Obesity-induced hypertension: role of sympathetic nervous system, leptin, and melanocortins

Adipose tissue and metabolic syndrome: too much, too little or neither

Obesity is strongly associated with metabolic syndrome. Recent research suggests that excess adipose tissue plays an important role in development of the syndrome. On the other hand, persons with a deficiency of adipose tissue (e.g. lipodystrophy) also manifest the metabolic syndrome. In some animal models, expansion of adipose tissue pools mitigates adverse metabolic components (e.g. insulin resistance, hyperglycaemia and dyslipidemia). Hence, there are conflicting data as to whether adipose tissue worsens the metabolic syndrome or protects against it. This conflict may relate partly to locations of adipose tissue pools. For instance, lower body adipose tissue may be protective whereas upper body adipose tissue may promote the syndrome. One view holds that in either case, the accumulation of ectopic fat in muscle and liver is the driving factor underlying the syndrome. If so, there may be some link between adipose tissue fat and ectopic fat. But the mechanisms underlying this connection are not clear. A stronger association appears to exist between excessive caloric intake and ectopic fat accumulation. Adipose tissue may act as a buffer to reduce the impact of excess energy consumption by fat storage; but once a constant weight has been achieved, it is unclear whether adipose tissue influences levels of ectopic fat. Another mechanism whereby adipose tissue could worsen the metabolic syndrome is through release of adipokines. This is an intriguing mechanism, but the impact of adipokines on metabolic syndrome risk factors is uncertain. Thus, many potential connections between adipose tissue and metabolic syndrome remain to unravelled.

Deletion of protein tyrosine phosphatase 1b in proopiomelanocortin neurons reduces neurogenic control of blood pressure and protects mice from leptin- and sympatho-mediated hypertension

Protein tyrosine phosphatase 1b (Ptp1b), which represses leptin signaling, is a promising therapeutic target for obesity. Genome wide deletion of Ptp1b, increases leptin sensitivity, protects mice from obesity and diabetes, but alters cardiovascular function by increasing blood pressure (BP). Leptin-control of metabolism is centrally mediated and involves proopiomelanocortin (POMC) neurons. Whether these neurons contribute to leptin-mediated increases in BP remain unclear. We hypothesized that increasing leptin signaling in POMC neurons with Ptp1b deletion will sensitize the cardiovascular system to leptin and enhance neurogenic control of BP. We analyzed the cardiovascular phenotype of Ptp1b+/+ and POMC-Ptp1b-/- mice, at baseline and after 7 days of leptin infusion or sympatho-activation with phenylephrine. POMCPtp1b deletion did not alter baseline cardiovascular hemodynamics (BP, heart rate) but reduced BP response to ganglionic blockade and plasma catecholamine levels that suggests a decreased neurogenic control of BP. In contrast, POMC-Ptp1b deletion increased vascular adrenergic reactivity and aortic α-adrenergic receptors expression. Chronic leptin treatment reduced vascular adrenergic reactivity and blunted diastolic and mean BP increases in POMC-Ptp1b-/- mice only. Similarly POMC-Ptp1b-/- mice exhibited a blunted increased in diastolic and mean BP accompanied by a gradual reduction in adrenergic reactivity in response to chronic vascular sympatho-activation with phenylephrine. Together these data rule out our hypothesis but suggest that deletion of Ptp1b in POMC neurons protects from leptin- and sympatho-mediated increases in BP. Vascular adrenergic desensitization appears as a protective mechanism against hypertension, and POMC-Ptp1b as a key therapeutic target for the treatment of metabolic and cardiovascular dysfunctions associated with obesity.

Lean heart: Role of leptin in cardiac hypertrophy and metabolism

Leptin is an adipokine that has been linked with the cardiovascular complications resulting from obesity such as hypertension and heart disease. Obese patients have high levels of circulating leptin due to increased fat mass. Clinical and population studies have correlated high levels of circulating leptin with the development of cardiac hypertrophy in obesity. Leptin has also been demonstrated to increase the growth of cultured cardiomyocytes. However, several animal studies of obese leptin deficient mice have not supported a role for leptin in promoting cardiac hypertrophy so the role of leptin in this pathological process remains unclear. Leptin is also an important hormone in the regulation of cardiac metabolism where it supports oxidation of glucose and fatty acids. In addition, leptin plays a critical role in protecting the heart from excess lipid accumulation and the formation of toxic lipids in obesity a condition known as cardiac lipotoxicity. This paper focuses on the data supporting and refuting leptin’s role in promoting cardiac hypertrophy as well as its important role in the regulation of cardiac metabolism and protection against cardiac lipotoxicity.

Clinical predictors of ventilatory threshold achievement in patients with claudication

PURPOSE

Ventilatory threshold (VT) is considered a clinically important marker of cardiovascular function in several populations, including patients with claudication, because it is related to walking capacity and hemodynamics. The purpose of this study was to identify clinical predictors for VT achievement in patients with intermittent claudication.

METHODS

One hundred and seventy-seven (n = 177) patients with intermittent claudication performed a progressive graded cardiopulmonary treadmill test until maximal claudication pain. Oxygen uptake (V˙O2) was continuously measured during the test, and afterwards, VT was visually detected. Clinical characteristics, demographic data, comorbid conditions, and cardiovascular risk factors were obtained. Patients who achieved and did not achieve VT were compared, as well as the workload that VT occurred in the former group.

RESULTS

VT was achieved in 134 patients (76%), and the mean V˙O2 at VT for these patients was 10.8 ± 2.4 mL·kg(-1)·min(-1). Patients who did not achieve VT presented lower ankle brachial index (ABI), claudication onset time, peak walking time, and V˙O2peak, and the proportion of women was higher compared with patients who achieved VT (P < 0.05). Multiple linear regression analysis identified that sex (b = 0.25, P = 0.002), body mass index (b = -0.18, P = 0.025), peak walking time (b = 0.17, P = 0.044), and ABI (b = 0.23, P = 0.006) were predictors of V˙O2 at VT.

CONCLUSIONS

Forty-three patients (24%) with intermittent claudication did not achieve VT, and these patients were mostly women and those with greater severity of disease. Moreover, in those who reached VT, the predictors of poor VT were female sex, high body mass index, low peak walking time, and low ABI.

Effects of leptin on sympathetic nerve activity in conscious mice

The adipocyte-derived hormone, leptin, has emerged as an important regulator of regional sympathetic nerve activity (SNA) with pathophysiological implications in obesity. Genetically engineered mice are useful to understand the molecular pathways underlying the SNA responses evoked by leptin. However, so far the effect of leptin on direct SNA in mice has been studied under general anesthesia. Here, we examined the sympathetic responses evoked by leptin in conscious mice. Mice were instrumented, under ketamine/xylazine anesthesia, with renal or lumbar SNA recordings using a thin (40 gauge) bipolar platinum-iridium wire. The electrodes were exteriorized at the nape of the neck and mice were allowed (5 h) to recover from anesthesia. Interestingly, the reflex increases in renal and lumbar SNA caused by sodium nitroprusside (SNP)-induced hypotension was higher in the conscious phase versus the anesthetized state, whereas the increase in both renal and lumbar SNA evoked by leptin did not differ between anesthetized or conscious mice. Next, we assessed whether isoflurane anesthesia would yield a better outcome. Again, the SNP-induced increase in renal SNA and baroreceptor-renal SNA reflex were significantly elevated in the conscious states relative to isoflurane-anesthetized phase, but the renal SNA response induced by leptin in the conscious states were qualitatively comparable to those evoked above. Thus, despite improvement in sympathetic reflexes in conscious mice the sympathetic responses evoked by leptin mimic those induced during anesthesia.

Role of the Paraventricular Nucleus of the Hypothalamus in the Sympathoexcitatory Effects of Leptin

Leptin binds to receptors in multiple hypothalamic nuclei to increase sympathetic nerve activity; however, the neurocircuitry is unclear. Here, using anesthetized male Sprague-Dawley rats, we investigated the role of the paraventricular nucleus of the hypothalamus. Intracerebroventricular injection of leptin slowly increased lumbar sympathetic nerve activity (LSNA), heart rate, mean arterial pressure, and baroreflex control of LSNA and heart rate. Inhibition of the paraventricular nucleus with muscimol completely reversed leptin's effects. Blockade of paraventricular melanocortin 3/4 receptors with SHU9119 or ionotropic glutamate receptors with kynurenate, alone or together, each partially reversed the effects of leptin, implicating increased activation of glutamate and melanocortin 3/4 receptors. Conversely, although blockade of neuropeptide Y Y1 receptors in the paraventricular nucleus increased LSNA, mean arterial pressure, and heart rate, these responses were prevented by intracerebroventricular or arcuate nucleus injections of leptin, suggesting that, at least in part, leptin also increases sympathetic nerve activity by suppression of tonic neuropeptide Y inhibitory inputs from the arcuate nucleus. Injection of the melanocortin 3/4 receptor agonist melanotan-II into the paraventricular nucleus increased LSNA, mean arterial pressure, and heart rate only after blockade of neuropeptide Y Y1 receptors. Therefore, we conclude that leptin increases LSNA in part via increased glutamatergic and α-melanocyte-stimulating hormone drive of paraventricular sympathoexcitatory neurons, the latter of which requires simultaneous withdrawal of tonic neuropeptide Y inhibition.

Adipocyte-Derived Hormone Leptin Is a Direct Regulator of Aldosterone Secretion, Which Promotes Endothelial Dysfunction and Cardiac Fibrosis

BACKGROUND

In obesity, the excessive synthesis of aldosterone contributes to the development and progression of metabolic and cardiovascular dysfunctions. Obesity-induced hyperaldosteronism is independent of the known regulators of aldosterone secretion, but reliant on unidentified adipocyte-derived factors. We hypothesized that the adipokine leptin is a direct regulator of aldosterone synthase (CYP11B2) expression and aldosterone release and promotes cardiovascular dysfunction via aldosterone-dependent mechanisms.

METHODS AND RESULTS

Immunostaining of human adrenal cross-sections and adrenocortical cells revealed that adrenocortical cells coexpress CYP11B2 and leptin receptors. Measurements of adrenal CYP11B2 expression and plasma aldosterone levels showed that increases in endogenous (obesity) or exogenous (infusion) leptin dose-dependently raised CYP11B2 expression and aldosterone without elevating plasma angiotensin II, potassium or corticosterone. Neither angiotensin II receptors blockade nor α and β adrenergic receptors inhibition blunted leptin-induced aldosterone secretion. Identical results were obtained in cultured adrenocortical cells. Enhanced leptin signaling elevated CYP11B2 expression and plasma aldosterone, whereas deficiency in leptin or leptin receptors blunted obesity-induced increases in CYP11B2 and aldosterone, ruling out a role for obesity per se. Leptin increased intracellular calcium, elevated calmodulin and calmodulin-kinase II expression, whereas calcium chelation blunted leptin-mediated increases in CYP11B2, in adrenocortical cells. Mineralocorticoid receptor blockade blunted leptin-induced endothelial dysfunction and increases in cardiac fibrotic markers.

CONCLUSIONS

Leptin is a newly described regulator of aldosterone synthesis that acts directly on adrenal glomerulosa cells to increase CYP11B2 expression and enhance aldosterone production via calcium-dependent mechanisms. Furthermore, leptin-mediated aldosterone secretion contributes to cardiovascular disease by promoting endothelial dysfunction and the expression of profibrotic markers in the heart.

Perirenal Fat and Association With Metabolic Risk Factors: The Uberlândia Heart Study

Perirenal fat (PRF) is associated with cardiovascular risk factors. Gender differences in the correlations of cardiovascular disease risk factors and PRF in the Brazilian population are lacking.Cross-sectional study with 101 (50.49% men; mean age 56.5 ± 18, range 19-74 years) drawn from the Uberlândia Heart Study underwent ultrasonography assessment of abdominal adipose. For the PRF, a 3.5 MHz transducer was measured in the middle third of the right kidney, with the transducer positioned at the axillary midline. The examinations were always performed by the same examiner. The PRF thickness was examined in relation to waist circumference, blood pressure, and metabolic risk factors. The PRF was significantly associated with the levels of gamma-glutamyl transferase (P < 0.05, r = 0.08), fasting plasma glucose (P < 0.05, r = 0.07), waist circumference (P < 0.05, r = 0.10), and metabolic syndrome (P < 0.001, r = 0.38) in men, and with the levels of fasting plasma glucose (P < 0.05) in women.The PRF was correlated with most cardiovascular risk factors in men and only in glucose at the women.

Obesity-induced changes in kidney mitochondria and endoplasmic reticulum in the presence or absence of leptin

We investigated obesity-induced changes in kidney lipid accumulation, mitochondrial function, and endoplasmic reticulum (ER) stress in the absence of hypertension, and the potential role of leptin in modulating these changes. We compared two normotensive genetic mouse models of obesity, leptin-deficient ob/ob mice and hyperleptinemic melanocortin-4 receptor-deficient mice (LoxTB MC4R-/-), with their respective lean controls. Compared with controls, ob/ob and LoxTB MC4R-/- mice exhibit significant albuminuria, increased creatinine clearance, and high renal triglyceride content. Renal ATP levels were decreased in both obesity models, and mitochondria isolated from both models showed alterations that would lower mitochondrial ATP production. Mitochondria from hyperleptinemic LoxTB MC4R-/- mice kidneys respired NADH-generating substrates (including palmitate) at lower rates due to an apparent decrease in complex I activity, and these mitochondria showed oxidative damage. Kidney mitochondria of leptin-deficient ob/ob mice showed normal rates of respiration with no evidence of oxidative damage, but electron transfer was partially uncoupled from ATP synthesis. A fourfold induction of C/EBP homologous protein (CHOP) expression indicated induction of ER stress in kidneys of hyperleptinemic LoxTB MC4R-/- mice. In contrast, ER stress was not induced in kidneys of leptin-deficient ob/ob mice. Our findings show that obesity, in the absence of hypertension, is associated with renal dysfunction in mice but not with major renal injury. Alterations to mitochondria that lower cellular ATP levels may be involved in obesity-induced renal injury. The type and severity of mitochondrial and ER dysfunction differs depending upon the presence or absence of leptin.

The emerging epidemic of hypertension in Asian children and adolescents

Hypertension has become a serious global public health burden because of its high incidence and concomitant risk of cardiovascular disease. Many studies have verified that risk factors, such as hypertension and obesity which are responsible for cardiovascular disease, start in early childhood. In Asian countries, the prevalence of hypertension in the pediatric age group has become more prevalent than ever before with the increasing obesity epidemic. To tackle the epidemic of cardiovascular disease, a leading cause of death and disability of non-communicable diseases in Asian countries, population-based measures aiming at reducing harmful environmental factors to blood pressure and body weight must be applied to individuals in their early childhood, as early as the fetal stage. This review focused on the prevalence of pediatric hypertension in Asian countries and outlined several considerations for accurate blood pressure (BP) measurement and evaluation, along with an overview of pathophysiology of fetal programming and obesity related with childhood hypertension.

Augmented Endothelial-Specific L-Arginine Transport Blunts the Contribution of the Sympathetic Nervous System to Obesity Induced Hypertension in Mice

Augmenting endothelial specific transport of the nitric oxide precursor L-arginine via cationic amino acid transporter-1 (CAT1) can prevent obesity related hypertension. We tested the hypotheses that CAT1 overexpression prevents obesity-induced hypertension by buffering the influence of the sympathetic nervous system (SNS) on the maintenance of arterial pressure and by buffering pressor responses to stress. Wild type (WT; n=13) and CAT1 overexpressing mice (CAT+; n=13) were fed a normal or a high fat diet for 20 weeks. Mice fed a high fat diet were returned to the control diet before experiments commenced. Baseline mean arterial pressure (MAP) and effects of restraint-, shaker- and almond feeding-stress and ganglionic blockade (pentolinium; 5 mg/kg; i.p.) on MAP were determined in conscious mice. Fat feeding increased body weight to a similar extent in WT and CAT+ but MAP was greater only in WT compared to appropriate controls (by 29%). The depressor response to pentolinium was 65% greater in obese WT than lean WT (P < 0.001), but was similar in obese and lean CAT+ (P = 0.65). In lean WT and CAT+, pressor responses to shaker and feeding stress, but not restraint stress, were less in the latter genotype compared to the former (P ≤ 0.001). Pressor responses to shaker and feeding stress were less in obese WT than lean WT (P ≤ 0.001), but similar in obese and lean CAT+. The increase in MAP in response to restraint stress was less in obese WT (22 ± 2%), but greater in obese CAT+ (37 ± 2%), when compared to respective lean WT (31 ± 3%) and lean CAT+ controls (27 ± 2%; P ≤ 0.02). We conclude that CAT1 overexpression prevents obesity-induced hypertension by reducing the influence of the SNS on the maintenance of arterial pressure but not by buffering pressor responses to stress.

Should the sympathetic nervous system be a target to improve cardiometabolic risk in obesity?

The sympathetic nervous system (SNS) plays a key role in both cardiovascular and metabolic regulation; hence, disturbances in SNS regulation are likely to impact on both cardiovascular and metabolic health. With excess adiposity, in particular when visceral fat accumulation is present, sympathetic activation commonly occurs. Experimental investigations have shown that adipose tissue releases a large number of adipokines, cytokines, and bioactive mediators capable of stimulating the SNS. Activation of the SNS and its interaction with adipose tissue may lead to the development of hypertension and end-organ damage including vascular, cardiac, and renal impairment and in addition lead to metabolic abnormalities, especially insulin resistance. Lifestyle changes such as weight loss and exercise programs considerably improve the cardiovascular and metabolic profile of subjects with obesity and decrease their cardiovascular risk, but unfortunately weight loss is often difficult to achieve and sustain. Pharmacological and device-based approaches to directly or indirectly target the activation of the SNS may offer some benefit in reducing the cardiometabolic consequences of obesity. Preliminary evidence is encouraging, but more trials are needed to investigate whether sympathetic inhibition could be used in obesity to reverse or prevent cardiometabolic disease development. The purpose of this review article is to highlight the current knowledge of the role that SNS plays in obesity and its associated metabolic disorders and to review the potential benefits of sympathoinhibition on metabolic and cardiovascular functions.

Obesity depresses baroreflex control of renal sympathetic nerve activity and heart rate in Sprague Dawley rats: role of the renal innervation

AIM

This study investigated the role of the renal innervation in arterial and cardiopulmonary baroreflex regulation of renal sympathetic nerve activity (RSNA) and heart rate (HR) in rats fed a high-fat diet to induce obesity.

METHODS

Rats received either a normal (12% kcal) or high (45% kcal) fat diet for 60 days. On day 61, rats were anesthetized and prepared for recording left RSNA. In one group, the renal nerves remained intact, while in the other, both kidneys were denervated. Baroreflex gain curves for RSNA and HR were generated by increasing and decreasing blood pressure. Low-pressure baroreceptors were challenged by infusing a saline load.

RESULTS

Mean blood pressure was 135 mmHg in the fat-fed and 105 mmHg (P < 0.05) in normal rats. Weight gain, adiposity index and creatinine clearance were 37, 82 and 55% higher (P < 0.05-0.001), but urine flow rate and fractional sodium excretions were 53 and 65% (both P < 0.001) lower, respectively, in the fat-fed compared to normal rats. In fat-fed rats with innervated kidneys, RSNA and HR arterial baroreflex sensitivities were reduced by 73 and 72% (both P < 0.05) but were normal in renally denervated rats. Volume expansion decreased RSNA by 66% (P < 0.001) in normal rats, but not in the intact fat-fed rats and by 51% (P < 0.01) in renally denervated fat-fed rats.

CONCLUSION

Feeding a high-fat diet caused hypertension associated with dysregulation of the arterial and cardiopulmonary baroreflexes which was dependent on an intact renal innervation. This suggests that in obese states neural signals arising from the kidney contribute to a deranged autonomic control.

Obesity-induced hypertension: interaction of neurohumoral and renal mechanisms

Excess weight gain, especially when associated with increased visceral adiposity, is a major cause of hypertension, accounting for 65% to 75% of the risk for human primary (essential) hypertension. Increased renal tubular sodium reabsorption impairs pressure natriuresis and plays an important role in initiating obesity hypertension. The mediators of abnormal kidney function and increased blood pressure during development of obesity hypertension include (1) physical compression of the kidneys by fat in and around the kidneys, (2) activation of the renin-angiotensin-aldosterone system, and (3) increased sympathetic nervous system activity. Activation of the renin-angiotensin-aldosterone system is likely due, in part, to renal compression, as well as sympathetic nervous system activation. However, obesity also causes mineralocorticoid receptor activation independent of aldosterone or angiotensin II. The mechanisms for sympathetic nervous system activation in obesity have not been fully elucidated but may require leptin and activation of the brain melanocortin system. With prolonged obesity and development of target organ injury, especially renal injury, obesity-associated hypertension becomes more difficult to control, often requiring multiple antihypertensive drugs and treatment of other risk factors, including dyslipidemia, insulin resistance and diabetes mellitus, and inflammation. Unless effective antiobesity drugs are developed, the effect of obesity on hypertension and related cardiovascular, renal and metabolic disorders is likely to become even more important in the future as the prevalence of obesity continues to increase.

Central nervous system dysfunction in obesity-induced hypertension

The activation of the sympathetic nervous system is a major mechanism underlying both human and experimental models of obesity-related hypertension. While insulin and the adipokine leptin have long been thought to contribute to obesity-related neurogenic mechanisms, the evidence is now very strong that they play a major role, shown particularly in animal studies using selective receptor antagonists. There is not just maintenance of leptin's sympatho-excitatory actions as previously suggested but considerable amplification particularly in renal sympathetic nervous activity. Importantly, these changes are not dependent on short-term elevation or reduction in plasma leptin or insulin, but require some weeks to develop indicating a slow "neural adaptivity" within hypothalamic signalling. These effects can be carried across generations even when offspring are raised on a normal diet. A better understanding of the underlying mechanism should be a high research priority given the prevalence of obesity not just in the current population but also for future generations.

Overweight, adipocytokines and hypertension: a prospective population-based study

OBJECTIVE

The adipocytokines, leptin, adiponectin, and interleukin-6, which stimulate liver C-reactive protein (CRP) production, are regarded as potential candidate intermediates between adipose tissue and overweight-induced hypertension.

METHODS

We examined the associations between leptin, adiponectin, and CRP levels with both prevalent and 5-year incident hypertension (IHT) in a general population of Danish adults (n = 5,868, 51.3% women, mean age 45.8 ± 7.9 years).

RESULTS

We recorded 2195 prevalent and 379 incident cases of hypertension. In models including leptin, CRP, adiponectin, sex, age, lifestyle risk factors, lipids, insulin, hemoglobin A1c, and in the incident model also baseline heart rate and blood pressure, only leptin of the three candidate intermediates was significantly associated with both prevalent and IHT [odds ratio (OR) = 1.18, 95% confidence interval (CI) 1.06-1.32, P = 0.002, and OR = 1.24, 95% CI 1.01-1.54, P = 0.044] for one standard deviation increase in log-transformed leptin levels, respectively. Log-transformed CRP was associated with prevalent (OR = 1.16, 95% CI 1.07-1.26, P < 0.001) but not IHT (OR = 0.98, 95% CI 0.84-1.14, P = 0.76). Log-transformed adiponectin was neither associated with prevalent nor IHT (OR = 0.94, 95% CI 0.87-1.02, P = 0.11 and OR = 0.93, 95% CI 0.80-1.08, P = 0.33). Comparing the lowest with the highest quintile of sex-specific BMI levels, there was an almost two-fold increase in IHT (OR = 1.89, 95% CI 1.10-3.25, P = 0.023) in the fully adjusted model. The population attributable risk estimate of IHT owing to overweight was 31%.

CONCLUSION

Leptin, but not adiponectin or CRP, may play a mediating role in overweight-induced hypertension. However, as BMI was a strong independent predictor of hypertension, other factors than leptin must be involved in the pathogenesis of overweight-related hypertension.

Reduced carotid baroreceptor distensibility-induced baroreflex resetting contributes to impairment of sodium regulation in rats fed a high-fat diet

Decreased carotid arterial compliance has been reported in obese subjects and animals. Carotid baroreceptors are located at the bifurcation of the common carotid artery, and respond to distension of the arterial wall, suggesting that higher pressure is required to obtain the same distension in obese subjects and animals. A hyperosmotic NaCl solution induces circulatory volume expansion and arterial pressure (AP) increase, which reflexively augment renal excretion. Thus, we hypothesized that sodium regulation via the baroreflex might be impaired in response to chronic hyperosmotic NaCl infusion in rats fed a high-fat diet. To examine this hypothesis, we used rats fed a high-fat (Fat) or normal (NFD) diet, and measured mean AP, water and sodium balance, and renal function in response to chronic infusion of hyperosmotic NaCl solution via a venous catheter. Furthermore, we examined arterial baroreflex characteristics with static open-loop analysis and distensibility of the common carotid artery. Significant positive water and sodium balance was observed on the 1st day of 9% NaCl infusion; however, this disappeared by the 2nd day in Fat rats. Mean AP was significantly higher during 9% NaCl infusion in Fat rats compared with NFD rats. In the open-loop analysis of carotid sinus baroreflex, a rightward shift of the neural arc was observed in Fat rats compared with NFD rats. Furthermore, distensibility of the common carotid artery was significantly reduced in Fat rats. These results indicate that a reduced baroreceptor distensibility-induced rightward shift of the neural arc might contribute to impairment of sodium regulation in Fat rats.

The role of leptin in the ventricular remodeling process and its mechanism

OBJECTIVE

This study aims to explore the role of leptin in the ventricular remodeling process and its mechanism in the diabetic rats' model.

METHODS

The diabetic SD rats model induced by streptozotocin was established. The SD rats were randomly divided into 4 groups: control group (20 rats treated with citric acid/sodium citrate buffer); M0 group (10 rats treated with physiological saline); M1 group (10 rats treated with 50 μg/kg LP); M2 group (10 rats treated with 100 μg/kg LP). Ang-II was detected by ELISA. The expression levels of LP and Ob-Rb were detected by RT-PCR. MAPK phosphorylation changes were detected by western blotting. Myocardial morphology was observed.

RESULTS

Compared with control group, the blood glucose concentration and Ang-II significantly increased in diabetic model groups (P < 0.01) and body weight decreased (P < 0.05). The expression levels of LP and Ob-Rb increased and heart function decreased in diabetic model groups.

CONCLUSIONS

LP may be involved in the myocardial cell hypertrophy through the neuroendocrine system and associated with the JAK-STAT, Ras-Raf-MEK-MAPK and PI-3K signaling pathway, which provides a new concept for the pathogenesis of cardiac hypertrophy.

The brain melanocortin system, sympathetic control, and obesity hypertension

Excess weight gain is the most significant, preventable cause of increased blood pressure (BP) in patients with primary (essential) hypertension and increases the risk for cardiovascular and renal diseases. In this review, we discuss the role of the brain melanocortin system in causing increased sympathetic activity in obesity and other forms of hypertension. In addition, we highlight potential mechanisms by which the brain melanocortin system modulates metabolic and cardiovascular functions.

Activation of the brain melanocortin system is required for leptin-induced modulation of chemorespiratory function

Melanocortin receptors (MC3/4R) mediate most of the metabolic and cardiovascular actions of leptin.

AIM

Here, we tested if MC4R also contributes to leptin's effects on respiratory function.

METHODS

After control measurements, male Holtzman rats received daily microinjections of leptin, SHU9119 (MC3/4R antagonist) or SHU9119 combined with leptin infused into the brain lateral ventricle for 7 days. On the 6th day of treatment, tidal volume (VT ), respiratory frequency (fR ) and pulmonary ventilation (VE ) were measured by whole-body plethysmography during normocapnia or hypercapnia (7% CO2 ). Baseline mean arterial pressure (MAP), heart rate (HR) and metabolic rate were also measured. VE , VT and fR were also measured in mice with leptin receptor deletion in the entire central nervous system (LepR/Nestin-cre) or only in proopiomelanocortin neurones (LepR/POMC-cre) and in MC4R knockout (MC4R(-/-) ) and wild-type mice.

RESULTS

Leptin (5 μg day(-1) ) reduced body weight (~17%) and increased ventilatory response to hypercapnia, whereas SHU9119 (0.6 nmol day(-1) ) increased body weight (~18%) and reduced ventilatory responses compared with control-PBS group (Lep: 2119 ± 90 mL min(-1)  kg(-1) and SHU9119: 997 ± 67 mL min(-1)  kg(-1) , vs. PBS: 1379 ± 91 mL min(-1)  kg(-1) ). MAP increased after leptin treatment (130 ± 2 mmHg) compared to PBS (106 ± 3 mmHg) or SHU9119 alone (109 ± 3 mmHg). SHU9119 prevented the effects of leptin on body weight, MAP (102 ± 3 mmHg) and ventilatory response to hypercapnia (1391 ± 137 mL min(-1)  kg(-1) ). The ventilatory response to hypercapnia was attenuated in the LepR/Nestin-cre, LepR/POMC-cre and MC4R(-/-) mice.

CONCLUSION

These results suggest that central MC4R mediate the effects of leptin on respiratory response to hypercapnia.

Fetal programming and cardiovascular pathology

Low birth weight serves as a crude proxy for impaired growth during fetal life and indicates a failure for the fetus to achieve its full growth potential. Low birth weight can occur in response to numerous etiologies that include complications during pregnancy, poor prenatal care, parental smoking, maternal alcohol consumption, or stress. Numerous epidemiological and experimental studies demonstrate that birth weight is inversely associated with blood pressure and coronary heart disease. Sex and age impact the developmental programming of hypertension. In addition, impaired growth during fetal life also programs enhanced vulnerability to a secondary insult. Macrosomia, which occurs in response to maternal obesity, diabetes, and excessive weight gain during gestation, is also associated with increased cardiovascular risk. Yet, the exact mechanisms that permanently change the structure, physiology, and endocrine health of an individual across their lifespan following altered growth during fetal life are not entirely clear. Transmission of increased risk from one generation to the next in the absence of an additional prenatal insult indicates an important role for epigenetic processes. Experimental studies also indicate that the sympathetic nervous system, the renin angiotensin system, increased production of oxidative stress, and increased endothelin play an important role in the developmental programming of blood pressure in later life. Thus, this review will highlight how adverse influences during fetal life and early development program an increased risk for cardiovascular disease including high blood pressure and provide an overview of the underlying mechanisms that contribute to the fetal origins of cardiovascular pathology.

Control of respiratory and cardiovascular functions by leptin

Leptin, a peptide hormone produced by adipose tissue, acts in brain centers that control critical physiological functions such as metabolism, breathing and cardiovascular regulation. The importance of leptin for respiratory control is evident by the fact that leptin deficient mice exhibit impaired ventilatory responses to carbon dioxide (CO2), which can be corrected by intracerebroventricular leptin replacement therapy. Leptin is also recognized as an important link between obesity and hypertension. Humans and animal models lacking either leptin or functional leptin receptors exhibit many characteristics of the metabolic syndrome, including hyperinsulinemia, insulin resistance, hyperglycemia, dyslipidemia and visceral adiposity, but do not exhibit increased sympathetic nerve activity (SNA) and have normal to lower blood pressure (BP) compared to lean controls. Even though previous studies have extensively focused on the brain sites and intracellular signaling pathways involved in leptin effects on food intake and energy balance, the mechanisms that mediate the actions of leptin on breathing and cardiovascular function are only beginning to be elucidated. This mini-review summarizes recent advances on the effects of leptin on cardiovascular and respiratory control with emphasis on the neural control of respiratory function and autonomic activity.

The sympathetic nervous system alterations in human hypertension

Several articles have dealt with the importance and mechanisms of the sympathetic nervous system alterations in experimental animal models of hypertension. This review addresses the role of the sympathetic nervous system in the pathophysiology and therapy of human hypertension. We first discuss the strengths and limitations of various techniques for assessing the sympathetic nervous system in humans, with a focus on heart rate, plasma norepinephrine, microneurographic recording of sympathetic nerve traffic, and measurements of radiolabeled norepinephrine spillover. We then examine the evidence supporting the importance of neuroadrenergic factors as promoters and amplifiers of human hypertension. We expand on the role of the sympathetic nervous system in 2 increasingly common forms of secondary hypertension, namely hypertension associated with obesity and with renal disease. With this background, we examine interventions of sympathetic deactivation as a mode of antihypertensive treatment. Particular emphasis is given to the background and results of recent therapeutic approaches based on carotid baroreceptor stimulation and radiofrequency ablation of the renal nerves.

Chronic hyperleptinemia results in the development of hypertension in pregnant rats

Despite the fact that obesity is a major risk factor for preeclampsia (PE), the pathophysiological mechanisms whereby obesity and metabolic factors such as leptin increase this risk are unclear. While human data have shown that hyperleptinemia is associated with PE, the long-term effect of hyperleptinemia on blood pressure during pregnancy is unknown. Thus we tested the hypothesis whether chronic circulating leptin elevations in pregnant rats increase blood pressure and placental factors known to play a role in PE. On gestational day (GD)14, rats were assigned to the normal pregnant group with food intake ad libitum (control), leptin-treated (0.5 μg·kg(-1)·min(-1) ip) pregnant group with food intake ad libitum (pregnant+LEP), and normal pregnant group with food intake adjusted to the food intake of pregnant+LEP rats (pregnant-FR). On GD19, mean arterial pressure (MAP) was assessed and tissues were collected. Serum leptin concentration was elevated in pregnant+LEP compared with control and pregnant-FR (18.0 ± 2.8 vs. 0.8 ± 0.1 vs. 0.3 ± 0.1 ng/ml; P < 0.05), which was associated with increased MAP (121.3 ± 8.1 vs. 102.4 ± 2.4 vs. 101.3 ± 1.8 mmHg; P < 0.05). Food intake and body weight were reduced in pregnant+LEP and pregnant-FR by the end of gestation. Additionally, placentas and fetuses of these groups were lighter than those of control. However, placental expression of tumor necrosis factor-α was significantly greater in pregnant+LEP compared with controls (1.6 ± 0.1 vs. 1.1 ± 0.1 pg/mg; P < 0.05). In conclusion, leptin increases blood pressure and placental tumor necrosis factor-α during pregnancy despite its effect of reducing food intake and body weight, and represents a mechanism whereby obesity can promote the development of hypertension in PE.

Leptin links with plasminogen activator inhibitor-1 in human obesity: the SABPA study

The relationship between obesity and the development of cardiovascular disease is well established. However, the underlying mechanisms contributing to vascular disease and increased cardiovascular risk in the obese remain largely unexplored. Since leptin exerts direct vascular effects, we investigated leptin and the relationship thereof with circulating markers of vascular damage, namely plasminogen activator inhibitor-1 antigen (PAI-1(ag)), von Willebrand factor antigen (vWF(ag)) and urinary albumin-to-creatinine ratio (ACR). The study included a bi-ethnic population of 409 African and Caucasian teachers who were stratified into lean (<0.5) and obese (⩾0.5) groups according to waist-to-height ratio. We obtained ambulatory blood pressure measurements and determined serum leptin levels, PAI-1(ag), vWF(ag) and ACR, as markers of vascular damage. The obese group had higher leptin (P<0.001) and PAI-1(ag) (P<0.001) levels and a tendency existed for higher vWF(ag) (P=0.068). ACR did not differ between the two groups (P=0.21). In single regression analyses positive associations existed between leptin and all markers of vascular damage (all P<0.001) only in the obese group. After adjusting for covariates and confounders in multiple regression analyses, only the association between leptin and PAI-1(ag) remained (R(2)=0.440; β=0.293; P=0.0021). After adjusting for gender, ethnicity and age, additional analyses indicated that leptin also associated with fibrinogen and clot lysis time in both lean and obese groups, which in turn is associated with 24- h blood pressure and pulse pressure. This result provides evidence that elevated circulating leptin may directly contribute to vascular damage, possibly through mechanism related to thrombotic vascular disease.

Roles for the sympathetic nervous system, renal nerves, and CNS melanocortin-4 receptor in the elevated blood pressure in hyperandrogenemic female rats

Women with polycystic ovary syndrome (PCOS) have hyperandrogenemia and increased prevalence of risk factors for cardiovascular disease, including elevated blood pressure. We recently characterized a hyperandrogenemic female rat (HAF) model of PCOS [chronic dihydrotestosterone (DHT) beginning at 4 wk of age] that exhibits similar characteristics as women with PCOS. In the present studies we tested the hypotheses that the elevated blood pressure in HAF rats is mediated in part by sympathetic activation, renal nerves, and melanocortin-4 receptor (MC4R) activation. Adrenergic blockade with terazosin and propranolol or renal denervation reduced mean arterial pressure (MAP by telemetry) in HAF rats but not controls. Hypothalamic MC4R expression was higher in HAF rats than controls, and central nervous system MC4R antagonism with SHU-9119 (1 nmol/h icv) reduced MAP in HAF rats. Taking a genetic approach, MC4R null and wild-type (WT) female rats were treated with DHT or placebo from 5 to 16 wk of age. MC4R null rats were obese and had higher MAP than WT control rats, and while DHT increased MAP in WT controls, DHT failed to further increase MAP in MC4R null rats. These data suggest that increases in MAP with chronic hyperandrogenemia in female rats are due, in part, to activation of the sympathetic nervous system, renal nerves, and MC4R and may provide novel insights into the mechanisms responsible for hypertension in women with hyperandrogenemia such as PCOS.

Leptin differentially increases sympathetic nerve activity and its baroreflex regulation in female rats: role of oestrogen

Obesity and hypertension are commonly associated, and activation of the sympathetic nervous system is considered to be a major contributor, at least in part due to the central actions of leptin. However, while leptin increases sympathetic nerve activity (SNA) in males, whether leptin is equally effective in females is unknown. Here, we show that intracerebroventricular (i.c.v.) leptin increases lumbar (LSNA) and renal (RSNA) SNA and baroreflex control of LSNA and RSNA in α-chloralose anaesthetized female rats, but only during pro-oestrus. In contrast, i.c.v. leptin increased basal and baroreflex control of splanchnic SNA (SSNA) and heart rate (HR) in rats in both the pro-oestrus and dioestrus states. The effects of leptin on basal LSNA, RSNA, SSNA and HR were similar in males and pro-oestrus females; however, i.c.v. leptin increased mean arterial pressure (MAP) only in males. Leptin did not alter LSNA or HR in ovariectomized rats, but its effects were normalized with 4 days of oestrogen treatment. Bilateral nanoinjection of SHU9119 into the paraventricular nucleus of the hypothalamus (PVN), to block α-melanocyte-stimulating hormone (α-MSH) type 3 and 4 receptors, decreased LSNA in leptin-treated pro-oestrus but not dioestrus rats. Unlike leptin, i.c.v. insulin infusion increased basal and baroreflex control of LSNA and HR similarly in pro-oestrus and dioestrus rats; these responses did not differ from those in male rats. We conclude that, in female rats, leptin's stimulatory effects on SNA are differentially enhanced by oestrogen, at least in part via an increase in α-MSH activity in the PVN. These data further suggest that the actions of leptin and insulin to increase the activity of various sympathetic nerves occur via different neuronal pathways or cellular mechanisms. These results may explain the poor correlation in females of SNA with adiposity, or of MAP with leptin.

Obesity-related hypertension: possible pathophysiological mechanisms

Hypertension is one of the major risk factors of cardiovascular diseases, but despite a century of clinical and basic research, the discrete etiology of this disease is still not fully understood. The same is true for obesity, which is recognized as a major global epidemic health problem nowadays. Obesity is associated with an increasing prevalence of the metabolic syndrome, a cluster of risk factors including hypertension, abdominal obesity, dyslipidemia, and hyperglycemia. Epidemiological studies have shown that excess weight gain predicts future development of hypertension, and the relationship between BMI and blood pressure (BP) appears to be almost linear in different populations. There is no doubt that obesity-related hypertension is a multifactorial and polygenic trait, and multiple potential pathogenetic mechanisms probably contribute to the development of higher BP in obese humans. These include hyperinsulinemia, activation of the renin-angiotensin-aldosterone system, sympathetic nervous system stimulation, abnormal levels of certain adipokines such as leptin, or cytokines acting at the vascular endothelial level. Moreover, some genetic and epigenetic mechanisms are also in play. Although the full manifestation of both hypertension and obesity occurs predominantly in adulthood, their roots can be traced back to early ontogeny. The detailed knowledge of alterations occurring in the organism of experimental animals during particular critical periods (developmental windows) could help to solve this phenomenon in humans and might facilitate the age-specific prevention of human obesity-related hypertension. In addition, better understanding of particular pathophysiological mechanisms might be useful in so-called personalized medicine.

Autonomic activity and leptin in Africans and whites: the SABPA study

OBJECTIVES

Evidence exists that leptin enhances sympathetic activity and may thereby contribute to the development of obesity-related hypertension. Sympathetic activation also seems more prominent in Africans than whites. We compared leptin levels, and different markers of autonomic activity between Africans and whites, and determined whether a relationship exists between leptin and autonomic activity.

METHODS

The study included 409 African and white school teachers (aged, 44.6 ± 9.6 years). We determined leptin in serum and measured ambulatory blood pressure. Markers reflecting autonomic activity included renin, cortisol, baroreflex sensitivity, ambulatory heart rate and heart rate variability (HRV) components (assessed by 24-h ECG recordings in the frequency and geometric domain).

RESULTS

Africans had higher leptin levels, BMI, blood pressure and heart rate (all P < 0.001) as well as lower HRV triangular index and HRV total power (P < 0.001). After also adjusting for BMI in multivariate regression analyses, in African men, renin (β = 0.228; P = 0.033), night-time heart rate (β = 0.184; P = 0.034), HRV triangular index (β = -0.230; P = 0.010) and HRV total power (β = -0.214; P = 0.046) associated with leptin. In white men, leptin associated with 24-h heart rate (β = 0.376; P < 0.001), as well as day and night-time heart rate (both P < 0.01), HRV triangular index (β = -0.335; P < 0.001) and HRV total power (β = -0.403; P < 0.001). In African women, we observed an association of leptin with the total power component of HRV (β = -0.221; P = 0.015) and a borderline association with renin (β = 0.219; P = 0.057). No significant associations were apparent in the white women.

CONCLUSION

We found that leptin is independently associated with different markers of autonomic activity, especially in men.

Obesity-induced increases in sympathetic nerve activity: sex matters

Abundant evidence obtained largely from male human and animal subjects indicates that obesity increases sympathetic nerve activity (SNA), which contributes to hypertension development. However, recent studies that included women reported that the strong relationships between muscle SNA and waist circumference or body mass index (BMI) found in men are not present in overweight and obese women. A similar sex difference in the association between adiposity and hypertension development has been identified in animal models of obesity. In this brief review, we consider two possible mechanisms for this sex difference. First, visceral adiposity, leptin, insulin, and angiotensin II have been identified as potential culprits in obesity-induced sympathoexcitation in males. We explore if these factors wield the same impact in females. Second, we consider if sex differences in vascular reactivity to sympathetic activation contribute. Our survey of the literature suggests that premenopausal females may be able to resist obesity-induced sympathoexcitation and hypertension in part due to differences in adipose disposition as well as its muted inflammatory response and reduced production of pressor versus depressor components of the renin-angiotensin system. In addition, vascular responsiveness to increased SNA may be reduced. However, more importantly, we identify the urgent need for further study, not only of sex differences per se, but also of the mechanisms that may mediate these differences. This information is required not only to refine treatment options for obese premenopausal women but also to potentially reveal new therapeutic avenues in obese men and women.

Leptin regulates CD16 expression on human monocytes in a sex-specific manner

Fat mass is linked mechanistically to the cardiovascular system through leptin, a 16 kDa protein produced primarily by adipocytes. In addition to increasing blood pressure via hypothalamic‐sympathetic pathways, leptin stimulates monocyte migration, cytokine secretion, and other functions that contribute to atherosclerotic plaque development. These functions are also characteristics of CD16‐positive monocytes that have been implicated in the clinical progression of atherosclerosis. This investigation sought to determine if leptin promoted the development of such CD16‐positive monocytes. Cells from 45 healthy men and women with age ranging from 20 to 59 years were analyzed. Circulating numbers of CD14⁺⁺16⁺⁺ monocytes, which are primary producers of TNFα, were positively related to plasma leptin concentrations (P < 0.0001), with a stronger correlation in men (P < 0.05 for leptin × sex interaction). In vitro, recombinant human leptin induced CD16 expression in a dose‐related manner (P = 0.02), with a stronger influence on monocytes from men (P = 0.03 for leptin × sex interaction). There were no sex‐related differences in total leptin receptor expression on any monocyte subtypes, relative expression of long versus short isoforms of the receptor, or soluble leptin receptor concentrations in the plasma. The number of circulating CD14⁺16⁺⁺ monocytes, which preferentially migrate into nascent plaques, was positively related to systolic blood pressure (R = 0.56, P = 0.0008) and intima‐media thickness (R = 0.37, P = 0.03), and negatively related to carotid compliance (R = −0.39, P = 0.02). These observations indicate that leptin promotes the development of CD16‐positive monocyte populations in a sex‐specific manner and that these subpopulations are associated with diminished vascular function.

e12177

Recombinant leptin induced CD16 expression on human monocytes in vitro in a dose‐ and sex‐specific manner. In vivo, CD16 expression on human monocytes correlated with plasma leptin concentrations in a sex‐specific manner. Blood pressure, carotid intima‐media thickness and carotid compliance were related to the number of circulating CD16‐positive monocytes.

20 years of leptin: leptin in common obesity and associated disorders of metabolism

The molecular mechanisms of body weight and body composition regulation have long been a research focus in the hopes of identifying tractable pathways for therapeutic interventions for obesity and diabetes, as well as related disorders such as nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) and polycystic ovary syndrome. The metabolic consequences of obesity and type 2 diabetes (T2D) were already a focus of the world's attention in 1994 when the discovery of leptin generated enormous enthusiasm for the potential to treat common (non-monogenic) obesity and its associated metabolic disorders with an adipokine hormone that regulated body weight as well as lipid and carbohydrate metabolism. Recombinant human leptin and many leptin analogs were developed and studied in animals and a few in human clinical trials. Overall, the opportunity for leptin as a therapeutic in unselected patients with obesity and T2D has not been substantiated in clinical trials. The potential for combination therapy suggested by clinical studies with leptin and pramlintide supports a path toward obesity treatment through the leptin pathway. The profound metabolic benefits seen with leptin in numerous forms of leptin deficiency, including lipodystrophy, provide hope for the opportunity to identify selected subsets of patients who could benefit from leptin treatment. This review provides a comprehensive overview of the clinical data on a subset of the potential utilities of leptin, specifically as a therapeutic for general or common obesity and its metabolic consequences including T2D and NAFLD/NASH.

Ghrelin and obestatin levels in hypertensive obese patients

Objectives

To investigate plasma total ghrelin and obestatin levels and the ghrelin/obestatin ratio prospectively, in hypertensive obese patients.

Methods

Height, weight, and waist and hip circumferences were measured in hypertensive and normotensive obese patients and matched healthy controls; the body mass index and waist to hip ratio were calculated. Fasting glucose and insulin levels were measured and the homeostasis model assessment of insulin resistance (HOMA-IR) was determined. Fasting ghrelin and obestatin concentrations were measured by radioimmunoassay and the ghrelin/obestatin ratio was calculated.

Results

A total of 38 hypertensive obese patients, 40 normotensive obese patients and 38 controls were enrolled. Hypertensive obese patients had lower plasma levels of ghrelin and obestatin than normotensive obese patients or controls. In addition, normotensive obese patients had lower plasma ghrelin and obestatin levels than controls. In hypertensive obese patients, ghrelin and obestatin levels were negatively associated with systolic and diastolic blood pressure, fasting insulin and HOMA-IR. In normotensive obese patients, ghrelin, obestatin and the ghrelin/obestatin ratio were negatively associated with fasting insulin and HOMA-IR. In both patient groups, fasting obestatin and ghrelin concentrations were significantly and positively correlated with each other.

Conclusion

Changes in the levels of ghrelin and obestatin may play a role in the pathophysiology of obesity and hypertension.

The effect of leptin promoter and leptin receptor gene polymorphisms on lipid profile among the diabetic population: modulations by atorvastatin treatment and environmental factors

PURPOSE

This study investigated the effect of leptin (LEP) 2548A/G and leptin receptor (LEPR) Q223R polymorphisms on the levels of HDL, LDL, TG, and total cholesterol (t-chol). In addition, the interactions between examined polymorphisms, statin therapy and environmental factors on lipid profile were examined.

METHODS

Adult diabetic patients (n-418) were recruited from diabetes/endocrine clinics in north of Jordan. Lipid profile was measured using standard protocols. Genotyping of LEP 2548A/G and LEPR Q223R polymorphisms was carried out using polymerase chain reaction-restriction fragment length polymorphisms.

RESULTS

No significant association between LEP 2548A/G and LEPR genotypes and levels of HDL (P = 0.83), LDL (P = 0.40), TG (P = 0.23) and t-chol (P = 0.91). However, in patient on atorvastatin, those with GG or GA genotypes of LEP 2548 experienced significantly higher levels of LDL compared with AA genotype of LEP 2548 (P < 0.002). Patients with dyslipidemia had higher TG in comparison with those without (P < 0.03). Smokers had lower HDL and higher TG levels compared with none smokers or previous smokers (P < 0.002 and P < 0.02, respectively). Female patients tend to have a higher HDL in comparison with male patients (P < 0.05). Patients with HbA1c value greater than or equal to 7 had higher LDL and t-chol compared with patients who had an HbA1c levels of <7 (P < 0.02 and < 0.005, respectively). Patients with disease duration of 5 or more years had a lower HDL compared with those patients with duration of <5 years (P < 0.03).

CONCLUSION

In conclusion, and although lipid profile regulation is a multifactorial process, -2548G/A LEP polymorphism seems to affect statins treatment response among diabetic patients. More studies are required to specifically define factors that influence lipid profiles interaction with statin treatment response especially among patients with diabetes.

Leptin into the rostral ventral lateral medulla (RVLM) augments renal sympathetic nerve activity and blood pressure

Leptin is a hormone released from adipose tissue. While this hormone normally acts to reduce feeding behavior and increase energy expenditure, in obesity, resistance to these effects occurs even though the hormone is released in large amounts. Although leptin no longer works to suppress feeding in the obese, leptin retains its potent effects on other autonomic functions such as blood pressure regulation. Leptin has been associated with hypertension and increased sympathetic autonomic activity. Therefore, leptin is emerging as a major contributor to the hypertensive state observed in obesity. Sympathetic control of blood pressure is maintained principally by autonomic reflex control circuits in the caudal brainstem. The rostral ventral-lateral medulla (RVLM) is the primary regulator of the sympathetic nervous system, sending excitatory fibers to sympathetic preganglionic neurons to regulate sympathetic control over resistance vessels and blood pressure. Previous studies from our laboratory have shown that neurons in the ventral lateral medulla express leptin receptors (ObRb). Our present study using pseudo-rabies multi-synaptic retrograde tract tracing and immunohistochemical methods revealed that neurons within the RVLM that send sympathetic projections to the kidney express leptin receptors. Acute microinjection of leptin (1 and 3 μg; 40 nL) into the RVLM evoked a significant increase in Mean Arterial Pressure (MAP) and renal sympathetic nerve activity (RSNA). When the 3 μg dose of leptin was preceded with a leptin antagonist, (SLAN-4; 1 ng), it attenuated the cardiovascular response of leptin. Taken together, these data suggest that leptin's actions within the RVLM may influence blood pressure and renal sympathetic nerve activity.

Biphasic effect of melanocortin agonists on metabolic rate and body temperature

The melanocortin system regulates metabolic homeostasis and inflammation. Melanocortin agonists have contradictorily been reported to both increase and decrease metabolic rate and body temperature. We find two distinct physiologic responses occurring at similar doses. Intraperitoneal administration of the nonselective melanocortin agonist MTII causes a melanocortin-4 receptor (Mc4r)-mediated hypermetabolism/hyperthermia. This is preceded by a profound, transient hypometabolism/hypothermia that is preserved in mice lacking any one of Mc1r, Mc3r, Mc4r, or Mc5r. Three other melanocortin agonists also caused hypothermia, which is actively achieved via seeking a cool environment, vasodilation, and inhibition of brown adipose tissue thermogenesis. These results suggest that the hypometabolic/hypothermic effect of MTII is not due to a failure of thermoregulation. The hypometabolism/hypothermia was prevented by dopamine antagonists, and MTII selectively activated arcuate nucleus dopaminergic neurons, suggesting that these neurons may contribute to the hypometabolism/hypothermia. We propose that the hypometabolism/hypothermia is a regulated response, potentially beneficial during extreme physiologic stress.

Rescue of cardiac leptin receptors in db/db mice prevents myocardial triglyceride accumulation

Increased leptin levels have been suggested to contribute to cardiac hypertrophy and attenuate cardiac lipid accumulation in obesity, although it has been difficult to separate leptin's direct effects from those caused by changes in body weight and adiposity. To determine whether leptin attenuates cardiac lipid accumulation in obesity or directly causes left ventricular hypertrophy (LVH), we generated a novel mouse model in which the long form of the leptin receptor (LepR) was "rescued" only in cardiomyocytes of obese db/db mice. Reexpression of cardiomyocyte leptin receptors in db/db mice did not cause LVH but reduced cardiac triglycerides and improved cardiac function. Compared with lean wild-type (WT) or db/db-cardiac LepR rescue mice, db/db mice exhibited significantly lower E/A ratio, a measurement of early to late diastolic filling, which averaged 1.5 ± 0.07 in db/db vs. 1.9 ± 0.08 and 1.8 ± 0.11 in WT and db/db-cardiac LepR rescue mice, respectively. No differences in systolic function were observed. Although db/db and db/db-cardiac LepR rescue mice exhibited similar increases in plasma triglycerides, insulin, glucose, and body weight, cardiac triglycerides were significantly higher in db/db compared with WT and db/db cardiac LepR rescue mice, averaging 13.4 ± 4.2 vs. 3.8 ± 1.6 vs. 3.8 ± 0.7 mg/g, respectively. These results demonstrate that despite significant obesity and increases in plasma glucose and triglycerides, db/db cardiac LepR rescue mice are protected against myocardial lipid accumulation. However, we found no evidence that leptin directly causes LVH.

Role of vascular oxidative stress in obesity and metabolic syndrome

Obesity is associated with vascular diseases that are often attributed to vascular oxidative stress. We tested the hypothesis that vascular oxidative stress could induce obesity. We previously developed mice that overexpress p22phox in vascular smooth muscle, tg(sm/p22phox), which have increased vascular ROS production. At baseline, tg(sm/p22phox) mice have a modest increase in body weight. With high-fat feeding, tg(sm/p22phox) mice developed exaggerated obesity and increased fat mass. Body weight increased from 32.16 ± 2.34 g to 43.03 ± 1.44 g in tg(sm/p22phox) mice (vs. 30.81 ± 0.71 g to 37.89 ± 1.16 g in the WT mice). This was associated with development of glucose intolerance, reduced HDL cholesterol, and increased levels of leptin and MCP-1. Tg(sm/p22phox) mice displayed impaired spontaneous activity and increased mitochondrial ROS production and mitochondrial dysfunction in skeletal muscle. In mice with vascular smooth muscle-targeted deletion of p22phox (p22phox(loxp/loxp)/tg(smmhc/cre) mice), high-fat feeding did not induce weight gain or leptin resistance. These mice also had reduced T-cell infiltration of perivascular fat. In conclusion, these data indicate that vascular oxidative stress induces obesity and metabolic syndrome, accompanied by and likely due to exercise intolerance, vascular inflammation, and augmented adipogenesis. These data indicate that vascular ROS may play a causal role in the development of obesity and metabolic syndrome.

The nucleus of the solitary tract and the coordination of respiratory and sympathetic activities

It is well known that breathing introduces rhythmical oscillations in the heart rate and arterial pressure levels. Sympathetic oscillations coupled to the respiratory activity have been suggested as an important homeostatic mechanism optimizing tissue perfusion and blood gas uptake/delivery. This respiratory-sympathetic coupling is strengthened in conditions of blood gas challenges (hypoxia and hypercapnia) as a result of the synchronized activation of brainstem respiratory and sympathetic neurons, culminating with the emergence of entrained cardiovascular and respiratory reflex responses. Studies have proposed that the ventrolateral region of the medulla oblongata is a major site of synaptic interaction between respiratory and sympathetic neurons. However, other brainstem regions also play a relevant role in the patterning of respiratory and sympathetic motor outputs. Recent findings suggest that the neurons of the nucleus of the solitary tract (NTS), in the dorsal medulla, are essential for the processing and coordination of respiratory and sympathetic responses to hypoxia. The NTS is the first synaptic station of the cardiorespiratory afferent inputs, including peripheral chemoreceptors, baroreceptors and pulmonary stretch receptors. The synaptic profile of the NTS neurons receiving the excitatory drive from afferent inputs is complex and involves distinct neurotransmitters, including glutamate, ATP and acetylcholine. In the present review we discuss the role of the NTS circuitry in coordinating sympathetic and respiratory reflex responses. We also analyze the neuroplasticity of NTS neurons and their contribution for the development of cardiorespiratory dysfunctions, as observed in neurogenic hypertension, obstructive sleep apnea and metabolic disorders.

Neuroendocrine circuits governing energy balance and stress regulation: functional overlap and therapeutic implications

Significant comorbidities between obesity-related metabolic disease and stress-related psychological disorders suggest important functional interactions between energy balance and brain stress integration. Largely overlapping neural circuits control these systems, and this anatomical arrangement optimizes opportunities for mutual influence. Here we first review the current literature identifying effects of metabolic neuroendocrine signals on stress regulation, and vice versa. Next, the contributions of reward-driven food intake to these metabolic and stress interactions are discussed. Lastly, we consider the interrelationships between metabolism, stress, and reward in light of their important implications in the development of therapies for metabolism- or stress-related disease.

The pathophysiology of hypertension in patients with obesity

The combination of obesity and hypertension is associated with high morbidity and mortality because it leads to cardiovascular and kidney disease. Potential mechanisms linking obesity to hypertension include dietary factors, metabolic, endothelial and vascular dysfunction, neuroendocrine imbalances, sodium retention, glomerular hyperfiltration, proteinuria, and maladaptive immune and inflammatory responses. Visceral adipose tissue also becomes resistant to insulin and leptin and is the site of altered secretion of molecules and hormones such as adiponectin, leptin, resistin, TNF and IL-6, which exacerbate obesity-associated cardiovascular disease. Accumulating evidence also suggests that the gut microbiome is important for modulating these mechanisms. Uric acid and altered incretin or dipeptidyl peptidase 4 activity further contribute to the development of hypertension in obesity. The pathophysiology of obesity-related hypertension is especially relevant to premenopausal women with obesity and type 2 diabetes mellitus who are at high risk of developing arterial stiffness and endothelial dysfunction. In this Review we discuss the relationship between obesity and hypertension with special emphasis on potential mechanisms and therapeutic targeting that might be used in a clinical setting.

Hypertension in children with obesity

The prevalence of obesity related hypertension has dramatically increased in children with the parallel increase in pediatric obesity. This pediatric health problem may adversely affect cardiovascular health in adult life. The pathogenesis of hypertension in obese children is not widely understood. We therefore undertake this review to raise public awareness. Early childhood parameters like birth weight and postnatal weight gain may play important roles in risk for obesity and obesity related hypertension later in childhood and adult life. Further information is required to confirm this origin of hypertension so that appropriate measures are taken in the peri-natal period. The role of sympathetic nervous system has now been well established as one of the principle mechanisms involved in obesity related hypertension. The Renin-Angiotensin system, insulin resistance due to obesity and as a part of metabolic syndrome along with imbalance in adipokines such as leptin and adiponectin, cause activation of the sympathetic system, vasoconstriction, endothelial dysfunction and sodium reabsorption among other perturbations. Multi-step interventions targeting these various mechanisms are required to break the cycle of obesity and metabolic syndrome. Vitamin D deficiency, sleep apnea due to airway obstruction and hyperuricemia may also play a significant role and should not be ignored in its early stages. Obesity is a risk factor for other co-morbid conditions like chronic kidney disease and fatty liver which further accentuate the risk of hypertension. Increased awareness is required to prevent, diagnose and treat obesity related hypertension among the pediatric population.

Sex differences in blood pressure control in SHR: lack of a role for EETs

The mechanisms responsible for the gender difference in blood pressure (BP) in humans are not clear. Over the past several years we have studied the spontaneously hypertensive rat (SHR) as a model of sex differences in BP control. In the present study, we tested the hypothesis that renal vascular and microsomal epoxyeicosatrienoic acid (EET) levels are higher in females than males, and increasing vascular EETs by blocking epoxide hydrolase with AUDA will reduce BP more in males than females. Renal vascular and microsomal EETs were higher in female SHR than males. Mean arterial pressure (MAP by telemetry) was higher in males than females during the baseline period of 6 days, and although the epoxide hydrolase inhibitor, AUDA, given for 10 days increased renal microvascular EETs in both groups, AUDA did not affect MAP in either group. These data suggest that EETs do not contribute to the sex differences in hypertension in young SHR.

Leptin into the ventrolateral medulla facilitates chemorespiratory response in leptin-deficient (ob/ob) mice

AIM

Leptin, an adipocyte-derived hormone, is suggested to participate in the central control of breathing. We hypothesized that leptin may facilitate ventilatory responses to chemoreflex activation by acting on respiratory nuclei of the ventrolateral medulla. The baseline ventilation and the ventilatory responses to CO2 were evaluated before and after daily injections of leptin into the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG) for 3 days in obese leptin-deficient (ob/ob) mice.

METHODS

Male ob/ob mice (40-45 g, n = 7 per group) received daily microinjections of vehicle or leptin (1 μg per 100 nL) for 3 days into the RTN/pFRG. Respiratory responses to CO2 were measured by whole-body plethysmography.

RESULTS

Unilateral microinjection of leptin into the RTN/pFRG in ob/ob mice increased baseline ventilation (VE ) from 1447 ± 96 to 2405 ± 174 mL min(-1) kg(-1) by increasing tidal volume (VT ) from 6.4 ± 0.4 to 9.1 ± 0.8 mL kg(-1) (P < 0.05). Leptin also enhanced ventilatory responses to 7% CO2 (Δ = 2172 ± 218 mL min(-1) kg(-1) , vs. control: Δ = 1255 ± 105 mL min(-1) kg(-1) ), which was also due to increased VT (Δ = 4.71 ± 0.51 mL kg(-1) , vs. control: Δ = 2.27 ± 0.20 mL kg(-1) ), without changes in respiratory frequency. Leptin treatment into the RTN/pFRG or into the surrounding areas decreased food intake (83 and 70%, respectively), without significantly changing body weight.

CONCLUSION

The present results suggest that leptin acting in the respiratory nuclei of the ventrolateral medulla improves baseline VE and VT and facilitates respiratory responses to hypercapnia in ob/ob mice.