right, remains to be solved.

Short-term fasting-induced autonomic activation and changes in catecholamine levels are not mediated by changes in leptin levels in healthy humans

OBJECTIVE

In animal models, the adipocyte-secreted hormone leptin increases energy expenditure by increasing sympathetic outflow but its role in humans remains to be elucidated. We evaluated whether inducing hypoleptinaemia (with and without administration of leptin at replacement doses) for 3 days would influence catecholamine levels and sympathetic and parasympathetic activity in healthy humans.

METHODS

We studied six normal-weight subjects in the General Clinical Research Center (GCRC) under three conditions: baseline fed state (control study) and two 72-h fasting studies (to decrease leptin levels), with administration of either placebo or replacement-dose recombinant methionyl human leptin (r-metHuLeptin) in a randomized, double-blind fashion. In each condition, 24-h urinary catecholamine levels, heart rate and heart rate variability (HRV), a standard tool for assessing cardiac autonomic modulation, were measured.

RESULTS

Study parameters remained stable during the control condition and the baseline assessment of all three studies. In response to 72-h fasting, which decreased serum leptin levels by 80%, 24-h urinary norepinephrine and dopamine levels and heart rate increased while cardiac vagal modulation decreased (all P < 0.05). Replacement-dose r-metHuLeptin to keep leptin levels within the physiological range during fasting did not alter fasting-associated changes in heart rate, catecholamine levels or cardiac vagal tone.

CONCLUSIONS

The findings of this controlled, interventional study indicate that changes in heart rate, catecholamine levels and cardiac vagal modulation associated with 72-h fasting are independent of regulation by leptin. Thus, changes in leptin levels within the physiological range do not seem to play a role in regulating autonomic function during short-term starvation in healthy humans.

The effect of gender on the sympathetic nerve hyperactivity of essential hypertension

We planned to determine whether or not there is a difference in the level of muscle sympathetic nerve activity (MSNA) between hypertensive women and hypertensive men. Sympathetic activation of essential hypertension (EHT) has been associated with increased cardiovascular events, which are known to be less likely to occur in women than in men. Normal women have been reported to have less sympathetic nerve activity than men, but no reported data are available regarding gender differences in sympathetic activity in hypertensive subjects. We examined 36 patients with untreated and uncomplicated EHT comprising 18 women and 18 men, and 36 normal controls comprising 18 women and 18 men. MSNA was quantified as the mean frequency of single units and as multiunit bursts using the technique of microneurography. The hypertensive groups had greater sympathetic nerve activity than the control groups. Female hypertensives had lower (P<0.001) single unit hyperactivity (56+/-1.7 impulses/100 cardiac beats) than male hypertensives (72+/-1.7 impulses/100 cardiac beats). Normotensive females had lower (P<0.01) single unit activity (42+/-3.6 impulses/100 cardiac beats) than normotensive males (56+/-4.6 impulses/100 cardiac beats). Similar results were obtained for the frequency of multiunit burst activity. Hypertension in women is associated with a lower level of central sympathetic hyperactivity than in men. It is suggested that this may at least partly explain the observed lower hypertension-related cardiovascular events in women than in men. In addition, the findings may have implications for gender-specific management of hypertension.

Role of leptin in blood pressure regulation and arterial hypertension

Leptin is a 16-kDa protein secreted by white adipose tissue that is primarily involved in the regulation of food intake and energy expenditure. Plasma leptin concentration is proportional to the amount of adipose tissue and is markedly increased in obese individuals. Recent studies suggest that leptin is involved in cardiovascular complications of obesity, including arterial hypertension. Acutely administered leptin has no effect on blood pressure, probably because it concomitantly stimulates the sympathetic nervous system and counteracting depressor mechanisms such as natriuresis and nitric oxide (NO)-dependent vasorelaxation. By contrast, chronic hyperleptinemia increases blood pressure because these acute depressor effects are impaired and/or additional sympathetic nervous system-independent pressor effects appear, such as oxidative stress, NO deficiency, enhanced renal Na reabsorption and overproduction of endothelin. Although the cause-effect relationship between leptin and high blood pressure in humans has not been demonstrated directly, many clinical studies have shown elevated plasma leptin in patients with essential hypertension and a significant positive correlation between leptin and blood pressure independent of body adiposity both in normotensive and in hypertensive individuals. In addition, leptin may contribute to end-organ damage in hypertensive individuals such as left ventricular hypertrophy, retinopathy and nephropathy, independent of regulating blood pressure. Here, current knowledge about the role of leptin in the regulation of blood pressure and in the pathogenesis of arterial hypertension is presented.

A Positive Association between Leptin and Blood Pressure of Normal Range in Japanese Men

The results of previous studies on the relationship between leptin and blood pressure are discordant. We investigated to what extent the serum leptin level was related to blood pressure independent of the degree of insulin resistance. The subjects were 1916 men aged 34-69 years whose mean body mass index (BMI) was 23.0 kg/m2. Blood pressure was regressed by leptin concentrations with adjustments for age, BMI, insulin resistance, triglyceride, high density lipoprotein cholesterol, low density lipoprotein cholesterol, physical activity, drinking habits and smoking status. Leptin was associated with diastolic blood pressure (DBP) (standardized beta: 0.092, p = 0.003), but not with systolic blood pressure (SBP) (standardized beta: 0.035, p = 0.25), although insulin resistance was positively associated with both SBP and DBP (standardized beta: 0.175 for SBP, p < 0.001 and 0.114 for DBP, p < 0.001) among all subjects. After subjects were divided into those with normal blood pressure (SBP <130 mmHg and DBP <85 mmHg) and those with higher blood pressure, leptin was positively and significantly associated with DBP (standardized beta: 0.106, p = 0.012) independent of the degree of insulin resistance, but not with SBP (standardized beta: 0.064, p = 0.13) among subjects in the normal blood pressure range. Among the subjects with higher blood pressure, however, neither the association of leptin with SBP nor that of leptin with DBP was statistically significant. These findings suggest that leptin may maintain and increase arterial tone, resulting in the elevation of DBP only within normal blood pressure range. It is also likely that leptin is a physiological mediator--or at least a marker--of some degree of DBP elevation in obesity.

Circulating leptin correlates with left ventricular mass in morbid (grade III) obesity before and after weight loss induced by bariatric surgery: a potential role for leptin in mediating human left ventricular hypertrophy

CONTEXT

Obesity is frequently associated with left ventricular hypertrophy, even when uncomplicated by hypertension or diabetes mellitus. Left ventricular hypertrophy is an important risk factor for congestive heart failure.

OBJECTIVE

The objective of this study was to evaluate the relationship between leptin and left ventricular mass in uncomplicated, morbid (grade 3) obesity and the existence of leptin receptors and intracellular signaling proteins in the human heart.

DESIGN

Left ventricular mass (LVM) was calculated through electrocardiogram reading in normotensive grade III obese patients (World Health Organization classification) undergoing bariatric surgery [laparoscopic adjustable gastric banding (LAGB)] at baseline and 1 yr later. The control group was composed of healthy lean normotensive subjects. Leptin receptors were detected by PCR and immunocytochemistry in human heart biopsies.

SETTING

This study was performed at university hospitals.

PATIENTS

Thirty-one grade 3 obese patients and 30 healthy nonobese normotensive, age- and sex-matched control subjects were studied.

INTERVENTION

Obese subjects underwent LAGB to induce weight loss and were evaluated at baseline and after 1 yr.

RESULTS

LVM, plasma leptin, glucose, insulin levels, and homeostasis model assessment index were higher in obese than in lean controls (P < 0.01); at univariate regression analysis, LVM correlated with body mass index, leptin, and homeostasis model assessment index; at multiple regression analysis, LVM only correlated with leptin levels (P = 0.001). Obese subjects were reevaluated 1 yr after LAGB, when their body mass index changed from 46.2 +/- 1.24 to 36.6 +/- 1.05 kg/m(2) (P < 0.01); the decrease in LVM correlated only with the decrease in leptin levels (P < 0.01). We demonstrated that long and short isoforms of the leptin receptor and intracellular proteins mediating leptin signaling were expressed in human heart by RT-PCR, immunocytochemistry, or both methods.

CONCLUSIONS

These data suggest that leptin could contribute to the left ventricular hypertrophy in humans.

Association of metabolic syndrome with exercise capacity and heart rate recovery in patients with coronary heart disease in the heart and soul study

It is not known whether the metabolic syndrome is associated with poor exercise capacity among patients who have established coronary heart disease. We evaluated the association of the metabolic syndrome with treadmill exercise capacity and heart rate recovery among patients who had coronary heart disease. We measured treadmill exercise capacity (METs) and heart rate recovery (beats per minute) in 943 subjects who had known coronary heart disease. Of these, 377 (40%) had the metabolic syndrome as defined by criteria of the National Cholesterol Education Program. Participants who had the metabolic syndrome were more likely to have poor exercise capacity (METs <5, 33% vs 18%, p <0.0001) and poor heart rate recovery (<or=16 beats/min, 34% vs 21%, p <0.0001) than those who did not have the metabolic syndrome. In ordinal logistic regression analyses, the metabolic syndrome was associated with decreased exercise capacity (odds ratio [OR] 2.2, 95% confidence interval [CI] 1.7 to 2.8, p <0.0001) and decreased heart rate recovery (OR 1.8, 95% CI 1.4 to 2.3, p <0.0001). These associations remained strong after adjusting for potential confounding variables (OR 1.6, 95% CI 1.2 to 2.1, p = 0.003 for decreased exercise capacity; OR 1.4, 95% CI 1.1 to 1.9, p = 0.02 for decreased heart rate recovery). The metabolic syndrome is independently associated with poor exercise capacity and poor heart rate recovery in patients who have established coronary heart disease. Decreased exercise capacity may contribute to the adverse outcomes associated with the metabolic syndrome.

Leptin and altitude in the cardiovascular diseases

OBJECTIVE

The lower mortality from coronary ischemic disease in populations living at high altitude has been related to an increase of high-density lipoprotein (HDL)-cholesterol at altitude. Leptin has been proposed as a cardiovascular risk factor. We investigated whether leptin varies according to the altitude at which people live.

RESEARCH METHODS AND PROCEDURES

This was a cross-sectional study of the first 889 people enrolled in a cohort study in the Canary Islands, Spain. The relationship among serum leptin, altitude, obesity, and other cardiovascular risk factors was analyzed by bivariate and multivariate tests.

RESULTS

Leptin levels showed an inverse correlation to altitude expressed in meters (r = -0.10). Obese subjects had this leptin-altitude association (r = -0.19), but they also had a direct correlation of leptin to HDL-cholesterol (r = 0.27) and an inverse correlation of leptin to the total cholesterol-to-HDL-cholesterol ratio (r = -0.34), triglycerides (r = -0.29), apolipoprotein B (r = -0.21), and glycemia (r = -0.19). Nonobese subjects had only the leptin-altitude association (r = -0.11). The final regression model included altitude as predictor. Other associated variables were gender, physical activity, BMI, age, smoking (reducing leptin independently of BMI), alcohol, heart rate, and income.

DISCUSSION

Serum leptin level decreases when altitude increases, and this association could help to explain the lower cardiovascular mortality rate at high altitude. However, because in obese subjects there is a direct association of leptin with HDL-cholesterol and an inverse association with the lipid atherogenic fractions, we suggest the hypothesis of different roles for bound and free leptin, with free leptin being a cardiovascular protective factor in obese people.

Leptin does not induce hypertrophy, cell cycle alterations, or production of MCP-1 in cultured rat and mouse cardiomyocytes

BACKGROUND

Leptin has been proposed as an important mediator in cardiovascular pathophysiology. Patients with congestive heart failure (CHF) present high plasma leptin levels. CHF is generally preceded by myocardial remodeling involving hypertrophy, necrosis, and apoptosis.

AIM

To investigate whether leptin causes hypertrophy or cell cycle alterations, or induces MCP-1 synthesis in cardiomyocytes.

METHODS

Primary cultures of neonatal rat cardiomyocytes (PC) and murine cell line HL-1 were used. RT-PCR was used to identify Ob-Rb gene expression. Metabolic activity and proliferation of cardiomyocytes was studied using MTT and BrdU uptake, while apoptosis was assayed with Hoechst dye vital staining and flow cytometry. Measurement of the cell surface area was used to determine hypertrophy. MCP-1 levels were measured by ELISA.

RESULTS

RT-PCR showed Ob-Rb mRNA expression in HL-1 cells. Exposure to leptin induced no changes in metabolic activity, proliferation, and apoptotic rates, and did not alter cell cycle in cardiomyocytes. Leptin did not increase cell size of cardiomyocytes, and MCP-1 synthesis was not detected in PC and HL-1 cells treated with leptin.

CONCLUSION

This work shows that leptin does not induce changes in viability, proliferation, size or apoptosis of rat neonatal and HL-1 cardiomyocytes, and it does not induce MCP-1 secretion in these cells.

The global epidemic of obesity: are we becoming more sympathetic?

The relationship between obesity and sympathetic nervous system (SNS) behavior has been controversial. Existing paradigms have been opposed in their views of the directional changes in SNS activity in obesity. In addition, limitations of previous approaches to assess SNS activity have produced inconsistent findings. However, the use of state-of-the-art neurochemical and neurophysiologic techniques has improved our current understanding of this issue. There is regional heterogeneity in the SNS activation associated with obesity, with the renal and skeletal muscle circulations, but not the heart, being targets for SNS activation. Abdominal visceral fat appears to be an important depot linking obesity and skeletal muscle SNS activation. The impact of this depot on SNS activity to the kidney or other regions is unknown. Future studies are needed to address this issue as well as the mechanisms and consequences of SNS activation in visceral obesity.

Leptin, obesity and cardiovascular disease

PURPOSE OF REVIEW

Obesity is a risk factor for cardiovascular diseases. Leptin levels are increased in obesity and leptin exhibits cardiovascular actions that may contribute to increased cardiovascular risk. We review the sympathetic, renal and vascular actions of leptin and their relevance to cardiovascular disease.

RECENT FINDINGS

Leptin possesses cardio-renal actions potentially contributing to obesity-related hypertension including generalized sympathoactivation. However, given that leptin resistance occurs in obesity, it has been difficult to link hyperleptinemia with hypertension. One possibility is that leptin resistance is confined to the metabolic effects of leptin, with preservation of its sympathoexcitatory actions. Other mechanisms may contribute to the pressor effects of leptin. For instance, angiotensin II induces leptin generation. Leptin also potentiates the pressor effect of insulin. Therefore, interactions between angiotensin II and insulin with leptin could have deleterious cardiovascular effects in obesity. Additionally, leptin appears to stimulate vascular inflammation, oxidative stress and hypertophy. These actions may contribute to the pathogenesis of hypertension, atherosclerosis, and left ventricular hypertrophy.

SUMMARY

The potential actions of leptin in the pathophysiology of cardiovascular complications of obesity are diverse, despite evidence of leptin resistance to its metabolic actions. However, most information about cardiovascular actions of leptin derives from in-vitro and animal studies. Future research in humans is widely awaited.

Leptin, sympathetic nervous system, and baroreflex function

In addition to its direct effects on energy metabolism and caloric intake, leptin exerts several circulatory effects that appear to be mediated by an interaction with the sympathetic nervous system and the major reflexogenic area involved in cardiovascular homeostatic control--that is, the arterial baroreflex. In this paper, the relationships between the adipocyte hormone and the neuroadrenergic function are reviewed, taking into account data collected in experimental animal models as well as in human cardiovascular (hypertension and heart failure) and noncardiovascular (obesity) diseases that are characterized by a hyperadrenergic state coupled with a hyperleptinemia.

Obesity-related hypertension: Is there a role for selective leptin resistance?

Obesity is a risk factor for cardiovascular diseases, in particular for hypertension. Serum leptin levels and sympathetic nerve activity are both increased in obesity. Leptin has been demonstrated to increase sympathetic nerve activity. Thus, leptin-dependent sympathoactivation might contribute to obesity-related hypertension. However, leptin resistance occurs in obesity. One possibility is that leptin resistance is selective to the metabolic effects of leptin, sparing its sympathoexcitatory actions. In this article, we review experimental evidence supporting the novel concept of selective leptin resistance. We also discuss the sympathetic actions of leptin that are relevant to blood pressure modulation and potential mechanisms of leptin resistance. Disruption of leptin intracellular signaling pathways and resistance of specific leptin-responsive neural networks provide theoretic models of selective leptin resistance. However, most information about leptin-sympathetic actions and leptin-resistance mechanisms derive from in vitro and animal studies. Future research in humans is widely awaited.

Obesity and hypertension: two epidemics or one?

The association between obesity and hypertension is well documented, although the exact nature of this relation remains unclear. Sympathetic nervous and renin-angiotensin-aldosterone system activation appear to play an important role in the sodium and water retention, rightward shift in the pressure-natriuresis, and blood pressure elevation observed in obese individuals. Visceral obesity and the ectopic deposition of adipose tissue may be important in the activation of these systems and in the target organ damage that ensues. Weight loss is critical in the effective management of obesity hypertension and the accompanying target organ damage, although recidivism rates are high. However, prevention of weight gain should be the major priority for combating hypertension and its consequences in the future. The present review will provide an overview of our understanding of the etiology, pathophysiology, and treatment of obesity hypertension. Our focus is on the state of knowledge in humans. The potential role of abdominal obesity is considered throughout our review. We refer to relevant animal literature for supportive evidence and where little or no data in humans are available.

Leptin increases cardiomyocyte hyperplasia via extracellular signal-regulated kinase- and phosphatidylinositol 3-kinase-dependent signaling pathways

Obesity is a major risk factor for the development of heart failure. Importantly, it is now appreciated that a change in the number of myocytes is one of multiple structural and functional alterations (remodeling) leading to heart failure. Here we investigate the effect of leptin, the product of the obese (ob) gene, on proliferation of human and murine cardiomyocytes. Leptin caused a time- and dose-dependent significant increase in proliferation of HL-1 cells that was inhibited by preincubation with PD98059 and LY294002, suggesting that leptin mediated proliferation via extracellular signal-regulated kinase-1/2- and phosphatidylinositol-3-kinase-dependent signaling pathways. We confirmed that leptin activates both extracellular signal-regulated kinase-1/2 phosphorylation and association of phosphatidylinositol-3-kinase (regulatory p85 subunit) with phosphotyrosine immunoprecipitates. We also examined bromodeoxyuridine incorporation as a measure of new DNA synthesis and demonstrated a stimulatory effect of leptin in both HL-1 cells and human cardiomyocytes. Bromodeoxyuridine incorporation in HL-1 cells was inhibited by PD98059 and LY294002. Our results establish a mitogenic effect of leptin in cardiomyocytes and provide additional evidence for a potential direct link between leptin and cardiac remodeling in obesity.

Subcutaneous obesity is not associated with sympathetic neural activation

We tested the hypothesis that muscle sympathetic nerve activity (MSNA) would not differ in subcutaneously obese (SUBOB) and nonobese (NO) men with similar levels of abdominal visceral fat despite higher plasma leptin concentrations in the former. We further hypothesized that abdominal visceral fat would be the strongest body composition- or regional fat distribution-related correlate of MSNA among these individuals. To accomplish this, we measured MSNA (via microneurography), body composition (via dual-energy X-ray absorptiometry), and abdominal fat distribution (via computed tomography) in 15 NO (body mass index </= 25 kg/m(2); 22.4 +/- 1.4 yr) and 9 SUBOB (25 </= body mass index </= 35 kg/m(2); 23.4 +/- 2.1 yr) sedentary men. As expected, body mass (94 +/- 4 vs. 71 +/- 2 kg), total fat mass (25 +/- 2 vs. 12 +/- 1 kg), and abdominal subcutaneous fat (307 +/- 36 vs. 132 +/- 12 cm(2)) were significantly higher in the SUBOB group compared with NO peers. However, the level of abdominal visceral fat did not differ significantly in the two groups (69 +/- 7 vs. 55 +/- 5 cm(2)). MSNA was not different between SUBOB and NO men (23 +/- 3 vs. 24 +/- 2 bursts/min; P > 0.05, respectively) despite approximately 2.6-fold higher (P < 0.05) plasma leptin concentration in the SUBOB men. Furthermore, abdominal visceral fat was the only body composition- or regional fat distribution-related correlate (r = 0.45; P < 0.05) of MSNA in the pooled sample. In addition, abdominal visceral fat was related to MSNA in NO (r = 0.58; P = 0.0239) but not SUBOB (r = 0.39; P = 0.3027) men. Taken together with our previous observations, our findings suggest that the relation between obesity and MSNA is phenotype dependent. The relation between abdominal visceral fat and MSNA was evident in NO but not in SUBOB men and at levels of abdominal visceral fat below the level typically associated with elevated cardiovascular and metabolic disease risk. Our observations do not support an obvious role for leptin in contributing to sympathetic neural activation in human obesity and, in turn, are inconsistent with the concept of selective leptin resistance.

Association between ghrelin and cardiovascular indexes in healthy obese and lean men

OBJECTIVE

Obesity is an increasingly common condition and is associated with excess morbidity and mortality, including clinical and subclinical cardiac dysfunction. The role of hormones involved in energy homeostasis, including ghrelin and leptin, in cardiovascular function remains incompletely understood. Therefore, we sought to evaluate the association between systemic ghrelin and leptin levels with indexes of cardiovascular structure and function.

DESIGN AND MEASUREMENTS

We measured serum ghrelin and leptin levels in 25 clinically healthy obese men and 25 lean controls, using commercially available immunoassays. We also assessed right and left ventricular structure and function using cardiac magnetic resonance imaging. We then investigated the association between serum ghrelin and leptin levels with cardiac indexes, using univariate and multivariate analysis.

RESULTS

There was an independent association between serum ghrelin levels and height-adjusted right ventricular mass (r = -0.324, P = 0.026), right ventricular end-diastolic volume (r = -0.363, P = 0.017) and right ventricular end-systolic volume (r = -0.398, P = 0.009) as well as right ventricular ejection fraction (r = 0.317, P = 0.050). There was no significant association between serum ghrelin and indexes of left ventricular structure or function. We also identified an association between serum leptin levels and resting heart rate (r = 0.391, P = 0.002). There was an association between serum leptin and height-adjusted left ventricular mass on univariate, but not on multivariate, analysis.

CONCLUSIONS

Serum ghrelin is associated with right ventricular cardiovascular indexes and serum leptin is associated with resting heart rate. These associations indicate a close interaction between the endocrine and cardiovascular systems in obesity.

Leptin and the ventilatory response to exercise in heart failure

OBJECTIVES

The aim of the study was to test the hypothesis that leptin is involved in the regulation of ventilatory responses to exercise in chronic heart failure (CHF).

BACKGROUND

Exercise-induced hyperventilation is a negative prognostic factor in CHF. Studies in animals suggest that leptin, a hormone secreted by adipocytes, contributes to the regulation of respiration. Plasma leptin levels are elevated in non-cachectic CHF, suggesting the possibility that leptin might be involved in dysregulation of ventilation in CHF.

METHODS

We studied 50 patients with stable CHF without cachexia. All subjects underwent anthropometric measurements, resting echocardiography, pulmonary function tests, and a cardiopulmonary exercise test. The ventilatory response to exercise was assessed by calculating the VE/VCO(2) and VE/VO(2) slopes (VE = ventilation per unit time, VCO(2) = carbon dioxide production, VO(2) = oxygen consumption).

RESULTS

Using a multiple regression model, leptin was significantly and positively correlated with both VE/VCO(2) slope (regression coefficient = 0.87, F = 39.32, p < 0.001) and VE/VO(2) slope (regression coefficient = 0.84, F = 24.04, p < 0.001). This correlation was independent of age, gender, body mass index, body fat, ejection fraction, New York Heart Association functional class, pulmonary function, plasma norepinephrine, angiotensin II, brain natriuretic peptide levels, and medications. Also, the greatest VE/VCO(2) slope was seen in subjects in the highest tertile of leptin.

CONCLUSIONS

Leptin is an independent predictor of VE/VCO(2) slope in heart failure, and may be a link between metabolic, cardiovascular, and respiratory abnormalities in CHF.

Sympathetic nerve activity in metabolic control--some basic concepts

A role for the sympathetic nervous system in hypertension has been looked for in relation to the 'metabolic syndrome' with associations between body weight, insulin sensitivity and hypertension. By use of microneurography human sympathetic responses to hypoglycaemia, normoglycaemic hyperinsulinaemia and food intake have been studied. A strong but differentiated influence of insulin-induced hypoglycaemia comprises increase in muscle sympathetic nerve activity (MSNA) and the sudomotor part of skin sympathetic nerve activity (SSNA), whereas vasoconstrictor SSNA is inhibited. Responses to infusion of 2-deoxy-D-glucose are identical, suggesting central nervous system glucopenia and not insulin to be the causative factor. Insulin infusion during normoglycaemia evokes a moderate increase in MSNA; SSNA and blood pressure does not change. After glucose ingestion MSNA displays a sustained increase, which is only partly elicited by insulin. A significant albeit weaker increase occurs after pure protein or fat meals, and after glucose ingestion in C-peptide-negative diabetic patients, with no insulin secretion. In healthy elderly people the MSNA response to food intake is weak, because of a high outflow already at rest; this is suggested to explain postprandial hypotension in the elderly, a paradoxical mechanism behind clinical autonomic failure. A pathophysiological role of MSNA in the metabolic syndrome with hypertension has been speculated. An association between obesity and elevated level of MSNA at rest is established; observed relationships to chronic insulin levels and hypertension are less unanimous. The adipose tissue regulating hormone leptin has become one focus of interest in ongoing attempts to elucidate a possible role of the human sympathetic nervous system in the 'metabolic syndrome' and hypertension.

Plasma leptin and blood pressure in men: graded association independent of body mass and fat pattern

OBJECTIVE

The role of leptin in the association between body mass, central adiposity, and blood pressure (BP) is controversial. This study evaluated the relationship between leptin and BP in relation to body mass index (BMI) and fat distribution in a large sample of untreated male adults.

RESEARCH METHODS AND PROCEDURES

The study population was made up of 457 untreated male employees of the Olivetti factory in Naples. Plasma leptin, complete anthropometry, BP, and relevant biochemical variables were measured.

RESULTS

Log-transformed plasma leptin levels were directly associated with BMI (r = 0.661, p < 0.001) and waist circumference (r = 0.630; p < 0.001). Leptin also correlated with systolic (r = 0.258) and diastolic (r = 0.277) BP (p < 0.001). The association between leptin and BP was maintained after accounting for age, BMI (or waist circumference), log-insulin, and serum creatinine (p < 0.01); this association was stronger than that with BMI. Logistic regression analysis showed that an increased prevalence of hypertension (BP >or= 140 and/or 90 mm Hg) was associated with high plasma leptin levels when controlling for age and waist circumference (odds ratio, 1.99; 95%CI, 1.06 to 3.72) or for age and BMI (odds ratio, 1.92; 95%CI, 1.02 to 3.61).

DISCUSSION

A graded positive relationship between plasma leptin levels and BP was observed in this sample of untreated male adults. This association was independent of age, BMI, abdominal adiposity, and fasting plasma insulin. Moreover, elevated plasma leptin concentrations were associated with greater probability of hypertension, again independently of potential confounders.

Obesity-related hypertension: role of the sympathetic nervous system, insulin, and leptin

Heightened sympathetic nervous system activity, hyperinsulinemia, insulin resistance, and hyperleptinemia contribute to obesity-related hypertension. However, the precise mechanism and sequence of events in this pathophysiologic event have not been clarified. This review concentrates on studies helping to clarify the mechanisms of blood pressure elevation associated with weight change, concentrating on the temporal changes in neuroendocrine factors that are known to control energy metabolism and blood pressure. A better understanding of the pathophysiologic mechanisms of obesity-related hypertension may help in prevention, treatment, and slowing of the cardiovascular complications of obesity.