The alpha2 -adrenergic receptors in hypertension and heart failure: experimental and clinical studies

The Discovery of Novel α2a Adrenergic Receptor Agonists Only Coupling to Gαi/O Proteins by Virtual Screening

Most α2-AR agonists derived from dexmedetomidine have few structural differences between them and have no selectivity for α2A/2B-AR or Gi/Gs, which can lead to side effects in drugs. To obtain novel and potent α2A-AR agonists, we performed virtual screening for human α2A-AR and α2B-AR to find α2A-AR agonists with higher selectivity. Compound P300-2342 and its three analogs significantly decreased the locomotor activity of mice (p < 0.05). Furthermore, P300-2342 and its three analogs inhibited the binding of [3H] Rauwolscine with IC50 values of 7.72 ± 0.76 and 12.23 ± 0.11 μM, respectively, to α2A-AR and α2B-AR. In α2A-AR-HEK293 cells, P300-2342 decreased forskolin-stimulated cAMP production without increasing cAMP production, which indicated that P300-2342 activated α2A-AR with coupling to the Gαi/o pathway but without Gαs coupling. P300-2342 exhibited no agonist but slight antagonist activities in α2B-AR. Similar results were obtained for the analogs of P300-2342. The docking results showed that P300-2342 formed π-hydrogen bonds with Y394, V114 in α2A-AR, and V93 in α2B-AR. Three analogs of P300-2342 formed several π-hydrogen bonds with V114, Y196, F390 in α2A-AR, and V93 in α2B-AR. We believe that these molecules can serve as leads for the further optimization of α2A-AR agonists with potentially few side effects.

In Vitro Activation of Human Adrenergic Receptors and Trace Amine-Associated Receptor 1 by Phenethylamine Analogues Present in Food Supplements

Pre-workout supplements are popular among sport athletes and overweight individuals. Phenethylamines (PEAs) and alkylamines (AA) are widely present in these supplements. Although the health effects of these analogues are not well understood yet, they are hypothesised to be agonists of adrenergic (ADR) and trace amine-associated receptors (TAARs). Therefore, we aimed to pharmacologically characterise these compounds by investigating their activating properties of ADRs and TAAR1 in vitro. The potency and efficacy of the selected PEAs and AAs was studied by using cell lines overexpressing human ADRα1A/α1B/α1D/α2a/α2B/β1/β2 or TAAR1. Concentration-response relationships are expressed as percentages of the maximal signal obtained by the full ADR agonist adrenaline or the full TAAR1 agonist phenethylamine. Multiple PEAs activated ADRs (EC50 = 34 nM-690 µM; Emax = 8-105%). Almost all PEAs activated TAAR1 (EC50 = 1.8-92 µM; Emax = 40-104%). Our results reveal the pharmacological profile of PEAs and AAs that are often used in food supplements. Several PEAs have strong agonistic properties on multiple receptors and resemble potencies of the endogenous ligands, indicating that they might further stimulate the already activated sympathetic nervous system in exercising athletes via multiple mechanisms. The use of supplements containing one, or a combination of, PEA(s) may pose a health risk for their consumers.

Segregation of nascent GPCRs in the ER-to-Golgi transport by CCHCR1 via direct interaction

G protein-coupled receptors (GPCRs) constitute the largest superfamily of cell surface signaling proteins that share a common structural topology. When compared with agonist-induced internalization, how GPCRs are sorted and delivered to functional destinations after synthesis in the endoplasmic reticulum (ER) is much less well understood. Here, we demonstrate that depletion of coiled-coil α-helical rod protein 1 (CCHCR1) by siRNA and CRISPR-Cas9 significantly inhibits surface expression and signaling of α2A-adrenergic receptor (α2A-AR; also known as ADRA2A), without affecting α2B-AR. Further studies show that CCHCR1 depletion specifically impedes α2A-AR export from the ER to the Golgi, but not from the Golgi to the surface. We also demonstrate that CCHCR1 selectively interacts with α2A-AR. The interaction is mediated through multiple domains of both proteins and is ionic in nature. Moreover, mutating CCHCR1-binding motifs significantly attenuates ER-to-Golgi export, surface expression and signaling of α2A-AR. Collectively, these data reveal a novel function for CCHCR1 in intracellular protein trafficking, indicate that closely related GPCRs can be sorted into distinct ER-to-Golgi transport routes by CCHCR1 via direct interaction, and provide important insights into segregation and anterograde delivery of nascent GPCR members.

Virtual screening and biological evaluation to identify pharmaceuticals potentially causing hypertension and hypokalemia by inhibiting steroid 11β-hydroxylase

Several drugs were found after their market approval to unexpectedly inhibit adrenal 11β-hydroxylase (CYP11B1)-dependent cortisol synthesis. Known side-effects of CYP11B1 inhibition include hypertension and hypokalemia, due to a feedback activation of adrenal steroidogenesis, leading to supraphysiological concentrations of 11-deoxycortisol and 11-deoxycorticosterone that can activate the mineralocorticoid receptor. This results in potassium excretion and sodium and water retention, ultimately causing hypertension. With the risk known but usually not addressed in preclinical evaluation, this study aimed to identify drugs and drug candidates inhibiting CYP11B1. Two conceptually different virtual screening methods were combined, a pharmacophore based and an induced fit docking approach. Cell-free and cell-based CYP11B1 activity measurements revealed several inhibitors with IC50 values in the nanomolar range. Inhibitors include retinoic acid metabolism blocking agents (RAMBAs), azole antifungals, α2-adrenoceptor ligands, and a farnesyltransferase inhibitor. The active compounds share a nitrogen atom embedded in an aromatic ring system. Structure activity analysis identified the free electron pair of the nitrogen atom as a prerequisite for the drug-enzyme interaction, with its pKa value as an indicator of inhibitory potency. Another important parameter is drug lipophilicity, exemplified by etomidate. Changing its ethyl ester moiety to a more hydrophilic carboxylic acid group dramatically decreased the inhibitory potential, most likely due to less efficient cellular uptake. The presented work successfully combined different in silico and in vitro methods to identify several previously unknown CYP11B1 inhibitors. This workflow facilitates the identification of compounds that inhibit CYP11B1 and therefore pose a risk for inducing hypertension and hypokalemia.

Multitargeting in cardioprotection: An example of biaromatic compounds

A multitarget drug design approach is actively developing in modern medicinal chemistry and pharmacology, especially with regard to multifactorial diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. A detailed study of many well-known drugs developed within the single-target approach also often reveals additional mechanisms of their real pharmacological action. One of the multitarget drug design approaches can be the identification of the basic pharmacophore models corresponding to a wide range of the required target ligands. Among such models in the group of cardioprotectors is the linked biaromatic system. This review develops the concept of a "basic pharmacophore" using the biaromatic pharmacophore of cardioprotectors as an example. It presents an analysis of possible biological targets for compounds corresponding to the biaromatic pharmacophore and an analysis of the spectrum of biological targets for the five most known and most studied cardioprotective drugs corresponding to this model, and their involvement in the biological effects of these drugs.

Dexmedetomidine Attenuates Lipopolysaccharide-Induced Sympathetic Activation and Sepsis via Suppressing Superoxide Signaling in Paraventricular Nucleus

Sympathetic overactivity contributes to the pathogenesis of sepsis. The selective α2-adrenergic receptor agonist dexmedetomidine (DEX) is widely used for perioperative sedation and analgesia. We aimed to determine the central roles and mechanisms of DEX in attenuating sympathetic activity and inflammation in sepsis. Sepsis was induced by a single intraperitoneal injection of lipopolysaccharide (LPS) in rats. Effects of DEX were investigated 24 h after injection of LPS. Bilateral microinjection of DEX in the paraventricular nucleus (PVN) attenuated LPS-induced sympathetic overactivity, which was attenuated by the superoxide dismutase inhibitor DETC, cAMP analog db-cAMP or GABA_A receptor antagonist gabazine. Superoxide scavenger tempol, NADPH oxidase inhibitor apocynin, adenylate cyclase inhibitor SQ22536 or PKA inhibitor Rp-cAMP caused similar effects to DEX in attenuating LPS-induced sympathetic activation. DEX inhibited LPS-induced superoxide and cAMP production, as well as NADPH oxidase, adenylate cyclase and PKA activation. The roles of DEX in reducing superoxide production and NADPH oxidase activation were attenuated by db-cAMP or gabazine. Intravenous infusion of DEX inhibited LPS-induced sympathetic overactivity, NOX activation, superoxide production, TNF-α and IL-1β upregulation in the PVN and plasma, as well as lung and renal injury, which were attenuated by the PVN microinjection of yohimbine and DETC. We conclude that activation of α2-adrenergic receptors with DEX in the PVN attenuated LPS-induced sympathetic overactivity by reducing NADPH oxidase-dependent superoxide production via both inhibiting adenylate cyclase-cAMP-PKA signaling and activating GABA_A receptors. The inhibition of NADPH oxidase-dependent superoxide production in the PVN partially contributes to the roles of intravenous infusion of DEX in attenuating LPS-induced sympathetic activation, oxidative stress and inflammation.

Toll-Like Receptors in the Pathogenesis of Essential Hypertension. A Forthcoming Immune-Driven Theory in Full Effect

Essential hypertension (EH) is a highly heterogenous disease with a complex etiology. Recent evidence highlights the significant contribution of subclinical inflammation, triggered and sustained by excessive innate immune system activation in the pathogenesis of the disease. Toll-like receptors (TLRs) have been implied as novel effectors in this inflammatory environment since they can significantly stimulate the production of pro-inflammatory cytokines, the migration and proliferation of smooth muscle cells and the generation of reactive oxygen species (ROS), facilitating a low-intensity inflammatory background that is evident from the very early stages of hypertension. Furthermore, the net result of their activation is oxidative stress, endothelial dysfunction, vascular remodeling, and finally, vascular target organ damage, which forms the pathogenetic basis of EH. Importantly, evidence of augmented TLR expression and activation in hypertension has been documented not only in immune but also in several non-immune cells located in the central nervous system, the kidneys, and the vasculature which form the pathogenetic core systems operating in hypertensive disease. In this review, we will try to highlight the contribution of innate immunity in the pathogenesis of hypertension by clarifying the deleterious role of TLR signaling in promoting inflammation and facilitating hypertensive vascular damage.

Exercise training ameliorates adrenergic control in spontaneously hypertensive rats

The goal of this study was to examine vascular control after sympathetic stimulation by tyramine infusion in hypertensive rats submitted to swimming training. To this end, male rats were assigned to the following groups: sedentary (SN) and trained normotensive (TN), sedentary (SH) and trained hypertensive (TH). Arterial pressure (AP), heart rate (HR), HR variability (HRV), AP variability (APV), and cardiac autonomic function were recorded. Following, infusion of tyramine was administrated. The TN and TH showed a lower resting HR compared with their respective sedentary groups (p < .05). Pressure levels were less in TH than SH (p < .05). The TH showed a higher HRV together with a lower APV in comparison to SH (p < .05). The sympathetic modulation of HRV and APV was lower in TH than in SH (p < .05). Both trained groups presented an increased parasympathetic modulation of HRV compared with their respective sedentary groups (p < .05). The TN and TH groups had a higher vagal effect in comparison with their respective sedentary groups (p < .001). The sympathetic effect was lower in TH than in SH (p < .001). Pressor and HR responses to tyramine in different doses were attenuated in TH (p < .001). Further analysis showed a significant association between infusion of tyramine and normalized LF component of HRV (r = 0.84, p < .001), systolic APV (r = 0.58, p < .001) and diastolic APV (r = 0.49, p < .001). In conclusion, exercise training provokes less pressor response variation by tyramine infusion in hypertensive animals suggesting sympathetic nerve endings adjustments and decrease of the vasoconstrictor effect attenuates injury caused by hypertension improving cardiovascular autonomic dysfunction, which can be associated with sympathetic attenuation.

Approach and Management of Hypertension After Kidney Transplantation

Hypertension is one of the most common cardiovascular co-morbidities after successful kidney transplantation. It commonly occurs in patients with other metabolic diseases, such as diabetes mellitus, hyperlipidemia, and obesity. The pathogenesis of post-transplant hypertension is complex and is a result of the interplay between immunological and non-immunological factors. Post-transplant hypertension can be divided into immediate, early, and late post-transplant periods. This classification can help clinicians determine the etiology and provide the appropriate management for these complex patients. Volume overload from intravenous fluid administration is common during the immediate post-transplant period and commonly contributes to hypertension seen early after transplantation. Immunosuppressive medications and donor kidneys are associated with post-transplant hypertension occurring at any time point after transplantation. Transplant renal artery stenosis (TRAS) and obstructive sleep apnea (OSA) are recognized but common and treatable causes of resistant hypertension post-transplantation. During late post-transplant period, chronic renal allograft dysfunction becomes an additional cause of hypertension. As these patients develop more substantial chronic kidney disease affecting their allografts, fibroblast growth factor 23 (FGF23) increases and is associated with increased cardiovascular and all-cause mortality in kidney transplant recipients. The exact relationship between increased FGF23 and post-transplant hypertension remains poorly understood. Blood pressure (BP) targets and management involve both non-pharmacologic and pharmacologic treatment and should be individualized. Until strong evidence in the kidney transplant population exists, a BP of <130/80 mmHg is a reasonable target. Similar to complete renal denervation in non-transplant patients, bilateral native nephrectomy is another treatment option for resistant post-transplant hypertension. Native renal denervation offers promising outcomes for controlling resistant hypertension with no significant procedure-related complications. This review addresses the epidemiology, pathogenesis, and specific etiologies of post-transplant hypertension including TRAS, calcineurin inhibitor effects, OSA, and failed native kidney. The cardiovascular and survival outcomes related to post-transplant hypertension and the utility of 24-h blood pressure monitoring will be briefly discussed. Antihypertensive medications and their mechanism of actions relevant to kidney transplantation will be highlighted. A summary of guidelines from different professional societies for BP targets and antihypertensive medications as well as non-pharmacological interventions, including bilateral native nephrectomy and native renal denervation, will be reviewed.

Safety threshold of intravitreal clonidine in rabbit's eyes

AIM

To determine the safe dose of intravitreal clonidine (IVC), a potential drug for neuroprotection and angiogenesis inhibition in rabbits.

METHODS

A total of 28 rabbits were divided into four groups. Three groups received IVC with concentrations of 15 (Group A), 25 (Group B), and 50 (Group C) µg/0.1 mL and the control group (Group D) received 0.1 mL balanced salt solution (BSS). To investigate IVC safety, electroretinography (ERG) was performed at baseline, then at 1, 4 and 8wk after injection. After last ERG, all rabbits were euthanized, their eyes were enucleated and subjected to routine histopathological evaluation, immunohistochemistry for glial fibrillary acidic protein (GFAP) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) test.

RESULTS

Based on ERG, histopathology, GFAP and TUNEL assay findings, 15 µg IVC was determined as the safe dose in rabbit eyes. While, the results of routine histopathology and TUNEL assay were unremarkable in all groups, toxic effects attributed to 25 and 50 µg IVC were demonstrated by ERG and GFAP tests.

CONCLUSION

Totally 15 µg clonidine is determined as the safe dose for intravitreal injection in rabbits. Contribution of IVC in neuroprotection and inhibition of angiogenesis deserve more studies.

Antihypertensive methyldopa, labetalol, hydralazine, and clonidine reversed tumour necrosis factor-α inhibited endothelial nitric oxide synthase expression in endothelial-trophoblast cellular networks

Medications used to control hypertension in pregnancy also improve trophoblast and endothelial cellular interaction in vitro. Tumour necrosis factor-α (TNF-α) inhibits trophoblast and endothelial cellular interactions and simultaneously decreases endothelial nitric oxide synthase (eNOS) expression. This study investigated whether antihypertensive medications improved these cellular interactions by modulating eNOS and inducible nitric oxide synthase (iNOS) expression. Human uterine myometrial microvascular endothelial cells (UtMVECs) were pre-incubated with (or without) low dose TNF-α (0.5 ng/mL) or TNF-α plus soluble fms-like tyrosine kinase-1 (sFlt-1) (100 ng/mL). The endothelial cells were cultured on Matrigel. After endothelial cellular networks appeared, trophoblast derived HTR-8/SVneo cells were co-cultured in the presence of clinically relevant doses of methyldopa, labetalol, hydralazine or clonidine for 24 hours. Cells were retrieved from the Matrigel to extract mRNA and eNOS and iNOS expression were examined by quantitative PCR. Methyldopa, labetalol, hydralazine and clonidine reversed the inhibitory effect of TNF-α on eNOS mRNA expression. After pre-incubating endothelial cells with TNF-α and sFlt-1, all the medications except methyldopa lost their effect on eNOS mRNA expression. In the absence of TNF-α, antihypertensive medications did not change eNOS expression. The mRNA expression of iNOS was not affected by TNF-α or any medications. This study shows that selected antihypertensive medications used in the treatment of hypertension in pregnancy increase eNOS expression in vitro when induced by the inflammatory TNF-α. The anti-angiogenic molecule sFlt-1 may antagonise the potential benefit of these medications by interfering with the NOS pathway.

Increased platelet alpha2B-adrenergic receptor gene expression in well-controlled hypertensives: the effect of arterial stiffness

Catecholamines play a major role in atherothrombotic mechanisms in essential hypertension. Alpha_2B-adrenergic receptors (α2B-ARs) are implicated in the pathophysiology of platelet aggregation. In this study, we evaluated platelet α2B-AR gene expression levels in patients with well-controlled essential hypertension compared with normal individuals and investigated their association with increased arterial stiffness. Fifty-nine patients with well-controlled essential hypertension (34 men, mean age 65 ± 9 years) and 26 normotensives (19 men, mean age 64 ± 8 years) were included in the study. For each patient, carotid-femoral pulse wave velocity (PWV) and carotid-radial PWV were evaluated. In addition, blood samples were obtained and platelets were isolated. The α2B-AR gene expression levels in platelets were examined by real-time polymerase chain reaction for each participant. Well-controlled hypertensive patients showed significantly higher gene expression levels of α2B-Rs in platelets compared with normotensives (34.7 ± 29.5 vs 17.6 ± 12.5, respectively, P = .005). Interestingly, we found that carotid-femoral PWV and carotid-radial PWV were positively correlated with platelet α2B-R gene expression levels (r = 0.59, P < .001, and r = 0.39, P = .002, respectively).Platelet α2B-R gene expression levels are increased in patients with well-controlled essential hypertension compared with normotensives and are correlated with increased PWV in those patients. Our data indicate an association of arterial stiffness and platelet α2B-Rs gene expression and indicate the need for further research.

α1A-Adrenergic Receptor Antagonism Improves Erectile and Cavernosal Responses in Rats With Cavernous Nerve Injury and Enhances Neurogenic Responses in Human Corpus Cavernosum From Patients With Erectile Dysfunction Secondary to Radical Prostatectomy

INTRODUCTION

Cavernous nerve injury (CNI) in rats and radical prostatectomy (RP) in men result in loss of nitrergic function and increased adrenergic-neurogenic contractions of cavernosal tissue.

AIM

To evaluate the modulation of the α-adrenergic system as a strategy to relieve erectile dysfunction (ED) and functional cavernosal alterations induced by CNI.

METHODS

A non-selective α-blocker (phentolamine 1 mg/kg daily), a selective α_1A-blocker (silodosin [SILOD] 0.1 mg/kg daily), or vehicle was orally administered for 4 weeks after bilateral crush CNI (BCNI). Erectile and neurogenic responses of the corpus cavernosum (CC) were evaluated. The acute effects of SILOD also were evaluated in vivo (0.03 mg/kg intravenously) and ex vivo (10 nmol/L). The effects of SILOD and tadalafil (TAD) on nitrergic relaxations were determined in human CC from patients with ED with a vascular etiology or ED secondary to RP.

MAIN OUTCOME MEASURES

Erectile responses in vivo in rats and neurogenic contractions and relaxations of rat and human CC.

RESULTS

Long-term treatment with SILOD significantly improved erectile responses and allowed for the potentiation of erectile responses by acute treatment with TAD (0.3 mg/kg intravenously) in rats with BCNI. SILOD partly recovered nitrergic relaxations and normalized neurogenic contractions in CC from rats with BCNI. Long-term treatment with SILOD partly prevented BCNI-induced decreases in neuronal nitric oxide synthase expression. Acute administration of SILOD (0.03 mg/kg intravenously) improved erectile responses in vivo and potentiated nitrergic relaxation and decreased neurogenic contractions ex vivo in CC from rats with BCNI. In human CC from patients with ED with a vascular etiology, TAD (30 nmol/L), SILOD (10 nmol/L), or their combination increased nitrergic relaxations. Potentiation by TAD was lost in human CC from patients with ED after RP but was recovered after co-treatment with SILOD.

CONCLUSION

α-Adrenergic modulation, especially selective α_1A-blockade, improves erectile and cavernosal functions after BCNI. Modulation of the adrenergic system, mainly in combination strategies, could have a role in the management of ED after RP.

Can clonidine as a pre-anaesthetic drug decrease bleeding during rhinoplasty surgery?

Clonidine is an antihypertensive drug which acts through facilitation of Alph-2 post-synaptic receptors and in addition to its antihypertensive, anti-anxiety and analgesic effects, its beneficial effects in reducing the bleeding during Neurosurgery and Orthopedics surgeries, delicate surgeries of ear and nasal and sinus endoscopy have been proved. In this study we discuss the effects of this drug in reducing bleeding during rhinoplasty surgery. A double-blinded clinical trial 80 patients have been conducted 40 patients received 5 µg/Kg of oral Clonidine, and 40 patients where placebo. The patients after surgery were divided into 4 groups according to the number of bloody standard gauzes during the surgery. Group 1(less than 2 bloody gauzes), group 2(2-3 bloody gauzes), group 3(4-5 bloody gauzes), group 4(more than 5 bloody gauzes). All the graded achieved results were analyzed using Chi-Square test and Fisher test. Mean and standard deviation (SD) of the amount of bleeding in the group who were receiving Clonidine were less than the witness group. Number of the patients in groups 3 and 4 for those who were receiving Clonidine was obviously fewer (1.8 ± 0.04 vs. 3.1 ± 0.05), (P < 0.05). Oral Clonidine as a pre-anesthetic drug causes decrease in bleeding during rhinoplasty surgery.

Systems approaches and polypharmacology for drug discovery from herbal medicines: an example using licorice

ETHNOPHARMACOLOGICAL RELEVANCE

Licorice, one of the oldest and most popular herbal medicines in the world, has been widely used in traditional Chinese medicine as a cough reliever, anti-inflammatory, anti-anabrosis, immunomodulatory, anti-platelet, antiviral (hepatitis) and detoxifying agent. Licorice was used as an example to show drug discovery from herbal drugs using systems approaches and polypharmacology.

AIM OF THE STUDY

Herbal medicines are becoming more mainstream in clinical practice and show value in treating and preventing diseases. However, due to its extreme complexity both in chemical components and mechanisms of action, deep understanding of botanical drugs is still difficult. Thus, a comprehensive systems approach which could identify active ingredients and their targets in the crude drugs and more importantly, understand the biological basis for the pharmacological properties of herbal medicines is necessary.

MATERIALS AND METHODS

In this study, a novel systems pharmacology model that integrates oral bioavailability screening, drug-likeness evaluation, blood-brain barrier permeation, target identification and network analysis has been established to investigate the herbal medicines.

RESULTS

The comprehensive systems approach effectively identified 73 bioactive components from licorice and 91 potential targets for this medicinal herb. These 91 targets are closely associated with a series of diseases of respiratory system, cardiovascular system, and gastrointestinal system, etc. These targets are further mapped to drug-target and drug-target-disease networks to elucidate the mechanism of this herbal medicine.

CONCLUSION

This work provides a novel in silico strategy for investigation of the botanical drugs containing a huge number of components, which has been demonstrated by the well-studied licorice case. This attempt should be helpful for understanding definite mechanisms of action for herbal medicines and discovery of new drugs from plants.

'Volume-expanded' hypertension: the effect of fluid overload and the role of the sympathetic nervous system in salt-dependent hypertension

It is widely believed that salt-dependent hypertension is induced and maintained by expansion of intravascular fluid volume resulting from excessive retention of sodium. The purpose of this brief article is to present a series of arguments in support of the thesis that volume overload per se does not raise the arterial blood pressure. Several investigators in the 1960s and 1970s reported that excessive retention of salt - regardless of cause - leads to sympathetic activation mediated by the effects of the Na ion on α(2)-adrenergic receptors located mostly in the brainstem. In recent years, the cloning and characterization of α(2)-adrenergic receptors subtypes permitted differentiation of their hemodynamic effects via use of salt loading of nephrectomized animals submitted to genetic engineering or gene treatment. These studies indicate that sodium alters the balance between the sympathoinhibitory α(2A)-adrenergic receptors and the sympathoexcitatory α(2B)-adrenergic receptors, leading to a hyperadrenergic hypertensive state unrelated to volume overload.

Adrenergic signaling polymorphisms and their impact on cardiovascular disease

This review examines the impact of recent discoveries defining personal genetics of adrenergic signaling polymorphisms on scientific discovery and medical practice related to cardiovascular diseases. The adrenergic system is the major regulator of minute-by-minute cardiovascular function. Inhibition of adrenergic signaling with pharmacological beta-adrenergic receptor antagonists (beta-blockers) is first-line therapy for heart failure and hypertension. Advances in pharmacology, molecular biology, and genetics of adrenergic signaling pathways have brought us to the point where personal genetic differences in adrenergic signaling factors are being assessed as determinants of risk or progression of cardiovascular disease. For a few polymorphisms, functional data generated in cell-based systems, genetic mouse models, and pharmacological provocation of human subjects are concordant with population studies that suggest altered risk of cardiovascular disease or therapeutic response to beta-blockers. For the majority of adrenergic pathway polymorphisms however, published data conflict, and the clinical relevance of individual genotyping remains uncertain. Here, the current state of laboratory and clinical evidence that adrenergic pathway polymorphisms can affect cardiovascular pathophysiology is comprehensively reviewed and compared, with a goal of placing these data in the broad context of potential clinical applicability.

Polymorphisms in α- and β-Adrenergic Receptor Genes, Hypertension, and Obstructive Sleep Apnea: The Skaraborg Sleep Study

The sympathetic nervous system and the adrenergic receptors play an important role in regulation of blood pressure. This study explored the associations between functional polymorphisms of the α(2B)-, β(1)-, and β(2)-adrenergic receptor genes and obstructive sleep apnea (OSA) in hypertensive patients and hypertension in patients with OSA in a populationbased sample of 157 hypertensive patients and 181 healthy control subjects. Only the Arg389Gly polymorphism of the β(1)-adrenergic receptor gene was associated with increased risk for mild OSA in hypertensive patients (Arg/Arg versus Gly/Arg/Gly/Gly, 2.1, 95% CI, 1.02-4.7). Hypertensive men carrying the Arg389Arg genotype had higher crude and age-adjusted AHI than carriers of the Arg389Gly/Gly389Gly genotypes. When adjusted also for BMI this difference became borderline significant. This difference was not observed in women. The risk of hypertension in mild OSA was associated with increasing number of Arg-alleles (Arg/Arg OR 5.4, 95% CI 1.4-21.2).

Anti-Hypertensive Drugs Alter Cytokine Production from Preeclamptic Placentas and Peripheral Blood Mononuclear Cells

OBJECTIVE

Antihypertensive drugs are administered to women with preeclampsia to control blood pressure and fluid overload. Whether they modulate placental or circulating cytokine production in women with preeclampsia is unknown. This study examines the effect of pharmacological doses of antihypertensive drugs on the production of IL-10, tumor necrosis factor alpha (TNF-alpha), and IL-6 in placental tissue and peripheral blood mononuclear cells (PBMCs) from women with preeclampsia.

METHODS

Term placenta samples (n = 6) and PBMCs from whole blood (n = 6) were obtained from women with preeclampsia. Both villous explants and PBMCs were cultured with increasing concentrations of antihypertensive drugs (clonidine, diazoxide, hydralazine, and furosemide). The dose effect of drugs on the production of placental and circulating cytokines IL-10, TNF-alpha, and IL-6 was examined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our data suggest that clonidine can stimulate anti-inflammatory IL-10 production from PBMC while decreasing pro-inflammatory TNF-alpha, whereas low doses of hydralazine increased the production of IL-10, TNF-alpha, and IL-6 from preeclamptic PBMCs. There was a reduction in IL-10, TNF-alpha, and IL-6 production with increasing doses of clonidine and hydralazine by placentas in preeclampsia. IL-10, TNF-alpha, and IL-6 production from preeclamptic placenta and PBMCs were inhibited by diazoxide and furosemide.

CONCLUSIONS

Antihypertensive drugs may alter Th1/Th2 cytokine balance in preeclamptic tissues in vitro.

Hypertension in transgenic mice with brain-selective overexpression of the alpha(2B)-adrenoceptor

BACKGROUND

Previous studies have shown that the presynaptic alpha(2B)-adrenoceptor subtype in the central nervous system has a sympathoexcitatory function and its activation leads to a hyperadrenergic hypertensive state. The purpose of this project was to develop a novel hyperadrenergic model, a transgenic (TG) mouse model with brain-selective overexpression of the alpha(2B)-adrenergic receptor (alpha(2B)-AR).

METHODS

We used Southern blot analysis to confirm transgene, real-time PCR to assess gene expression, western Blot analysis and immunohistology to assess protein expression and localization in brain areas. Indirect blood pressure (BP) and heart rate were recorded.

RESULTS

In TG mice there was a 1.8-fold increase in alpha(2B)-AR protein expression compared to wild-type (WT) mice. Immunostaining of brain sections revealed that concentration of alpha(2B)-AR was much more pronounced in TG than in WT mice. Systolic BP at 8 weeks of age was significantly elevated in TG 130 +/- 6 mm Hg, compared with WT control nontransgenic littermates of the same age 107 +/- 7 mm Hg, (P < 0.05), indicating that the TG mice had indeed developed hypertension.

CONCLUSIONS

We have therefore documented that overexpression of the alpha(2B)-AR gene leads to increased production of alpha(2B)-AR protein in brain regions known to regulate central sympathetic outflow, thus resulting in sustained BP elevation. This is a unique model of experimental hypertension driven purely by overexpression of the alpha(2B)-AR that would result in an overactive sympathetic system and would be suitable for testing the pharmacologic properties of potential therapeutic agents.

[Perioperative pharmacological myocardial protection. Systematic literature-based process optimization]

Patients with major cardiac risk factors have been suggested to benefit from perioperative beta-blockade. However, the scientific literature on perioperative beta-blockade needs to be interpreted carefully. So far treatment recommendations for millions of patients are based on heterogeneous data from randomized trials with divergent study results. The evidence for a beneficial effect of perioperative beta-blockers is sufficient only for a limited subpopulation of high cardiac risk patients undergoing vascular surgery. Perioperative beta-blocker treatment is not useful in patients with intermediate risk and may even be harmful in patients with low cardiac risk. Therefore, an individualized risk-benefit analysis is an important prerequisite for a rational therapy that may be based on a standardized protocol including the Revised Cardiac Risk Index. Such a protocol is presented in this article. A recently reported trial (POISE) demonstrated that perioperative treatment with high doses of oral metoprolol efficiently reduces the incidence of cardiovascular events. However, due to severe adverse effects (hypotension, bradycardia, stroke) the total mortality was increased. Thus, dose adjustments, safety aspects, and monitoring of beta-blocker therapy seem to be mandatory. So far evidence from relevant trials about how to best implement perioperative beta-blockade is lacking. This article offers a simple clinical concept for this purpose.

The antiarrhythmic effect of centrally administered rilmenidine involves muscarinic receptors, protein kinase C and mitochondrial signalling pathways

BACKGROUND AND PURPOSE

We have previously demonstrated that stimulation of imidazoline receptors in the CNS prevented halothane-adrenaline arrhythmias during halothane anaesthesia and that stimulation of the vagus nerve may be critical to this effect. However, details of the mechanism(s) involved are not yet available. The present study was designed to examine the role of muscarinic receptors, protein kinase C (PKC), ATP-sensitive potassium channels (K(ATP)) and the mitochondrial permeability transition pore (MPTP) in the antiarrhythmic effect of rilmenidine, an imidazoline receptor agonist.

EXPERIMENTAL APPROACH

Rats were anaesthetized with halothane and monitored continuously for arterial blood pressure and premature ventricular contractions. The arrhythmogenic dose of adrenaline was defined as the lowest dose producing three or more premature ventricular contractions within a 15-s period. We confirmed that centrally administered rilmenidine prevented halothane-adrenaline arrhythmias and then examined the antiarrhythmic effect of rilmenidine in the presence of atropine methylnitrate, a muscarinic receptor antagonist, calphostin C, a PKC inhibitor, HMR-1098, a sarcolemmal K(ATP) inhibitor, 5-hydroxydecanoic acid, a mitochondrial K(ATP) inhibitor or atractyloside, an MPTP opener.

KEY RESULTS

The antiarrhythmic effect of rilmenidine was significantly inhibited by atropine methylnitrate, calphostin C, 5-hydroxydecanoic acid and atractyloside, but the effects of HMR-1098 in our model were not clear.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that muscarinic receptors, PKC, mitochondrial K(ATP) channels and MPTP may be crucial components of the mechanism involved in the antiarrhythmic effect of rilmenidine given into the CNS.

Cardiovascular adjustments for life at high altitude

The effects of hypobaric hypoxia in visitors depend not only on the actual elevation but also on the rate of ascent. There are increases in sympathetic activity resulting in increases in systemic vascular resistance, blood pressure and heart rate. Pulmonary vasoconstriction leads to pulmonary hypertension, particularly during exercise. The sympathetic excitation results from hypoxia, partly through chemoreceptor reflexes and partly through altered baroreceptor function. Systemic vasoconstriction may also occur as a reflex response to the high pulmonary arterial pressures. Many communities live permanently at high altitude and most dwellers show excellent adaptation although there are differences between populations in the extent of the ventilatory drive and the erythropoiesis. Despite living all their lives at altitude, some dwellers, particularly Andeans, may develop a maladaptation syndrome known as chronic mountain sickness. The most prominent characteristic of this is excessive polycythaemia, the cause of which has been attributed to peripheral chemoreceptor dysfunction. The hyperviscous blood leads to pulmonary hypertension, symptoms of cerebral hypoperfusion, and eventually right heart failure and death.

Clonidine reduces the excitability of spinal dorsal horn neurones

BACKGROUND

Clonidine has often been applied in combination with local anaesthetics for spinal or epidural anaesthesia. This study was designed to investigate the local anaesthetic-like action of clonidine in superficial dorsal horn neurones. The superficial laminae of the dorsal horn contain three groups of neurones: tonic-, adapting-, and single-spike-firing neurones which are important neuronal structures for pain transmission, receiving most of their primary sensory input from Adelta and C fibres.

METHODS

Whole cell patch clamp recordings from spinal cord slices of Wistar rats were used to study the action of clonidine on the generation of single and series of action potentials. Voltage clamp recordings in isolated somata were performed to study the effect of clonidine on voltage-gated Na(+) and different types of K(+) currents.

RESULTS

Firing frequencies of trains of action potentials in tonic-firing neurones are reduced at low concentrations (10 microM) of clonidine, but not in adapting- or single-spike-firing neurones. High concentrations of clonidine (700 microM) are necessary to modify the shape of single action potentials. Low concentrations of clonidine shift the steady-state inactivation curve of Na(+) currents to more negative potentials. At clinical concentrations (6-100 microM) clonidine partially inhibits voltage-gated Na(+) and K(+) channels.

CONCLUSIONS

Clonidine suppresses the generation of action potentials in tonic-firing spinal dorsal horn neurones. This may be explained, in part, by an interaction with voltage-gated Na(+) and K(+) currents. Clonidine could therefore contribute to analgesia during local anaesthesia.

The autonomic nervous system at high altitude

The effects of hypobaric hypoxia in visitors depend not only on the actual elevation but also on the rate of ascent. Sympathetic activity increases and there are increases in blood pressure and heart rate. Pulmonary vasoconstriction leads to pulmonary hypertension, particularly during exercise. The sympathetic excitation results from hypoxia, partly through chemoreceptor reflexes and partly through altered baroreceptor function. High pulmonary arterial pressures may also cause reflex systemic vasoconstriction. Most permanent high altitude dwellers show excellent adaptation although there are differences between populations in the extent of the ventilatory drive and the erythropoiesis. Some altitude dwellers, particularly Andeans, may develop chronic mountain sickness, the most prominent characteristic of which being excessive polycythaemia. Excessive hypoxia due to peripheral chemoreceptor dysfunction has been suggested as a cause. The hyperviscous blood leads to pulmonary hypertension, symptoms of cerebral hypoperfusion, and eventually right heart failure and death.

Inhibition of the alpha(1D)-adrenergic receptor gene by RNA interference (RNAi) in rat vascular smooth muscle cells and its effects on other adrenergic receptors

Sympathetic-induced vasoconstriction is mediated by various adrenergic receptor (AR) subtypes located on membranes of vascular smooth muscle cells (VSMC) located on the arterial wall, but is mostly attributed to activation of the alpha(1D)-AR. In order to study interaction and cross-talk among AR genes, we induced post-transcriptional silencing of the alpha(1D)-AR gene in cultured VSMC using the RNAi technique. A pSEC neo expression plasmid vector containing a small interfering RNA (siRNA) sequence selected to bind to the targeted mRNA of the alpha(1D)-AR gene was transfected into cultured VSMC from rat aorta. The RNA expression of all AR-subtype genes was assessed by Q-RT-PCR and the alpha(1D) and alpha(2A)-AR proteins quantified by Western blot. In siRNA-transfected cells, the alpha(1D)-AR protein levels decreased by 55%, 69% and 75% at 24 h, 48 h and 72 h, respectively (p<0.03-0.01) with progressive increases in its gene expression by 50%-61% and concurrent increase in alpha(2A)-AR protein peaking at 48 h. Decreases were noted in expression of the alpha(1A), alpha(2A), and beta(3) AR genes. We conclude that post-transcriptional silencing of the alpha(1D)-AR gene leads to significant decrease in receptor protein despite reactive increase in gene expression. However, suppression of one AR leads to reactive changes in other subtypes, indicating that cross-talk among related genes, whose products have overlapping functions, may partly offset anticipated effects in vivo.

TDIQ (5,6,7,8-tetrahydro-1,3-dioxolo [4,5-g]isoquinoline): discovery, pharmacological effects, and therapeutic potential

Chemically, TDIQ (5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline) can be viewed as a conformationally restricted phenylalkylamine that is related in structure to amphetamine but does not stimulate (or depress) locomotor activity in rodents. In radioligand binding studies TDIQ displays selective affinity for alpha(2)-adrenergic receptor subsites (i.e., alpha(2A)-, alpha(2B)-, and alpha(2C)-adrenergic receptors), and behavioral data suggest that it might exert an agonist (or partial agonist) effect at alpha(2)-adrenergic receptors or interact at alpha(2)-adrenergic heteroreceptors. Drug discrimination studies in rats indicate that TDIQ: (1) serves as a discriminative stimulus, (2) may be useful in the treatment of symptoms associated with the abuse of cocaine, and (3) exhibits a low potential for abuse. In addition, TDIQ exhibits a dose-dependent and wide dissociation between doses that produce an anxiolytic-like effect or an inhibition of "snack" consumption in mice and doses that produce minimal, if any, effects in tests that measure a potential for disruption of coordinated movement or motor activity. Also, TDIQ displays negligible effects on the heart rate (HR) and blood pressure (BP) of mice. Taken together, the preclinical data suggest that TDIQ exhibits a favorable ratio of therapeutic-like effects (anxiolytic, therapeutic adjunct in the treatment of cocaine abuse, and appetite suppression) to side effect-like activities (behavioral impairment, drug abuse, or adverse cardiovascular effect). As such, TDIQ could: (1) be a forerunner for a new type of chemical entity in the treatment of certain forms of anxiety and/or obesity and (2) serve as a structural template in the discovery and development of additional agents that might be selective for alpha(2)-adrenergic receptors.

Antihypertensive drugs clonidine, diazoxide, hydralazine and furosemide regulate the production of cytokines by placentas and peripheral blood mononuclear cells in normal pregnancy

BACKGROUND

Antihypertensive drugs such as clonidine, diazoxide, hydralazine and furosemide are used in the hypertensive disorders of pregnancy to control blood pressure, but it is not clear if they modulate the production of placental or circulating cytokines.

OBJECTIVE

To examine the effect of pharmaceutical doses of well known antihypertensive drugs used for blood pressure control on the production of the cytokines interleukin (IL)-6, IL-10 and tumour necrosis factor (TNF)-alpha in placental tissue and peripheral blood mononuclear cells (PBMCs) in normal pregnancy.

DESIGN

Placental biopsies were taken from the decidual surface of placentas after delivery of normal pregnancies (n = 6) and PBMCs were separated from the whole blood of normal term pregnant women (n = 7). Both villous explants and PBMCs were cultured with increasing concentrations of antihypertensive drugs. The dose effect of drugs on the production of placental and circulating cytokines (IL-6, IL-10 and TNF-alpha) were examined by enzyme-linked immunosorbent assay.

RESULTS

Placental production of IL-10 was not affected by clonidine, but decreased significantly after incubation of the tissue with diazoxide, hydralazine or furosemide. Production of IL-10 by PBMCs increased significantly: by from 3.4 +/- 2.7% [16.3 pg/ml (range 6.1-21.5 pg/ml)] to 24.5 +/- 3.3% [30.4 pg/ml (range 16.9-34.8 pg/ml)] with increasing concentrations of clonidine (0.08-1.3 microg/ml), and by 8.8 +/- 3.5% [4.1 pg/ml (range 3.0-17.8 pg/ml)] and 17.2 +/- 1.9% [22.6 pg/ml (range 13.2-23.2 pg/ml)] with lower doses of hydralazine (6.3 and 12.5 microg/ml) (all P values < 0.05). There was a stepwise reduction in production of TNF-alpha and IL-6 with increasing doses of diazoxide, hydralazine and furosemide by placentas and PBMCs from these women with normal pregnancies.

CONCLUSION

Our data suggest that the antihypertensive drugs clonidine and hydralazine can stimulate production of the circulating anti-inflammatory cytokine IL-10, whereas furosemide and diazoxide inhibit the production of this cytokine and the proinflammatory cytokines TNF-alpha and IL-6 by placentas and PBMCs.

Loss of alpha2B-adrenoceptors increases magnitude of hypertension following nitric oxide synthase inhibition

Vascular alpha(2B)-adrenoceptors (alpha(2B)-AR) may mediate vasoconstriction and contribute to the development of hypertension. Therefore, we hypothesized that blood pressure would not increase as much in mice with mutated alpha(2B)-AR as in wild-type (WT) mice following nitric oxide (NO) synthase (NOS) inhibition with N(omega)-nitro-l-arginine (l-NNA, 250 mg/l in drinking water). Mean arterial pressure (MAP) was recorded in heterozygous (HET) alpha(2B)-AR knockout mice and WT littermates using telemetry devices for 7 control and 14 l-NNA treatment days. MAP in HET mice was increased significantly on treatment days 1 and 4 to 14, whereas MAP did not change in WT mice (days 0 and 14 = 113 +/- 3 and 114 +/- 4 mmHg in WT, 108 +/- 0.3 and 135 +/- 13 mmHg in HET, P < 0.05). MAP was significantly higher in HET than in WT mice days 10 through 14 (P < 0.05). Thus blood pressure increased more rather than less in mice with decreased alpha(2B)-AR expression. We therefore examined constrictor responses to phenylephrine (PE, 10(-9) to 10(-4) M) with and without NOS inhibition to determine basal NO contributions to arterial tone. In small pressurized mesenteric arteries (inner diameter = 177 +/- 5 microm), PE constriction was decreased in untreated HET arteries compared with WT (P < 0.05). l-NNA (100 microM) augmented PE constriction more in HET arteries than in WT arteries, and responses were not different between groups in the presence of l-NNA. Acetylcholine dilated preconstricted arteries from HET mice more than arteries from WT mice. Endothelial NOS expression was increased in HET compared with WT mesenteric arteries by Western analysis. Griess assay showed increased NO(x) concentrations in HET plasma compared with those in WT plasma. These data demonstrate that diminished alpha(2B)-AR expression increases the dependence of arterial pressure and vascular tone on NO production and that vascular alpha(2B)-AR either directly or indirectly regulates vascular endothelial NOS function.

TDIQ (5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline) exhibits anxiolytic-like activity in a marble-burying assay in mice

Numerous studies have suggested that the central alpha2-adrenergic receptor system may exert an important role in some types of human anxiety. The anxiolytic-like activity and potential side effect-like activities of the novel and purported alpha2-adrenergic compound TDIQ (5,6,7,8-1,3-dioxolo[4,5-g]isoquinoline) were compared to those of the anxiolytic drugs diazepam and buspirone, and the nonselective alpha2-adrenergic agent clonidine. Anxiolytic-like behavior was assessed in an object (marble)-burying assay, a selective test for the evaluation of known anxiolytics and identification of putative antianxiety compounds, that used mice housed either alone or in groups (5/cage). The rodents' antianxiety-like effect was defined as dose-related increases in the number of marbles that remained uncovered in their bedding material without concomitant disruption of their motor activities. Rotarod and inclined screen procedures were employed as potential indicators of side effects. An additional test monitored the heart rate (HR) and blood pressure (BP) of mice after the intravenous (IV) administration of doses of TDIQ. The reference compounds inhibited marble-burying behavior in a dose-related manner and produced various degrees of impairment in the side effect tests. TDIQ also inhibited object burying and displayed a wide separation between doses that produced anxiolytic-like activity and doses that produced some, if any, disruption of coordinated movement and/or motor activity. Moreover, the IV administration of TDIQ, up to 10 mg/kg, produced negligible effects on the HR and BP of mice. TDIQ could be a lead candidate for a new type of structural compound in the treatment of certain forms of anxiety.

Pathophysiologie der chronischen Herzinsuffizienz

Heart failure is a progressive and often fatal disease process. In general, the pathophysiologic mechanisms responsible for progressive myocyte dysfunction and cell loss, cardiac remodeling and arrhythmias involve signaling mechanisms that alter myocardial gene expression. These changes in gene expression are complex and involve contractile proteins, ion channels, Ca(++) handling, apoptosis, cell metabolism, the extracellular matrix, signal transduction pathways and growth factors. In the failing heart, several changes occur in cardiac adrenergic receptor-signal transduction pathways. The most striking of these changes occur in beta-adrenergic receptors, and of the changes in beta-adrenergic receptors beta1-receptor down-regulation is the most prominent. Other changes include uncoupling of beta2-adrenergic receptors and increased activity of the inhibitory G-protein. Most of these changes appear to be related to increased activity of the adrenergic nervous system, i.e. increased exposure to norepinephrine. Antagonists of the adrenergic nervous system may improve left ventricular function and outcome in patients with heart failure. This fact supports the notion that activation of these neurohormonal systems exerts a net long-term detrimental effect on the natural history of chronic heart failure and that myocardial adrenergic desensitization phenomena are at least partially maladaptive in the setting of left ventricular dysfunction. In addition to functional alterations structural remodeling plays a major role in the progression of various heart diseases to congestive heart failure. Major contributors to this remodeling process in the heart include alterations in myocyte shape, myocyte number and extracellular matrix. However, it is unclear as to which of these changes is most critical in the development of congestive heart failure, and this may vary by etiology.

Alpha(2)-adrenergic receptor signalling in hypertension

Cardiovascular regulation by the sympathetic nervous system is mediated by activation of one or more of the nine known subtypes of the adrenergic receptor family; alpha(1A)-, alpha(1B)-, alpha(1D)-, alpha(2A)-, alpha(2B)-, alpha(2C)-, beta(1)-, beta(2)- and beta(3)-ARs (adrenoceptors). The role of the alpha(2)-AR family has long been known to include presynaptic inhibition of neurotransmitter release, diminished sympathetic efferent traffic, vasodilation and vasoconstriction. This complex response is mediated by one of three subtypes which all uniquely affect blood pressure and blood flow. All three subtypes are present in the brain, kidney, heart and vasculature. However, each differentially influences blood pressure and sympathetic transmission. Activation of alpha(2A)-ARs in cardiovascular control centres of the brain lowers blood pressure and decreases plasma noradrenaline (norepinephrine), activation of peripheral alpha(2B)-ARs causes sodium retention and vasoconstriction, whereas activation of peripheral alpha(2C)-ARs causes cold-induced vasoconstriction. In addition, non-selective agonists elicit endothelium-dependent vasodilation and presynaptic inhibition of noradrenaline release. The evidence that each of these receptor subtypes uniquely participates in cardiovascular control is discussed in this review.

Oral clonidine pretreatment prior to venous cannulation

Clonidine is a preferential alpha-2 agonist drug that has been used for over 35 years to treat hypertension. Recently, it has also been used as a preoperative medication and as a sedative/anxiolytic drug. This randomized, double-blind, placebo-controlled crossover clinical trial characterized the effects of oral clonidine pretreatment on intravenous catheter placement in 13 patients. Parameters measured included the bispectral index (BIS), Observer's Assessment of Alertness/Sedation Scale (OAA/S), frontal temporal electromyogram (EMG), 30-Second Blink Count (Blink), Digit Symbol Substitution Test (DSST), State Anxiety Inventory (SAI), fingertip versus forearm skin temperatures, and multiple questionnaires. Oral clonidine significantly decreased SAI scores, OAA/S, EMG, and Blink, but did not cause statistically significant BIS or DSST reductions. Subjects preferred oral clonidine pretreatment prior to venipuncture compared to placebo. Questionnaires also indicated that clonidine provided minimal sedation, considerable anxiolysis, and some analgesia. Fingertip versus forearm skin temperature differentials were decreased. Reduced fingertip versus forearm temperature differentials suggest increased peripheral cutaneous blood flow prior to venous cannulation. Oral clonidine pretreatment not only helped control patient anxiety and pain but also provided cardiovascular stability.

Role of alpha2A-adrenoceptors in the effects of MDMA on body temperature in the mouse

3,4-Methylenedioxymetamphetamine (MDMA) produces complex effects on body temperature, including hypo- and hyperthermic components that vary with ambient temperature and strain of rat. We have previously reported that MDMA is an alpha(2)-adrenoceptor agonist, and alpha(2)-adrenoceptor agonists such as clonidine produce hypothermia. The purpose of this study was to investigate the effects of MDMA on core body temperature measured by radiotelemetry in conscious wild-type (WT) and alpha(2A)-knockout (alpha(2A)-KO) mice. Clonidine (0.1 mg kg(-1), subcutaneously (s.c.)) produced a hypothermic response in WT mice, but did not significantly affect temperature in alpha(2)-KO mice. MDMA (20 mg kg(-1), s.c.) produced a significant hyperthermia in WT mice beginning at approximately 100 min after injection, recovering by 300 min, but produced a biphasic response, hypothermia followed by hyperthermia, in alpha(2)-KO mice. In WT mice, following the alpha(2A)-adrenoceptor antagonist 2-((4,5-dihydro-1H-imidazol-2-yl)methyl)-2,3-dihydro-1-methyl-1H-isoindole (1 mg kg(-1), s.c.), MDMA (20 mg kg(-1)) produced an initial hypothermia. Hence, alpha(2)-adrenoceptor agonist actions of MDMA contribute to its effects on body temperature, but in a surprising way. Although selective alpha(2A)-adrenoceptor agonism produces hypothermia, the alpha(2A)-adrenoceptor actions of MDMA alter the body temperature response to MDMA from biphasic (hypothermia followed by hyperthermia) to monophasic hyperthemia.

Cardiovascular and metabolic phenotypes in relation to the ADRA2B insertion/deletion polymorphism in a Chinese population

OBJECTIVE

The functional ADRA2B I/D polymorphism is associated with various cardiovascular and metabolic phenotypes in Caucasians. The purpose of our study was to investigate whether the ADRA2B I/D polymorphism is associated with such phenotypes in a Chinese population.

METHODS

We enrolled 247 women and 234 men in a family-based Chinese study. Our statistical methods included generalized estimating equations and quantitative transmission disequilibrium test.

RESULTS

The I allele (62.3 versus 50.8%, P = 0.015) and the II genotype (40.9 versus 23.4%, P = 0.017) were more prevalent among hypertensive than normotensive men. While adjusting for covariates and family clusters, male II homozygotes compared with D-allele carriers had higher systolic pressure (130.0 versus 125.0 mmHg, P = 0.016) and a 2.61 times greater (P = 0.008) risk of hypertension. On the other hand, II homozygous men had lower body weight (65.4 versus 69.6 kg, P = 0.008), body mass index (23.4 versus 24.5 kg/m2, P = 0.037), waist-to-hip ratio (0.838 versus 0.857, P = 0.024), serum insulin concentration (9.5 versus 13.2 mU/l, P = 0.026) and insulin resistance (homeostasis model assessment index 2.4 versus 3.2, P = 0.051). None of these associations reached statistical significance in women. In 65 informative male offspring, transmission of the I allele was associated with higher systolic pressure (+ 6.0 mmHg, P = 0.10), diastolic pressure (+ 5.5 mmHg, P = 0.021), and faster pulse rate (+ 5.8 beats/min, P = 0.019).

CONCLUSION

In Chinese men, the I allele of the ADRA2B gene is associated with higher blood pressure, but also with a more favourable metabolic phenotype.

Molecular-specific effects of angiotensin II antagonists: clinical relevance to treating hypertension?

Angiotensin II receptor blockers (ARBs) may produce a number of molecule-specific effects that appear to be independent of interaction with the angiotensin II type 1 (AT1)-receptor. These include antagonism of the thromboxane A2 receptor, inhibition of platelet aggregation, induction of peroxisome proliferator- activated receptor gamma (PPARgamma) activity, and reduction of serum uric acid levels. However, definitive evidence is lacking that these molecule-specific effects give rise to a therapeutic advantage of one ARB over another. Currently, the possibility of a link between a molecule-specific effect of an ARB and an improvement in clinical outcomes is best illustrated by a reduction in serum uric acid levels with losartan. Data from Losartan Intervention For Endpoint reduction in hypertension (LIFE) study suggest a treatment-induced decrease in serum uric acid may contribute to the treatment benefit of a losartan-based versus atenolol-based therapy on the composite endpoint (death, myocardial infarction, or stroke). This finding should prompt further studies to investigate the long-term cardioprotective benefits issue of reducing hyperuricaemia in hypertensive patients.

Activation of 5-HT1A receptors in the medullary raphe reduces cardiovascular changes elicited by acute psychological and inflammatory stresses in rabbits

The present strategy for the prevention of excessive sympathetic neural traffic to the heart relies on the use of beta-blockers, drugs that act at the heart end of the brain-heart axis. In the present study, we attempted to suppress cardiac sympathetic nerve activity by affecting the relevant cardiomotoneurons in the brain using the selective serotonin-1A (5-HT(1A)) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). In conscious, unrestrained rabbits, instrumented for recordings of heart rate, arterial pressure, or cardiac output, we provoked increases in cardiac sympathetic activity by psychological (loud sound, pinprick, and air jet) or inflammatory (0.5 microg/kg iv lipopolysaccharide) stresses. Pinprick and air-jet stresses elicited transient increases in heart rate (+50 +/- 7 and +38 +/- 4 beats/min, respectively) and in mean arterial pressure (+16 +/- 2 and +15 +/- 3 mmHg, respectively). Lipopolysaccharide injection caused sustained increases in heart rate (from 210 +/- 3 to 268 +/- 10 beats/min) and in arterial pressure (from 74 +/- 3 to 92 +/- 4 mmHg). Systemically administered 8-OH-DPAT (0.004-0.1 mg/kg) substantially attenuated these responses in a dose-dependent manner. Drug effects were prevented by a selective 5-HT(1A) receptor antagonist, WAY-100635 (0.1 mg/kg iv). Similarly to systemic administration, microinjection of 8-OH-DPAT (500 nl of 10 mM solution) into the medullary raphe-parapyramidal region caused antitachycardic effects during stressful stimulation and during lipopolysaccharide-elicited tachycardia. This is the first demonstration that activation of 5-HT(1A) receptors in the medullary raphe-parapyramidal area causes suppression of neurally mediated cardiovascular changes during acute psychological and immune stresses.

Haplotype-based analysis of alpha 2A, 2B, and 2C adrenergic receptor genes captures information on common functional loci at each gene

The alpha 2-adrenergic receptors (alpha2-AR) mediate physiological effects of epinephrine and norepinephrine. Three genes encode alpha2-AR subtypes carrying common functional polymorphisms (ADRA2A Asn251Lys, ADRA2B Ins/Del301-303 and ADRA2C Ins/Del322-325). We genotyped these functional markers plus a panel of single nucleotide polymorphisms evenly spaced over the gene regions to identify gene haplotype block structure. A total of 24 markers were genotyped in 96 Caucasians and 96 African Americans. ADRA2A and ADRA2B each had a single haplotype block at least 11 and 16 kb in size, respectively, in both populations. ADRA2C had one haplotype block of 10 kb in Caucasians only. For the three genes, haplotype diversity and the number of common haplotypes were highest in African Americans, but a similar number of markers (3-6) per block was sufficient to capture maximum diversity in either population. For each of the three genes, the haplotype was capable of capturing the information content of the known functional locus even when that locus was not genotyped. The alpha2-AR haplotype maps and marker panels are useful tools for genetic linkage studies to detect effects of known and unknown alpha2-AR functional loci.

Cellular mechanisms in sympatho-modulation of the heart

Cardiovascular function relies on complex servo-controlled regulation mechanisms that involve both fast-acting feedback responses and long-lasting adaptations affecting the gene expression. The adrenergic system, with its specific receptor subtypes and intracellular signalling cascades provides the major regulatory system, while the parasympathetic system plays a minor role. At the molecular level, Ca(2+) acts as the general signal trigger for the majority of cell activities including contraction, metabolism and growth. During recent years, important new results have emerged allowing an integrated view of how the multifarious Ca(2+)-signalling mechanisms transmit adrenergic impulses to intracellular target sites. These insights into cellular and molecular mechanisms are pivotal in improving pharmacological control of the sympathetic responses to surgical trauma and perioperative stress. They are examined in detail in this review, with particular emphasis being given to the differences in intracellular signalling between cardiomyocytes and vascular smooth muscle cells.

Effect of Clonidine on Cardiac Norepinephrine Spillover in Isolated Rat Heart

The purpose of this study is to determine the effect of clonidine on cardiac norepinephrine spillover utilizing an isolated rat heart preparation with attached cardiac sympathetic nerves. Following a 20-minute stabilization period, the sympathetic ganglion for each heart preparation was electrically stimulated with 10V and 2 Hz for 30 seconds (S1: 60 pulses). Heart rate, left ventricular developed pressure, and coronary perfusion pressure was allowed to return to baseline and the perfusate was randomly switched to Krebs buffer containing one of two treatments: placebo or clonidine (1 microM). After 10 minutes of treatment, the sympathetic ganglion was again electrically stimulated with 10V and 2 Hz for 30 seconds (S2: 60 pulses). The perfusate exiting the heart before, during, and after each electrical stimulation was collected for the determination of cardiac norepinephrine spillover. Clonidine administration significantly reduced cardiac norepinephrine spillover by approximately 50% (P < 0.05) and was associated with a 36% reduction in heart rate (P < 0.05). These findings provide evidence that clonidine can directly suppress NE spillover from cardiac sympathetic nerve terminals. Thus, suppression of cardiac NE by clonidine may be due to stimulation of presynaptic alpha2-adrenergic receptors or imidazoline subtype I receptors located on cardiac sympathetic nerve terminals. Results from our study demonstrate a reduction in cardiac NE spillover by clonidine and provide additional evidence that it can directly suppress peripheral sympathetic activity in that our results were obtained utilizing an isolated perfused heart preparation with attached cardiac sympathetic nerves devoid of any CNS input.