Structure and function of the beta 3-adrenergic receptor

Beta3-adrenergic receptors in cardiac and vascular tissues emerging concepts and therapeutic perspectives

Catecholamines released by the orthosympathetic system play a major role in the short- and long-term regulation of cardiovascular function. Beta1- and beta2-adrenoreceptors (ARs) have classically been considered as mediating most of their effects on cardiac contraction. After their initial cloning and pharmacologic characterization in the late 1980s, beta3-ARs have been mostly thought of as receptors mediating metabolic effects (e.g., lipolysis) in adipocytes. However, definitive evidence for their expression and functional coupling in cardiovascular tissues (including in humans) has recently initiated a re-examination of their implication in the pathophysiology of cardiovascular diseases. Distinctive pharmacodynamic properties of beta3-AR, e.g., their upregulation in disease and resistance to desensitization, suggest that they may be attractive targets for therapeutic intervention. They may substitute efficient vasodilating pathways when beta1/2-ARs are inoperative. In the heart, their contractile effects, which are functionally antipathetic to those of beta1/2-AR, may protect the myocardium against adverse effects of excessive catecholamine stimulation and perhaps mediate additional ancillary effects on key aspects of electrophysiology or remodeling. Longitudinal studies in animals and patients with different stages of heart failure are now needed to identify the optimal therapeutic scheme using specific combinations of agonists or antagonists at all three beta-ARs.

Uptake of propranolol, a cardiovascular pharmaceutical, from water into fish plasma and its effects on growth and organ biometry

Pharmaceuticals in the environment (PIE) are of importance since these compounds are designed to affect biological receptors/enzymes that are often conserved across vertebrate families. Across-species extrapolation of these therapeutic targets suggests potential for impacting amphibia and fish in the aquatic environment. Due to the scarcity of relevant ecotoxicological data, the long-tem impact of PIE remains a research question. Efficient use of mammalian data has been proposed to better understand and predict the potential for a given pharmaceutical to impact the environment. Using a model cardiovascular pharmaceutical (propranolol, a non-specific beta(1)/beta(2)-adrenergic antagonist), the hypothesis that mammalian data can be used to predict toxicity in fish was tested. Rainbow trout (Oncorhynchus mykiss (Walbaum)) have beta-adrenergic signalling mechanisms analogous to human cardiovascular receptors that respond to pharmacological doses of agonists and antagonists. Trout absorbed propranolol from water such that after 40 days of exposure, the linear relationship was [plasma] - 0.59[water] (n - 31, r - 0.96). Growth rate was affected only at very high aqueous concentrations (10-day (growth)NOEC - 1.0 and (growth)LOEC - 10 mg/l). Growth recovered with time (40-day (growth)NOEC - 10 mg/l), suggesting possible adaptation to the pharmaceutical, although the internal plasma concentration in trout exposed to 10mg propranolol/l of water was higher than the mammalian therapeutic plasma concentration. Additional endpoints suggested subtle changes of liver and heart size at much lower concentrations may have occurred, although these were not concentration-related. There was, however, a dose-dependent effect upon overall body condition. The trout plasma concentrations at these effective aqueous concentrations fell within the range of mammalian effective plasma concentrations, supporting the potential for developing 'read-across' from mammalian pharmacology safety data to fish ecotoxicology. Despite these effects at relatively high concentrations, propranolol is not expected to pose a risk to fish at the concentrations considered to be present in the aquatic environment.

The impact of alpha1-adrenoceptors up-regulation accompanied by the impairment of beta-adrenergic vasodilatation in hypertension

In human and animal hypertension models, increased activity of G-protein-coupled receptor kinase (GRK) 2 determines a generalized decrease of beta-adrenergic vasodilatation. We analyzed the possibility of differential changes in the expression and functionality of alpha(1A), alpha(1B), alpha(1D), beta(1), beta(2), and beta(3)-ARs also being involved in the process. We combined the quantification of mRNA levels with immunoblotting and functional studies in aortas of young and adult spontaneously hypertensive rats (SHRs) and their controls (Wistar Kyoto). We found the expression and function of beta(1)-adrenoceptors in young prehypertensive SHRs to be higher, whereas a generalized increase in the expression of the six adrenoceptors and GRK2 was observed in aortas of adult hypertensive SHRs. alpha(1D)- and beta(3)-adrenoceptors, the subtypes that are more resistant to GRK2-mediated internalization and mostly expressed in rat aorta, exhibited an increased functional role in hypertensive animals, showing two hemodynamic consequences: 1) an increased sensitivity to the vasoconstrictor stimulus accompanied by a decreased sensitivity to the vasodilator stimulus (alpha(1D)-ARs are the most sensitive to agonists, and beta(3)-ARs are the least sensitive to agonists); and 2) a slower recovery of the basal tone after adrenergic stimulus removal because of the kinetic characteristic of the alpha(1D) subtype. These functional changes might be involved in the greater sympathetic vasoconstrictor tone observed in hypertension.

beta3-adrenergic receptor activation increases human atrial tissue contractility and stimulates the L-type Ca2+ current

beta3-adrenergic receptor (beta3-AR) activation produces a negative inotropic effect in human ventricles. Here we explored the role of beta3-AR in the human atrium. Unexpectedly, beta3-AR activation increased human atrial tissue contractility and stimulated the L-type Ca2+ channel current (I Ca,L) in isolated human atrial myocytes (HAMs). Right atrial tissue specimens were obtained from 57 patients undergoing heart surgery for congenital defects, coronary artery diseases, valve replacement, or heart transplantation. The I(Ca,L) and isometric contraction were recorded using a whole-cell patch-clamp technique and a mechanoelectrical force transducer. Two selective beta3-AR agonists, SR58611 and BRL37344, and a beta3-AR partial agonist, CGP12177, stimulated I(Ca,L) in HAMs with nanomolar potency and a 60%-90% efficacy compared with isoprenaline. The beta3-AR agonists also increased contractility but with a much lower efficacy (approximately 10%) than isoprenaline. The beta3-AR antagonist L-748,337, beta1-/beta2-AR antagonist nadolol, and beta1-/beta2-/beta3-AR antagonist bupranolol were used to confirm the involvement of beta3-ARs (and not beta1-/beta2-ARs) in these effects. The beta3-AR effects involved the cAMP/PKA pathway, since the PKA inhibitor H89 blocked I(Ca,L) stimulation and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) strongly increased the positive inotropic effect. Therefore, unlike in ventricular tissue, beta3-ARs are positively coupled to L-type Ca2+ channels and contractility in human atrial tissues through a cAMP-dependent pathway.

Increased fat:carbohydrate oxidation ratio in Il1ra (-/-) mice on a high-fat diet is associated with increased sympathetic tone

AIMS/HYPOTHESIS

Proinflammatory cytokines, including IL-1, exert pleiotropic effects on the neuro-immuno-endocrine system. Previously, we showed that mice with knockout of the gene encoding IL-1 receptor antagonist (Il1ra (-/-), also known as Il1rn (-/-)) have a lean phenotype. The present study was designed to analyse the mechanisms leading to this lean phenotype.

METHODS

Il1ra (-/-) mice were fed a high-fat diet following weaning. Energy expenditure, body temperature, heart rate, blood parameters, urinary catecholamines and adipose tissue were analysed.

RESULTS

Il1ra (-/-) mice exhibited resistance to obesity induced by a high-fat diet; this resistance was associated with increased energy expenditure and a decreased respiratory quotient, indicating that the ratio of fat:carbohydrate metabolism in Il1ra (-/-) mice is greater than in controls. Activity level in Il1ra (-/-) mice was significantly decreased and body temperature was significantly increased, compared with wild-type (WT) mice. Inguinal white adipose tissues in Il1ra (-/-) mice express increased levels of Ucp1 and mitochondrial respiratory chain genes compared with WT mice. Histological analysis of adipose tissue in Il1ra (-/-) mice revealed that brown adipose tissue is hyperactive and inguinal white adipose tissue contains smaller cells, which exhibit the distinctive multilocular appearance of brown adipocytes. Urinary epinephrine and norepinephrine excretion in Il1ra (-/-) mice was significantly increased compared with WT mice, suggesting that Il1ra (-/-) mice have increased sympathetic tone. Consistent with this, heart rate in Il1ra (-/-) mice was also significantly increased.

CONCLUSIONS/INTERPRETATION

Our results show that Il1ra (-/-) mice have increased energy expenditure, fat:carbohydrate oxidation ratio, body temperature, heart rate and catecholamine production. All of these observations are consistent with an enhanced sympathetic tone.

Beta-adrenoceptor subtype expression in human placenta and umbilical arteries in normal and preeclamptic pregnancies

OBJECTIVES

Preeclampsia is characterised by an abnormal vascular response to placentation and is associated with increased systemic vascular resistance and endothelial cell dysfunction. This study investigated the mRNA and protein expression of the beta(2) and beta(3)-adrenoceptors (beta-ARs) in placenta, and umbilical arteries, from preeclamptic and normotensive patients, to determine if the presence of preeclampsia altered the expression of either receptor.

METHODS

RT-PCR was used to identify beta(2)-AR and beta(3)-AR mRNA transcripts in the human placenta and in human umbilical arteries. Real-time RT-PCR was performed on total RNA from normal and preeclamptic placentae and umbilical arteries. Western blotting using antibodies for beta(2)-AR, beta(3)-AR, and beta-actin was performed on total protein isolated from preeclamptic and normotensive placentae.

RESULTS

There was no significant difference in mRNA expression levels of beta(2)-AR and beta(3)-AR between normal and preeclamptic tissues (p > 0.05). No significant difference was observed in protein levels of beta(2)-AR and beta(3)-AR between placentae from normal and preeclamptic patients (p > 0.05).

CONCLUSIONS

Aberrations in the beta-adrenoceptor signalling systems, rather than in the regulation of expression of these receptors may occur in preeclampsia, as is the case in other hypertensive disorders.

Impact of rosiglitazone on the expression of beta3-AR in the stable cell lines expressed beta3-AR gene

BACKGROUND

The aim of the present study was to investigate the effect of rosiglitazone, a peroxisome proliferator-activated receptor gamma2 (PPAR-gamma2) agonist, on the expression of beta3-adrenergic receptor (beta3-AR) at transcriptional and translational level.

METHODS

We cloned the cDNA sequences of human PPAR-gamma2 (hPPAR-gamma2) gene and human wild type and mutant beta3-adrenergic receptor (hbeta3-AR) genes and established their eukaryotic expression vectors. The pcDNA3.1/hbeta3-AR (mutant and wild type) was transfected into SH-SY5Y cells using electroporation method. The expression level of beta3-AR protein was determined by Western blot analysis.

RESULTS

Our results showed that the reverse transcription-PCR products were consistent with theoretical fragment sizes of human PPAR-gamma2 (1544 bp) and human beta3-AR genes (1578 bp). The sequence analysis of PPAR-gamma2 and beta3-AR genes showed that the fragment sizes were the same as that of human PPAR-gamma2 and human beta3-AR genes in Genbank. The pcDNA3.1/hbeta3-AR (mutant and wild type) was successfully cloned to SH-SY5Y cells. We found that the expression of beta3-AR protein was significantly inhibited by rosiglitazone in a concentration-dependent manner in SH-SY5Y cell lines stably expressed beta3-AR genes.

CONCLUSIONS

The results suggest that rosiglitazone has a concentration-dependent inhibitory effect on the expression of beta3-AR protein, and this inhibitory effect may be due to activation of PPAR-gamma2 receptor.

Confirmation of antidepressant potential of the selective beta3 adrenoceptor agonist amibegron in an animal model of depression

The involvement of the noradrenergic system, particularly the beta1 and beta2 receptors, in depressive disorders has been frequently shown. Recently, however, it has been shown that the beta3 receptor may also contribute since amibegron (SR58611A), a selective beta3 receptor agonist, has antidepressant-like effects. The present experiment sought to confirm the antidepressant potential of amibegron by studying its effects in an animal model of depression, the Flinders Sensitive Line (FSL) rat. The FSL rat is innately highly immobile in the forced swim test and exhibits a decrease in immobility after chronic, not acute antidepressant treatment. FSL rats were treated for 14 consecutive days with amibegron (0.3, 1.0, or 3.0 mg/kg), fluoxetine (5 mg/kg) or desipramine (5 mg/kg) as positive controls, and vehicle, while the control strain, the Flinders Resistant Line (FRL) rats, was given either vehicle or 1.0 mg/kg amibegron. About 23-25 h after the last injection the rats were tested in the forced swim test. All doses of amibegron and the two active controls, fluoxetine and desipramine, significantly reduced immobility in the FSL rats. Thus, amibegron had a selective antidepressant-like effect in this study, confirming its antidepressant potential.

Stimulation of the beta3-Adrenoceptor as a novel treatment strategy for anxiety and depressive disorders

The characterization of the first selective orally active and brain-penetrant beta3-adrenoceptor agonist, SR58611A (amibegron), has opened new possibilities for exploring the involvement of this receptor in stress-related disorders. By using a battery of tests measuring a wide range of anxiety-related behaviors in rodents, including the mouse defense test battery, the elevated plus-maze, social interaction, stress-induced hyperthermia, four-plate, and punished drinking tests, we demonstrated for the first time that the stimulation of the beta3 receptor by SR58611A resulted in robust anxiolytic-like effects, with minimal active doses ranging from 0.3 to 10 mg/kg p.o., depending on the procedure. These effects paralleled those obtained with the prototypical benzodiazepine anxiolytic diazepam or chlordiazepoxide. Moreover, when SR58611A was tested in acute or chronic models of depression in rodents, such as the forced-swimming and the chronic mild stress tests, it produced antidepressant-like effects, which were comparable in terms of the magnitude of the effects to those of the antidepressant fluoxetine or imipramine. Supporting these behavioral data, SR58611A modified spontaneous sleep parameters in a manner comparable to that observed with fluoxetine. Importantly, SR58611A was devoid of side effects related to cognition (as shown in the Morris water maze and object recognition tasks), motor activity (in the rotarod), alcohol interaction, or physical dependence. Antagonism studies using pharmacological tools targeting a variety of neurotransmitters involved in anxiety and depression and the use of mice lacking the beta3 adrenoceptor suggested that these effects of SR58611A are mediated by beta3 adrenoceptors. Taken as a whole, these findings indicate that the pharmacological stimulation of beta3 adrenoceptors may represent an innovative approach for the treatment of anxiety and depressive disorders.

G protein-coupled receptor pharmacogenetics

Common G protein-coupled receptor (GPCR) gene variants that encode receptor proteins with a distinct sequence may alter drug efficacy without always resulting in a disease phenotype. GPCR genetic loci harbor numerous variants, such as DNA insertions or deletions and single-nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to interindividual differences in disease susceptibility/progression and drug responses. In this chapter, these pharmacogenetic phenomena are reviewed with respect to a limited sampling of GPCR systems, including the beta(2)-adrenergic receptors, the cysteinyl leukotriene receptors, and the calcium-sensing receptor. In each example, the nature of the disruption to receptor function that results from each variant is discussed with respect to the regulation of gene expression, expression on cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (by altering ligand binding, G protein coupling, and receptor constitutive activity). Despite the breadth of pharmacogenetic knowledge available, assessment for genetic variants is only occasionally applied to drug development projects involving pharmacogenomics or to optimizing the clinical use of GPCR drugs. The continued effort by the basic science of pharmacogenetics may draw the attention of drug discovery projects and clinicians alike to the utility of personalized pharmacogenomics as a means to optimize novel GPCR drug targets.

Reversal of cardiac remodeling by modulation of adrenergic receptors: a new frontier in heart failure

PURPOSE OF REVIEW

Heart failure is a common clinical syndrome, and despite intensive medical therapy it remains a leading cause of global morbidity and mortality. Pathological stimuli promote a general remodeling process in the heart.

RECENT FINDINGS

Recent animal studies have highlighted very promising novel therapeutic possibilities, based on the regulation of adrenergic receptor function, and novel signaling pathways are being discovered that could be relevant for future molecular approaches.

SUMMARY

This review highlights some of the novel approaches to reverse pathological remodeling and improve cardiac dysfunction, placing emphasis on strategies targeting the adrenergic receptors.

The association between hyperuricemia and the Trp64Arg polymorphism of the beta-3 adrenergic receptor

The object of this study was to determine the association of Trp64Arg polymorphism with hyperuricemia. This study is an age-matched, case-controlled study of 203 hyperuricemic and 203 normouricemic men. The frequency of genotypes was compared between the two groups. Possible confounding metabolic variables were included in a multiple logistic regression model for multivariate adjustment. The genotype frequencies of Trp64Trp, Trp64Arg, and Arg64Arg in hyperuricemic and normouricemic groups are respectively 130, 69, and 4 (64.0%, 34.0%, 2.0%) and 154, 45, and 4 (75.9%, 22.2%, 2.0%) (P = 0.029, Chi-square test). Simple logistic regression analysis indicated that the Trp64Arg genotype is significantly associated with hyperuricemia (OR = 1.816, 95% CI (1.167-2.827), P = 0.008). Multivariate analysis for controlling metabolic effects also showed a significant association with the occurrence of hyperuricemia (OR = 1.937, 95% CI (1.149-3.266), P = 0.013). Trp64Arg polymorphism of the beta-3 adrenergic receptor may be independently associated with hyperuricemia in males.

Beta3-adrenoceptors in urinary bladder

The beta-adrenoceptor (AR) is currently classified into beta(1), beta(2), and beta(3) subtypes. A third subtype, beta(3)-AR, was first identified in adipose tissue, but has also been identified in smooth muscle tissue, particularly in the gastrointestinal tract and urinary bladder smooth muscle. There is a predominant expression of beta(3)-AR messenger RNA (mRNA) in human bladder, with 97% of total beta-AR mRNA being represented by the beta(3)-AR subtype and only 1.5 and 1.4% by the beta(1)-AR and beta (2)-AR subtypes, respectively. Moreover, the presence of beta(1)-, beta(2)-, and beta(3)-AR mRNAs in the urothelium of human bladder has been identified. The distribution of beta-AR subtypes mediating detrusor muscle relaxation is species dependent, the predominant subtype being the beta(3)-AR in humans. Recent studies have suggested that cAMP-dependent routes are not exclusive mechanisms triggering the beta-AR-mediated relaxation of smooth muscle. It has been demonstrated in rats detrusor muscle that cAMP plays a greater role in beta-adrenergic relaxation against basal tone than against KCl-induced tone and that conversely calcium-activated K(+) channels (BKca channels) play a greater role under the latter circumstances. In rat models, beta(3)-AR agonists increase bladder capacity without influencing bladder contraction and have only weak cardiovascular side effects. Although this evidence points toward the clinical utility of beta(3)-AR agonists as therapy for overactive bladder (OAB), pharmacological differences exist between rat and human beta(3)-ARs. Development of compounds with high selectivity for the human beta(3)-AR, identified by screening techniques using cell lines transfected with the human beta(1)-, beta(2)-, and beta(3)-AR genes, may mitigate against such problems. The association between the tryptophan 64 arginine polymorphism in the beta(3)-AR gene and idiopathic OAB is discussed.

Effects of formoterol and BRL 37344 on human umbilical arteries in vitro in normotensive and pre-eclamptic pregnancy

Alterations in vascular responses to beta-adrenoceptor agonists in normotensive pregnancy and pre-eclampsia are not fully understood. Thus, we studied changes in vasodilator responses to beta(2)-adrenoceptor agonist formoterol and beta(3)-adrenoceptor agonist BRL 37344 on umbilical arteries isolated from normotensive (n=12) and pre-eclamptic (n=12) pregnant women. Changes in the relaxant effect of formoterol and BRL 37344 were investigated by measuring isometric tensions in endothelium-denuded strips of umbilical arteries in the presence or absence of metoprolol, ICI 118.551 and SR 59230A (beta(1), beta(2), beta(3)-adrenoceptor antagonists, respectively, 10(-6) mol/L). Effects of formoterol and BRL 37344 on cAMP levels of umbilical arteries were evaluated by radioimmunoassay kits. Formoterol (10(-10)-10(-4) mol/L) and BRL 37344 (10(-10)-10(-4) mol/L) caused concentration-dependent relaxation of the contraction induced by phenylephrine (10(-5) mol/L) in umbilical artery strips isolated from both groups. E(max) values of formoterol and BRL 37344 (for normotensive pregnant women: 87.33+/-0.87 and 53.25+/-1.17 vs. for pre-eclampsia: 73.68+/-1.58 and 43.64+/-1.19, n=12, P>0.05, respectively) were significantly smaller in strips from pre-eclamptic women (P<0.05), with no significant change in pD(2) values. E(max) values of formoterol were significantly higher than those of BRL 37344 in both tissue (P<0.05). ICI 118.551 and SR 59230A, but not metoprolol, antagonized the relaxant effects of formoterol and of BRL 37344 on umbilical artery strips isolated from normotensive and pre-eclamptic pregnant women. Formoterol and BRL 37344 increased cAMP levels in both groups, but less significant in pre-eclamptic strips (P<0.05). These results suggest that the relaxation caused in human umbilical arteries by formoterol and BRL 37344 is mediated by a mixed population of beta(2)- and beta(3)-adrenoceptor subtypes, with contribution of cAMP. Umbilical arteries from subjects with pre-eclampsia showed a weaker beta(2)- and beta(3)-receptor-mediated relaxation to formoterol and BRL 37344, suggesting that the reduced action of formoterol and BRL 37344 may be partly due to a decreased effect of cAMP.

Catechol-O-methyltransferase inhibition increases pain sensitivity through activation of both beta2- and beta3-adrenergic receptors

Catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, has recently been implicated in the modulation of pain. Our group demonstrated that human genetic variants of COMT are predictive for the development of Temporomandibular Joint Disorder (TMJD) and are associated with heightened experimental pain sensitivity [Diatchenko, L, Slade, GD, Nackley, AG, Bhalang, K, Sigurdsson, A, Belfer, I, et al., Genetic basis for individual variations in pain perception and the development of a chronic pain condition, Hum Mol Genet 2005;14:135-43.]. Variants associated with heightened pain sensitivity produce lower COMT activity. Here we report the mechanisms underlying COMT-dependent pain sensitivity. To characterize the means whereby elevated catecholamine levels, resulting from reduced COMT activity, modulate heightened pain sensitivity, we administered a COMT inhibitor to rats and measured behavioral responsiveness to mechanical and thermal stimuli. We show that depressed COMT activity results in enhanced mechanical and thermal pain sensitivity. This phenomenon is completely blocked by the nonselective beta-adrenergic antagonist propranolol or by the combined administration of selective beta(2)- and beta(3)-adrenergic antagonists, while administration of beta(1)-adrenergic, alpha-adrenergic, or dopaminergic receptor antagonists fail to alter COMT-dependent pain sensitivity. These data provide the first direct evidence that low COMT activity leads to increased pain sensitivity via a beta(2/3)-adrenergic mechanism. These findings are of considerable clinical importance, suggesting that pain conditions resulting from low COMT activity and/or elevated catecholamine levels can be treated with pharmacological agents that block both beta(2)- and beta(3)-adrenergic receptors.

Obesity

There is a widespread epidemic of obesity in the United States, which has been associated with an increased risk of diabetes mellitus, cancer, and cardiovascular diseases. Although lifestyle modifications and long-term dietary vigilance remain cornerstones of weight reduction treatment, the continued availability of U.S. Food and Drug Administration-approved pharmacotherapies has expanded the options available for the management of obesity. These agents include anorexiants, thermogenic drugs, and lipid-partitioning drugs. As knowledge regarding the possible causes of obesity increases, there are new drugs under investigation, which include beta3-adrenergic receptor agonists, modifiers of leptin, and cannabinoid receptor-1 antagonists (rimonabant). Also under investigation are antidiabetic agents (metformin, exenatide), anticonvulsant drugs (topiramate, zonisamide), antidepressants (bupropion, fluoxetine), and growth hormones. New targets for pharmacotherapy include uncoupling proteins, fatty acid synthase, neuropeptide Y, melanocortin, ghrelin, various regulatory gut peptides, and ciliary neurotropic factor. Pharmacologic agents are in clinical development that target these substances.

Molecular modeling of SWR-0342SA, a β3-selective agonist, with β1- and β3-adrenoceptor

The molecular dynamics (MD) simulations study in the formation of the complex between compound SWR-0342SA and beta-ARs suggested that upon binding SWR-0342SA stimulates receptor activation through residues network (Asp104, Leu335 in beta(1)-AR; Asp117, Ser209, Leu303, Ser191 in beta(3)-AR) in an active conformation state. The models suggest that the structural origin of the selectivity of SWR-0342SA to beta(3)-AR vs. beta(1)-AR comes from the following results: (a) the tight interaction between the agonist and the TMs 3, 5, 6 and 2 nd EC loop. Asp117 interacts with the cationic amino group of the agonist molecule. (b) Additional contacts are done with Ser209, Leu303 and Ser191. These results are in good agreement with the binding affinities (pKi values) of SWR-0342SA to beta-AR family expressed in recombinant mammalian cells.

Beta1-adrenergic receptor gene polymorphisms in Mexican patients with idiopathic dilated cardiomyopathy

The objective of the study was to evaluate the role of beta1-adrenergic receptor gene polymorphisms (Ser49Gly and Arg389Gly) as susceptibility markers for idiopathic dilated cardiomyopathy (IDC) in Mexican patients. The polymorphisms were analyzed in 47 patients with IDC and 93 ethnically matched healthy controls by polymerase chain reaction-restriction fragment length polymorphism. The Ser49Gly allele and genotype frequencies were similar in patients and healthy controls. On the other hand, the analysis of the Arg389Gly polymorphism showed an increased frequencies of the *Gly allele (pC = 0.022, OR = 2.16) and *Arg/*Gly genotype (pC = 0.027, OR = 2.70) in the group of IDC patients when compared to healthy controls. The data suggest that Arg389Gly polymorphism could be involved in the genetic susceptibility to develop IDC in Mexicans.

Benzisothiazoles and beta-adrenoceptors: synthesis and pharmacological investigation of novel propanolamine and oxypropanolamine derivatives in isolated rat tissues

In an attempt to examine the ability of benzisothiazole-based drugs to interact with beta-adrenoceptors, a series of 1,2-benzisothiazole derivatives, which were substituted with various propanolamine or oxypropanolamine side chains in the 2 or 3 position, were synthesised and tested. The pharmacological activity of these compounds at the beta-adrenoceptors was examined using isolated rat atria and small intestinal segments, which preferentially express the beta1- and beta3-adrenoceptor-mediated responses, respectively. None of these products showed any beta-adrenoceptor agonistic activity. In contrast, the 2- and 3-substituted isopropyl, tert-butyl, benzyl, and piperonyl derivatives 2a-d and 3a-d elicited surmountable inhibition of the isoprenaline-induced chronotropic effects in the atria, suggesting competitive antagonism at the beta1-recognition site. The pA2 values revealed tert-butyl 3b and the isopropyl substituted piperonyl derivatives 3a to be the most effective. Remarkably, many of the 2-substituted propanolamines were less active than the corresponding 3-substituted oxypropanolamines. With the exception of compound 3b, none of these drugs antagonised the muscle relaxant activity of isoprenaline in the intestine, suggesting no effect on the beta3-adrenoceptors. These results confirm the ability of the benzisothiazole ring to interact with the beta-adrenoceptors, and demonstrate that 2-substitution with propanolamine or 3-substitution with oxypropanolamine groups yields compounds with preferential antagonistic activity at the cardiac beta1-adrenoceptors. The degree of antagonism depends strongly on both the nature of the substituent and its position on the benzisothiazole ring.

Norepinephrine- and epinephrine-deficient mice gain weight normally on a high-fat diet

OBJECTIVE

Signaling through adrenergic receptors (ARs) by norepinephrine (NE) and epinephrine (Epi) regulates weight gain when mice are fed a high-fat diet (HFD) by controlling diet-induced thermogenesis. Thus, one would predict that mice unable to make NE/Epi because of inactivation of the dopamine beta-hydroxylase gene (Dbh-null mice) would have a propensity to become obese. We characterized the response of Dbh-null and control mice to a HFD.

RESEARCH METHODS AND PROCEDURES

Dbh-null and control mice were fed an HFD or a regular diet (RD) for 2 months. Body weight, adiposity, muscle triglyceride levels, and adipocyte size were measured, as were circulating leptin, adiponectin, triglyceride, glucose, and insulin levels. A glucose tolerance test was also preformed.

RESULTS

Dbh-null mice gain weight normally on an HFD and have the same adiposity. Their serum triglyceride and leptin levels are normal, but adipocytes are approximately 30% smaller than controls. Dbh-null mice maintain low blood glucose levels and glucose tolerance when exposed to the HFD in contrast to controls.

DISCUSSION

Complete lack of NE/Epi does not predispose to obesity. Because mice lacking all three betaARs become obese on an HFD, an imbalance of signaling through alpha- and betaARs seems to be responsible for obesity. Surprisingly, Dbh-null mice maintain glucose tolerance.

The G protein-coupled receptors: pharmacogenetics and disease

Genetic variation in G-protein coupled receptors (GPCRs) is associated with a wide spectrum of disease phenotypes and predispositions that are of special significance because they are the targets of therapeutic agents. Each variant provides an opportunity to understand receptor function that complements a plethora of available in vitro data elucidating the pharmacology of the GPCRs. For example, discrete portions of the proximal tail of the dopamine D1 receptor have been discovered, in vitro, that may be involved in desensitization, recycling and trafficking. Similar in vitro strategies have been used to elucidate naturally occurring GPCR mutations. Inactive, over-active or constitutively active receptors have been identified by changes in ligand binding, G-protein coupling, receptor desensitization and receptor recycling. Selected examples reviewed include those disorders resulting from mutations in rhodopsin, thyrotropin, luteinizing hormone, vasopressin and angiotensin receptors. By comparison, the recurrent pharmacogenetic variants are more likely to result in an altered predisposition to complex disease in the population. These common variants may affect receptor sequence without intrinsic phenotype change or spontaneous induction of disease and yet result in significant alteration in drug efficacy. These pharmacogenetic phenomena will be reviewed with respect to a limited sampling of GPCR systems including the orexin/hypocretin system, the beta2 adrenergic receptors, the cysteinyl leukotriene receptors and the calcium-sensing receptor. These developments will be discussed with respect to strategies for drug discovery that take into account the potential for the development of drugs targeted at mutated and wild-type proteins.

Chronic effects of AJ-9677 on energy expenditure and energy source utilization in rats

The effects of AJ-9677 on metabolic parameters were examined in rats that had or had not been chronically treated with this beta3-adrenoceptor agonist. A challenge administration of AJ-9677 increased both the temperature of brown adipose tissue and energy expenditure in both groups of rats. However, whereas the former effect was subject to desensitization, the latter effect was augmented by prior chronic administration of AJ-9677. Whereas a challenge administration of AJ-9677 induced a decrease in the respiratory quotient that persisted for at least 15 h in rats pretreated with vehicle, the initial decrease in this parameter lasted for only 4 h in rats pretreated with AJ-9677. These results suggest that, in rats subjected to chronic treatment with AJ-9677, a challenge administration of this drug increased energy expenditure by stimulation not only of fat oxidation but also of glucose oxidation.

Induction of β3-Adrenergic Receptor Functional Expression following Chronic Stimulation with Noradrenaline in Neonatal Rat Cardiomyocytes

This study aimed to characterize beta(3)-adrenergic receptors (ARs) in rat neonatal cardiomyocytes using the noradrenaline (NOR) properties to modulate the expression and function of the three beta-ARs. We assessed the effect of NOR (physiological nonselective agonist), isoprenaline (ISO, beta-nonselective agonist), dobutamine (DOB, beta(1)-selective agonist), and procaterol (PROC, beta(2)-selective agonist) on cAMP accumulation using cardiomyocytes untreated or treated with 100 microM NOR for 24 h. The inhibition of forskolin-stimulated cAMP accumulation was determined using NOR, isoprenaline, and the beta(3)-selective agonists 4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxyacetic acid (BRL 37344) and 5-[-2-([-2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL 316243). The experiments were performed in the absence or presence of propranolol or 2-hydroxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy]propyl]amino]ethoxy]-benzamide methanesulfonate (CGP 20712A) and/or 1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride (ICI 118551) to inhibit beta(1)- and beta(2)-AR stimulation and 1-(2-ethylphenoxy)-3-[[1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino-(2S)-2-propanol hydrochloride (SR 59230A) (beta(3)-selective antagonist). In addition, the level of the three subtypes was determined by reverse transcription polymerase chain reaction and Western blotting. NOR pretreatment decreased the activation of cAMP induced by NOR, isoprenaline, and DOB, whereas PROC response was abolished. The inhibition of NOR response by CGP 20712A or ICI 118551 demonstrated that beta(1)- and beta(2)-ARs are down-regulated and that beta(2)-AR functional activity was also abolished in cardiomyocytes exposed to chronic stimulation. beta(3)-AR function was observed with NOR and ISO when beta(1)-/beta(2)-ARs were blocked and with both beta(3)-selective agonists in NOR-treated cells only. This response was completely inhibited by SR 59230A and involved G(i) protein. Furthermore, the results from functional studies agree well with those from expression experiments. In conclusion, these data provide strong evidence that beta(3)-ARs are functionally up-regulated and coupled to G(i) protein in rat neonatal cardiomyocytes following chronic exposure to NOR when beta(1)- and beta(2)-ARs are down-regulated.

Stimulation of the ADRB3 adrenergic receptor induces relaxation of human placental arteries: influence of preeclampsia

Preeclampsia, which complicates 3-8% of pregnancies, is one of the leading causes of neonatal morbidity and mortality. Its pathophysiology remains unclear. The aim of the present study was to investigate the presence and the role of beta2- and beta2-adrenergic receptors (ADRB2 and ADRB3, respectively) in human placental arteries and to assess the influence of preeclampsia on ADRB responsiveness. SR 59119A, salbutamol, and isoproterenol (ADRB3, ADRB2, and nonselective ADRB agonists, respectively) induced a concentration-dependent relaxation of placental artery rings obtained from women with uncomplicated or preeclamptic pregnancies. SR 59119A-induced relaxation was unaffected by the blockade of ADRB1 and ADRB2 by 0.1 microM propranolol but was significantly decreased by the blockade of ADRB1, ADRB2, and ADRB3 by 10 microM propranolol. Both SR 59119A and salbutamol were associated with a significant increase in cAMP production that was significantly inhibited by pretreatment with 0.1 microM propranolol only for salbutamol. SR 59119A-induced relaxation (E(max) = 28% +/- 5% vs. 45% +/- 4%, respectively) and cAMP production (2.7 +/- 0.5 vs. 4.9 +/- 0.4 pmol/mg of protein, respectively; P < 0.01) were decreased in arteries obtained from preeclamptic compared to normotensive women. Both ADRB2 and ADRB3 transcripts were expressed at the same level between arteries from normotensive and preeclamptic women. Western blot analysis, however, revealed a decreased expression of the ADRB3 immunoreactive protein in arteries from preeclamptic compared to normotensive women. We suggest the presence of functional ADRB2 and ADRB3 in human placental arteries. Even if preeclampsia is associated with an impairment of the ADRB3 responsiveness, ADRB3 agonists may have future pharmaceutical implications in the management of pregnancy-related disorders.

Evidence for a secondary state of the human beta3-adrenoceptor

There are three members of the beta-adrenoceptor family, all of which are primarily coupled to G(s) proteins. Recent studies using the huge range of beta-ligands now available have given remarkable new insights into their pharmacology. beta1-adrenoceptors exist in at least two active conformations, whereas beta2-adrenoceptors are able to induce signaling via different agonist-induced receptor conformational states, and their affinity for antagonists can be altered by highly efficacious agonists. This study therefore examined the pharmacology of the human beta3-adrenoceptor stably expressed in Chinese hamster ovary cells. Several compounds described previously as beta-antagonists have agonist properties at the beta3-adrenoceptor. Antagonist affinity measurements varied at the beta3-adrenoceptor in a manner similar to those observed at human beta1-adrenoceptors and unlike those seen at beta2-adrenoceptors. Some ligands (e.g., fenoterol and cimaterol) were more readily inhibited by all antagonists, whereas other ligands [e.g., alprenolol and 1-(2-ethylphenoxy)-3-[[(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]-(2S)-2-propanol hydrochloride [SR 59230A]) stimulated responses that were more resistant to antagonism. Alprenolol inhibited fenoterol-induced beta3-adrenoceptor responses while acting as an agonist at higher concentrations. This is highly suggestive of two active conformational states of the beta3-adrenoceptor. (S)-4-[2-Hydroxy-3-phenoxypropylaminoethoxy]-N-(2-methoxyethyl)phenoxyacetamide (ZD 7114) stimulated a two-component response, of which the first component was more readily antagonized than the second. Taken together, these experiments suggest that the human beta3-adrenoceptor exists in at least two different agonist conformations with a similar high- and low-affinity pharmacology analogous to, if not as pronounced as, the beta1-adrenoceptor. Both conformations are present in living cells and can be distinguished by their pharmacological characteristics. In this respect, the human beta3-adrenoceptor seems similar to the human beta1-adrenoceptor.

Role of β2-adrenoceptors (ß-AR), but not ß1-, β3-AR and endothelial nitric oxide, in β-AR-mediated relaxation of rat intrapulmonary artery

The aim of this study was to analyze beta-adrenoceptor (beta-AR)-mediated relaxation in rat intralobar pulmonary artery. The relaxant responses of beta-AR agonists were characterized using beta-AR antagonists in prostaglandin F2alpha (PGF2alpha)-precontracted arteries. The role of nitric oxide (NO) and endothelium in beta-AR-mediated relaxation was also investigated. Isoprenaline (a non-selective beta-AR agonist) and salbutamol (a selective beta2-AR agonist) induced vasorelaxation. ICI 118551 (a selective beta2-AR antagonist) antagonized the effect of both isoprenaline and salbutamol (pA2 values of 9.57 and 9.51 respectively). In contrast, atenolol (1 microM) and CGP 20712A (0.1 microM), two beta1-AR antagonists, did not modify the relaxing effect of isoprenaline. The response to isoprenaline obtained in the presence of nadolol (10 microM, a beta1/beta2-AR antagonist) was not further inhibited by SR 59230A (1 microM, a selective beta3-AR antagonist). The non-beta1/beta2-AR agonists studied (BRL 37344, SR 58611A, and CGP 12177A) did not elicit vasorelaxation. Relaxation to isoprenaline and salbutamol was unaffected by L-N(G)-nitro-arginine methyl ester (100 microM, an inhibitor of NO synthase) or after endothelium removal. These results demonstrate the role of beta2-AR in mediating relaxation in rat intralobar pulmonary artery precontracted with PGF2alpha. They indicate that beta2-AR-mediated relaxation in this artery is NO- and endothelium-independent. Furthermore, they do not provide evidence of a relaxant role of either beta1- or beta3-AR in PGF2alpha-precontracted rat intrapulmonary artery.

No association of the Trp 64 Arg mutation of the beta3-adrenergic receptor gene with obesity, type 2 diabetes mellitus, hyperlipidemia, and hypertension in Japanese patients with schizophrenia

OBJECTIVE

This study was conducted to address the question of whether the beta3-adrenergic receptor gene mutation (Trp 64 Arg) is associated with metabolic disease in Japanese patients with schizophrenia.

METHODS

In a cross-sectional study, 89 participants were grouped into three genotypes. The 64 Arg allelic frequency in patients with or without metabolic disease was analyzed. Anthropometrics variables and biochemical parameters were compared among the genotypes.

RESULTS

The 64Arg allele, which had a frequency of 0.22, was not associated with obesity, type 2 diabetes mellitus, dyslipidemias, or hypertension. No significant differences among the genotypes were found in current age, age at diagnosis with schizophrenia, body mass index, waist-hip ratio, plasma glucose, plasma insulin, triglycerides, free fatty acids. Patients with the 64 Arg allele had greater 24-h excretion of norepinephrine than those lacking the variant (p = 0.019).

CONCLUSION

The 64 Arg allelic mutation is not associated with obesity, type 2 diabetes mellitus, lipid metabolism dysfunction, or hypertension in Japanese patients with schizophrenia.

Discovery of a novel, potent and selective human β3-adrenergic receptor agonist

The discovery of a novel, potent and selective beta(3)-adrenergic receptor (AR) agonist is described. SAR studies demonstrated the structural requirements for activity and selectivity. Compound 1c, which showed good beta(3)-AR activity and selectivity, was identified and pharmacokinetics were investigated.

Involvement of β3-Adrenergic Receptor Activation in Human Corpus Cavernosum Function

β3 adrenergic receptors are extensively studied, and in animal model it was demostrated their involvement in the vasorelaxation of smooth muscle cells. However the precise role and their exact distribution in human body is almost unknown. We studied the presence of β3 adrenergic receptors in human corpus cavernosum and the pathways involved in their activation:

Materials and Methods

Using strips isolated from human corpus cavernosum obtained from transsexual surgical procedures, we tested this receptors with a specific agonist BRL-37344 (10–5 −10–8) to understand their precise role. Removing endothelium and using L-NAME (100 μM), we tested the involvement of NO in the pathways of activation of this receptors.

Results

We demostrated the presence of β3 adrenergic receptors in the human corpora cavernosa and their mainly localization in the smooth muscle cells of vascular vessels. Our results dimostrated, making a stimulation with BRL-37344, that exists a mechanism of smooth muscle relaxation concentration-dependent. This relaxation is endothelium-indipendent too, like we showed removing it or using L-NAME. The vasorelaxation induced by BRL-37344 is realized by the increase of cGMP level of 7-fold like it was dimostrated by ELISA. Moreover the use of SR-59230A, an antagonist of β3 adrenergic receptors, removes the relaxant effect.

Conclusions

The vascular smooth muscle in human corpus cavernosum possesses tonic or continuous β3-adrenergic receptor activity (mediating relaxation), as suggested by the vasoconstrictor effect that results from selectively antagonizing the β3-adrenergic receptors. The presence of β3-adrenergic receptors in human corpus cavernosum and their possible involvement in promoting erectile function via cGMP but NO-indipendent, may open new approaches to develop new treatment of E.D.

Beta-adrenergic receptors and their interacting proteins

The three subtypes of beta-adrenergic receptor (beta AR) all interact with G proteins as a central aspect of their signaling. The various beta AR subtypes also associate differentially with a variety of other cytoplasmic and transmembrane proteins. These beta AR-interacting proteins play distinct roles in the regulation of receptor signaling and trafficking. The specificity of beta AR associations with various binding partners can help to explain key physiological differences between beta AR subtypes. Moreover, the differential tissue expression patterns of many of the beta AR-interacting proteins may contribute to tissue-specific regulation of beta AR function.

Fragmentation and conformation study of ephedrine by low- and high-resolution mass selective UV spectroscopy

The neurotransmitter molecule, ephedrine, has been studied by mass-selective low- and high-resolution UV resonance enhanced two-photon ionization spectroscopy. Under all experimental conditions we observed an efficient fragmentation upon ionization. The detected vibronic peaks in the spectrum are classified according to the efficiency of the fragmentation, which leads to the conclusion that there exist three different species in the molecular beam: ephedrine-water cluster and two distinct conformers. The two-color two-photon ionization experiment with a decreased energy of the second photon leads to an upper limit of 8.3 eV for the ionization energy of ephedrine. The high-resolution (70 MHz) spectrum of the strongest vibronic peak in the spectrum measured at the fragment (m/z=58) mass channel displays a pronounced and rich rotational structure. Its analysis by the use of a specially designed computer-aided rotational fit process yields accurate rotational constants for the S(0) and S(1) states and the transition moment ratio, providing information on the respective conformational structure.

Impairment of the low-affinity state beta1-adrenoceptor-induced relaxation in spontaneously hypertensive rats

1 In hypertension, a decrease of the vascular beta-adrenergic relaxation has been described. However, the specific involvement of each beta-adrenoceptor (beta-AR) subtype, in particular the low-affinity state of beta1-AR, has not yet been evaluated. We investigated whether the low-affinity state of beta1-AR-induced relaxation was impaired in Spontaneously Hypertensive Rats (SHR). 2 The relaxant responses to CGP 12177 and cyanopindolol, low-affinity state beta1-AR agonists (with beta1-/beta2-AR antagonistic and partial beta3-AR agonistic properties) were evaluated on thoracic aortic rings isolated from 12-weeks-old Wistar Kyoto rats (WKY) and SHR. 3 In WKY, CGP 12177 and cyanopindolol produced an endothelium and nitric oxide (NO)-independent relaxation. CGP 12177-induced endothelium-independent relaxation was not modified either by beta1-, beta2-AR (nadolol) or beta3-AR (L-748337 or SR 59230A) antagonists but was significantly reduced by high concentrations of CGP 20712A (P<0.05). This relaxation was also reduced by adenylyl cyclase inhibitors, SQ 22536 or MDL 12330A. 4 In SHR, CGP 12177 produced mainly an endothelium and NO-dependent relaxation. This effect was not modified by nadolol, but was strongly reduced by beta3-AR blockade. Endothelium-independent relaxation to CGP 12177 was not altered by adenylyl cyclase inhibition, but was amplified in preparations from pertussis toxin-pretreated SHR. 5 The immunohistochemical analysis revealed an upregulation of beta3-AR in the endothelial layer of SHR aorta, whereas the beta3-AR-induced relaxation was not modified. 6 In conclusion, we demonstrated an impaired low-affinity state of the beta1-AR-induced relaxation and an upregulation of the beta3-AR in hypertension. Some clinical implications of those findings are discussed.

Association study of adrenergic beta3 receptor (Trp64Arg) and G-protein beta3 subunit gene (C825T) polymorphisms and weight change during clozapine treatment

Weight gain, a common adverse effect of clozapine, may impair health and affect patient compliance during treatment with this agent. The aim of this study was to investigate the relationship between genetic variants of the adrenergic beta3 receptor (ADRB3) and the G-protein beta3 subunit (GNB3) and clozapine-induced body weight change (BWC). Eighty-seven treatment-resistant schizophrenic patients were weighed before and after 4 months of clozapine treatment, with the subjects gaining an average of 2.6 kg in body weight. No statistically significant relationship was demonstrated for the investigated ADRB3 Trp64Arg and the GNB3 C825T polymorphisms in terms of BWC post-treatment, suggesting these two polymorphisms do not play a significant role in clozapine-induced BWC. Further exploration of other genetic variants implicated in clozapine-induced BWC is important, however, in order to predict and reduce clozapine-associated weight gain.

Expression of functional beta2-adrenergic receptors in the lung epithelial cell lines 16HBE14o(-), Calu-3 and A549

Adrenergic drugs acting through the beta(2)-adrenoceptor (beta(2)-AR) adenylate cyclase (AC) signal transduction system elicit a variety of responses within the mammalian airway epithelium; however, its composition of multiple phenotypically differentiated cell types complicates the understanding of the regulation cascades within this tissue. The present study evaluates beta(2)-AR mRNA level, number, subtype and the cyclic adenosine-3',5'-monophosphate (cyclic AMP) response to isoproterenol (iso) in the human airway epithelial cell lines 16HBE14o(-), Calu-3 and A549, using reverse transcriptase polymerase chain reaction (RT-PCR), radioligand binding studies, [(3)H]-radioimmunoassay and immunocytochemical staining. After 4-5 days in culture, all three cell types produced beta(2)-AR mRNA and protein at a magnitude of gene expression levels Calu-3>or=16HBE14o(-)>A549, whereas control cells Cos-1 and Caco-2 were negative. The beta(2)-AR adenylate cyclase system was highly expressed and functional in the human airway epithelial cells Calu-3 and 16HBE14o(-). The mean beta(2)-AR density (B(max)), equilibrium dissociation constant (K(D)), and the percentage of beta-AR subtypes assessed by radioligand binding were approximately 9908+/-1127 and 6423+/-895 binding sites/cell, 32+/-2.7 pM and 25+/-1.1 pM, and approximately 100% in Calu-3 and 16HBE14o(-)cells, respectively. However, in the alveolar cell type A549 the cell surface beta(2)-AR was virtually undetectable by (-)-[(125)I]-iodocyanopindolol (ICYP) binding. Stimulation of cultured cells with (-)-isoproterenol enhanced the basal cyclic AMP accumulation only in Calu-3 and 16HBE14o(-) cells, which was blocked by the beta(2)-selective antagonist ICI 118,551, but not by the beta(1)-selective antagonist CGP 20712A, confirming functional coupling of the beta(2)-AR to adenylate cyclase in these cells. Immunocytochemical staining localised the receptor on the cell membrane and the cytoplasm in Calu-3 and 16HBE14o(-) cells, while it was confined to the cytoplasm only in A549 cells. In conclusion, the beta(2)-AR expression and its functional coupling to adenylyl cyclase was very high in the human airway epithelial cells Calu-3 and 16HBE14o(-), but not in A549, suggesting that the cell lines Calu-3 and 16HBE14o(-) present suitable models to study function and regulation of the beta-adrenoceptor signalling in the respiratory system.

Direct and remote modulation of L-channels in chromaffin cells: distinct actions on alpha1C and alpha1D subunits?

Understanding precisely the functioning of voltage-gated Ca2+ channels and their modulation by signaling molecules will help clarifying the Ca(2+)-dependent mechanisms controlling exocytosis in chromaffin cells. In recent years, we have learned more about the various pathways through which Ca2+ channels can be up- or down-modulated by hormones and neurotransmitters and how these changes may condition chromaffin cell activity and catecolamine release. Recently, the attention has been focused on the modulation of L-channels (CaV 1), which represent the major Ca2+ current component in rat and human chromaffin cells. L-channels are effectively inhibited by the released content of secretory granules or by applying mixtures of exogenous ATP, opioids, and adrenaline through the activation of receptor-coupled G proteins. This unusual inhibition persists in a wide range of potentials and results from a direct (membrane-delimited) interaction of G protein subunits with the L-channels co-localized in membrane microareas. Inhibition of L-channels can be reversed when the cAMP/PKA pathway is activated by membrane permeable cAMP analog or when cells are exposed to isoprenaline (remote action), suggesting the existence of parallel and opposite effects on L-channel gating by distinctly activated membrane autoreceptors. Here, the authors review the molecular components underlying these two opposing signaling pathways and present new evidence supporting the presence of two L-channel types in rat chromaffin cells (alpha1C and alpha1D), which open new interesting issues concerning Ca(2+)-channel modulation. In light of recent findings on the regulation of exocytosis by Ca(2+)-channel modulation, the authors explore the possible role of L-channels in the autocontrol of catecholamine release.

Endogenous β3-adrenoreceptor activation contributes to left ventricular and cardiomyocyte dysfunction in heart failure

The objective of the present study was to test the hypothesis that endogenous β3-adrenoreceptor (AR) activation contributes to left ventricular (LV) and cardiomyocyte dysfunction in heart failure (CHF). Stimulation of the β3-AR inhibits cardiac contraction. In the failing myocardium, β3-ARs are upregulated, suggesting that stimulation of β3-ARs may contribute to depressed cardiac performance in CHF. We assessed the functional significance of endogenous β3-AR activation in 10 conscious dogs before and after pacing-induced CHF. Under normal conditions, L-748,337, a specific β3-AR antagonist, produced a mild increase in LV contractile performance assessed by the slope ( Ees) of the LV pressure-volume relation (18%, 6.2 ± 0.9 vs. 7.3 ± 1.2 mmHg/ml, P < 0.05) and the improved LV relaxation time constant (τ; 28.4 ± 1.9 vs. 26.8 ± 1.0 ms, P < 0.05). After CHF, the plasma norepinephrine concentration increased eightfold, and L-748,337 produced a larger increase in Ees (34%, 3.8 ± 0.7 vs. 5.1 ± 0.8 mmHg/ml, P < 0.05) and a greater decrease in τ (46.4 ± 4.2 vs. 41.0 ± 3.9 ms, P < 0.05). Similar responses were observed in isolated myocytes harvested from LV biopsies before and after CHF. In the normal myocyte, L-748,337 did not cause significant changes in contraction or relengthening. In contrast, in CHF myocytes, L-748,337 produced significant increases in contraction (5.8 ± 0.9 vs. 6.8 ± 0.9%, P < 0.05) and relengthening (33.5 ± 4.2 vs. 39.7 ± 4.0 μm/s, P < 0.05). The L-748,337-induced myocyte response was associated with improved intracellular Ca2+ concentration regulation. In CHF myocytes, nadolol caused a decrease in contraction and relengthening, and adding isoproterenol to nadolol caused a further depression of myocyte function. Stimulation of β3-AR by endogenous catecholamine contributes to the depression of LV contraction and relaxation in CHF.

The Trp64Arg polymorphism of the beta3-adrenergic receptor is not increased in women with preeclampsia

OBJECTIVE

Insulin resistance is greater and obesity is more common in women with preeclampsia. The Trp64Arg polymorphism in the beta(3)-adrenergic receptor is associated with these metabolic changes. This study investigated whether the Trp64Arg polymorphism is more common in women with preeclampsia.

STUDY DESIGN

beta(3)-Adrenergic receptor genotypes were determined in 177 women with a history of preeclampsia and in 179 normal pregnancies. We also compared prepregnancy body mass index (BMI), length of gestation, baby weight percentile, and glucose values during an oral tolerance test in women with and without the polymorphism.

RESULTS

The genotypes and allele frequency did not differ significantly between women with preeclamptic and normal pregnancies (P=.17). Women with and without the polymorphism had similar prepregnancy BMI, glucose at 1-hour screening, gestational age at delivery, and adjusted baby weight.

CONCLUSION

The Trp64Arg polymorphism of the beta(3)-receptor does not predispose to preeclampsia, and it is it not associated with obesity and carbohydrate intolerance in a population of young pregnant women.

Role of alpha-adrenergic receptors in the effect of the beta-adrenergic receptor ligands, CGP 12177, bupranolol, and SR 59230A, on the contraction of rat intrapulmonary artery

This study investigates the effect of the aryloxypropanolamines 4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one (CGP 12177), bupranolol, and 3-(2-ethylphenoxy)-1[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol oxalate (SR 59230A) [commonly used as beta(3)- and/or atypical beta-adrenergic receptors (beta-AR) ligands] on the contractile function of rat intralobar pulmonary artery. Affinities of beta-AR ligands for alpha(1)-adrenergic receptors (alpha(1)-AR) were also evaluated using [(3)H]prazosin binding competition experiments performed in rat cortical membranes. In intralobar pulmonary artery, CGP 12177 did not modify the basal tone, but antagonized the contraction induced by the alpha(1)-AR agonist phenylephrine (PHE). In arteries precontracted with PHE, CGP 12177 elicited relaxation, whereas in those precontracted with prostaglandin F(2alpha) (PGF(2alpha)), it further enhanced contraction. CGP 12177 induced an increase in intracellular calcium concentration in pressurized arteries loaded with Fura PE-3 and precontracted with PGF(2alpha). In PGF(2alpha) precontracted arteries, phentolamine (an alpha-AR antagonist) and phenoxybenzamine (an irreversible alpha-AR antagonist) antagonized the contractile responses to PHE and CGP 12177. Both responses were also decreased by bupranolol and SR 59230A. Specific [(3)H]prazosin binding was displaced by CGP 12177, bupranolol, and SR 59230A with pK(i) values of 5.2, 5.7, and 6.6, respectively. In contrast, (+/-)-(R*,R*)-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid sodium (BRL 37344) and disodium 5-[(2R)-2-([(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL 316243) (nonaryloxypropanolamines beta(3)-AR agonists) displayed very low affinity for [(3)H]prazosin binding sites (pK(i) values below 4). These data suggest that CGP 12177 exhibits partial agonist properties for alpha(1)-AR in rat pulmonary artery. They also show that bupranolol and SR 59230A exert an alpha(1)-AR antagonist effect. As a consequence, these aryloxypropanolamine compounds should be used with caution when investigating the role of beta(3)- and atypical beta-AR in the regulation of vascular tone.

Stereoselectivity for interactions of agonists and antagonists at mouse, rat and human β3-adrenoceptors

This study examines the stereoselectivity profile of recombinant mouse, rat and human beta(3)-adrenoceptors expressed in Chinese Hamster Ovary (CHO-K1) cells using radioligand binding, in comparison with endogenously expressed beta(3)-adrenoceptors mediating relaxation responses in mouse ileum. The enantiomeric ratios for several beta-adrenoceptor agonists and antagonists at the cloned mouse, rat and human beta(3)-adrenoceptor were less than those reported at the cloned beta(1)-/beta(2)-adrenoceptor but higher than those reported in previous studies. The degree of stereoselectivity was relatively low for the agonists isoprenaline and noradrenaline but higher for antagonists and, in particular, tertatolol and propranolol. In mouse ileum, stereoselectivity of propranolol and tertatolol was observed under beta(1)-/beta(2)-adrenoceptor blockade. The (-)-enantiomers of propranolol and tertatolol were more effective at antagonism of (-)-isoprenaline-mediated relaxation of mouse ileum than their (+)-enantiomers. The recombinant mouse, rat and human beta(3)-adrenoceptors display stereoselective interactions for agonists and antagonists similar to the stereoselective profile of beta(3)-adrenoceptors in mouse ileum. The degree of stereoselectivity varied between species and the human beta(3)-adrenoceptor displayed higher affinities and enantiomeric ratios than the mouse or rat beta(3)-adrenoceptors.