Beta-adrenergic Responsiveness Research Articles

P.2.a.007 Beta-adrenergic receptor responsiveness may predict treatment response in panic disorder

P.2.a.007 Beta-adrenergic receptor responsiveness may predict treatment response in panic disorder

Effect of repeated administration of clenbuterol on the regulation of beta-adrenoceptors in the central nervous system of the rat.

The effect of the centrally acting beta-adrenoceptor agonist clenbuterol on beta-adrenergic responsiveness, beta-receptor density and N-protein coupling was studied in the rat cerebral cortex (which contains primarily beta 1-receptors) and cerebellum (containing mostly beta 2-receptors). The objective was to determine whether clenbuterol's effect on these variables was similar to that produced by standard antidepressants. When given to rats repeatedly, clenbuterol caused a decrease in beta-adrenergic responsiveness in slices from either the cerebral cortex or the cerebellum. The decreased beta-responsiveness in the cerebellum was associated with a decrease both in the density of beta-receptors and in receptor/N-protein coupling. In the cortex, only reduced receptor/N-protein coupling was observed by in vitro ligand-binding methods. However, when quantitative autoradiography was employed, clenbuterol treatment was found to reduce the binding of [125I]iodopindolol to beta 2-receptors throughout the brain, whereas binding to beta 1-receptors was not reduced. The down-regulation of beta 2-receptors by clenbuterol is due to its acting centrally as a beta 2-agonist. Although clenbuterol has about an equal affinity for beta 1-receptors and beta 2-receptors, no evidence was found for agonist activity of this drug at beta 1-receptors in the cerebral cortex. The strategies described here should be helpful in investigating important properties of centrally acting beta-agonists that might have potential as antidepressants.

Multi-parameter in vivo cardiac magnetic resonance imaging demonstrates normal perfusion reserve despite severely attenuated β-adrenergic functional response in neuronal nitric oxide synthase knockout mice

The role of neuronal nitric oxide synthase (nNOS) in regulating contractile function remains controversial, and in regulating myocardial perfusion is uninvestigated. We used magnetic resonance imaging (MRI) to phenotype nNOS(-/-) and wild-type (WT) mice regarding left ventricular (LV) structure, baseline function, beta-adrenergic responsiveness, and perfusion reserve. Cine MRI showed higher LV mass to end-diastolic volume ratio (2.3 +/- 0.2 mg/microL nNOS(-/-) vs. 1.7 +/- 0.1 mg/microL WT; P=0.032) and LV ejection fraction (64.9 +/- 2.1% nNOS(-/-) vs. 55.8 +/- 1.1% WT; P = 0.003) in nNOS(-/-). Myocardial tagging demonstrated similar baseline systolic circumferential strain (Ecc) in nNOS(-/-) and WT. With dobutamine, the normal change in Ecc was nearly absent in nNOS(-/-) (-0.5 +/- 0.3% nNOS(-/-) vs. -2.2 +/- 0.3% WT; P = 0.001), and the systolic strain rate (dEcc/dt) response to dobutamine seen in WT was reduced in nNOS(-/-) (-29 +/- 13%/s nNOS(-/-) vs. -106+/-16%/s WT; P = 0.001). Diastolic strain rate increased significantly with dobutamine only in WT. Arterial spin labelling showed that baseline perfusion and perfusion reserve with either dobutamine or an adenosine receptor agonist are normal in nNOS(-/-). MRI provides non-invasive in vivo evidence that nNOS does not play a role in basal contractile function or myocardial perfusion, but is required for increasing cardiac inotropy and lusitropy upon beta-adrenergic stimulation.

A new mechanism for respiratory syncytial virus-induced β2-adrenergic receptor insensitivity

respiratory syncytial virus (RSV) is the most common infectious cause of wheezing in infants and children and is a frequent initiator of acute asthma exacerbations ([13][1]). The mechanism by which RSV results in airway obstruction is not completely understood but includes an increase in airway

Cardiomyocytes as effectors of nitric oxide signalling

Nitric oxide (NO) generated constitutively within the heart has long been known to influence myocardial function; however, the precise nature of these effects has been controversial--at least in part--because of the experimental use of non-isoform-selective inhibitors of NO synthases (NOS) and unwarranted extrapolation from results obtained with NO donors. Recent studies using NOS-selective inhibitors and genetically modified models are beginning to redress the balance. It is well established that agonist-stimulated release of NO from eNOS in the coronary endothelium exerts paracrine effects on cardiomyocytes, predominantly affecting the timing of relaxation as well as myocardial oxygen consumption. A significant recent advance has been the finding that both eNOS and nNOS are constitutively expressed in distinct subcellular locations within cardiomyocytes. The relative autocrine role of these isoforms in the cardiomyocyte remains to be fully clarified but evidence suggests that the autocrine effects of nNOS may include the modulation of basal inotropy and relaxation, beta-adrenergic responsiveness, and the force-frequency relationship. Myocardial eNOS, on the other hand, may be involved in mediating the inotropic response to sustained stretch. These effects may change significantly in the diseased heart where the expression, activity and/or coupling of NOS isoforms to downstream effectors may be altered. In this article, we review the current understanding of this important but complex field, focussing particularly on contractile function and on recent advances in knowledge regarding the autocrine functions of nNOS-derived NO.

Effect of cold adaptation of α-and β-adrenergic responses of blood pressure in hindlimb and small intestine in situ and systemic blood pressure in rabbits

Changes in the main parameters of alpha- and beta-adrenergic responses, sensitivity to agonists (EC50) and maximum response (Pm) of hindlimb and small intestinal blood pressure in situ and systemic blood pressure were studied in rabbits adapted to cold for 1-30 days (daily exposures to -10 degrees C for 6 h). The responses to phenylephrine, noradrenaline. adrenaline, clonidine (alpha-agonists), and isopropylnoradrenaline (beta-agonist) corresponded to the equation p = (PmAn)/(EC50n + An) with n = 1 and n = 2, respectively. Cold adaptation induced reciprocal changes in the response of both EC50 and Pm to alpha-agonists and in the response of Pm alone to isopropylnoradrenaline. The significant differences of the parameters from control observed during the first 5 days of adaptation gradually decreased by day 30. After 10 days of adaptation, the efficiency (E = Pm/2EC50) of response to alpha- and beta-agonists of adrenoceptors significantly increased.

Defective Adrenergic Responses in Patients With Arsenic-induced Peripheral Vascular Disease

Blackfoot disease is an endemic arsenic-induced peripheral vascular disease in southern Taiwan. The main pathologic feature is atherosclerosis, which may relate to imbalances of the adrenergic system. The purpose of this study is to investigate the peripheral adrenergic responses of patients with blackfoot disease. Eight patients with blackfoot disease and four age-matched healthy controls were enrolled in this study. Baseline cutaneous perfusion was measured with a laser Doppler flowmeter. The response of alpha-adrenoceptors in the cutaneous microcirculation was assessed with laser Doppler flowmetry with iontophoresis of phenylephrine into the nailfold. In vitro binding with (125)I-cyanopindolol determined beta-adrenoceptor density in lymphocytes. The cyclic adenosine monophosphate (cAMP) level at baseline and after isoproterenol stimulation reflects lymphocyte beta-adrenergic responsiveness. Results revealed persistently decreased skin perfusion in patients with blackfoot disease. In contrast, there was a transient decrease in skin perfusion in healthy controls after iontophoresis of phenylephrine. Both beta-2 receptor density and isoproterenol-stimulated cAMP levels in lymphocytes decreased. Increased peripheral alpha-adrenergic response and decreased beta-2-adrenergic response are related to increased vascular tone and result in atherosclerosis. Our findings of accentuated alpha-adrenergic response in microcirculation and decreased lymphocyte beta-2-adrenoceptor response play an important role in the pathogenesis of atherosclerosis in blackfoot disease.

Gender Differences in Na/Ca Exchanger Current and β‐Adrenergic Responsiveness in Heart Failure in Pig Myocytes

Clinical trials suggest females experience less heart failure (HF) progression, mortality, and arrhythmia frequency. HF increases Na/Ca exchanger (NCX) expression and activity contributing to both depressed contractility and ventricular arrhythmias, but whether gender modifies this effect is unknown. Left ventricular myocytes were isolated from control and from tachycardic pacing-induced failing swine hearts of both sexes. The Ni-sensitive NCX current (I(NCX)) was measured in voltage clamp after blocking other channels. In control myocytes there is no difference in basal I(NCX) and beta-adrenergic responsiveness between male and female animals. HF greatly increased I(NCX) and reduced beta-adrenergic responsiveness in males compared to females, an effect that was eliminated by PP1. Diuretic therapy (furosemide, 1 mg/kg/day) further enhanced I(NCX) and reduced beta-adrenergic responsiveness in females and eliminated the gender difference. Gender-specific differences in calcium handling may contribute to improved survival of females in HF.

A matched crossover design for clinical trials

Two design principles are used frequently in clinical trials: 1) A subject is “matched” or “paired” with a similar subject to reduce the chance that other variables obscure the primary comparison of interest. 2) A subject serves as his/her own control by “crossing over” from one treatment to another during the course of an experiment. There are situations in which it may be advantageous to use the two design principles — crossing over and matching — simultaneously. That is, it may be advantageous to conduct a “paired crossover design,” in which each subject, while paired with a similar subject, crosses over and receives each experimental treatment. In this paper, we describe two clinical trials conducted by the National Heart, Lung and Blood Institute's Asthma Clinical Research Network that used a paired 2 × 2 crossover design. The Beta Adrenergic Response by GEnotype (BARGE) Study compared the effects of regular use of inhaled albuterol on mildly asthmatic patients with different genotypes at the 16th position of the beta-agonist receptor gene. The Smoking Modulates Outcomes of Glucocorticoid (SMOG) Therapy in Asthma Study evaluated the hypothesis that smoking reduces the response to inhaled corticosteroids. For such paired crossover designs, the primary parameter of interest is typically the treatment-by-pairing interaction term. In evaluating the relative efficiency of the paired 2 × 2 crossover design to two independent crossover designs with respect to this interaction term, we show that the paired 2 × 2 crossover design is more efficient if the correlations between the paired members on the same treatments are greater than their correlations on different treatments. This condition should hold in most circumstances, and therefore the paired crossover design deserves serious consideration for any clinical trial in which the crossing over and matching of subjects is deemed simultaneously beneficial.

Blunted Beta Adrenergic Responsiveness in Prenatally Stressed Rats

We previously reported a significant decrease in percentage fractional shortening (%FS) in pre-natally stressed rats (PS) + restraint (R) compared with the non pre-natally stressed rats (C) + R (45.8¡À3.9 vs 61.9¡À2.4 %FS; n=12; p<0.01) by echocardiography in anesthetized rats. No differences in %FS were noted between PS + R vs C without R. We now report a defect in beta adrenergic responsiveness in PS + R compared with C without R. In vivo hemodynamics were measured in awake rats using polyurethane tubing inserted percutaneously into the left ventricle and the right femoral artery. Drugs were administered through a right external jugular vein catheter. PS + R had increased heart rates and mean blood pressures compared with age and sex matched C without R (412¡À22 bpm vs 374¡À14 bpm; n=6–8; p<0.01) (134.6¡À6.1 vs 117.0¡À5.1 mmHg; p<0.01). There was no significant difference in positive and negative left ventricular dp/dt between PS + R and C without R (12297¡À328 vs 11557¡À998 +dp/dt mmHg/s; 9572¡À396 vs 9385 ¡À 862 ¨Cdp/dt mmHg/s; n=6–8; p>0.5). However, PS + R had a significantly diminished negative left ventricular dp/dt in response to increasing doses (from 25 to 400 ng/kg) of isoproterenol vs C without R (9511¡À981 vs10771¡À423; 10015¡À1137 vs 11552¡À396; 9589¡À1402 vs 12170¡À159; 10030¡À1375 vs 12098¡À408; 10704¡À1363 vs 12556¡À485 ¨Cdp/dt mmHg; n=6–8; p<0.01). We conclude that PS + R affects beta adrenergic signaling in vivo.

PDK-1 plays a crucial role in cell size regulation, beta-adrenergic response and cell survival in the heart

PDK-1 plays a crucial role in cell size regulation, beta-adrenergic response and cell survival in the heart

PDK-1 Plays Essential Roles in the Regulation of Cell Size, Beta-adrenergic Response and Cell Survival in the Heart

PDK-1 Plays Essential Roles in the Regulation of Cell Size, Beta-adrenergic Response and Cell Survival in the Heart

Normal Aging Impairs Upregulation of the Beta-adrenergic but not the Alpha-Adrenergic Response: Aging and Adrenergic Upregulation

To determine if centrally reducing sympathetic tone with clonidine will reverse the downregulation in the alpha-adrenergic (alphaAR) and beta-adrenergic (betaAR) responses seen with normal aging. Twelve rigorously screened young adult (mean age, 26 years) and 15 older adult (mean age, 69 years) subjects were studied before and after using the clonidine patch (TTS-2) for 2 weeks. betaAR (isoproterenol at 35 ng/kg/min) and alphaAR (phenylephrine at 1.0 microg/kg/min) were assessed using radionuclide measures of end diastolic, end systolic, and stroke volume indices, cardiac index, and ejection fraction. Clonidine reduced resting plasma norepinephrine and this reduction was greater in older subjects (-47 +/- 3 versus -26 +/- 6%, P = 0.001). After 2 weeks of clonidine patch, upregulation of the betaAR was significantly higher in young subjects for heart rate (+10.7 +/- 1.5 versus +4.6 +/- 1.5 bpm; P = 0.01). There was no significant age-associated difference in the upregulation of the alphaAR with clonidine for systolic, diastolic, and mean blood pressure or systemic vascular resistance. With aging, there is an impaired resensitization of the chronotropic betaAR response with central sympathetic downregulation that is not seen with the alphaAR.

Prolonged treatment with the β3-adrenergic agonist CL 316243 induces adipose tissue remodeling in rat but not in guinea pig: 1) fat store depletion and desensitization of β-adrenergic responses

Beta3-adrenergic agonists have been considered as potent antiobesity and antidiabetic agents mainly on the basis of their beneficial actions discovered twenty years ago in obese and diabetic rodents. The aim of this work was to verify whether prolonged treatment with a beta3-adrenergic agonist known to stimulate lipid mobilisation, could promote desensitization of beta-adrenergic responses. Wistar rats and guinea pigs were treated during one week with CL 316243 (CL, 1 mg/kg/d) by implanted osmotic minipumps. In control animals, beta3-adrenergic agonists were lipolytic in rat but not in guinea pig adipocytes. CL-treatment did not alter body weight gain in both species, but reduced fat stores in rats. Lipolysis stimulation by forskolin was unmodified but responses to beta1-, beta2- and beta3-agonists were reduced in visceral or subcutaneous white adipose tissues of CL-treated rats. Similarly, the beta3-adrenergic-dependent impairment of insulin action on glucose transport and lipogenesis in rat adipocytes was diminished after CL-treatment. In rat adipocytes, [125I]ICYP binding and beta3-adrenoceptor mRNA levels were reduced after sustained CL administration. These findings show that CL 316243 exerts (beta3-adrenergic lipolytic and antilipogenic effects in rat adipocytes. These actions, which are likely involved in the fat depletion observed in rat, also lead to the desensitization of all beta-adrenergic responses. Therefore this desensitization, together with the lack of slimming action in guinea pig, seriously attenuates the usefulness of beta3-agonists as antiobesity agents, and may explain why such agonists have not been conducted to a widespread clinical use.

A new look at phospholamban in pressure-overload hypertrophy

THE QUESTION OF THE MECHANISMS of pathological cardiac hypertrophy and the relationship of changes in cellular function to a myriad of clinical symptoms has long been an important and intriguing puzzle to researchers. How is it that exercise induces signaling changes that are beneficial to heart function but pathological conditions such as hypertension or valvular disease are associated with a loss of hemodynamic function and neurohumoral response, although both produce muscular hypertrophy? What are the interactions between hypertrophic and contractile signaling pathways? One point of interest is the increase in sympathetic drive observed in the pressure-overloaded (PO) hypertrophic heart that is accompanied by decreased -adrenergic sensitivity and diminished contractile reserve. This condition is significant to patients in that it causes a loss of ability to tolerate exercise and can lead to myocyte death and heart failure, but the cellular changes underlying the loss of contractile reserve are not entirely clear. A number of researchers have identified mechanisms for this loss of contractile reserve, but this picture is not complete. One prominent mechanism involved in the loss of adrenergic response is a downregulation of -adrenergic receptor (-AR) density, which is improved by administration of -blockers (4). Another is upregulation of -receptor kinase 1 (or G proteincoupled receptor kinase 2, GRK2; see Ref. 1), which inactivates -ARs and is reversible by exercise training (2). In the current issue of the American Journal of PhysiologyHeart and Circulatory Physiology, Mills et al. (3) have addressed the question of what downstream mechanisms may be involved in the diminution of adrenergic contractile reserve using a feline model of PO-induced left ventricular hypertrophy. They propose that altered abundance or basal phosphorylation state of target regulatory proteins, specifically phospholamban (PLB), is a central cause of the loss of inotropic responsiveness in PO animals. They have presented compelling in vivo evidence that aortic banded animals have a blunted systolic function that is not restored with dobutamine, concurrent with reduced total PLB and a significant increase in total PLB phosphorylation that is mainly attributed to the calmodulin kinase II site, Thr 17 . They also report that the less the response to dobutamine, the greater the level of Thr 17 phos

Section 15: Management of Heart Failure in Special Populations

Section 15: Management of Heart Failure in Special Populations

Caveolae modulate excitation–contraction coupling and β2-adrenergic signalling in adult rat ventricular myocytes

Caveolae, flask shaped invaginations of the cell membrane, influence signalling cascades in many cell types. We have tested the hypothesis that caveolae modulate excitation-contraction coupling (ECC) and beta-adrenergic stimulation in the adult cardiac myocyte. Shortening, [Ca(2+)](i) and L-type Ca(2+) current (I(Ca,L)) were recorded in rat ventricular myocytes. Caveolae were disrupted with methyl-beta-cyclodextrin (MbetaC). Shortening and [Ca(2+)](i) transient amplitude were reduced in myocytes treated with MbetaC. MbetaC did not alter the density or characteristics of I(Ca,L) or the sarcoplasmic reticulum (SR) Ca(2+) load, but significantly reduced fractional SR Ca(2+) release. The inotropic response of myocytes to beta(1)-adrenoceptor stimulation was insensitive to caveolae disruption. By contrast, the increase in shortening, [Ca(2+)](i) transient and I(Ca,L) seen following beta(2) stimulation was markedly enhanced (3-5 fold) following MbetaC treatment, and the effect on I(Ca,L) could be mimicked by dialyzing cells with an antibody to caveolin 3. When the G(alphai) pathway was disabled with pertussis toxin (PTX), control cells showed a similar response to beta(2) stimulation as seen in MbetaC-treated myocytes, whereas MbetaC-treated cells were insensitive to PTX. Caveolae modulate ECC via the efficiency of the Ca(2+)-induced Ca(2+) release process, rather than Ca(2+) influx. Our data are also consistent with the hypothesis that interaction of G(i) protein cascade components with caveolin in the caveolae is necessary for effective signalling by this pathway. This suggests that changes in caveolin expression in the adult heart seen during aging and in disease will have consequences for baseline cardiac function and beta-adrenergic responsiveness.

The Impact of Blunted β-Adrenergic Responsiveness on Growth Regulatory Pathways in Hypertension

The effects of vasodilator hormones acting through receptors linked to adenylyl cyclase are impaired in the hypertensive state. This has been ascribed to impaired receptor-G protein coupling. However, these receptors also act via effectors not linked to adenylyl cyclase activation. These "alternate" mechanisms may be especially important in growth regulation and might be unaffected (or enhanced) with G protein-coupled receptor-G protein uncoupling. Therefore, we assessed the effects of beta-adrenergic activation on 1) regulation of phosphatidylinositol 3-kinase (PI3 kinase) and extracellular signal-regulated kinase (ERK) activation-two tyrosine kinase-dependent enzymes linked to cell growth-and 2) microarray analysis in vascular smooth muscle cells from spontaneously hypertensive rats (SHR). Isoproterenol-stimulated phosphorylation of ERK1/2 was impaired in SHR. The effect of forskolin was unaltered. In contrast, both vasopressin and angiotensin 2-mediated stimulation of ERK activation was enhanced in SHR. In addition, beta-adrenergic-mediated inhibition of PI3 kinase activity was attenuated in SHR (whereas the effect of forskolin remained intact). In microarray studies, the effect of isoproterenol to regulate transcription was significantly impaired in SHR (as was the effect of forskolin). Together, these data support the hypothesis that the blunted vasodilator effects of hormones linked to adenylyl cyclase activation are an index of a more generalized impairment in modulating growth regulatory pathways. Furthermore, this study supports the hypothesis that the blunting of beta-adrenergic responses relating to increased G protein-coupled receptor kinase 2 expression reflects a "generalized uncoupling" of beta-adrenergic-mediated responses and do not support the concept of "enhanced coupling" of "alternate" pathways of beta-adrenergic growth regulatory pathways in the hypertensive state.

Disruption of inhibitory G-proteins mediates a reduction in atrial β-adrenergic signaling by enhancing eNOS expression

Cardiac parasympathetic nerve activity is reduced in most cardiovascular disease states, and this may contribute to enhanced cardiac sympathetic responsiveness. Disruption of inhibitory G-proteins (Gi) ablates the cholinergic pathway and increases cardiac endothelial nitric oxide (NO) synthase (eNOS) expression, suggesting that NO may offset the impaired attenuation of beta-adrenergic regulation of supraventricular excitability. To test this, we investigated the role of endogenous NO production on beta-adrenergic regulation of rate (HR), contraction (CR) and calcium (Ca2+) handling in atria following blockade of Gi-coupled muscarinic receptors. Mice were administered pertussis toxin (PTx, n=105) or saline (C, n=100) intraperitoneally. After 3 days, we measured CR, HR, and NOS protein levels in isolated atria. Intracellular calcium (Ca2+) transients and Ca2+ current density (I(Ca)) were also measured in atrial myocytes. PTx treatment increased atrial myocyte eNOS protein levels compared to C (P<0.05). This did not affect basal atrial function but was associated with a significant reduction in the CR and HR response to isoprenaline (ISO) compared with C. NOS inhibition normalized responses in PTx atria with respect to responses in C atria (P<0.05), which were unaffected. Furthermore, PTx did not affect ISO-stimulated HR and CR in eNOS gene knockout mice (n=40). In agreement with these findings, the ISO-mediated increase in Ca2+ transient was suppressed in PTx-treated myocytes (P<0.05), whereas I(Ca) did not differ between groups. eNOS-derived NO inhibits beta-adrenergic responses following disruption of Gi signaling. This suggests that increased eNOS expression may be a compensatory mechanism which reduces beta-adrenergic regulation of heart rate when cardiac parasympathetic control is impaired.

Endothelin-1 and isoprenaline co-stimulation causes contractile failure which is partially reversed by MEK inhibition

The mitogen-activated kinase kinases (MEK)-extracellular signal-regulated kinases (ERK) signaling pathway is activated by agonists like catecholamines or endothelin-1 (ET-1) and has been implicated in cardiac pathology, such as the progression from cardiac hypertrophy to failure. The purpose of the present study, performed in an in vitro model of contractile failure, was to evaluate whether MEK inhibition prevents functional deterioration. Contractile dysfunction was induced in reconstituted rat heart tissue by concomitant treatment with ET-1 (10 nmol/l) and isoprenaline (ISO, 10 nmol/l) for 5 days. While basal force of contraction was unchanged, contractile responsiveness to beta-adrenoceptor agonists was markedly impaired (active force declined to 51% of controls) and was associated with decreased lusitropy. Moreover, in ET-1+ISO-treated heart tissues, reprogramming of gene expression was observed with an increased ratio of beta-myosin heavy chain (MHC) to alpha-MHC mRNA and increased transcript levels of ANF and skeletal/smooth muscle alpha-actin isoforms. The MEK inhibitor U0126 (10 micromol/l) almost completely prevented the reduction in beta-adrenergic responsiveness and the negative lusitropic effect of ET-1+ISO co-stimulation. In addition, U0126 completely normalized ANF gene expression, but did not affect or only marginally affected expression of MHC and alpha-actin isoforms. These results suggest that interruption of the MEK-ERK signaling pathway with a specific MEK inhibitor prevents, in part, the occurrence of a pathologic phenotype secondary to excessive stimulation with neurohumoral factors. The MEK-ERK pathway seems to be an important but not exclusive regulatory pathway responsible for the development of contractile dysfunction.