Influences of norepinephrine transporter function on the distribution of sympathetic activity in humans

Obstructive sleep apnea hypopnea syndrome and vascular lesions: An update on what we currently know

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is the most prevalent sleep and respiratory disorder. This syndrome can induce severe cardiovascular and cerebrovascular complications, and intermittent hypoxia is a pivotal contributor to this damage. Vascular pathology is closely associated with the impairment of target organs, marking a focal point in current research. Vascular lesions are the fundamental pathophysiological basis of multiorgan ailments and indicate a shared pathogenic mechanism among common cardiovascular and cerebrovascular conditions, suggesting their importance as a public health concern. Increasing evidence shows a strong correlation between OSAHS and vascular lesions. Previous studies predominantly focused on the pathophysiological alterations in OSAHS itself, such as intermittent hypoxia and fragmented sleep, leading to vascular disruptions. This review aims to delve deeper into the vascular lesions affected by OSAHS by examining the microscopic pathophysiological mechanisms involved. Emphasis has been placed on examining how OSAHS induces vascular lesions through disruptions in the endothelial barrier, metabolic dysregulation, cellular phenotype alterations, neuroendocrine irregularities, programmed cell death, vascular inflammation, oxidative stress and epigenetic modifications. This review examines the epidemiology and associated risk factors for OSAHS and vascular diseases and subsequently describes the existing evidence on vascular lesions induced by OSAHS in the cardiovascular, cerebrovascular, retinal, renal and reproductive systems. A detailed account of the current research on the pathophysiological mechanisms mediating vascular lesions caused by OSAHS is provided, culminating in a discussion of research advancements in therapeutic modalities to mitigate OSAHS-related vascular lesions and the implications of these treatment strategies.

Palmitoylation regulates norepinephrine transporter trafficking and expression and is potentially involved in the pathogenesis of postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is an adrenergic signaling disorder characterized by excessive plasma norepinephrine, postural tachycardia, and syncope. The norepinephrine transporter (NET) modulates adrenergic homeostasis via reuptake of extracellular catecholamines and is implicated in the pathogenesis of adrenergic and neurological disorders. Previous research has outlined that NET activity and trafficking is modulated via reversible post-translational modifications like phosphorylation and ubiquitylation. S-palmitoylation, or the addition of a 16-carbon saturated fatty acid, is another post-translational modification responsible for numerous biological mechanisms. In this study, we reveal that NET is dynamically palmitoylated and inhibition of this modification with the palmitoyl acyltransferase (DHHC) inhibitor, 2-bromopalmitate (2BP), results in decreased NET palmitoylation within 90 min of treatment. This result was followed closely with a reduction in transport capacity, cell surface, and total cellular NET expression after 120 min of treatment. Increasing 2BP concentrations and treatment time revealed a nearly complete loss of total NET protein. Co-expression with individual DHHCs revealed a single DHHC enzyme, DHHC1, promoted WT hNET palmitoylation and elevated NET protein levels. The POTS associated NET mutant, A457P, exhibits dramatically decreased transport capacity and cell surface levels which we have confirmed in the current study. In an attempt to recover A457P NET expression we co-expressed the A457P variant with DHHC1 to drive expression as seen with the WT protein but instead saw an increase in NET N-terminal immuno-detectable fragments. Further investigation of A457P NET palmitoylation and surface expression is necessary, but our preliminary novel findings reveal palmitoylation as a mechanism of NET regulation and suggest that dysregulation of this process may contribute to the pathogenesis of POTS.

Relationship between SLC6A2 gene polymorphisms and brain volume in Han Chinese adults who lost their sole child

BACKGROUND

Norepinephrine transporter (NET) is encoded by the SLC6A2 gene and is a potential target for studying the pathogenesis of PTSD. To the best of our knowledge, no prior investigations have examined SLC6A2 polymorphism-related neuroimaging abnormalities in PTSD patients.

METHODS

In 218 Han Chinese adults who had lost their sole child, we investigated the association between the T-182 C SLC6A2 genotype and gray matter volume (GMV). Participants included 57 PTSD sufferers and 161 non-PTSD sufferers, and each group was further separated into three subgroups based on each participant's SLC6A2 genotype (TT, CT, and CC). All participants received magnetic resonance imaging (MRI) and clinical evaluation. To assess the effects of PTSD diagnosis, genotype, and genotype × diagnosis interaction on GMV, 2 × 3 full factorial designs were used. Pearson's correlations were used to examine the association between GMV and CAPS, HAMD, and HAMA.

RESULTS

The SLC6A2 genotype showed significant main effects on GMV of the left superior parietal gyrus (SPG) and the bilateral middle cingulate gyrus (MCG). Additionally, impacts of the SLC6A2 genotype-diagnosis interaction were discovered in the left superior frontal gyrus (SFG). The CAPS, HAMA, and HAMD scores, as well as the genotype main effect and diagnostic SLC6A2 interaction, did not significantly correlate with each other.

CONCLUSION

These findings indicate a modulatory effect that the SLC6A2 polymorphism exerts on the SPG and MCG, irrespective of PTSD diagnosis. We found evidence to suggest that the SLC6A2 genotype-diagnosis interaction on SFG may potentially contribute to PTSD pathogenesis in adults who lost their sole child.

Drug-disease interaction: Clinical consequences of inflammation on drugs action and disposition

Inflammation is a culprit in many conditions affecting millions of people worldwide. A plethora of studies has revealed that inflammation and inflammatory mediators such as cytokines and chemokines are associated with altered expression and activity of various proteins such as those involved in drug metabolism, specifically cytochrome P450 enzymes (CYPs). Emphasis of most available reports is on the inflammation-induced downregulation of CYPs, subsequently an increase in their substrate concentrations, and the link between the condition and the inflammatory mediators such as interleukin-6 and tumor necrosis factor alpha. However, reports also suggest that inflammation influences expression and/or activity of other proteins such as those involved in the drug-receptor interaction. These multifaced involvements render the clinical consequence of the inflammation unexpected. Such changes are shown in many inflammatory conditions including rheumatoid arthritis, Crohn's disease, acute respiratory illnesses as well as natural processes such as aging, among others. For example, some commonly used cardiovascular drugs lose their efficacy when patients get afflicted with inflammatory conditions such as rheumatoid arthritis and Crohn's disease. Interestingly, this is despite increased concentration subsequent to reduced clearance. The observation is attributed to a simultaneous reduction in the expression of target receptor proteins such as the calcium and potassium channel and β-adrenergic receptor as well as the metabolic enzymes. This narrative review summarizes the current understanding and clinical implications of the inflammatory effects on both CYPs and drug-receptor target proteins.

Analysis of secondary pharmacology assays received by the US Food and Drug Administration

Secondary pharmacology studies are a time-efficient and cost-effective method for determining the safety profile of a potential new drug before it enters human trials. The results of these multi-target screens are commonly submitted with Investigational New Drug (IND) applications, but there currently is little guidance on how such information is presented and which targets are chosen for testing. In this study, we expand on our previous analysis of secondary pharmacology reports by manually curating and analyzing all secondary pharmacology results received by the FDA received as part of an IND submission. A total of 1120 INDs submitted by 480 sponsors between 1999 and October 2020 were included in this study. The overall results were largely consistent with previous internal and external studies, showing that the most tested target in our set was the histamine 1 receptor (tested 938 times), the most hit target was sodium channel site 2 (hit 141 times), and the target with the highest hit percentage was the vesicular monoamine transporter 2 (hit 42.2% of the time). Additionally, this study demonstrated that improvements in the secondary pharmacology submission process, such as changes in formatting and nomenclature, could enhance the utility of these assays for regulatory review, including assisting with identifying the safety liabilities of a drug candidate early in development. This updated data set will allow FDA-industry collaborative working groups to continue developing the best methods for regulatory submission of secondary pharmacology data and evaluate the need for a standard target panel.

Aggregation and analysis of secondary pharmacology data from investigational new drug submissions at the US Food and Drug Administration

Secondary pharmacology studies are utilized by the pharmaceutical industry as a cost-efficient tool to identify potential safety liabilities of drugs before entering Phase 1 clinical trials. These studies are recommended by the Food and Drug Administration (FDA) as a part of the Investigational New Drug (IND) application. However, despite the utility of these assays, there is little guidance on which targets should be screened and which format should be used. Here, we evaluated 226 secondary pharmacology profiles obtained from close to 90 unique sponsors. The results indicated that the most tested target in our set was the GABA benzodiazepine receptor (tested 168 times), the most hit target was adenosine 3 (hit 24 times), and the target with the highest hit percentage was the quinone reductase 2 (NQO2) receptor (hit 29% of the time). The overall results were largely consistent with those observed in previous publications. However, this study also identified the need for improvement in the submission process of secondary pharmacology studies by industry, which could enhance their utility for regulatory purpose. FDA-industry collaborative working groups will utilize this data to determine the best methods for regulatory submission of these studies and evaluate the need for a standard target panel.

Age-dependent association of polymorphisms in the promoter and 5'-untranslated region of the norepinephrine transporter gene with generalized anxiety disorder

BACKGROUND

Norepinephrine transporter (NET), which regulates synaptic norepinephrine for noradrenergic signaling, is involved in the pathogenesis of anxiety, while expression of the NET gene differs at different ages. Here, we examine whether genetic variants in the NET gene are associated, in an age-specific manner, with increased risk of generalized anxiety disorder (GAD), one of the most disabling anxiety disorders.

METHODS

Three common single-nucleotide polymorphisms (SNPs) in the promoter (rs168924: A/G; rs2242446: T/C) and 5'-untranslated region (5'-UTR) (rs2397771: G/C) of the NET gene were genotyped in 2,317 Han-Chinese participants (791 GAD patients and 1,526 controls; age: 20-65). Potential confounding factors, such as gender, stress levels and psychiatric comorbidities, were included as covariates.

RESULTS

An interaction between age and NET genotypes and haplotypes was found for the risk of GAD. In the younger participants, rs168924 minor allele G homozygotes had the lowest incidence of GAD; however, older subjects displayed an inverse pattern, with homozygous G/G carriers presenting the highest prevalence of GAD. Additionally, younger individuals carrying 2 copies of the GGT haplotype composed of rs2397771-rs168924-rs2242446 had the lowest rate of GAD. However, those with 2 copies of the same haplotype exhibited the highest risk of GAD in the older groups.

LIMITATIONS

Only 3 common SNPs in the promoter and 5'-UTR of the NET gene were analyzed.

CONCLUSIONS

Our findings are the first to demonstrate that potentially functional SNPs in the NET promoter and 5'-UTR are associated with an increased risk of GAD, and that such associations are determined in an age-specific way.

Upregulation of gastric norepinephrine with beta-adrenoceptors and gastric dysmotility in a rat model of functional dyspepsia

Disordered motility is one of the most important pathogenic characteristics of functional dyspepsia (FD), although the underlying mechanisms remain unclear. Since the sympathetic system is important to the regulation of gastrointestinal motility, the present study aimed to investigate the role of norepinephrine (NE) and adrenoceptors in disordered gastric motility in a rat model with FD. The effect of exogenous NE on gastric motility in control and FD rats was measured through an organ bath study. The expression and distribution of beta-adrenoceptors were examined by real-time PCR, Western blotting and immunofluorescence. The results showed that endogenous gastric NE was elevated in FD rats, and hyperreactivity of gastric smooth muscle to NE and delayed gastric emptying were observed in the rat model of FD. The mRNA levels of beta1-adrenoceptor and norepinephrine transporter (NET) and the protein levels of beta2-adrenoceptor and NET were increased significantly in the gastric corpus of FD rats. All three subtypes of beta-adrenoceptors were abundantly distributed in the gastric corpus of rats. In conclusion, the enhanced NE and beta-adrenoceptors and NETs may be contributed to the disordered gastric motility in FD rats.

Synergistic Pressor Effect of Atomoxetine and Pyridostigmine in Patients With Neurogenic Orthostatic Hypotension

Patients with autonomic failure are characterized by disabling orthostatic hypotension because of impaired sympathetic activity, but even severely affected patients have residual sympathetic tone which can be harnessed for their treatment. For example, norepinephrine transporter blockade with atomoxetine raises blood pressure (BP) in autonomic failure patients by increasing synaptic norepinephrine concentrations; acetylcholinesterase inhibition with pyridostigmine increases BP by facilitating ganglionic cholinergic neurotransmission to increase sympathetic outflow. We tested the hypothesis that pyridostigmine will potentiate the pressor effect of atomoxetine and improve orthostatic tolerance and symptoms in patients with severe autonomic failure. Twelve patients received a single oral dose of either placebo, pyridostigmine 60 mg, atomoxetine 18 mg or the combination on separate days in a single blind, crossover study. BP was assessed seated and standing before and 1-hour postdrug. In these severely affected patients, neither pyridostigmine nor atomoxetine improved BP or orthostatic tolerance compared with placebo. The combination, however, significantly increased seated BP in a synergistic manner (133±9/80±4 versus 107±6/66±4 mm Hg for placebo, 105±5/67±3 mm Hg for atomoxetine, and 99±6/64±4 mm Hg for pyridostigmine; P<0.001); the maximal increase in seated BP with the combination was 33±8/18±3 mm Hg at 60 minutes postdrug. Only the combination showed a significant improvement of orthostatic tolerance and symptoms. In conclusion, the combination pyridostigmine and atomoxetine had a synergistic effect on seated BP which was associated with improvement in orthostatic tolerance and symptoms. This pharmacological approach could be useful in patients with severe autonomic failure but further safety and long-term efficacy studies are needed.

Cardiac pacemaker channel (HCN4) inhibition and atrial arrhythmogenesis after releasing cardiac sympathetic activation

Clinical trials and studies with ivabradine implicate cardiac pacemaker channels (HCN4) in the pathogenesis of atrial arrhythmias. Because acute changes in cardiac autonomic tone predispose to atrial arrhythmias, we studied humans in whom profound cardiac sympathetic activation was rapidly relieved to test influences of HCN4 inhibition with ivabradine on atrial arrhythmias. We tested 19 healthy participants with ivabradine, metoprolol, or placebo in a double blind, randomized, cross-over fashion on top of selective norepinephrine reuptake inhibition with reboxetine. Subjects underwent combined head up tilt plus lower body negative pressure testing followed by rapid return to the supine position. In the current secondary analysis with predefined endpoints before data unblinding, continuous finger blood pressure and ECG recordings were analyzed by two experienced cardiac electrophysiologists and a physician, blinded for treatment assignment. The total atrial premature activity (referred to as atrial events) at baseline did not differ between treatments. After backwards tilting, atrial events were significantly higher with ivabradine compared with metoprolol or with placebo. Unlike beta-adrenoreceptor blockade, HCN4 inhibition while lowering heart rate does not protect from atrial arrhythmias under conditions of experimental cardiac sympathetic activation. The model in addition to providing insight in the role of HCN4 in human atrial arrhythmogenesis may have utility in gauging potential atrial pro-arrhythmic drug properties.

Clozapine-Induced Cardiovascular Side Effects and Autonomic Dysfunction: A Systematic Review

Background: Clozapine is the antipsychotic of choice for treatment-resistant schizophrenia and has minimal risk for extrapyramidal symptoms. Therapeutic benefits, however, are accompanied by a myriad of cardiometabolic side-effects. The specific reasons for clozapine's high propensity to cause adverse cardiometabolic events remain unknown, but it is believed that autonomic dysfunction may play a role in many of these.

Objective: This systematic review summarizes the literature on autonomic dysfunction and related cardiovascular side effects associated with clozapine treatment.

Method: A search of the EMBASE, MEDLINE, and EBM Cochrane databases was conducted using the search terms antipsychotic agents, antipsychotic drug^*, antipsychotic^*, schizophrenia, schizophren^*, psychos^*, psychotic^*, mental ill^*, mental disorder^*, neuroleptic^*, cardiovascular^*, cardiovascular diseases, clozapine^*, clozaril^*, autonomic^*, sympathetic^*, catecholamine^*, norepinephrine, noradrenaline, epinephrine, adrenaline.

Results: The search yielded 37 studies that were reviewed, of which only 16 studies have used interventions to manage cardiovascular side effects. Side effects reported in the studies include myocarditis, orthostatic hypotension and tachycardia. These were attributed to sympathetic hyperactivity, decreased vagal contribution, blockade of cholinergic and adrenergic receptors, reduced heart rate variability and elevated catecholamines with clozapine use. Autonomic neuropathy was identified by monitoring blood pressure and heart rate changes in response to stimuli and by spectral analysis of heart rate variability. Metoprolol, lorazepam, atenolol, propranolol, amlodipine, vasopressin and norepinephrine infusion were used to treat tachycardia and fluctuations in blood pressure, yet results were limited to case reports.

Conclusion: The results indicate there is a lack of clinical studies investigating autonomic dysfunction and a limited use of interventions to manage cardiovascular side effects associated with clozapine. As there is often no alternative treatment for refractory schizophrenia, the current review highlights the need for better designed studies, use of autonomic tests for prevention of cardiovascular disease and development of novel interventions for clozapine-induced side effects.

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

The In Vitro Pharmacological Profile of Drugs as a Proxy Indicator of Potential In Vivo Organ Toxicities

The potential of a drug to cause certain organ toxicities is somehow implicitly contained in its full pharmacological profile, provided the drug reaches and accumulates at the various organs where the different interacting proteins in its profile, both targets and off-targets, are expressed. Under this assumption, a computational approach was implemented to obtain a projected anatomical profile of a drug from its in vitro pharmacological profile linked to protein expression data across 47 organs. It was observed that the anatomical profiles obtained when using only the known primary targets of the drugs reflected roughly the intended organ targets. However, when both known and predicted secondary pharmacology was considered, the projected anatomical profiles of the drugs were able to clearly highlight potential organ off-targets. Accordingly, when applied to sets of drugs known to cause cardiotoxicity and hepatotoxicity, the approach is able to identify heart and liver, respectively, as the organs where the proteins in the pharmacological profile of the corresponding drugs are specifically expressed. When applied to a set of drugs linked to a risk of Torsades de Pointes, heart is again the organ clearly standing out from the rest and a potential protein profile hazard is proposed. The approach can be used as a proxy indicator of potential in vivo organ toxicities.

Exploratory Biomarker Study of the Triple Reuptake Inhibitor SEP-432 Compared to the Dual Reuptake Inhibitor Duloxetine in Healthy Normal Subjects

INTRODUCTION

SEP-432 is a triple monoamine reuptake inhibitor of norepinephrine (NE), serotonin (5-HT), and dopamine (DA), based on in vitro binding studies. We sought evidence that SEP-432 engages these monoamine systems by measuring concentrations of monoamines and/or their main metabolites in cerebrospinal fluid (CSF) and plasma and comparing results to duloxetine, a dual reuptake inhibitor of NE and 5-HT.

METHODS

Eighteen healthy normal subjects received either SEP-432 (300 mg/day), duloxetine (60 mg/day), or placebo for 14 days in-clinic (double blind) with CSF and plasma collections at baseline (single lumbar puncture) and Day 14 (24-h CSF and plasma collection). Concentrations of monoamines and their metabolites, as well as pharmacokinetic concentrations of SEP-432 and metabolite, were quantified by liquid chromatography-tandem mass spectrometry.

RESULTS

Compared to placebo in the Day 14 area under the curve 24-h (AUC0-24 h ) analysis, SEP-432 significantly (P < 0.05) decreased the NE metabolite dihydroxyphenylglycol (DHPG) in CSF and plasma, decreased 5-HT in plasma, and did not affect DA metabolites, while duloxetine had significant effects on DHPG and 5-HT. Time-matched baseline to Day 14 biomarker comparisons confirmed these findings.

CONCLUSION

CSF monoamine biomarkers confirmed central NET activity for SEP-432 and duloxetine's dual reuptake inhibition.

Evaluation of blood pressure and heart rate in patients with hypertension who received tapentadol extended release for chronic pain: a post hoc, pooled data analysis

Background and Objectives

Hypertension is one of the most common co-existing conditions in patients with chronic pain, and the potential effects of an analgesic on heart rate and blood pressure are of particular concern for patients with hypertension. The purpose of this analysis was to evaluate changes in blood pressure and heart rate with tapentadol extended release (ER) treatment in patients with hypertension.

Methods

We performed a post hoc analysis of data pooled from three randomized, placebo- and active-controlled, phase III studies of tapentadol ER for managing chronic osteoarthritis knee (NCT00421928, NCT00486811) or low back (NCT00449176) pain (15-week, double-blind treatment period). Data were independently analyzed for patients with a listed medical history of hypertension at baseline and patients with at least one listed concomitant antihypertensive medication at baseline. Heart rate, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were measured at each visit.

Results

In patients with a listed medical history of hypertension (n = 1,464), least-squares mean (LSM [standard error (SE)]) changes from baseline to endpoint with placebo, tapentadol ER, and oxycodone HCl controlled release (CR), respectively, were −0.7 (0.44), 0.2 (0.43), and −0.9 (0.45) beats per minute (bpm) for heart rate; −2.4 (0.64), −2.7 (0.64), and −3.7 (0.67) mmHg for SBP; and −1.0 (0.39), −1.3 (0.39), and −2.3 (0.41) mmHg for DBP; in patients with at least one listed concomitant antihypertensive medication (n = 1,376), the LSM (SE) changes from baseline to endpoint were −0.6 (0.45), 0.1 (0.44), and −0.7 (0.47) bpm for heart rate; −1.8 (0.66), −3.3 (0.65), and −3.7 (0.69) mmHg for SBP; and −0.7 (0.40), −1.4 (0.40), and −2.3 (0.42) mmHg for DBP.

Conclusion

No clinically meaningful mean changes in heart rate or blood pressure were observed for the evaluated cohorts of patients with hypertension who were treated with tapentadol ER (100–250 mg twice daily).

Regulation of transepithelial ion transport in the rat late distal colon by the sympathetic nervous system

The colorectum (late distal colon) is innervated by the sympathetic nervous system, and many colorectal diseases are related to disorders of the sympathetic nervous system. The sympathetic regulation of colorectal ion transport is rarely reported. The present study aims to investigate the effect of norepinephrine (NE) in the normal and catecholamine-depleted condition to clarify the regulation of the sympathetic adrenergic system in ion transport in the rat colorectum. NE-induced ion transport in the rats colorectum was measured by short-circuit current (I(sc)) recording; the expression of beta-adrenoceptors and NE transporter (NET) were quantified by real-time PCR, and western blotting. When the endogenous catecholamine was depleted by reserpine, the baseline I(sc) in the colorectum was increased significantly comparing to controls. NE evoked downward deltaI(sc) in colorectum of treated rats was 1.8-fold of controls. The expression of beta(2)-adrenoceptor protein in the colorectal mucosa was greater than the control, though the mRNA level was reduced. However, NET expression was significantly lower in catecholamine-depleted rats compared to the controls. In conclusion, the sympathetic nervous system plays an important role in regulating basal ion transport in the colorectum. Disorders of sympathetic neurotransmitters result in abnormal ion transport, beta-adrenoceptor and NET are involved in the process.

Pacemaker current inhibition in experimental human cardiac sympathetic activation: a double-blind, randomized, crossover study

Hyperpolarization-activated, cyclic nucleotide-gated 4 (HCN4) channels comprise the final pathway for autonomic heart rate (HR) regulation. We hypothesized that HCN4 inhibition could reverse autonomic imbalance in a human model of cardiac sympathetic activation. Nineteen healthy men ingested oral metoprolol+reboxetine, ivabradine+reboxetine, or placebo+reboxetine in a double-blind, randomized, crossover fashion. We assessed HR, blood pressure (BP), stroke volume, and cardiac output during rest and profound orthostatic stress. HR variability, BP variability, and baroreflex sensitivity were analyzed. Metoprolol, but not ivabradine, decreased resting HR and BP. Ivabradine attenuated the HR increase to orthostatic stress, albeit to a lesser extent than metoprolol. Stroke volume and cardiac output at a given HR were significantly lower with metoprolol. Unlike metoprolol, ivabradine did not affect HR variability, BP variability, or baroreflex sensitivity. Ivabradine attenuates sympathetic influences on HR at the sinus node level, leaving myocardial sympathetic activation unopposed. Reversal of parasympathetic dysfunction by ivabradine appears limited.

Peripheral cardiac sympathetic hyperactivity in cardiovascular disease: role of neuropeptides

High levels of sympathetic drive in several cardiovascular diseases including postmyocardial infarction, chronic congestive heart failure and hypertension are reinforced through dysregulation of afferent input and central integration of autonomic balance. However, recent evidence suggests that a significant component of sympathetic hyperactivity may also reside peripherally at the level of the postganglionic neuron. This has been studied in depth using the spontaneously hypertensive rat, an animal model of genetic essential hypertension, where larger neuronal calcium transients, increased release and impaired reuptake of norepinephrine in neurons of the stellate ganglia lead to a significant tachycardia even before hypertension has developed. The release of additional sympathetic cotransmitters during high levels of sympathetic drive can also have deleterious consequences for peripheral cardiac parasympathetic neurotransmission even in the presence of β-adrenergic blockade. Stimulation of the cardiac vagus reduces heart rate, lowers myocardial oxygen demand, improves coronary blood flow, and independently raises ventricular fibrillation threshold. Recent data demonstrates a direct action of the sympathetic cotransmitters neuropeptide Y (NPY) and galanin on the ability of the vagus to release acetylcholine and control heart rate. Moreover, there is as a strong correlation between plasma NPY levels and coronary microvascular function in patients with ST-elevation myocardial infarction being treated with primary percutaneous coronary intervention. Antagonists of the NPY receptors Y1 and Y2 may be therapeutically beneficial both acutely during myocardial infarction and also during chronic heart failure and hypertension. Such medications would be expected to act synergistically with β-blockers and implantable vagus nerve stimulators to improve patient outcome.

Norepinephrine transporter variant A457P knock-in mice display key features of human postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is a common autonomic disorder of largely unknown etiology that presents with sustained tachycardia on standing, syncope and elevated norepinephrine spillover. Some individuals with POTS experience anxiety, depression and cognitive dysfunction. Previously, we identified a mutation, A457P, in the norepinephrine (NE; also known as noradrenaline) transporter (NET; encoded by SLC6A2) in POTS patients. NET is expressed at presynaptic sites in NE neurons and plays a crucial role in regulating NE signaling and homeostasis through NE reuptake into noradrenergic nerve terminals. Our in vitro studies demonstrate that A457P reduces both NET surface trafficking and NE transport and exerts a dominant-negative impact on wild-type NET proteins. Here we report the generation and characterization of NET A457P mice, demonstrating the ability of A457P to drive the POTS phenotype and behaviors that are consistent with reported comorbidities. Mice carrying one A457P allele (NET(+/P)) exhibited reduced brain and sympathetic NE transport levels compared with wild-type (NET(+/+)) mice, whereas transport activity in mice carrying two A457P alleles (NET(P/P)) was nearly abolished. NET(+/P) and NET(P/P) mice exhibited elevations in plasma and urine NE levels, reduced 3,4-dihydroxyphenylglycol (DHPG), and reduced DHPG:NE ratios, consistent with a decrease in sympathetic nerve terminal NE reuptake. Radiotelemetry in unanesthetized mice revealed tachycardia in NET(+/P) mice without a change in blood pressure or baroreceptor sensitivity, consistent with studies of human NET A457P carriers. NET(+/P) mice also demonstrated behavioral changes consistent with CNS NET dysfunction. Our findings support that NET dysfunction is sufficient to produce a POTS phenotype and introduces the first genetic model suitable for more detailed mechanistic studies of the disorder and its comorbidities.

Reducing antipsychotic-induced weight gain in schizophrenia: a double-blind placebo-controlled study of reboxetine-betahistine combination

RATIONALE

Combination treatment with reboxetine, a selective norepinephrine reuptake inhibitor, and betahistine, a histamine H1 receptor agonist/H3 antagonist, was developed to produce complementary action in CNS pathways regulating appetite and body weight. In the present placebo-controlled study, we evaluated whether a reboxetine-betahistine combination attenuates olanzapine-induced weight gain in schizophrenia patients.

METHOD

Forty-three inpatients with DSM-IV schizophrenic disorder participated in a randomized double-blind study. Reboxetine (4 mg/day) with betahistine (48 mg/day) (N = 29) or placebo (N = 14) was co-administered with olanzapine (10 mg/day) for 6 weeks. Mental status was assessed at baseline and endpoint with relevant rating scales. Intention-to-treat method was used for statistical analysis.

RESULTS

Seven patients in the study group and four in the placebo group discontinued the trial. At the end of the trial, patients in the olanzapine/reboxetine + betahistine group gained significantly less weight than those in the olanzapine/placebo group [2.02 ± 2.37 and 4.77 ± 3.16 kg, respectively; t = 2. 89, degrees of freedom (df) = 41, p = 0.006]. The weight-attenuating effect of this combination was twofold larger than the weight-attenuating effect previously demonstrated with reboxetine alone. Significantly fewer patients in the study group than in the comparison group increased their initial weight by >7 %, the cutoff for clinically significant weight gain [3/29 (10.3 %) and 6/14 (42.9 %), respectively; χ (2) = 6.03, df = 1, p = 0.014]. The reboxetine-betahistine combination was safe and well tolerated.

CONCLUSIONS

Reboxetine-betahistine combination produces a clinically meaningful attenuation of olanzapine-induced weight gain. These results justify direct comparison between the reboxetine-betahistine combination and reboxetine alone.

Ganglion-specific impairment of the norepinephrine transporter in the hypertensive rat

Hypertension is associated with enhanced cardiac sympathetic transmission, although the exact mechanisms underlying this are still unknown. We hypothesized that defective function of the norepinephrine uptake transporter (NET) may contribute to the sympathetic phenotype of the spontaneously hypertensive rat, and that this may occur before the development of hypertension itself. The dynamic kinetics of NET were monitored temporally using a novel fluorescent assay of the transporter in cultured postganglionic sympathetic neurons from the cardiac stellate ganglion, the superior cervical ganglion, the celiac ganglia/superior mesenteric ganglia, and the renal sympathetic chain. All NET activity was blocked by desipramine. NET rate was significantly impaired in cardiac stellate sympathetic neurons from the prehypertensive spontaneously hypertensive rat compared with age-matched normotensive Wistar-Kyoto rats. A similar response was seen in hypertensive spontaneously hypertensive rats stellate sympathetic neurons. However, no reduction in transporter rate was observed at either age in the other major noncardiac sympathetic ganglia. Depolarization of cardiac stellate neurons by electrical field stimulation further potentiated the difference in transporter rate observed between the hypertensive and normotensive rats at both developmental ages. In conclusion, dysregulation of the norepinephrine transporter in the hypertensive rat is ganglion-specific, where NET impairment in the stellate neurons may contribute to the increased cardiac norepinephrine spillover seen in hypertension.

Norepinephrine transporter function and human cardiovascular disease

Approximately 80-90% of the norepinephrine released in the brain or in peripheral tissues is taken up again through the neuronal norepinephrine transporter (NET). Pharmacological studies with NET inhibitors showed that NET has opposing effects on cardiovascular sympathetic regulation in the brain and in the periphery. Furthermore, NET is involved in the distribution of sympathetic activity between vasculature, heart, and kidney. Genetic NET dysfunction is a rare cause of the postural tachycardia syndrome. The condition is characterized by excessive adrenergic stimulation of the heart, particularly with standing. Conversely, NET inhibition may be beneficial in hypoadrenergic states, such as central autonomic failure or neurally mediated syncope, which results from acute sympathetic withdrawal. Biochemical studies suggested reduced NET function in some patients with essential hypertension. Furthermore, cardiac NET function appears to be reduced in common heart diseases, such as congestive heart failure, ischemic heart disease, and stress-induced cardiomyopathy. Whether NET dysfunction is a consequence or cause of progressive heart disease in human subjects requires further study. However, studies with the nonselective NET inhibitor sibutramine suggest that reduced NET function could have an adverse effect on the cardiovascular system. Given the widespread use of medications inhibiting NET, the issue deserves more attention.

Neurocardiology: therapeutic implications for cardiovascular disease

The term "neurocardiology" refers to physiologic and pathophysiological interplays of the nervous and cardiovascular systems. This selective review provides an update about cardiovascular therapeutic implications of neurocardiology, with emphasis on disorders involving primary or secondary abnormalities of catecholamine systems. Concepts of scientific integrative medicine help understand these disorders. Scientific integrative medicine is not a treatment method or discipline but a way of thinking that applies systems concepts to acute and chronic disorders of regulation. Some of these concepts include stability by negative feedback regulation, multiple effectors, effector sharing, instability by positive feedback loops, allostasis, and allostatic load. Scientific integrative medicine builds on systems biology but is also distinct in several ways. A large variety of drugs and non-drug treatments are now available or under study for neurocardiologic disorders in which catecholamine systems are hyperfunctional or hypofunctional. The future of therapeutics in neurocardiology is not so much in new curative drugs as in applying scientific integrative medical ideas that take into account concurrent chronic degenerative disorders and interactions of multiple drug and non-drug treatments with each other and with those disorders.

Norepinephrine transporter -3081(A/T) and alpha-2A-adrenergic receptor MspI polymorphisms are associated with cardiovascular side effects of OROS-methylphenidate treatment

The purpose of this study was to investigate a possible association between norepinephrine genes and cardiovascular side effects of the Osmotic Controlled-Release Oral Delivery System-methylphenidate (OROS-MPH) in Korean children with attention-deficit/hyperactivity disorder (ADHD). One hundred and one children with ADHD (8.7 ± 1.7 years) were recruited from child psychiatric centers at six university hospitals in South Korea. All participants were drug-naive ADHD children treated with OROS-MPH for 12 weeks. During the treatment period the investigators titrated the OROS-MPH dosage on the basis of symptom severity and side effects. Resting heart rate (HR), diastolic blood pressure (DBP), and systolic blood pressure (SBP) were examined before and after treatment. The percentage change score (post-treatment - pretreatment/pretreatment × 100) of each parameter was calculated. Genotyping of SLC6A2 -3081(A/T) and G1287A, and alpha-2A-adrenergic receptor (ADRA2A) MspI and DraI polymorphisms was performed. Clinically significant changes were not found in cardiovascular monitoring during the course of treatment. An increase of HR after OROS-MPH treatment was found to be statistically significant (t = 3.54, p = 0.001). Changes in SBP and DBP were not significant and no specific change was found in the ECGs. However, an additive regression analysis demonstrated a significant association between SLC6A2 -3081(A/T) and percentage change in HR post-treatment (p = 0.01) after controlling for age, gender, dosage of MPH and response and baseline pulse rate. Children with ADHD having the T/T genotype of SLC6A2 showed a 12.5% increase in HR compared to baseline, whereas children with the A/T or A/A genotype showed a 3.5% and 2.5% increase after OROS-MPH treatment, respectively. There was also a significant association between the ADRA2A MspI genotype and percentage change of DBP post-treatment after controlling for age, gender, dosage of MPH and response and baseline DBP (p = 0.009). Children with ADHD having the C/C genotype of ADRA2A MspI showed an 18.5% increase in DBP compared to baseline, but children with the G/G or G/C genotype showed a 0.2% decrease after OROS-MPH treatment. The overall cardiovascular effects of OROS-MPH were modest. However, our findings show a positive association between norepinephrine-related gene polymorphisms and cardiovascular response induced by MPH in Korean children with ADHD. Consideration must be given to such children or adults with specific norepinephrine-related genotypes, especially if they show significant changes in HR or DBP after OROS-MPH administration.

Synergistic effect of norepinephrine transporter blockade and α-2 antagonism on blood pressure in autonomic failure

Patients with autonomic failure have disabling orthostatic hypotension because of impaired sympathetic activity. Norepinephrine transporter blockade with atomoxetine raises blood pressure in autonomic failure by increasing synaptic norepinephrine concentrations in postganglionic sympathetic neurons. This effect requires tonic release of norepinephrine, which is decreased in patients with low sympathetic tone. We hypothesized that increasing residual sympathetic outflow with the α-2 antagonist yohimbine would potentiate the pressor effect of norepinephrine transporter blockade with atomoxetine and improve orthostatic tolerance in peripheral autonomic failure. Seventeen patients received a single oral dose of either placebo, yohimbine 5.4 mg or atomoxetine 18.0 mg, and the combination yohimbine and atomoxetine in a single blind, crossover study. Blood pressure was assessed while patients were seated and standing for ≤10 minutes before and 1 hour postdrug. Neither yohimbine nor atomoxetine significantly increased seated systolic blood pressure or orthostatic tolerance compared with placebo. The combination, however, significantly increased seated systolic blood pressure and orthostatic tolerance (P<0.001 and P=0.016, respectively) in a synergistic manner. The maximal increase in seated systolic blood pressure seen with the combination was 31±33 mm Hg at 60 minutes postdrug. Only the combination showed a significant improvement in orthostatic symptoms. In conclusion, the combination of yohimbine and atomoxetine had a synergistic effect on blood pressure and orthostatic tolerance in peripheral autonomic failure, which may be explained by an increased release of norepinephrine in peripheral sympathetic neurons by α-2 antagonism combined with a reduced norepinephrine clearance by norepinephrine transporter blockade. Safety studies are required to address the clinical usefulness of this pharmacological approach.

Systematic Review and Meta-analysis of Pharmacological Interventions for Weight Gain from Antipsychotics and Mood Stabilizers

Pharmacological treatments for serious mental illness (SMI) can cause weight gain and adverse metabolic effects. Many second generation antipsychotics and mood stabilizers appear to be particularly problematic in this regard. Several studies have investigated interventions for antipsychotic-induced, or less commonly mood stabilizer -induced, weight gain. Both lifestyle and pharmacological interventions have demonstrated effectiveness. We systematically review randomized controlled trials of pharmacological interventions for weight gain related to these medications. We conducted a meta-analysis of clinical trials for the most studied agents to estimate mean weight loss: metformin (2.93 kg, 95% C.I. 0.97-4.89, p=0.003), H(2) antagonists (1.78 kg (95% C.I. -0.50-4.06, p=0.13), topiramate (3.95 kg 95% C.I. 1.77-6.12, p=0.0004), and norepinephrine reuptake inhibitors (1.30 kg (95% C.I. -0.06-2.66, p=0.06). Among the studied options for antipsychotic-related weight gain, metformin has the strongest evidence base and may improve vascular risk factors beyond obesity. The use of topiramate is also supported by the literature and may improve psychotic symptoms in those refractory to treatment. A marginal benefit is seen with norepinephrine reuptake inhibitors, and any vascular benefits from such weight loss may be counteracted by increases in blood pressure or heart rate. Pharmacological therapies may offer benefits as a means of supplementing the effects of lifestyle changes for weight loss. However, the existing evidence provides little evidence of specificity for pharmacological therapies to antipsychotic-induced weight gain and has not studied any connection between benefits and reduced incidence of diabetes mellitus or any vascular outcomes.

[Antidepressant therapy in coronary artery disease]

Depression is considered an independent risk factor for coronary artery disease (CAD) and other vascular conditions. Moreover, comorbid depressive disorder in CAD patients carries an increased risk of cardiac events and mortality. Among survivors of acute myocardial infarction, up to 20% meet diagnostic criteria for major depression, the presence of which carries a fivefold increased risk of cardiac death within 6 months. Heart patients with depressive comorbidity require particular care for both adequate treatment of their affective disorder and reduction of their cardiac risk. Antidepressant treatment must follow established guidelines; special care is needed to avoid cardiac side effects. In this review, we discuss the pathophysiological and prognostic significance of comorbid depression in CAD and weigh risks and benefits of available treatment options - particularly different drug classes and psychotherapy - in light of recent study results.

Sex, hormones and neuroeffector mechanisms

Incidence and rate of cardiovascular disease differ between men and women across the life span. Although hypertension is more prominent in men than women, there is a group of vasomotor disorders [i.e. Raynaud's disease, postural orthostatic tachycardia syndrome and vasomotor symptoms (hot flashes) of menopause and migraine] with a female predominance. Both sex and hormones interact to modulate neuroeffector mechanisms including integrated regulation of the Sry gene and direct effect of sex steroid hormones on synthesis, release and disposition of monoamine neurotransmitters, and distribution and sensitivity of their receptors in brain areas associated with autonomic control. The interaction of the sex chromosomes and steroids also modulates these effector tissues, that is, the heart, vascular smooth muscle and endothelium. Although involvement of central serotonergic centres has been studied in regard to mood disorders such as depression, their contribution to cardiovascular risk is gaining attention. Studies are needed to further evaluate how hormonal treatments and drugs used to modulate adrenergic and serotonergic activity affect progression and risk for cardiovascular disease in men and women.

Catecholamines 101

This review of clinical catecholamine neurochemistry is based on the Streeten Memorial Lecture at the 19th annual meeting of the American Autonomic Society and lectures at a satellite of the 6th Congress of the International Society of Autonomic Neuroscience. Here I provide historical perspective, describe sources and meanings of plasma levels of catecholamines and their metabolites, present a model of a sympathetic noradrenergic neuron that conveys how particular aspects of sympathetic nervous function affect plasma levels of catecholamines and their metabolites, and apply the model to understand plasma neurochemical patterns associated with some drugs and disease states.

The Valsalva maneuver: screening for drug-induced baroreflex dysfunction

OBJECTIVE

Many drugs can interfere with baroreflex mechanisms thereby impairing blood pressure control, but few have undergone sufficient testing. The state of affairs may be explained by the lack of simple and inexpensive screening tests.

METHODS

In eleven healthy men, we tested the hypothesis that a simple Valsalva maneuver could detect drug-induced changes in baroreflex function that have previously been described using more elaborate and invasive methodologies. They performed Valsalva maneuvers after selective pharmacological inhibition of the norepinephrine transporter (NET) in a placebo-controlled, double-blind, randomized, crossover fashion. Patients with severe autonomic failure served as positive controls.

RESULTS

NET inhibition profoundly augmented the blood pressure decrease during phase II and attenuated the blood pressure overshoot in phase IV compared with placebo. Furthermore, NET inhibition increased the heart rate response during the Valsalva maneuver.

INTERPRETATION

The Valsalva maneuver recapitulated complex alterations in baroreflex regulation during NET inhibition. Thus, this simple and inexpensive test could be employed as a screening tool for drug-induced baroreflex dysfunction.

Regulation of the neuronal norepinephrine transporter by endothelin-1 and -3 in the rat anterior and posterior hypothalamus

We previously reported that endothelin-1 and endothelin-3 modulate norepinephrine neuronal release and tyrosine hydroxylase activity and expression in the hypothalamus. In the present study we sought to establish the role of endothelin-1 and -3 in the regulation of norepinephrine uptake in the anterior and posterior hypothalamus. Results showed that in the anterior hypothalamus endothelin-3 increased neuronal norepinephrine uptake whereas endothelin-1 decreased it. Conversely, in the posterior hypothalamic region both endothelins diminished the neuronal uptake of the amine. Endothelins response was concentration dependent and maintained at all studied times. Endothelins also modified the kinetic and internalization of the NE neuronal transporter. In the anterior hypothalamic region endothelin-3 increased the V(max) and the B(max) whereas endothelin-1 decreased them. However, in the posterior hypothalamic region both endothelins diminished the V(max) as well as B(max). Neither endothelin-1 nor endothelin-3 modified neuronal norepinephrine transporter K(d) in the studied hypothalamic regions. These findings support that in the posterior hypothalamic region both endothelins diminished neuronal norepinephrine transporter activity by reducing the amine transporter expression on the plasmatic membrane. Conversely, in the anterior hypothalamic region endothelin-3 enhanced neuronal norepinephrine transporter activity by increasing the expression of the transporter on the presynaptic membrane, whereas endothelin-1 induced the opposite effect. Present results permit us to conclude that both endothelins play an important role in the regulation of norepinephrine neurotransmission at the presynaptic nerve endings in the hypothalamus.

Metabolism in adipose tissue in response to citalopram and trimipramine treatment--an in situ microdialysis study

The intake of antidepressants is often accompanied by weight gain. Antidepressants may influence lipid and carbohydrate metabolism that can result in metabolic changes and obesity. We investigated the effect of citalopram and trimipramine on interstitial glycerol, glucose and lactate concentration and blood flow in subcutaneous adipose tissue of obese subjects by means of the microdialysis technique. In addition, the effect of stimulation with norepinephrine on metabolic response was investigated. Each subject was compared to a control subject matched for BMI and age. Each group comprised 10 subjects. Circulating plasma triglyceride concentrations were higher in drug-treated groups. In subcutaneous adipose tissue, microdialysis experiments revealed a higher and prolonged glycerol release in the presence of norepinephrine, but not under basal conditions. In citalopram treated subjects, basal glucose and lactate concentrations were higher compared with controls or with the trimipramine treated group. Local administration of norepinephrine induced a decrease in glucose levels and an increase in lactate levels, but without significant differences between groups. Local adipose tissue blood flow decreased in control groups following norepinephrine application, but remained constant in the antidepressant groups. In conclusion, citalopram and trimipramine affected glucose and lipid metabolism in adipose tissue and resulted in enhanced release of glycerol and free fatty acids into the circulation.

Altered sympathetic nervous reactivity and norepinephrine transporter expression in patients with postural tachycardia syndrome

BACKGROUND

Clinical observations in patients with postural tachycardia syndrome (POTS) suggest abnormal sympathetic nervous system activity and a dysfunction of the norepinephrine (NE) transporter (NET).

METHODS AND RESULTS

We examined sympathetic nervous system responses to head-up tilt by combining NE plasma kinetics measurements and muscle sympathetic nerve activity recordings and by quantifying NET protein content in peripheral sympathetic nerves in patients with POTS compared with that in controls. POTS patients had an elevated heart rate during supine rest (81+/-2 bpm versus 66+/-2 bpm in healthy subjects [HS], P<0.01). Head-up tilt to 40 degrees induced a greater rise in heart rate in patients with POTS (+24+/-4 bpm versus +13+/-2 bpm in HS, P<0.001). During rest in the supine position, muscle sympathetic nerve activity, arterial NE concentration, and whole-body NE spillover to plasma were similar in both groups. Muscle sympathetic nerve activity response to head-up tilt was greater in the POTS group (+29+/-3 bursts/min in patients with POTS and +13+/-2 bursts/min in HS, P<0.001), but the NE spillover rise was similar in both groups (51% in the POTS subjects and 50% in the HS). Western blot analysis of NET protein extracted from forearm vein biopsies in patients with POTS and HS demonstrated a decrease in the expression of NET protein in patients with POTS.

CONCLUSIONS

Patients with POTS exhibit a decrease in NET protein in their peripheral sympathetic nerves. Paradoxically, whole-body NE spillover to plasma during rest in the supine position and in response to head-up tilt is not altered despite excessive nerve firing rate in response to the head-up tilt.

Norepinephrine transporter inhibition alters the hemodynamic response to hypergravitation

Sympathetically mediated tachycardia and vasoconstriction maintain blood pressure during hypergravitational stress, thereby preventing gravitation-induced loss of consciousness. Norepinephrine transporter (NET) inhibition prevents neurally mediated (pre)syncope during gravitational stress imposed by head-up tilt testing. Thus it seems reasonable that NET inhibition could increase tolerance to hypergravitational stress. We performed a double-blind, randomized, placebo-controlled crossover study in 11 healthy men (26 ± 1 yr, body mass index 24 ± 1 kg/m2), who ingested the selective NET inhibitor reboxetine (4 mg) or matching placebo 25, 13, and 1 h before testing on separate days. We monitored heart rate, blood pressure, and thoracic impedance in three different body positions (supine, seated, standing) and during a graded centrifuge run (incremental steps of 0.5 g for 3 min each, up to a maximal vertical acceleration load of 3 g). NET inhibition increased supine blood pressure and heart rate. With placebo, blood pressure increased in the seated position and was well maintained during standing. However, with NET inhibition, blood pressure decreased in the seated and standing position. During hypergravitation, blood pressure increased in a graded fashion with placebo. With NET inhibition, the increase in blood pressure during hypergravitation was profoundly diminished. Conversely, the tachycardic responses to sitting, standing, and hypergravitation all were greatly increased with NET inhibition. In contrast to our expectation, short-term NET inhibition did not improve tolerance to hypergravitation. Redistribution of sympathetic activity to the heart or changes in baroreflex responses could explain the excessive tachycardia that we observed.

Sympathetic vasomotor tone determines blood pressure response to long-term sibutramine treatment

CONTEXT

The serotonin and norepinephrine transporter inhibitor sibutramine is a widely used antiobesity drug. In acute studies, the peripheral sympathomimetic effect of sibutramine was counteracted by a central sympatholytic action.

OBJECTIVE

The objective was to test the hypothesis that blood pressure responses to long-term sibutramine therapy may be related to sympathetic nerve traffic before treatment in a prospective open-label study in an academic clinical research center.

PATIENTS

This study comprised 20 obese subjects (body mass index, 30-40 kg/m2; age, 30-57 yr) receiving 5 d of placebo treatment followed by open-label 15 mg/d sibutramine and hypocaloric diet over 12 wk.

MAIN OUTCOME MEASURES

Body weight, blood pressure, heart rate, muscle sympathetic nerve activity (MSNA) (microneurography), plasma catecholamines, and adipose tissue gene expression were measured.

RESULTS

Open-label sibutramine treatment decreased body weight 4.1 kg (P<0.01) and MSNA 17 bursts per minute (P=0.001), and increased diastolic blood pressure 3 mm Hg (P<0.05) and heart rate 8 bpm (P<0.01). The change in blood pressure with sibutramine treatment was inversely correlated with initial MSNA (r2=0.34; P<0.01). Chronic sibutramine treatment increased adrenoreceptor gene expression and plasma catecholamines.

CONCLUSIONS

The blood pressure response to sibutramine treatment is related to initial MSNA so that subjects with higher MSNA exhibit a smaller increase or even a decrease in blood pressure. The phenomenon might be explained by a sustained reduction in central sympathetic activity with sibutramine treatment.