Detailed insight on β-adrenoceptors as therapeutic targets

Research progress on the protective effect of hormones and hormone drugs in myocardial ischemia-reperfusion injury

Ischemic heart disease (IHD) is a condition where the heart muscle does not receive enough blood flow, leading to cardiac dysfunction. Restoring blood flow to the coronary artery is an effective clinical therapy for myocardial ischemia. This strategy helps lower the size of the myocardial infarction and improves the prognosis of patients. Nevertheless, if the disrupted blood flow to the heart muscle is restored within a specific timeframe, it leads to more severe harm to the previously deprived heart tissue. This condition is referred to as myocardial ischemia/reperfusion injury (MIRI). Until now, there is a dearth of efficacious strategies to prevent and manage MIRI. Hormones are specialized substances that are produced directly into the circulation by endocrine organs or tissues in humans and animals, and they have particular effects on the body. Hormonal medications utilize human or animal hormones as their active components, encompassing sex hormones, adrenaline medications, thyroid hormone medications, and others. While several studies have examined the preventive properties of different endocrine hormones, such as estrogen and hormone analogs, on myocardial injury caused by ischemia-reperfusion, there are other hormone analogs whose mechanisms of action remain unexplained and whose safety cannot be assured. The current study is on hormones and hormone medications, elucidating the mechanism of hormone pharmaceuticals and emphasizing the cardioprotective effects of different endocrine hormones. It aims to provide guidance for the therapeutic use of drugs and offer direction for the examination of MIRI in clinical therapy.

β2-adrenoceptors kick osteoarthritis - Time to rethink prevention and therapy

Although, during the past decades, substantial advances emerged in identifying major local and systemic factors contributing to initiation and progression of osteoarthritis (OA), some neuroendocrine mechanisms are still not understood or even neglected when thinking about novel therapeutic options. One of which is the sympathetic nervous system that exhibits various OA-promoting effects in different tissues of the joint. Interestingly, the β2-adrenoceptor (AR) mediates the majority of these effects as demonstrated by several in vitro, in vivo as well as in clinical studies. This review article does not only summarize studies of the past two decades demonstrating that the β2-AR plays an OA-promoting role in different tissues of the joint but also aims to encourage the reader to think about next-level research to discover novel and innovative preventive and/or therapeutic strategies targeting the β2-AR in OA.

The Wiser Strategy of Using Beta-Agonists in Asthma: Mechanisms and Rationales

Concerns regarding the safety of beta-2 agonists have led to revisions of the major asthma guidelines to better address these issues. Although these updates allow for a combination of previous and current strategies, they may confuse clinical practitioners. Beta-2 agonists are vital for alleviating asthma symptoms by relaxing smooth muscles; however, they also pose significant risks by inducing pro-inflammatory mediators both in vitro and in vivo. In addition to the risks of overuse and symptom masking, the use of beta-agonists alone at therapeutic doses can worsen airway inflammation and enhance virus-induced inflammation during asthma exacerbation. Inhaled corticosteroids (ICS) can effectively prevent these adverse effects. With new insights into the mechanisms of these adverse events, reserving short-acting beta-agonists for acute symptom relief during exacerbations and only for those who are already on ICS or oral steroids represents a careful approach to using beta-agonists with least adverse effects in patients with asthma. However, a major drawback of this approach is the potential non-compliance with ICS, leading to beta-agonist use without the necessary counteraction by ICS. An optimal strategy, both during and outside exacerbations, would integrate beta-agonists into an anti-inflammatory regimen that includes ICS, ideally combined with the same inhaler to ensure their concurrent use where finances allow. This would maintain the beneficial effects of beta-agonists, such as bronchodilation, while preventing the adverse effects from the induction of inflammatory mediators. This method is aligned with diverse clinical settings, maximizes the safe use of beta-agonists, and supports a comprehensive guideline-compliant management strategy.

"Photo-Adrenalines": Photoswitchable β2 -Adrenergic Receptor Agonists as Molecular Probes for the Study of Spatiotemporal Adrenergic Signaling

β2 -adrenergic receptor (β2 -AR) agonists are used for the treatment of asthma and chronic obstructive pulmonary disease, but also play a role in other complex disorders including cancer, diabetes and heart diseases. As the cellular and molecular mechanisms in various cells and tissues of the β2 -AR remain vastly elusive, we developed tools for this investigation with high temporal and spatial resolution. Several photoswitchable β2 -AR agonists with nanomolar activity were synthesized. The most potent agonist for β2 -AR with reasonable switching is a one-digit nanomolar active, trans-on arylazopyrazole-based adrenaline derivative and comprises valuable photopharmacological properties for further biological studies with high structural accordance to the native ligand adrenaline.

Boosting Mitochondrial Biogenesis Diminishes Foam Cell Formation in the Post-Stroke Brain

Following ischemic stroke, the degradation of myelin and other cellular membranes surpasses the lipid-processing capabilities of resident microglia and infiltrating macrophages. This imbalance leads to foam cell formation in the infarct and areas of secondary neurodegeneration, instigating sustained inflammation and furthering neurological damage. Given that mitochondria are the primary sites of fatty acid metabolism, augmenting mitochondrial biogenesis (MB) may enhance lipid processing, curtailing foam cell formation and post-stroke chronic inflammation. Previous studies have shown that the pharmacological activation of the β2-adrenergic receptor (β2-AR) stimulates MB. Consequently, our study sought to discern the effects of intensified β2-AR signaling on MB, the processing of brain lipid debris, and neurological outcome using a mouse stroke model. To achieve this goal, aged mice were treated with formoterol, a long-acting β2-AR agonist, daily for two and eight weeks following stroke. Formoterol increased MB in the infarct region, modified fatty acid metabolism, and reduced foam cell formation. However, it did not reduce markers of post-stroke neurodegeneration or improve recovery. Although our findings indicate that enhancing MB in myeloid cells can aid in the processing of brain lipid debris after stroke, it is important to note that boosting MB alone may not be sufficient to significantly impact stroke recovery.

Ligand-Free Signaling of G-Protein-Coupled Receptors: Physiology, Pharmacology, and Genetics

G-protein-coupled receptors (GPCRs) are ubiquitous sensors and regulators of cellular functions. Each GPCR exists in complex aggregates with multiple resting and active conformations. Designed to detect weak stimuli, GPCRs can also activate spontaneously, resulting in basal ligand-free signaling. Agonists trigger a cascade of events leading to an activated agonist-receptor G-protein complex with high agonist affinity. However, the ensuing signaling process can further remodel the receptor complex to reduce agonist affinity, causing rapid ligand dissociation. The acutely activated ligand-free receptor can continue signaling, as proposed for rhodopsin and μ opioid receptors, resulting in robust receptor activation at low agonist occupancy with enhanced agonist potency. Continued receptor stimulation can further modify the receptor complex, regulating sustained ligand-free signaling-proposed to play a role in opioid dependence. Basal, acutely agonist-triggered, and sustained elevated ligand-free signaling could each have distinct functions, reflecting multi-state conformations of GPCRs. This review addresses basal and stimulus-activated ligand-free signaling, its regulation, genetic factors, and pharmacological implications, focusing on opioid and serotonin receptors, and the growth hormone secretagogue receptor (GHSR). The hypothesis is proposed that ligand-free signaling of 5-HT2A receptors mediate therapeutic effects of psychedelic drugs. Research avenues are suggested to close the gaps in our knowledge of ligand-free GPCR signaling.

β-Adrenoreceptors as Therapeutic Targets for Ocular Tumors and Other Eye Diseases-Historical Aspects and Nowadays Understanding

β-adrenoreceptors (ARs) are members of the superfamily of G-protein-coupled receptors (GPCRs), and are activated by catecholamines, such as epinephrine and norepinephrine. Three subtypes of β-ARs (β₁, β₂, and β₃) have been identified with different distributions among ocular tissues. Importantly, β-ARs are an established target in the treatment of glaucoma. Moreover, β-adrenergic signaling has been associated with the development and progression of various tumor types. Hence, β-ARs are a potential therapeutic target for ocular neoplasms, such as ocular hemangioma and uveal melanoma. This review aims to discuss the expression and function of individual β-AR subtypes in ocular structures, as well as their role in the treatment of ocular diseases, including ocular tumors.

The β-adrenergic hypothesis of synaptic and microglial impairment in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease originating partly from amyloid β protein-induced synaptic failure. As damaging of noradrenergic neurons in the locus coeruleus (LC) occurs at the prodromal stage of AD, activation of adrenergic receptors could serve as the first line of defense against the onset of the disease. Activation of β₂ -ARs strengthens long-term potentiation (LTP) and synaptic activity, thus improving learning and memory. Physical stimulation of animals exposed to an enriched environment (EE) leads to the activation of β₂ -ARs and prevents synaptic dysfunction. EE also suppresses neuroinflammation, suggesting that β₂ -AR agonists may play a neuroprotective role. The β₂ -AR agonists used for respiratory diseases have been shown to have an anti-inflammatory effect. Epidemiological studies further support the beneficial effects of β₂ -AR agonists on several neurodegenerative diseases. Thus, I propose that β₂ -AR agonists may provide therapeutic value in combination with novel treatments for AD.

ß-Adrenoreceptors in Human Cancers

Cancer is the leading cause of death and represents a significant economic burden worldwide. The numbers are constantly growing as a result of increasing life expectancy, toxic environmental factors, and adoption of Western lifestyle. Among lifestyle factors, stress and the related signaling pathways have recently been implicated in the development of tumors. Here we present some epidemiological and preclinical data concerning stress-related activation of the ß-adrenoreceptors (ß-ARs), which contributes to the formation, sequential transformation, and migration of different tumor cell types. We focused our survey on research results for breast and lung cancer, melanoma, and gliomas published in the past five years. Based on the converging evidence, we present a conceptual framework of how cancer cells hijack a physiological mechanism involving ß-ARs toward a positive modulation of their own survival. In addition, we also highlight the potential contribution of ß-AR activation to tumorigenesis and metastasis formation. Finally, we outline the antitumor effects of targeting the ß-adrenergic signaling pathways, methods for which primarily include repurposed ß-blocker drugs. However, we also call attention to the emerging (though as yet largely explorative) method of chemogenetics, which has a great potential in suppressing tumor growth either by selectively modulating neuronal cell groups involved in stress responses affecting cancer cells or by directly manipulating specific (e.g., the ß-AR) receptors on a tumor and its microenvironment.

Rational design, synthesis, and pharmacological evaluation of a cohort of novel beta-adrenergic receptors ligands enables an assessment of structure-activity relationships

Biomedical applications of molecules that are able to modulate β-adrenergic signaling have become increasingly attractive over the last decade, revealing that β-adrenergic receptors (β-ARs) are key targets for a plethora of therapeutic interventions, including cancer. Despite successes in β-AR drug discovery, identification of β-AR ligands that are useful as selective chemical tools in pharmacological studies of the three β-AR subtypes, or lead compounds for drug development is still a highly challenging task. This is mainly due to the intrinsic plasticity of β-ARs as G protein-coupled receptors in conjunction with the requirement for functional receptor subtype selectivity, tissue specificity and minimal off-target effects. With the aim to provide insight into structure-activity relationships for the three β-AR subtypes, we have synthesized and obtained the pharmacological profile of a series of structurally diverse compounds (named MC) that were designed based on the aryloxy-propanolamine scaffold of SR59230A. Comparative analysis of their predicted binding mode within the active and inactive states of the receptors in combination with their pharmacological profile revealed key structural elements that control their activity as agonists or antagonists, in addition to clues about substituents that mediate selectivity for one receptor subtype over the others. We anticipate that these results will facilitate selective β-AR drug development efforts.

Enhanced Bystander BRET (ebBRET) Biosensors as Biophysical Tools to Map the Signaling Profile of Neuropsychiatric Drugs Targeting GPCRs

Bioluminescence resonance energy transfer (BRET) is a non-radiative energy transfer between a bioluminescent donor and a fluorescent acceptor with far-reaching applications in detecting physiologically relevant protein-protein interactions. The recently developed enhanced bystander BRET (ebBRET) biosensors have made it possible to rapidly determine the signaling profile of a series of ligands across a large number of GPCRs and their signaling repertoires, which has tremendous implications in the drug discovery process. Here we describe BRET and the ebBRET biosensors as investigational tools in establishing functional selectivity downstream of GPCRs.

Associations between the use of β-adrenoceptor acting drugs and the risk of dementia in older population

Objective

Age-related decline within the noradrenergic system is associated with reduced cognition. The β-adrenoceptors are widely expressed in the brain as well as in the peripheral. Medications targeting β-adrenoceptor activity have been widely used in older adults. The aim of this study was to explore the associations between β-adrenoceptor acting drugs and the risk of dementia in the older population.

Methods

The subjects' information was collected from the electronic medical record (EMR) database. A propensity score matching strategy was conducted to select control participants for users of β2-agonists or β-antagonists. Logistic regression analysis was performed to estimate the risk of dementia with the use of β2-agonists or β-antagonists.

Results

A total of 1,429 participants in the EMR database were included in the study. The use of β2-agonists was strongly associated with a decreased risk of dementia [OR = 0.324, 95% confidence interval (CI): 0.149-0.707, P = 0.005]. This decreased risk showed a statistically significant inverse time-dependent pattern (P _trend = 0.014). However, the use of non-selective β-antagonists significantly correlated with an increased dementia risk (OR = 1.961, 95% CI: 1.144-3.359, P = 0.014), although no time-dependent manner was found (P _trend = 0.220). There was no association between selective β1-antagonists usage and dementia risk (OR = 1.114, P = 0.625).

Conclusion

The use of β-adrenoceptor acting drugs seems to be associated with the risk of dementia. Pharmacological interventions modulating β2-adrenoceptor activity might be a potential target in therapeutics for dementia.

GRK2 in cardiovascular disease and its potential as a therapeutic target

Cardiovascular diseases (CVDs) represent the leading cause of death globally. Despite major advances in the field of pharmacological CVD treatments, particularly in the field of heart failure (HF) research, case numbers and overall mortality remain high and have trended upwards over the last few years. Thus, identifying novel molecular targets for developing HF therapeutics remains a key research focus. G protein-coupled receptors (GPCRs) are critical myocardial signal transducers which regulate cardiac contractility, growth, adaptation and metabolism. Additionally, GPCR dysregulation underlies multiple models of cardiac pathology, and most pharmacological therapeutics currently used in HF target these receptors. Currently-approved treatments have improved patient outcomes, but therapies to stop or reverse HF are lacking. A recent focus on GPCR intracellular-regulating proteins such as GPCR kinases (GRKs) has uncovered GRK2 as a promising target for combating HF. Current literature strongly establishes increased levels and activity of GRK2 in multiple models of CVD. Additionally, the GRK2 interactome includes numerous proteins which interact with differential domains of GRK2 to modulate both beneficial and deleterious signaling pathways in the heart, indicating that these domains can be targeted with a high level of specificity unique to various cardiac pathologies. These data support the premise that GRK2 should be at the forefront of a novel investigative drug search. This perspective reviews cardiac GPCRs, describes the structure and functions of GRK2 in cardiac function and maladaptive pathology, and summarizes the ongoing and future research for targeting this critical kinase across cellular, animal and human models of cardiac dysfunction and HF.

Caged-carvedilol as a new tool for visible-light photopharmacology of β-adrenoceptors in native tissues

Adrenoceptors are G protein-coupled receptors involved in a large variety of physiological processes, also under pathological conditions. This is due in large part to their ubiquitous expression in the body exerting numerous essential functions. Therefore, the possibility to control their activity with high spatial and temporal precision would constitute a valuable research tool. In this study, we present a caged version of the approved non-selective β-adrenoceptor antagonist carvedilol, synthesized by alkylation of its secondary amine with a coumarin derivative. Introducing this photo-removable group abolished carvedilol physiological effects in cell cultures, mouse isolated perfused hearts and living zebrafish larvae. Only after visible light application, carvedilol was released and the different physiological systems were pharmacologically modulated in a similar manner as the control drug. This research provides a new photopharmacological tool for a wide range of research applications that may help in the development of future precise therapies.

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We report a diffusible caged antagonist based on the beta blocker carvedilol (C-C)

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Carvedilol release from C-C is produced by light on the visible range (405 nm)

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Light-dependent effects are assessed in cells, mice hearts, and zebrafish larvae

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Physiological processes can be regulated by C-C and light (heart rate and behavior)

Drug repurposing in cancer neuroscience: From the viewpoint of the autophagy-mediated innervated niche

Based on the bidirectional interactions between neurology and cancer science, the burgeoning field “cancer neuroscience” has been proposed. An important node in the communications between nerves and cancer is the innervated niche, which has physical contact with the cancer parenchyma or nerve located in the proximity of the tumor. In the innervated niche, autophagy has recently been reported to be a double-edged sword that plays a significant role in maintaining homeostasis. Therefore, regulating the innervated niche by targeting the autophagy pathway may represent a novel therapeutic strategy for cancer treatment. Drug repurposing has received considerable attention for its advantages in cost-effectiveness and safety. The utilization of existing drugs that potentially regulate the innervated niche via the autophagy pathway is therefore a promising pharmacological approach for clinical practice and treatment selection in cancer neuroscience. Herein, we present the cancer neuroscience landscape with an emphasis on the crosstalk between the innervated niche and autophagy, while also summarizing the underlying mechanisms of candidate drugs in modulating the autophagy pathway. This review provides a strong rationale for drug repurposing in cancer treatment from the viewpoint of the autophagy-mediated innervated niche.

A Photoswitchable Ligand Targeting the β 1 ‐Adrenoceptor Enables Light‐Control of the Cardiac Rhythm**

Catecholamine‐triggered β‐adrenoceptor (β‐AR) signaling is essential for the correct functioning of the heart. Although both β₁‐ and β₂‐AR subtypes are expressed in cardiomyocytes, drugs selectively targeting β₁‐AR have proven this receptor as the main target for the therapeutic effects of beta blockers in the heart. Here, we report a new strategy for the light‐control of β₁‐AR activation by means of photoswitchable drugs with a high level of β₁‐/β₂‐AR selectivity. All reported molecules allow for an efficient real‐time optical control of receptor function in vitro. Moreover, using confocal microscopy we demonstrate that the binding of our best hit, pAzo‐2, can be reversibly photocontrolled. Strikingly, pAzo‐2 also enables a dynamic cardiac rhythm management on living zebrafish larvae using light, thus highlighting the therapeutic and research potential of the developed photoswitches. Overall, this work provides the first proof of precise control of the therapeutic target β₁‐AR in native environments using light.

Linked biaromatic compounds as cardioprotective agents

Cardiovascular diseases (CVDs) are widespread in the modern world, and their number is constantly growing. For a long time, CVDs have been the leading cause of morbidity and mortality worldwide. Drugs for the treatment of CVD have been developed almost since the beginning of the 20th century, and a large number of effective cardioprotective agents of various classes have been created. Nevertheless, the need for the design and development of new safe drugs for the treatment of CVD remains. Literature data indicate that a huge number of cardioprotective agents of various generations and mechanisms correspond to a single generalized pharmacophore model containing two aromatic nuclei linked by a linear linker. In this regard, we put forward a concept for the design of a new generation of cardioprotective agents with a multitarget mechanism of action within the indicated pharmacophore model. This review is devoted to a generalization of the currently known compounds with cardioprotective properties and corresponding to the pharmacophore model of biaromatic compounds linked by a linear linker. Particular attention is paid to the history of the creation of these drugs, approaches to their design, and analysis of the structure-action relationship within each class.

Immunolocalization of Adrenoceptors in the Reproductive Tract of Male Domestic Cats in Comparison to Rats

Simple Summary

In cats, semen is collected by pharmacological stimulation. The administration of a drug that stimulates α2-adrenoceptors causes the expulsion of spermatozoa into the urethra. However, as the results are not always satisfactory, this method needs to be improved. There are nine subtypes of adrenoceptors that are involved in the contraction of smooth muscle, including those in the reproductive tract, so adrenoceptors other than the α2-subtype are potential targets in any new, optimized protocol. The aim of this study was to analyze the immunolocalization of the adrenergic receptors in the reproductive tract of the male cat for the first time in this species. The expression of all adrenoceptor subtypes was noted in the peritubular smooth muscle in cats, indicating a potential clinical application for agonists of these receptors for the optimization of the pharmacological semen collection in felids. In a broader context, the development of a new procedure for semen collection in the male cat, using active substances from groups other than those currently used, will support the wider application of reproductive biotechnologies in felids.

Abstract

Adrenoceptors mediate the action of the sympathetic nervous system, including the contraction of the epididymis and vas deferens. The aim of this study was to immunolocalize the adrenergic receptors in the reproductive tract of the male cat, as this information is not yet available. The epididymis and vas deferens of domestic cats and rats (the biological controls) were analyzed by immunohistochemistry to determine the localization of the α1A-, α1B-, α1D-, α2A-, α2B-, α2C-, β1-, β2-, and β3-adrenoceptors. All the receptors were expressed in the peritubular smooth muscles of the cat, but the α1D-, α2C-, and β1-adrenoceptors were not detected in this tissue in the rat. For the α2A-adrenoceptor, the intensity of immunostaining differed significantly between the caput epididymis (weakest staining) and the vas deferens (strongest staining). The presence of all the types of the receptors was also detected in the cytoplasm of the epithelial cells in all the regions of the reproductive tract. The strong expression of the α2A-adrenoreceptor suggests it has a leading role in the contraction of the reproductive tract in the cat. The presence of other adrenergic receptors in the smooth muscle of the epididymis and vas deferens indicates a potential clinical application for α1-mimetics in the optimization of pharmacological semen collection in felids.

Biased agonism at β-adrenergic receptors

The β-adrenergic receptors (βARs) include three subtypes, β₁, β₂ and β₃. These receptors are widely expressed and regulate numerous physiological processes including cardiovascular and metabolic functions and airway tone. The βARs are also important targets in the treatment of many diseases including hypertension, heart failure and asthma. In some cases, the use of current βAR ligands to treat a disease is suboptimal and can lead to severe side effects. One strategy to potentially improve such treatments is the development of biased agonists that selectively regulate a subset of βAR signaling pathways and responses. Here we discuss the compounds identified to date that preferentially activate a G_s- or β-arrestin-mediated signaling pathway through βARs. Mechanistic insight on how these compounds bias signaling sheds light on the potential development of even more selective compounds that should have increased utility in treating disease.

Activation of β2 adrenergic receptor signaling modulates inflammation: a target limiting the progression of kidney diseases

Beta 2 adrenergic receptor (β₂-AR)-agonists, widely used as bronchodilators, have demonstrated wide-spectrum anti-inflammatory properties in both immune and non-immune cells in various tissues. Their anti-inflammatory properties are mediated primarily, but not exclusively, via activation of the canonical β₂-AR signaling pathway (β₂-AR/cAMP/PKA). As non-canonical β₂-AR signaling also occurs, several inconsistent findings on the anti-inflammatory effect of β₂-agonists are notably present. Increasing amounts of evidence have unveiled the alternative mechanisms of the β₂-AR agonists in protecting the tissues against injuries, i.e., by augmenting mitochondria biogenesis and SIRT1 activity, and by attenuating fibrotic signaling. This review mainly covers the basic mechanisms of the anti-inflammatory effects of β₂-AR activation along with its limitations. Specifically, we summarized the role of β₂-AR signaling in regulating kidney function and in mediating the progression of acute and chronic kidney diseases. Given their versatile protective effects, β₂-agonists can be a promising avenue in the treatment of kidney diseases.

Pharmacological properties of β-adrenoceptors mediating rat superior mesenteric artery relaxation and the effects of chemical sympathetic denervation

AIMS

β-Adrenoceptors (β-ADRs) mediating the relaxation of rat superior mesenteric arteries (SMAs) were pharmacologically identified, and the effects of chemical sympathetic denervation on β-ADR-mediated relaxation were examined.

MAIN METHODS

The tension changes of endothelium-denuded SMAs were isometrically recorded and the mRNA of endothelium-denuded SMA β-ADR was detected using RT-PCR.

KEY FINDINGS

In endothelium-denuded SMAs contracted with ≥10^-7 M phenylephrine (an α₁-ADR agonist), isoprenaline (a β-ADR agonist)-induced relaxation was competitively inhibited by 3 × 10^-9-10^-8 M propranolol (a β_1,2-ADR antagonist), but not further affected by ≥10^-8 M propranolol. Although isoprenaline-induced relaxation was not affected by ICI-118,551 (10^-9-10^-8 M; a β₂-ADR antagonist), it was competitively inhibited by atenolol (10^-7-3 × 10^-7 M; a β₁-ADR antagonist) in the presence of ICI-118,551. In the presence of 10^-7 M propranolol, isoprenaline- and CGP-12177A (a β₃-ADR partial agonist)-induced relaxation was competitively inhibited by high concentrations of bupranolol (a β_1,2,3-ADR antagonist), with pA₂ values of 6.49 and 5.76, respectively. We detected the mRNA of β₁- and β₃-ADRs in endothelium-denuded SMAs. Treatment with 6-hydroxydopamine (a catecholaminergic neurotoxin) reduced maximal isoprenaline-induced relaxation in the presence and absence of 10^-7 M propranolol, but not CGP-12177A-induced relaxation.

SIGNIFICANCE

Isoprenaline-induced relaxation of rat SMAs is mediated by β₁- and β₃-ADRs. β-ADR-mediated relaxation of rat SMAs is shown to be attenuated by chemical sympathetic denervation. The differences in the effects of bupranolol and chemical sympathetic denervation on the responses to isoprenaline and CGP-12177A in rat SMAs might be explained by the possible presence of multiple β₃-ADRs with different pharmacological properties.