The rat lipolytic beta-adrenoceptor: studies using novel beta-adrenoceptor agonists

Is the β3-Adrenoceptor a Valid Target for the Treatment of Obesity and/or Type 2 Diabetes?

β3-Adrenoceptors mediate several functions in rodents that could be beneficial for the treatment of obesity and type 2 diabetes. This includes promotion of insulin release from the pancreas, cellular glucose uptake, lipolysis, and thermogenesis in brown adipose tissue. In combination, they lead to a reduction of body weight in several rodent models including ob/ob mice and Zucker diabetic fatty rats. These findings stimulated drug development programs in various pharmaceutical companies, and at least nine β3-adrenoceptor agonists have been tested in clinical trials. However, all of these projects were discontinued due to the lack of clinically relevant changes in body weight. Following a concise historical account of discoveries leading to such drug development programs we discuss species differences that explain why β3-adrenoceptors are not a meaningful drug target for the treatment of obesity and type 2 diabetes in humans.

Cardiac β3 -adrenoceptors-A role in human pathophysiology?

As β₃ -adrenoceptors were first demonstrated to be expressed in adipose tissue they have received much attention for their metabolic effects in obesity and diabetes. After the existence of this subtype had been suggested to be present in the heart, studies focused on its role in cardiac function. While the presence and functional role of β₃ -adrenoceptors in the heart has not uniformly been detected, there is a broad consensus that they become up-regulated in pathological conditions associated with increased sympathetic activity such as heart failure and diabetes. When detected, the β₃ -adrenceptor has been demonstrated to mediate negative inotropic effects in an inhibitory G protein-dependent manner through the NO-cGMP-PKG signalling pathway. Whether these negative inotropic effects provide protection from the adverse effects induced by overstimulation of β₁ /β₂ -adrenoceptors or in themselves are potentially harmful is controversial, but ongoing clinical studies in patients with congestive heart failure are testing the hypothesis that β₃ -adrenceptor agonism has a beneficial effect. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

BRL37344 stimulates GLUT4 translocation and glucose uptake in skeletal muscle via β2-adrenoceptors without causing classical receptor desensitization

The type 2 diabetes epidemic makes it important to find insulin-independent ways to improve glucose homeostasis. This study examines the mechanisms activated by a dual β₂-/β₃-adrenoceptor agonist, BRL37344, to increase glucose uptake in skeletal muscle and its effects on glucose homeostasis in vivo. We measured the effect of BRL37344 on glucose uptake, glucose transporter 4 (GLUT4) translocation, cAMP levels, β₂-adrenoceptor desensitization, β-arrestin recruitment, Akt, AMPK, and mammalian target of rapamycin (mTOR) phosphorylation using L6 skeletal muscle cells as a model. We further tested the ability of BRL37344 to modulate skeletal muscle glucose metabolism in animal models (glucose tolerance tests and in vivo and ex vivo skeletal muscle glucose uptake). In L6 cells, BRL37344 increased GLUT4 translocation and glucose uptake only by activation of β₂-adrenoceptors, with a similar potency and efficacy to that of the nonselective β-adrenoceptor agonist isoprenaline, despite being a partial agonist with respect to cAMP generation. GLUT4 translocation occurred independently of Akt and AMPK phosphorylation but was dependent on mTORC2. Furthermore, in contrast to isoprenaline, BRL37344 did not promote agonist-mediated desensitization and failed to recruit β-arrestin1/2 to the β₂-adrenoceptor. In conclusion, BRL37344 improved glucose tolerance and increased glucose uptake into skeletal muscle in vivo and ex vivo through a β₂-adrenoceptor-mediated mechanism independently of Akt. BRL37344 was a partial agonist with respect to cAMP, but a full agonist for glucose uptake, and importantly did not cause classical receptor desensitization or internalization of the receptor.

Adrenergic regulation of cellular plasticity in brown, beige/brite and white adipose tissues

The discovery of brown adipose tissue in adult humans along with the recognition of adipocyte heterogeneity and plasticity of white fat depots has renewed the interest in targeting adipose tissue for therapeutic benefit. Adrenergic activation is a well-established means of recruiting catabolic adipocyte phenotypes in brown and white adipose tissues. In this article, we review mechanisms of brown adipocyte recruitment by the sympathetic nervous system and by direct β-adrenergic receptor activation. We highlight the distinct modes of brown adipocyte recruitment in brown, beige/brite, and white adipose tissues, UCP1-independent thermogenesis, and potential non-thermogenic, metabolically beneficial effects of brown adipocytes.

Classification of Therapeutic and Experimental Drugs for Brown Adipose Tissue Activation: Potential Treatment Strategies for Diabetes and Obesity

OBJECTIVE

Increasing efforts are being made towards pharmacologic activation of brown adipose tissue (BAT) in animals and humans for potential use in the treatment of obesity and diabetes. We and others have reported a number of animal studies using either experimental or therapeutic drugs. There are now efforts to translate these findings to human studies. The goal of this review is to evaluate the various drugs currently being used that have the potential for BAT activation.

METHODS

Drugs were classified into 4 classes based on their mechanism of action. Class 1 drugs include the use of β3 adrenoceptor agonists for BAT activation. Class 2 drugs include drugs that affect norepinephrine levels and activate BAT with the potential of reducing obesity. Class 3 includes activators of peroxisome proliferator-activated receptor-γ in pursuit of lowering blood sugar, weight loss and diabetes and finally Class 4 includes natural products and other emerging drugs with limited information on BAT activation and their effects on diabetes and weight loss.

RESULTS

Class 1 drugs are high BAT activators followed by Class 2 and 3. Some of these drugs have now been extended to diabetes and obesity animal models and human BAT studies. Drugs in Class 3 are used clinically for Type 2 diabetes, but the extent of BAT involvement is unclear.

CONCLUSION

Further studies on the efficacy of these drugs in diabetes and measuring their effects on BAT activation using noninvasive imaging will help in establishing a clinical role of BAT.

Feeding Scallop Shell Powder Induces the Expression of Uncoupling Protein 1 (UCP1) in White Adipose Tissue of Rats

Previously we found that the organic components in scallop shell promote lipolysis in differentiated 3T3-L1 and C3H10T1/2 adipocyte cells, and that incorporating scallop shell powder into the diet of rats reduced the amount of white adipose tissue. In this study, we used RT-PCR to investigate the effect of ingesting scallop shell powder on the gene expression profile of uncoupling proteins (UCPs) regulating energy metabolism in rats. Feeding of scallop shell powder increased mRNA levels of UCP1 and UCP2 in white adipose tissue. By contrast, scallop shell powder had no effect on the expression of UCP1 in brown adipose tissue, although the expression level of UCP2 mRNA decreased significantly. These results suggest that feeding scallop shell powder increases gene expression of UCP1 that may regulate energy metabolism in white adipose tissue, resulting in the observed reduction in weight of white adipose tissue.

Angiotensin II Stimulates Sympathetic Neurotransmission to Adipose Tissue

Angiotensin II (AngII) facilitates sympathetic neurotransmission by regulating norepinephrine (NE) synthesis, release, and uptake. These effects of AngII contribute to cardiovascular control. Previous studies in our laboratory demonstrated that chronic AngII infusion decreased body weight of rats. We hypothesized that AngII facilitates sympathetic neurotransmission to adipose tissue and may thereby decrease body weight. The effect of chronic AngII infusion on the NE uptake transporter and NE turnover was examined in metabolic (interscapular brown adipose tissue, ISBAT; epididymal fat, EF) and cardiovascular tissues (left ventricle, LV; kidney) of rats. To examine the uptake transporter saturation isotherms were performed using [³H]nisoxetine (NIS). At doses that lowered body weight, AngII significantly increased ISBAT [³H]NIS binding density. To quantify NE turnover, alpha-methyl-para-tyrosine (AMPT) was injected in saline-infused, AngII-infused, or saline-infused rats that were pair-fed to food intake of AngII-infused rats. AngII significantly increased the rate of NE decline in all tissues compared to saline. The rate of NE decline in EF was increased to a similar extent by AngII and by pair feeding. In rats administered AngII and propranolol, reductions in food and water intake and body weight were eliminated. These data support the hypothesis that AngII facilitates sympathetic neurotransmission to adipose tissue. Increased sympathetic neurotransmission to adipose tissue following AngII exposure is suggested to contribute to reductions in body weight.

β-adrenoreceptor blocking and antihypertensive activity of PP-24, a newly synthesized aryloxypropanolamine derivative

PP-24 is a newly synthesized putative β-adrenoceptor antagonist. The objective of the study was to the evaluate β-adrenoceptor blocking activity of PP-24 on isolated rat preparations: right atria, uterus and colon. Effects on the rat ECG and renal hypertension (induced by left renal artery ligation) were also investigated. Treatment with PP-24 (3 and 10 mg kg−1) for 7 days in rats with renal hypertension significantly reduced the mean atrial blood pressure. Single i.v. injections of isoprenaline (0.3, 1 and 3 μg kg−1) alone in normal anaesthetized rat caused hypotension and tachycardia, while PP-24 alone produced dose-dependent falls in mean aterial pressure and bradycardia. Pretreatment of anaesthetized rats with test compounds significantly blocked the hypotension response but not the tachycardia induced by isoprenaline (0.3, 1 and 3 μg kg−1). The pA2 of PP-24 to β1-, β2- and β3-adrenoceptors was 7.72 ± 0.082, 7.40 ± 0.082 and 6.39 ± 0.16, respectively. The β1/β2 selectivity ratio was 2.08, compared with 1.27 for propranolol and 39.17 for atenolol. It is concluded that PP-24 possesses β-adrenoceptor blockade activity but with non-specific affinity for β1- and β2-adrenoceptor subtypes. The rank order of potency of the antagonists for β1-adrenoceptors was atenolol > PP-24 > propranolol. The antihypertensive activity of PP-24 in rats with renal hypertension appears to be due to blockade of β-adrenoceptors.

The rush to adrenaline: drugs in sport acting on the beta-adrenergic system

Athletes attempt to improve performance with drugs that act on the beta-adrenergic system directly or indirectly. Of three beta-adrenoceptor (AR) subtypes, the beta(2)-AR is the main target in sport; they have bronchodilator and anabolic actions and enhance anti-inflammatory actions of corticosteroids. Although demonstrable in animal experiments and humans, there is little evidence that these properties can significantly improve performance in trained athletes. Their actions may also be compromised by receptor desensitization and by common, naturally occurring receptor mutations (polymorphisms) that can influence receptor signalling and desensitization properties in individuals. Indirectly acting agents affect release and reuptake of noradrenaline and adrenaline, thereby influencing all AR subtypes including the three beta-ARs. These agents can have potent psychostimulant effects that provide an illusion of better performance that does not usually translate into improvement in practice. Amphetamines and cocaine also have considerable potential for cardiac damage. beta-AR antagonists (beta-blockers) are used in sports that require steadiness and accuracy, such as archery and shooting, where their ability to reduce heart rate and muscle tremor may improve performance. They have a deleterious effect in endurance sports because they reduce physical performance and maximum exercise load. Recent studies have identified that many beta-AR antagonists not only block the actions of agonists but also activate other (mitogen-activated PK) signalling pathways influencing cell growth and fate. The concept that many compounds previously regarded as 'blockers' may express their own spectrum of pharmacological properties has potentially far-reaching consequences for the use of drugs both therapeutically and illicitly.

The discovery of drugs for obesity, the metabolic effects of leptin and variable receptor pharmacology: perspectives from beta3-adrenoceptor agonists

Although beta3-adrenoceptor (beta3AR) agonists have not become drugs for the treatment of obesity or diabetes, they offer perspectives on obesity drug discovery, the physiology of energy expenditure and receptor pharmacology. beta3AR agonists, some of which also stimulate other betaARs in humans, selectively stimulate fat oxidation in rodents and humans. This appears to be why they improve insulin sensitivity and reduce body fat whilst preserving lean body mass. Regulatory authorities ask that novel anti-obesity drugs improve insulin sensitivity and reduce mainly body fat. Drugs that act on different targets to stimulate fat oxidation may also offer these benefits. Stimulation of energy expenditure may be easy to detect only when the sympathetic nervous system is activated. Leptin resembles beta3AR agonists in that it increases fat oxidation, energy expenditure and insulin sensitivity. This is partly because it raises sympathetic activity, but it may also promote fat oxidation by directly stimulating muscle leptin receptors. The beta1AR and beta2AR can, like the beta3AR, display atypical pharmacologies. Moreover, the beta3AR can display variable pharmacologies of its own, depending on the radioligand used in binding studies or the functional response measured. Studies on the beta3AR demonstrate both the difficulties of predicting the in vivo effects of agonist drugs from in vitro data and that there may be opportunities for identifying drugs that act at a single receptor but have different profiles in vivo.

Metabolic responses to BRL37344 and clenbuterol in soleus muscle and C2C12 cells via different atypical pharmacologies and beta2-adrenoceptor mechanisms

BACKGROUND AND PURPOSE

Picomolar concentrations of the beta3-adrenoceptor agonist BRL37344 stimulate 2-deoxyglucose uptake in soleus muscle via undefined receptors. Higher concentrations alter uptake, apparently via beta2-adrenoceptors. Effects of BRL37344 and beta2-adrenoceptor agonists are compared.

EXPERIMENTAL APPROACH

Mouse soleus muscles were incubated with 2-deoxy[1-(14)C]-glucose, [1-(14)C]-palmitate or [2-(14)C]-pyruvate, and BRL37344, beta2-adrenoceptor agonists and selective beta-adrenoceptor antagonists. Formation of 2-deoxy[1-(14)C]-glucose-6-phosphate or (14)CO2 was measured. 2-Deoxy[1-(14)C]-glucose uptake and beta-adrenoceptor mRNA were measured in C2C12 cells.

KEY RESULTS

10 pM BRL37344, 10 pM clenbuterol and 100 pM salbutamol stimulated 2-deoxyglucose uptake in soleus muscle by 33-54%. The effect of BRL37344 was prevented by 1 microM atenolol but not by 300 nM CGP20712A or IC3118551, or 1 microM SR59230A; that of clenbuterol was prevented by ICI118551 but not atenolol. 10 nM BRL37344 stimulated 2-deoxyglucose uptake, whereas 100 nM clenbuterol and salbutamol inhibited uptake. These effects were blocked by ICI118551. Similar results were obtained in C2C12 cells, in which only beta2-adrenoceptor mRNA could be detected by RT-PCR. 10 nM BRL37344 and 10 pM clenbuterol stimulated muscle palmitate oxidation. In the presence of palmitate, BRL37344 no longer stimulated 2-deoxyglucose uptake and the effect of clenbuterol was not significant.

CONCLUSIONS AND IMPLICATIONS

Stimulation of glucose uptake by 10 pM BRL37344 and clenbuterol involves different atypical pharmacologies. Nanomolar concentrations of BRL37344 and clenbuterol, probably acting via beta2-adrenoceptors, have opposite effects on glucose uptake. The agonists preferentially stimulate fat rather than carbohydrate oxidation, but stimulation of endogenous fat oxidation cannot explain why 100 nM clenbuterol inhibited 2-deoxyglucose uptake.

Synthesis and evaluation of potent and selective β3 adrenergic receptor agonists containing heterobiaryl carboxylic acids

The design, synthesis, and SAR of a novel series of heterobiaryl phenethanolamine beta3 adrenergic receptor agonists are described. The furan analogue 49 was shown to elicit a significant dose-dependent lowering of plasma glucose in a rodent model of type 2 diabetes.

Role of Beta-3-Adrenoceptor in Catecholamine-Induced Relaxations in Gastric Fundus from Control and Diabetic Rats

The contribution of beta-adrenoceptor subtypes to the catecholamine-mediated relaxations in gastric fundus from control and streptozotocin (STZ)-induced diabetic rats were investigated. Isolated organ bath studies and molecular techniques were used to characterize the beta-adrenoceptor subtypes mediating relaxation of rat gastric fundus. Isoprenaline-mediated relaxation was not significantly changed by nadolol (beta(1)-/beta(2)-adrenoceptor antagonist; 1 micromol/l) but only shifted to the right by SR59230A (3-(2-ethylphenoxy)-1-[[(1S)-1,2,3,4-tetrahydronaphth-1-yl]amino]-(2S)-2-propanol oxalate salt, 0.1-1 micromol/l), a selective beta(3)-adrenoceptor antagonist, in a competitive manner. Relaxant responses to noradrenaline were antagonized in a concentration-dependent manner by SR59230A (0.1-1 micromol/l), but not by metoprolol (selective beta(1)-adrenoceptor antagonist; 0.1-1 micromol/l) and ICI-118551 (1-[2,3-(dihydro-7-methyl-1Hinden- 4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride, selective beta(2)-adrenoceptor antagonist; 0.1-1 micromol/l). SR59230A (1 micromol/l) also caused a significant rightward shift in fenoterol-induced relaxation while ICI-118551 (1 micromol/l) did not have any effect. Selective beta(3)-adrenoceptor agonist, BRL37344 ([4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid), caused biphasic relaxation which was not affected by nadolol (1 micromol/l). SR59230A (1 micromol/l) abolished only the first phase of BRL37344 response. beta(1)-, beta(2)- and beta(3)-adrenoceptor mRNA expressions have been detected in a similar intensity in gastric fundus from control rats. Experimental diabetes caused a significant decrease in E(max) and pD(2) values of isoprenaline and noradrenaline. Diabetes also reduced E(max) but not pD(2) value of the first component of BRL37344-induced relaxation response. The band intensity of mRNA transcript of beta(3)-adrenoceptor was reduced in diabetics while no alteration has been found for beta(1)- and beta(2)-adrenoceptor mRNA transcripts between groups. These results show that functional beta-adrenoceptor subtype involved in catecholamine-mediated relaxations is beta(3)-adrenoceptor, and its function and mRNA expression are decreased in diabetes.

Pharmacological characterization of the β-adrenoceptor that mediates the relaxant response to noradrenaline in guinea-pig tracheal smooth muscle

Pharmacological characteristics of beta-adrenoceptors (beta-ARs) mediating noradrenaline-induced relaxation were investigated in guinea-pig tracheal smooth muscle. The inhibitory effects of several types of beta-AR antagonists on noradrenaline-induced relaxation against histamine contraction were scrutinized with Schild plot analysis. The concentration-response curve for noradrenaline obtained in the absence of phentolamine and uptake inhibitors was competitively antagonized by all of the beta-AR antagonists used in this study (propranolol, bupranolol, atenolol, butoxamine and ICI-118,551). However, their pA2 values were markedly less than the expected values for beta1-AR and beta2-AR. On the other hand, pA2 values of ICI-118,551 (6.85) determined in the presence of phentolamine suggested a contribution of a beta1 -AR rather than beta2 -AR. In the presence of phentolamine and uptake inhibitors (desipramine and deoxycorticosterone), the Schild plot for atenolol was a better fit, with two distinct straight lines. The pA2 values of atenolol provided by the regression were: approximately 7.0, which corresponds to the expected beta1-AR value, and approximately 6.5, which was 3 times less than the expected value for beta1 -AR, and thus the possible presence of two classes of beta1 -AR (beta1(Low) and beta1(High)) was suggested. This view was also supported by Schild plot analysis for propranolol, which fit two straight lines each with a slope of 1.0. The present findings indicate that beta1 -ARs contributing to noradrenaline-elicited relaxation in guinea-pig tracheal smooth muscle exhibit diverse pharmacological characteristics and may be subdivided into at least two classes with distinct affinities for atenolol. Under physiological conditions, beta1(Low) rather than beta1(High) seems to play a more significant role in noradrenaline-regulated airway smooth muscle tone.

Discovery of a novel and potent human and rat beta3-adrenergic receptor agonist, [3-[(2R)-[[(2R)-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1H-indol-7-yloxy]acetic acid

In search for potent and selective beta3-adrenergic receptor (beta3-AR) agonists as potential drugs for the treatment of type II diabetes and obesity, a novel series of 1-(3-chlorophenyl)-2-aminoethanol derivatives were prepared and evaluated for their biological activity at human beta1-, beta2-, and beta3-ARs and rat beta3-AR expressed in Chinese hamster ovary (CHO) cells. Replacement of the right-hand side (RHS, benzene ring) in the 'first generation' beta3-AR agonists BRL 37344 and CL 316243 with a 1H-indole ring gave compound 31 with unique pharmacological properties among beta3-AR agonists. Initial in vitro assays showed that 31 possesses modest rat and human beta3-ARs agonistic activity. Introduction of various substituent into the indole nucleus of 31 afforded a number of compounds with good beta3-ARs agonistic activity. In particular, 90 having a carboxylic acid functionality at the 7-position of the indole nucleus showed the most potent human beta3-AR agonistic activity. Finally, optical resolution of 90 led to the identification of the most promising compound, [3-[(2R)-[[(2R)-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1H-indol-7-yloxy]acetic acid (96, AJ-9677). This compound exhibited potent human beta3-AR agonistic activity (EC50=0.062 nM, IA=116%) with 210- and 103-fold selectivity over human beta2-AR and beta1-AR, respectively. Compound 96 also exhibited potent rat beta3-AR agonistic activity (EC50=0.016 nM, IA=110%). Moreover, repeated oral administration of 96 inhibited body weight gain and significantly decreased glucose, insulin, free fatty acid, and triglyceride concentrations in plasma in KK-Ay/Ta mice. On the basis of this pharmacological profile, 96 entered clinical development as a drug for the treatment of type II diabetes and obesity.

β3-adrenergic agonists: potential therapeutics for obesity

During the last decade a number of beta3-adrenergic receptor agonists have been advanced to clinical trials. The results of human studies to date have been disappointing with respect to sustained increases in metabolic rate and weight loss. Cloning of beta3-adrenoceptors in a number of species and subsequent pharmacological evaluations revealed these early investigational drugs to be weakly active against the human receptor, suggesting an explanation for the poor performance of these compounds in clinical trials. This information has been integrated into subsequent research efforts resulting in the discovery of agents with activities optimised for the human receptor. This new generation of compounds is in late preclinical/early clinical development and are poised to address the role beta3-adrenoceptor signalling plays in the obese state. Issues related to the potential for beta3-adrenergic agonists to positively impact metabolic parameters in humans are also discussed.

Response to intra- and extracellular lipolytic agents and hormone-sensitive lipase translocation are impaired in adipocytes from rats adapted to a high-protein, carbohydrate-free diet

We showed previously that rats adapted to a high-protein (70%), carbohydrate-free (HP) diet have reduced lipolytic activity. To clarify the underlying biochemical mechanisms, several metabolic processes involved in adipose tissue lipolysis were investigated. The experiments were performed in rats adapted for 15 d to an HP or a balanced diet. In agreement with previous results, microdialysis experiments showed that the concentrations of adipose tissue interstitial and arterial plasma glycerol were lower in rats adapted to the HP diet. Under nonstimulated conditions, rates of lipolysis, estimated by glycerol release to the incubation medium, were reduced in adipocytes from HP rats. Under the same conditions, there was a small, but significant (17%) reduction in the activity of hormone sensitive lipase (HSL), with no change in the content of the enzyme. Upon stimulation with isoproterenol, the percentage of the enzyme in the adipocyte cytosol translocated to the fat droplet was 20-25%in HP rats and 40-50% in rats fed the balanced diet. Adipocytes from HP diet-adapted rats had a significantly reduced response (approximately 40%) to the lipolytic action of nonspecific (norepinephrine, epinephrine, isoproterenol) and specific (CL316,243, BRL37,344, dobutamine, clenbuterol) beta-adrenergic agonists. Adipocytes from HP rats also had a reduced lipolytic response to the intracellular agents, dibutyryl cAMP (44%), forskolin (46%), and isobutyl-methylxanthine (29%). The data suggest that the main mechanism responsible for the reduced basal and stimulated lipolysis in HP diet-adapted rats is an impairment in the intracellular process of lipolysis activation, with a deficient translocation of HSL to the fat droplet.

Molecular characterization of pharmacological properties and selectivity of SWR-0315NA for beta3-adrenoceptors

The pharmacological properties of SWR-0315NA, (E,Z)-[4[[1-[2-[(3-phenoxy-2-hydroxy propyl)]amino]ethyl]-1-propenyl]phenoxy]acetic acid sodium, were compared with those of (-)-isoproterenol. In the radioligand binding studies of [(125)I]iodocyanopindolol with COS-7 cell membranes that transiently expressed human beta-adrenoceptor (beta-AR) subtypes, SWR-0315NA exhibited 1-fold and 2-fold greater binding affinities for beta(3)-AR than those for beta(1)- and beta(2)-ARs, respectively. The maximal stimulatory effects of SWR-0315NA on cAMP accumulation in CHO cells expressing all the beta-AR subtypes were 79%, 3% and 93% for beta(1)-, beta(2)- and beta(3)-ARs of those produced by (-)-isoproterenol, respectively. SWR-0315NA has 26.3-fold and more than 630-fold greater selectivity for beta(3)-AR than those for beta(1)- and beta(2)-ARs in potency, respectively. These results indicate that although SWR-0315NA has lower binding selectivity towards beta-AR subtypes, it is a selective agonist with high intrinsic activity for beta(3)-AR as compared with (-)-isoproterenol.

Beta-adrenoceptor polymorphisms

There can be no doubt that beta(1)-, beta(2)- and beta(3)-adrenoceptor genes have genetic polymorphisms. Two single nucleotide polymorphisms have been described for the beta(1)- (Ser49Gly; Gly389Arg), three for the beta(2)- (Arg16Gly; Gln27Glu; Thr164Ile) and one for the beta(3)-adrenoceptor subtype (Trp64Arg) that might be of functional importance. The possibility that changes in expression or properties of the beta-adrenoceptors due to single nucleotide polymorphisms might have phenotypic consequences influencing their cardiovascular or metabolic function or may contribute to the pathophysiology of several disorders like hypertension, congestive heart failure, asthma or obesity is an idea that has attracted much interest during the last 10 years. At present, it appears that these beta-adrenoceptor polymorphisms are very likely not disease-causing genes, but might be risk factors, might modify disease and/or might influence progression of disease. The aim of this review is to provide an overview of the functional consequences of such beta-adrenoceptor polymorphisms in vitro, ex vivo and in vivo.

Microbial/enzymatic synthesis of chiral drug intermediates

Biocatalytic processes were used to prepare chiral intermediates for pharmaceuticals. These include the following processes. Enzymatic synthesis of [4S-(4a,7a,10ab)]1-octahydro-5-oxo-4-[[(phenylmethoxy) carbonyl]amino]-7H-pyrido-[2,1-b] [1,3]thiazepine-7-carboxylic acid methyl ester (BMS-199541-01), a key chiral intermediate for synthesis of a new vasopeptidase inhibitor. Enzymatic oxidation of the epsilon-amino group of lysine in dipeptide dimer N2-[N[[(phenylmethoxy)carbonyl] L-homocysteinyl] L-lysine)1,1-disulfide (BMS-201391-01) to produce BMS-199541-01 using a novel L-lysine epsilon-aminotransferase from S. paucimobilis SC16113 was demonstrated. This enzyme was overexpressed in E. coli, and a process was developed using recombinant enzyme. The aminotransferase reaction required alpha-ketoglutarate as the amine acceptor. Glutamate formed during this reaction was recycled back to alpha-ketoglutarate by glutamate oxidase from S. noursei SC6007. Synthesis and enzymatic conversion of 2-keto-6-hydroxyhexanoic acid 5 to L-6-hydroxy norleucine 4 was demonstrated by reductive amination using beef liver glutamate dehydrogenase. To avoid the lengthy chemical synthesis of ketoacid 5, a second route was developed to prepare the ketoacid by treatment of racemic 6-hydroxy norleucine (readily available from hydrolysis of 5-(4-hydroxybutyl) hydantoin, 6) with D-amino acid oxidase from porcine kidney or T. variabilis followed by reductive amination to convert the mixture to L-6-hydroxynorleucine in 98% yield and 99% enantiomeric excess. Enzymatic synthesis of (S)-2-amino-5-(1,3-dioxolan-2-yl)-pentanoic acid (allysine ethylene acetal, 7), one of three building blocks used for synthesis of a vasopeptidase inhibitor, was demonstrated using phenylalanine dehydrogenase from T. intermedius. The reaction requires ammonia and NADH. NAD produced during the reaction was recycled to NADH by oxidation of formate to CO2 using formate dehydrogenase. Efficient synthesis of chiral intermediates required for total chemical synthesis of a beta 3 receptor agonist was demonstrated. These include: (a) microbial reduction of 4-benzyloxy-3-methanesulfonylamino-2'-bromoacetophenone 9 to corresponding (R)-alcohol 10 by S. paucimobilis SC16113, (b) enzymatic resolution of racemic alpha-methyl phenylalanine amide 11 and alpha-methyl-4-hydroxyphenylalanine amide 13 by amidase from M. neoaurum ATCC 25795 to prepare corresponding (S)-amino acids 12 and 14, and (c) asymmetric hydrolysis of methyl-(4-methoxyphenyl)-propanedioic acid ethyl diester 15 to corresponding (S)-monoester 16 by pig liver esterase. (S)[1-(acetoxyl)-4-(3-phenyl)butyl]phosphonic acid diethyl ester 21, a key chiral intermediate required for total chemical synthesis of BMS-188494 (an anticholesterol drug) was prepared by stereoselective acetylation of racemic [1-(hydroxy)-4-(3-phenyl)butyl]phosphonic acid diethyl ester 22 using G. candidum lipase. Lipase-catalyzed stereoselective acetylation of racemic 7-[N,N'-bis-(benzyloxy-carbonyl)N-(guanidinoheptanoyl)]-alpha-hydroxy-glycine 24 to corresponding S-(-)-acetate 25 was demonstrated. S-(-)-acetate 25 is a key intermediate for total chemical synthesis of (-)-15-deoxyspergualin 23, an immunosuppressive agent and antitumor antibiotic. Stereoselective microbial reduction of (1S)[3-chloro-2-oxo-1-(phenyl-methyl)propyl] carbamic acid, 1,1-dimethyl-ethyl ester 26 to corresponding chiral alcohol 27a (a key chiral intermediate for HIV protease inhibitors) was also demonstrated. Stereospecific enzymatic hydrolysis of racemic epoxide RS-1-[2',3'-dihydro benzo[b]furan-4'-yl]-1,2-oxirane 29 the corresponding R-diol 30 and unreacted chiral S-epoxide 28 was demonstrated using R. glutinis and A. niger. Dynamic resolution of racemic diol RS-1-[2',3'-dihydrobenzo[b]furan-4'-yl]-ethane-1,2-diol 32 to corresponding S-diol S-1-[2',3'-dihydrobenzo[b]furan-4'-yl]-ethane-1,2-diol 31 was demonstrated using C. boidinii and P. methanolica. Chiral (S)-epoxide 28 and (S)-diol 31 are key intermediates for a new prospective circadian modulator drug. Enzymatic resolution of racemic 2-pentanol and 2-heptanol by lipase B from Candida antarctica was demonstrated. S-(+)-2-pentanol is a key chiral intermediate required for synthesis of anti-Alzheimer's drugs.

Evidence against beta 3-adrenoceptors or low affinity state of beta 1-adrenoceptors mediating relaxation in rat isolated aorta

1 The presence of beta(3)-adrenoceptors and the low affinity state of the beta(1)-adrenoceptor (formerly "putative beta(4)-adrenoceptor") was investigated in ring preparations of rat isolated aorta preconstricted with phenylephrine or prostaglandin F(2alpha) (PGF(2alpha)). Relaxant responses to isoprenaline, selective beta(3)-adrenoceptor agonists (BRL 37344, SR 58611A, CL 316243) and non-conventional partial agonists (CGP 12177A, cyanopindolol, pindolol) were obtained. 2 In phenylephrine-constricted, but not PGF(2alpha)-constricted rings, relaxations to isoprenaline showed a propranolol-resistant component. 3 In phenylephrine-constricted rings, relaxations to BRL 37344 (pEC(50), 4.64) and SR 58611A (pEC(50), 4.94) were not antagonized by the selective beta(3)-adrenoceptor antagonist SR 59230A (< or =1 microM). CL 316243 (< or =100 microM) failed to produce relaxation. In PGF(2alpha)-constricted rings only SR 58611A produced relaxation, which was not affected by SR 59230A (< or =3 microM). 4 Non-conventional partial agonists produced relaxation in phenylephrine-constricted but not PGF(2alpha)-constricted rings. The relaxation to CGP 12177A was unaffected by SR 59230A (< or =1 microM) or by CGP 20712A (10 microM), reported to block the low affinity state of the beta(1)-adrenoceptor. 5 beta-adrenoceptor antagonists also produced relaxation in phenylephrine-constricted rings with an order of potency of (pEC(50) values): bupranolol (5.5) approximately 38;SR 59230A (5.47) approximately 38;cyanopindolol (5.47)>pindolol (5.30)>alprenolol (5.10)>propranolol (4.83)>ICI 118551 (4.60)>CGP 12177A (4.38) approximately 38;CGP 20712A (4.35). Bupranolol (100 microM), alprenolol (30 microM), propranolol (100 microM) and SR 59230A (10 microM) produced no relaxation in PGF(2alpha)-constricted rings. 6 These results provide no evidence for the presence of functional beta(3)-adrenoceptors or the low affinity state of the beta(1)-adrenoceptor in rat aorta.

Estrogen levels influence beta-3-adrenoceptor-mediated relaxation of the female rat detrusor muscle

OBJECTIVES

To observe the expression of beta-3-adrenoceptor in the detrusor muscle in female rats and investigate the relaxant effect of beta-adrenoceptor agonists on detrusor muscle in ovariectomized rats with or without estrogen replacement therapy.

METHODS

We first performed reverse transcriptase-polymerase chain reaction to demonstrate mRNA encoding the beta-3-adrenoceptor in the detrusor muscle from female rats. We then performed pharmacologic and physiologic studies to determine the effect of estrogen replacement therapy on the beta-adrenoceptor-mediated relaxation of the detrusor muscle of the ovariectomized rats.

RESULTS

Beta-3-adrenoceptor was expressed in the detrusor muscle in female rats with or without ovariectomy. A nonselective beta-adrenoceptor agonist relaxed precontracted detrusor muscle irrespective of ovariectomy or estrogen replacement in a dose-dependent manner; and a selective beta-3-adrenoceptor agonist relaxed the detrusor muscle more in ovariectomized rats than in ovariectomized rats with estrogen replacement or in control rats.

CONCLUSIONS

Selective beta-3-adrenoceptor agonists relaxed the detrusor muscle of female rats with low estrogen levels. This result may give a clue to the treatment of frequent urination or incontinence in postmenopausal women who are not receiving hormonal replacement therapy.

Synthesis and evaluation of potent and selective beta(3) adrenergic receptor agonists containing acylsulfonamide, sulfonylsulfonamide, and sulfonylurea carboxylic acid isosteres

Starting from phenethanolamine aniline leads 3a and 3b, we have identified a series of functionally potent and selective beta(3) adrenergic receptor (AR) agonists containing acylsulfonamide, sulfonylsulfonamide, or sulfonylurea groups within the aniline phenethanolamine series. In beta(3), beta(2), and beta(1) AR cAMP functional assays, 3a and other right-hand side (RHS) carboxylate analogues were found to be full agonists that were modestly selective against beta(1) or beta(2) ARs, while analogues lacking RHS acid functionality were active at beta(3) AR but not selective. Replacement of the carboxylate with acylthiazole and acylmethylsulfone gave potent, but only modestly selective, compounds. Increasing the size of the RHS sulfonamide substituent with phenyl or p-toluene afforded compounds with good potency and functional selectivity (beta(3) AR pEC(50) greater than 8; beta(1) and beta(2) AR selectivity greater than 40- and 500-fold, respectively). Our SAR studies suggest that the potency and selectivity profile of the best analogues reported here is a result of both the steric bulk and acidity of the RHS sulfonamide NH group. Although all of the analogues had a pharmacokinetic half-life of less than 2 h, acylsulfonamides 43 and 44 did show moderately low clearance in dogs. These two compounds were further evaluated by thermographic imaging in mice and were found to produce a robust thermogenic response via oral administration.

Beta(3)-adrenoceptor agonists for the treatment of frequent urination and urinary incontinence: 2-[4-(2-[[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino]ethyl)phenoxy]-2-methylpropionic acid

In a search for novel analogues of beta(3)-adrenoceptor (AR) agonists relaxing the bladder for treatment of urinary dysfunction, 2-[4-(2-[[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino]ethyl)phenoxy]-2-methylpropionic acids (1a-e), into which a fibrate-like structure had been incorporated, were synthesised. Compound 1a was found to be a selective beta(3)-AR agonist in functional assays using the ferret detrusor (beta(3)-AR), rat uterus (beta(2)-AR), and rat atrium (beta(1)-AR); beta(3): EC(50)=7.8 nM, beta(2): IC(50)=7,300 nM, beta(1): EC(20)=23,000 nM. The introduction of a chlorine atom or methyl substituent at the ortho-position on the phenyl ring of 1a further improved beta(3)-AR selectivity. In an in vivo study, 1a lowered intrabladder pressure (ED(50)=31 microg/kg) in rats, without increasing heart rate, in keeping with the in vitro results. Consequently, it is proposed that 1a and its analogues (1b-e), possess beta(3)-AR agonistic activity in the absence of undesirable beta(1)- or beta(2)-AR mediated actions, and may be useful for clinical treatment and pharmacological studies.

Coexistence of at least three distinct beta-adrenoceptors in human internal mammary artery

The internal mammary artery (IMA) is currently the preferred conduit for myocardial revascularization. However, perioperative vasospasm and a hypoperfusion state during maximal exercise may limit its use as a bypass graft. The mechanism of spasm has not been clearly defined. Since beta-adrenoceptor activation plays a major role in vasorelaxation, the present study was carried out to investigate the beta-adrenoceptor responsiveness of human IMA smooth muscle. Isoproterenol produced a concentration-dependent relaxation in endothelium-denuded IMA segments, precontracted with phenylephrine (maximal relaxation 46.33+/-5.45%). Atenolol (10(-6)M) and propranolol (2x10(-7)M) inhibited isoproterenol-induced relaxation. While atenolol produced partial inhibition, propranolol caused a complete inhibition in a majority of the segments and a partial inhibition in a minority. BRL 37344, a selective beta 3-adrenoceptor agonist, produced a concentration-dependent relaxation in phenylephrine-precontracted rings of endothelium-denuded IMA (maximal relaxation 40.35+/-4.07%). Cyanopindolol, a beta-adrenoceptor partial agonist, produced a marked relaxation (58.65+/-6.2%) in endothelium-denuded IMA rings, precontracted with phenylephrine. Cyanopindolol-induced relaxation was resistant to blockade by propranolol (2x10(-7)M). Spontaneous contractions of IMA rings were also observed in some cases that were inhibited by isoproterenol and BRL 37344. This observation implies the important role of beta-adrenoceptor activation in prevention of human IMA spasm. The results obtained in present study indicate that human IMA smooth muscle possesses an atypical beta-adrenoceptor together with beta1- and beta2-adrenoceptors. Regarding the relaxation induced in IMA rings by adding BRL 37344, the possible identical entities of IMA atypical beta-adrenoceptors and beta 3-adrenoceptors are suggested.

Discovery of novel N-phenylglycine derivatives as potent and selective beta(3)-adrenoceptor agonists for the treatment of frequent urination and urinary incontinence

With a novel assay using isolated ferret detrusor to estimate beta(3)-adrenoceptor agonistic activity, we found that a series of glycine derivatives of ritodrine, a beta(2)-adrenoceptor agonist, are potent beta(3)-adrenoceptor agonists, with excellent selectivity versus beta(1) and beta(2) subtypes. Substitution of halogens in the phenyl ring increased potency and selectivity for the beta(3)-adrenoceptor, and this was dependent upon the position of the halogens. The chlorine-substituted derivatives 3f-i exhibited potent beta(3)-adrenoceptor-mediated relaxation of ferret detrusor (EC(50) = 0.93, 11, 14, and 160 nM) and higher potency at beta(3)-adrenoceptors than at beta(1) or beta(2). The intravenous administration of 3h significantly reduced the urinary bladder pressure in anesthetized male rats (ED(50) = 48 microg/kg) without cardiovascular side effects. This article is the first report of structure-activity relationships (SAR) concerning beta(3)-adrenoceptor agonists as agents for the treatment of urinary frequency and incontinence.

Activity of N-(phenethyl)phenylethanolamines at beta(1) and beta(2) adrenoceptors: structural modifications can result in selectivity for either subtype

A series of phenylethanolamines bearing a 2-[1-phenylpropyl] substituent on the nitrogen atom was evaluated in vitro for activity at beta(1)- and beta(2)-adrenoceptors. As previously observed, the presence of 3,4-dihydroxy substitution on phenylethanolamine is required for potent activation of both subtypes, whereas the 3,5-dihydroxy analog showed selectivity for the beta(2)-subtype. Replacement by a carboxyl group of the 4-hydroxyl group on the aralkyl nitrogen substituent produced only a small reduction in beta(1) potency (5-fold), whereas beta(2) potency was reduced by more than 100-fold. Hence this structural class includes agonists having either a beta(1), nonselective beta(1)/beta(2) or beta(2) selectivity profile.

BRL37344, but not CGP12177, stimulates fuel oxidation by soleus muscle in vitro

The beta(3)-adrenoceptor agonist, (RR+SS)-(+/-)-4-[2-)2-)3-chlorophenyl)-2-hydroxyethyl)amino)propyl]ph enoxyacetate (BRL37344), stimulated fuel utilisation by isolated mouse soleus muscle at concentrations 10- to 100-fold lower than those required to stimulate lipolysis in brown adipocytes. At 1x10(-10) M BRL37344, uptake and phosphorylation of 2-deoxyglucose was increased (40%), as was glucose-oxidation (50%), palmitate-oxidation (70%) and oxidation of [2-14C]pyruvate (2-fold), indicating stimulation of tricarboxylic acid cycle reactions. Oxidation of [1-14C]pyruvate was unaffected, indicating no stimulation of pyruvate dehydrogenase activity. Other beta(3)-adrenoceptor agonists, disodium(RR)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]- 1,3-benzodioxazole-2,2-dicarboxylate (CL316,243, 1x10(-7) M) and (S)-4-¿2-[2-hydroxy-3-(4-hydroxyphenoxy)propylamino]ethyl¿pheno xymeth ylcyclohexylphosphiric acid lithium salt (SB226552, 1x10(-9) M), achieved similar stimulation of 2-deoxyglucose uptake and phosphorylation but (+/-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one (CGP12177A) had no effect. The inhibitor of protein kinase A, H-89 (isoquinolinesulfonamide), had little effect on the stimulation of pyruvate-oxidation by BRL37344, while the specific inhibitor of protein kinase C, bisindolylmaleimide IX, reduced the stimulated rate to slightly below basal values. We consider that these responses provide evidence of the presence of a novel beta-adrenoceptor in skeletal muscle, which we have termed beta(skel)-adrenoceptor.

Carbohydrate availability affects ammonemia during exercise after beta 2-adrenergic blockade

PURPOSE

Beta-adrenergic blockade increases blood ammonia concentration during exercise. The purpose of this study was to assess the role of decreased carbohydrate availability in this process.

METHODS

Wistar rats (N = 47) were injected intravenously with a selective beta 2-adrenoceptor blocker (ICI 118,551), placebo, or beta 2-blocker + glucose 1 h before a treadmill exercise test. Blood samples were taken to measure the concentration of ammonia, glucose, lactic acid, free fatty acids (FFA), glycerol, branched-chain amino acids (BCAA), and muscle samples for determination of glycogen content.

RESULTS

Beta 2-adrenergic blockade shortened running time to exhaustion (23 +/- 4.3 min compared to 44 +/- 5.2 min with placebo), increased blood ammonia levels (146.7 +/- 16.21 micromol x L(-1) compared to 47.5 +/- 0.92 micromol x L(-1) with placebo) and prevented exercise-induced glycogen breakdown in soleus and gastrocnemius muscles. Pre-exercise supplementation of glucose during beta 2-blockade restored exercise-induced glycogen breakdown and reduced blood ammonia concentration during exercise (66.5 +/- 5.65 mmol x L(-1)) but did not improve exercise capacity (26 +/- 3.2 min) when compared with beta2-blockade alone.

CONCLUSION

The results suggest that the enhanced rise in blood ammonia concentration during exercise after beta-blockade is caused by impaired carbohydrate availability.

Beta-adrenergic receptor subtypes mediating lipolysis in porcine adipocytes. Studies with BRL-37344, a putative beta3-adrenergic agonist

The beta3-selective adrenergic receptor ligand BRL 37344 (BRL) was used to differentiate the presence and functional role of beta-adrenergic receptor (betaAR) subtypes in pig tissues. BRL did not stimulate adenylyl cyclase in membrane preparations or increase lipolysis from pig adipocytes. In contrast to some species, BRL appears to be a poor agonist for the pig betaAR and is not a useful betaAR ligand. Based on displacement of [3H]dihydroalprenolol binding, BRL exhibited a 100-fold selectivity for pig betaAR subtypes in adipose and skeletal muscle membranes. The high affinity site was proposed to be the beta2AR. When used as an antagonist, BRL blockade of the high affinity site did not interfere with isoproterenol-stimulated lipolysis but did inhibit adenylyl cyclase activation. Results indicate that the high affinity betaAR (betaAR) is not linked to lipolysis, possibly due to intracellular compartmentalization. Therefore, betaAR subtypes may have function-specific effects.

Adrenoceptor subclassification: an approach to improved cardiovascular therapeutics

The subdivision of alpha adrenoceptors into the alpha 1 and alpha 2 classes was the impetus for the design of the selective alpha 1-adrenoceptor antagonists, which remain useful antihypertensives. alpha 2-Adrenoceptor agonists also have application as antihypertensive drugs, based on their ability to reduce sympathetic outflow. Likewise, subdivision of the beta adrenoceptors has lead to the development of selective beta 1-adrenoceptor antagonists as antihypertensive and selective beta 2 agonists as bronchodilators. In the past decade, both the alpha 1 and alpha 2 adrenoceptors have been further subdivided, each into three subclasses. In addition, there is strong functional evidence to suggest the presence of additional adrenoceptor subtypes, such as the "alpha 1L" adrenoceptor and "beta 4" adrenoceptor. alpha 1A (or alpha 1L)-Adrenoceptor antagonists have been evaluated for benign prostatic hyperplasia (BPH), and selective alpha 1A agonists for stress incontinence. Gene knockout experiments in mice suggest an important role for the alpha 1B adrenoceptor in the control of vascular tone. Hence, selective alpha 1B antagonists may offer a new approach toward hypertension. Although targeting of specific adrenoceptors can be used to optimize the therapeutic profile of a drug, there are also cases where blockade of multiple adrenoceptors is desirable, as with the alpha/beta-adrenoceptor antagonist carvedilol in congestive heart failure. It is possible that combination of affinities for selected adrenoceptor subtypes within a single molecule may be desirable for certain applications.

Beta 1-, beta 2- and atypical beta-adrenoceptor-mediated relaxation in rat isolated aorta

beta-adrenoceptor-mediated relaxation was investigated in ring preparations of rat isolated thoracic aorta. Rings were pre-constricted with a sub-maximal concentration of noradrenaline (1 microM) and relaxant responses to cumulative concentrations of beta-adrenoceptor agonists obtained. The concentration-response curve (CRC) to isoprenaline was shifted to the right by propranolol (0.3 microM) with a steepening of the slope. Estimation of the magnitude of the shift from EC(50) values gave a pA(2) of 7.6. Selective beta(1)- and beta(2)-adrenoceptor antagonists, CGP 20712A (0.1 microM) and ICI 118551 (0.1 microM), respectively, produced 4 and 14 fold shifts of the isoprenaline CRC. Atypical beta-adrenoceptor agonists also produced concentration-dependent relaxation of aortic rings. The order of potency of the beta-adrenoceptor agonists was (-log EC(50)): isoprenaline (6. 25)>cyanopindolol (5.59)>isoprenaline+propranolol (5.11)>CGP 12177A (4.40)>ZD 2079 (4.24)>ZM 215001 (4.07)>BRL 37344 (3.89). Relaxation to CGP 12177A and ZM 215001 was unaffected by propranolol (0.3 microM). SR 59230A ( Collapse

Key Words

• atypical β-adrenoceptors
• β₃-adrenoceptors
• β₄-adrenoceptors
• β₁-adrenoceptors
• β₂-adrenoceptors
• vascular smooth muscle
• rat aorta

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MESH Headings

• Acetylcholine/pharmacology
• Adrenergic alpha-Agonists/pharmacology
• Adrenergic beta-Agonists/pharmacology
• Adrenergic beta-Antagonists/pharmacology
• Animals
• Aorta, Thoracic/drug effects
• Aorta, Thoracic/physiology
• Bupranolol/pharmacology
• Dose-Response Relationship, Drug
• Imidazoles/pharmacology
• In Vitro Techniques
• Isoproterenol/pharmacology
• Male
• Muscle Relaxation/drug effects
• Muscle Relaxation/physiology
• Muscle, Smooth, Vascular/drug effects
• Muscle, Smooth, Vascular/physiology
• Norepinephrine/pharmacology
• Pindolol/analogs & derivatives
• Pindolol/pharmacology
• Propanolamines/pharmacology
• Propranolol/pharmacology
• Rats
• Rats, Wistar
• Receptors, Adrenergic, beta/classification
• Receptors, Adrenergic, beta/physiology
• Receptors, Adrenergic, beta-1/physiology
• Receptors, Adrenergic, beta-2/physiology
• Substrate Specificity
• Vasodilator Agents/pharmacology

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Grants Collapse

Affiliation(s)

L Brawley School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow G4 0BA
A M Shaw School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow G4 0BA
A MacDonald School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow G4 0BA

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The effects of beta-adrenoceptor agonists on KCl-induced rhythmic contraction in the ureter of guinea pig

In the present study, we tried to determine what effects were induced by beta-adrenoceptor agonists on 40 mM KCl-induced rhythmic contraction and to clarify which beta-adrenoceptor subtypes are involved in the regulation of ureter motility in the guinea pig by using in vitro functional analysis. 40 mM KCl-induced rhythmic contraction was abolished by papaverine (10(-6) M), nicardipine (10(-5) M) and cromakalim (10(-5) M), but was not influenced by atropine (10(-6) M). Isoprenaline decreased the amplitude, and changed the pattern of 40 mM KCl-induced rhythmic contraction in concentration-dependent manner. These results suggest the possibility that the stimulation of beta-adrenoceptors may regulate the ureteral peristalsis. Salbutamol (selective beta2-AR agonist) and CGP12177 (beta(1,2)-AR antagonist and beta3-AR partial agonist) were also effective in decreasing the amplitude and changing the pattern of the rhythmic contraction. The pD2 values of agonists were 7.57 (isoprenaline), 5.80 (CGP12177) and 7.63 (salbutamol), respectively. The concentration-response curves of isoprenaline and salbutamol were rightward shifted by the presence of propranolol, and the apparent pA2 values for propranolol against isoprenaline and salbutamol were 7.12 and 6.29, respectively. These results suggest that inhibition for 40 mM KCl-induced rhythmic contraction of the ureter by isoprenaline and salbutamol mediated mainly via atypical beta-adrenoceptor subtype.

Function and distribution of beta3-adrenoceptors in rat, rabbit and human urinary bladder and external urethral sphincter

1. Activation of beta-adrenoceptors causes relaxation of the urinary bladder and contraction of the external urethral sphincter, which consists of fast-contracting skeletal muscles. A beta2-adrenoceptor agonist, clenbuterol, recently has been developed as a therapeutic drug for the treatment of urinary incontinence, however beta2-adrenoceptor agonists have undesirable effects on cardiac and striated muscle function. 2. In this study, we compared the effects of the beta2-adrenoceptor agonist, clenbuterol and of a novel beta3-adrenoceptor agonist, GS332, on urinary bladder and external urethral sphincter function in rat, rabbit and human. We also determined the distribution of beta3-adrenoceptors in human urinary bladder and external urethral sphincter, using radioligand-binding techniques. 3. Clenbuterol induced marked relaxations in rat, rabbit and human urinary bladder smooth muscles and also induced marked contractions in rat periurethral striated muscles (external urethral sphincter), while GS332 induced marked relaxations in rat and human, but not in rabbit, urinary bladder smooth muscles and induced small contractions in rat periurethral striated muscles. 4. The radioligand binding studies showed presence of beta2- and beta3-adrenoceptors in human urinary bladder, external urethral sphincter and abdominal rectus muscles. The affinities of GS332 were the highest in urinary bladder and the lowest in the skeletal (abdominal rectus) muscles, while the affinities of clenbuterol were similar in urinary bladder, external urethral sphincter and the skeletal (abdominal rectus) muscles. 5. These results suggest that GS332 could, similarly clenbuterol, have a role in the treatment of urinary frequency and urinary incontinence.

Atypical beta-adrenoceptors of rat thoracic aorta

The possible existence of atypical beta-adrenoceptors in vascular smooth muscle of rat isolated thoracic aorta was investigated. Isoprenaline (10(-8)-10(-4) M) produced concentration-dependent relaxation of phenylephrine (10(-5) M) precontracted rings of endothelium-denuded rat aorta in vitro. Isoprenaline-induced relaxation was resistant to blockade by atenolol (10(-6) M). But, propranolol (2 x 10(-7) M) caused a non-competitive inhibition and SR 59230A (6.6 x 10(-6) M), a beta3-adrenoceptor selective antagonist, failed to produce additional antagonism in presence of propranolol. BRL 37344 (10(-8)-10(-4) M), a beta3-selective agonist, did not relax ring segments precontracted with phenylephrine (10(-5) M) in the absence of endothelium. The non-conventional partial agonist (-)-cyanopindolol (5 x 10(-6)-10(-4) M) induced a marked relaxation in phenylephrine (10(-5)M) precontracted aortic rings without endothelium. This vasodilation was resistant to blockade by propranolol (2 x 10(-7) M) and SR 59230A (10(-5) M). Salbutamol (10(-8)-10(-4) M) produced concentration-dependent relaxation in isolated endothelium-denuded aortic rings precontracted with phenylephrine (10(-5) M). Propranolol (2 x 10(-7) M), but not atenolol (10(-6) M), inhibited this relaxant response. It is concluded that in endothelium-denuded thoracic aorta, salbutamol acts through beta2-adrenoceptors whereas isoprenaline seems to activate both beta2-adrenoceptors and an atypical beta-adrenergic receptor. This atypical beta-adrenoceptor is distinct from putative beta3-adrenoceptor and maybe resembles the reported fourth cardiac beta-adrenoceptor.

LK 204-545, a highly selective beta1-adrenoceptor antagonist at human beta-adrenoceptors

LK 204-545 ((+/-)-1-(2-(3-(2-cyano-4-(2-cyclopropyl-methoxy-ethoxy)phenoxy)-2-hydro xy-propyl-amino)-ethyl)-3-(4-hydrxy-phenyl) urea), an antagonist that possesses high beta1-/beta2-selectivity in the rat, and a range of cardio-selective and non-selective beta-adrenoceptor antagonists were examined to compare their radioligand binding affinities for human beta1-, beta2- and beta3-adrenoceptors transfected into CHO cells. LK 204-545 and CGP 20712A displayed the highest beta1-/beta2- (approximately 1800 and approximately 650, respectively) and beta1-/beta3-selectivity (approximately 17000 and approximately 2200, respectively) at human beta-adrenoceptors with LK 204-545 being approximately 2.75-fold more beta1-/beta2-selective and approximately 8-fold beta1-/beta3-selective than CGP 20712A. The high potency of LK 204-545 at transfected human beta1-adrenoceptors and in functional models of rat beta1-adrenoceptors together with its high selectivity, identify it as a useful ligand for studying beta1-adrenoceptors and suggest that it may be the preferred ligand for human beta-adrenoceptor studies.

Insulin resistance, impaired glucose tolerance and non-insulin-dependent diabetes, pathologic mechanisms and treatment: current status and therapeutic possibilities

Impaired glucose tolerance and non-insulin-dependent diabetes (NIDDM) are the pathologic consequence of two co-incident and interacting conditions, namely insulin resistance and relative insulin deficiency. Recognised by the World Health Authority as a global health problem there are at 1995 estimates at least 110 million diagnosed diabetics world wide with at least the same number undiagnosed. Diabetes is the 4th leading cause of death in developed countries and its management exerts a vast economic and social burden. Insulin resistance is established as the characteristic pathologic feature of patients with glucose intolerance and NIDDM describing a state in which insulin stimulated glucose uptake and utilisation in liver, skeletal muscle and adipose tissue is impaired and coupled to impaired suppression of hepatic glucose output. Although the biochemical mechanisms underpinning both defects are becoming better understood, the genetic and molecular causes remain elusive; and whether insulin resistance or relative insulin deficiency represents the primary defect in patients with NIDDM is the matter of some debate. In this article we review the biochemical and molecular nature of the defects in insulin sensitivity and glucose uptake, and discuss some of the potential causative mechanisms. The genetic and environmental basis of insulin resistance is reviewed and presented, and potential therapeutic targets including thiazolidinediones are discussed.

Thermogenesis is beta3- but not beta1-adrenergically mediated in rat brown fat cells, even after cold acclimation

To examine if acclimation of rats to cold led to alterations in the coupling between different beta-receptor subtypes and thermogenesis in brown fat cells, we investigated the adrenergic response patterns in brown fat cells isolated from warm-acclimated (28 degreesC) and cold-acclimated (4 degreesC) rats. In the cells from warm-acclimated rats, the relative affinities (EC50) for different agonists (isoprenaline, BRL-37344, norepinephrine, CGP-12177, dobutamine, and salbutamol) were those expected from their interaction with a beta3-receptor. The response to norepinephrine was competitively inhibited by propranolol with a pA2 of approximately 6, implying interaction at the beta3-receptor. No evidence for a beta1-receptor-mediated response to the beta1-selective agonist dobutamine could be obtained; the low-affinity response observed was most likely through the beta3-receptor. The beta1-antagonist ICI-89406 could not inhibit a specific fraction of the thermogenic response to norepinephrine. Thus beta3-receptors were the only beta-receptors involved in the control of thermogenesis in brown fat cells from warm-acclimated rats. A modified method of preparation was developed to isolate functional cells from cold-acclimated animals. Also in these cells, the beta-receptor coupled to thermogenesis was the beta3-receptor, although the response was desensitized with an approximately sevenfold shift in EC50 values. The pA2 for propranolol inhibition of norepinephrine-induced thermogenesis was also 6 here, and that for ICI-89406 was 5.5, also implying interaction at the beta3-receptor. Thus acclimation to cold did not alter the beta-adrenergic receptor subtype (beta3) involved in the control of thermogenesis.

The effects of the beta3-adrenoceptor agonist BRL 35135 on UCP isoform mRNA expression

The mitochondrial uncoupling protein UCP-1 uncouples respiration from ATP synthesis in brown adipose tissue (BAT) and thus energy is dissipated as heat. Recently two further isoforms have been identified which may play a similar role in other tissues. We have determined the effects of the rodent-selective beta3-adrenoceptor (beta3-AR) agonist BRL 35135, on beta3-AR and UCP mRNA levels in tissues from lean and obese (fa/fa) Zucker rats. beta3-AR mRNA levels were reduced in fa/fa white (WAT) and brown (BAT) adipose tissue relative to levels in lean littermates. BRL 35135 treatment increased expression levels of beta3-AR mRNA in both genotypes. UCP-2 and UCP-3 mRNA levels in BAT, WAT and skeletal muscle were reduced by 2-3 fold in the fa/fa rats relative to the lean rats. We confirm that BRL 35135 increases BAT UCP-1 mRNA in lean rats, and find that BAT UCP-3 mRNA was reduced 3.2 fold, with no changes in UCP-2 expression. In WAT BRL 35135 increased UCP-2 and UCP-3 expression 2-3 fold in both lean and fa/fa rats. In lean rats, skeletal muscle UCP-3 mRNA was increased 2.3 fold by BRL 35135 whereas UCP-2 was reduced by 2.2 fold. BRL 35135 had no effects on UCP-2 and UCP-3 expression in skeletal muscle of the fa/fa rats. Our results demonstrate that mechanisms regulating UCP isoform synthesis in fa/fa rats are impaired and that WAT could be involved in the thermogenic response of BRL 35135.

Atypical adrenoceptor-mediated relaxation of canine pulmonary artery through a cAMP-dependent pathway

We studied the existence of beta 3-adrenoceptors in canine pulmonary artery smooth muscle under isometric conditions in vitro. A rank order potency of vascular relaxation was isoproterenol > salbutamol > selective beta 3-adrenoceptor agonists, CL 316243 and BRL 37344. A marked desensitization to salbutamol occurred by pretreatment with salbutamol but not with CL 316243. When beta 1-adrenoceptors were blocked, the relaxant responses to salbutamol were competitively antagonized by the beta 2-adrenoceptor antagonist ICI 118551, whereas the response to CL 316243 was not. Cyanopindolol, a non-selective beta-adrenoceptor antagonist, antagonized CL 316243-induced relaxation in a competitive manner with a pA2 of 6.10, and this value was lower than that when salbutamol was used as an agonist (6.69). Intracellular cAMP levels were increased by CL 316243, an effect that was not altered by ICI 118551. Therefore, beta 3-adrenoceptors may be present and functioning in canine pulmonary artery.

Beta3-adrenoceptor mechanisms in guinea-pig taenia caecum

Beta-adrenoceptor-mediated relaxation of guinea-pig taenia caecum was investigated by studying the effects of BRL37344, CGP12177 and norepinephrine. These drugs caused graded relaxation of the guinea-pig taenia caecum. The concentration-response curves for these drugs were unaffected by propranolol, atenolol, butoxamine, prazosin, yohimbine and phentolamine. Bupranolol produced shifts of the concentration-response curves for these drugs. Schild regression analyses carried out for bupranolol against BRL37344, CGP12177 and norepinephrine gave pA2 values of 5.79, 5.61 and 5.53, respectively. CGP12177 and norepinephrine significantly increased cyclic AMP levels in this preparation. Bupranolol significantly decreased cyclic AMP levels elicited by CGP12177 and norepinephrine, whereas propranolol produced no effect. These results suggest that the relaxant responses to BRL37344, CGP12177 and norepinephrine in the guinea-pig taenia caecum are mediated by beta3-adrenoceptors.

Characterization of beta-adrenoceptors in urinary bladder: comparison between rat and rabbit

1. beta-Adrenoceptor subtypes in rat and rabbit urinary bladder were investigated in functional experiments by use of several agonists and antagonists. 2. All agonists tested produced concentration-dependent relaxation, but the relative potencies varied between both species: BRL 37344 (pD2:8.0) > isoprenaline (7.3) > adrenaline (6.7) = noradrenaline (6.6) in rat bladder, and isoprenaline (8.7) = adrenaline (8.5) > noradrenaline (7.7) = BRL 37344 (7.4) in rabbit bladder. 3. The relaxation response to isoprenaline in rat bladder was relatively resistant to propranolol and ICI 118551, and the slopes of Schild plot for both antagonists were different from unity. The apparent pKB values estimated by single concentrations of propranolol (1, 10 microM) and ICI 118551(10 microM) were 6.6 and 5.4, respectively. 4. On the other hand, the relaxation response to isoprenaline in rabbit bladder was antagonized by lower concentrations (1 nM-100 nM) of propranolol and ICI 118551 in a competitive manner, resulting in pA2 values of 8.7 and 8.6, respectively. 5. These results suggest species-heterogeneity of beta-adrenoceptors in urinary bladder; beta 3 and beta 2 subtypes in rat and beta 2 subtype in rabbit.

Lipolytic effects of conventional beta 3-adrenoceptor agonists and of CGP 12,177 in rat and human fat cells: preliminary pharmacological evidence for a putative beta 4-adrenoceptor

1. The nature of rat and human fat cell beta 3-adrenoceptors was investigated by studying the effects of the new beta 3-adrenoceptor selective antagonist, SR 59,230A, on lipolysis induced by the conventional beta 3-adrenoceptor agonists, CL 316,243 and SR 58,611A, and by the non-conventional partial beta 3-adrenoceptor agonist CGP 12,177 (a potent beta 1- and beta 2-adrenoceptor antagonist with partial beta 3-adrenoceptor agonist property). 2. In rat fat cells, the rank order of potency of agonists was: CL 316,243 > isoprenaline > SR 58,611A > CGP 12,177. The three former agents were full agonists whereas CGP 12,177 was a partial agonist (intrinsic activity of 0.70). In human fat cells, the lipolytic effect of CGP 12,177 reached 25% of isoprenaline effect. CL 316,243 was a poor inducer of lipolysis and SR 58,611A was ineffective. 3. In rat fat cells, lipolysis induced by CL 316,243 and SR 58,611A was competitively antagonized by SR 59,230A. Schild plots were linear with pA2 value of 6.89 and 6.37, respectively. Conversely, 0.1, 0.5 and 1 microM SR 59,230A did not modify the concentration-response curve of CGP 12,177. A rightward shift of the curve was however observed with 10 and 100 microM of SR 59,230A. The apparent pA2 value was 5.65. The non-selective beta-adrenergic antagonist, bupranolol, competitively displaced the concentration-response curve of CGP 12,177 and CL 316,243. Schild plots were linear with pA2 values of 6.70 and 7.59, respectively. CL316,243-mediated lipolytic effect was not antagonized by CGP 20,712A. In human fat cells, CGP 12,177-mediated lipolytic effect was antagonized by bupranolol and CGP 20,712A. SR 59,230A (0.1, 1 and 10 microM) did not modify the concentration-response curve of CGP 12,177. A rightward shift was however observed at 100 microM leading to an apparent pA2 value of 4.32. 4. The results suggest that the non-conventional partial agonist CGP 12,177 can activate lipolysis in fat cells through the interaction with a beta-adrenoceptor pharmacologically distinct from the beta 3-adrenoceptor, i.e. through a putative beta 4-adrenoceptor. They suggest that the two subtypes coexist in rat fat cells whereas only the putative beta 4-adrenoceptor mediates lipolytic effect of CGP12,177 in human fat cells.

Beta3-adrenoceptors mediate relaxation of guinea pig taenia caecum by BRL37344A and BRL35135A

Beta-adrenoceptor-mediated relaxation of guinea pig taenia caecum was investigated by studying the effects of the beta3-adrenoceptor agonists, BRL37344A [(R*,R*)-(+/-)-4-[2'-[2-hydroxy-2-(3-chlorophenyl) ethylamino] propyl] phenoxyacetic acid sodium salt sesquihydrate] and BRL35135A [(R*,R*)-(+/-)-methyl-4-[2-[2-hydroxy-2-(3-chlorophenyl) ethylamine] propyl] phenoxyacetate hydrobromide]. BRL37344A and BRL35135A caused dose-dependent relaxation of the guinea pig taenia caecum. The concentration-response curves for BRL37344A and BRL35135A were unaffected by propranolol, ICI118551 [erythro-1-(7-methylindan-4-yloxy)-3-(isopropylamine)-but an-2-ol], atenolol, butoxamine, prazosin, yohimbine and phentolamine. Bupranolol produced shifts of the concentration-response curves for BRL37344A and BRL35135A. Schild regression analyses carried out for bupranolol against BRL37344A and BRL35135A gave pA2 values of 5.79 and 5.84, respectively. These results suggest that the relaxant response to BRL37344A and BRL35135A of the guinea pig taenia caecum is mediated by beta3-adrenoceptors.