The effect of bladder outlet obstruction on alpha1- and beta-adrenoceptor expression and function

Adrenoceptors in the Lower Urinary Tract

Adrenoceptors importantly contribute to the physiological regulation of lower urinary tract (LUT) function and have become a target of several clinically successful treatments for major LUT diseases. In the bladder dome, β-adrenoceptor subtypes are found in multiple cell types and mediate relaxation of detrusor smooth muscle, perhaps partly indirectly by acting on afferent nerves and cells of the mucosa. β3-adrenoceptor agonists such as mirabegron and vibegron are used to treat overactive bladder syndrome. In the bladder trigone and urethra, α1-adrenoceptors cause contraction and thereby physiologically contribute to bladder outlet resistance. α1-adrenoceptors in the prostate also cause contraction and pathophysiologically elevate bladder outlet resistance leading to voiding dysfunction in benign prostatic hyperplasia. α1-adrenoceptor antagonist such as tamsulosin is widely used as a first-line option to treat LUT symptoms in men, but it remains unclear to which extent and how smooth muscle relaxation contributes to symptom relief.

A Concise and Useful Guide to Understand How Alpha1 Adrenoceptor Antagonists Work

Adrenoceptors are the receptors for the catecholamines, adrenaline and noradrenaline. They are divided in α (α1 and α2) and β (β1, β2 and β3). α1-Adrenoceptors are subdivided in α1A, α1B and α1D. Most tissues express mixtures of α1-adrenoceptors subtypes, which appear to coexist in different densities and ratios, and in most cases their responses are probably due to the activation of more than one type. The three subtypes of α1-adrenoceptors are G-protein-coupled receptors (GPCR), specifically coupled to Gq/11. Additionally, the activation of these receptors may activate other signaling pathways or different components of these pathways, which leads to a great variety of possible cellular effects. The first clinically used α1 antagonist was Prazosin, for Systemic Arterial Hypertension (SAH). It was followed by its congeners, Terazosin and Doxazosin. Nowadays, there are many classes of α-adrenergic antagonists with different selectivity profiles. In addition to SAH, the α1-adrenoceptors are used for the treatment of Benign Prostatic Hyperplasia (BPH) and urolithiasis. This antagonism may be part of the mechanism of action of tricyclic antidepressants. Moreover, the activation of these receptors may lead to adverse effects such as orthostatic hypotension, similar to what happens with the antidepressants and with some antipsychotic. Structure-activity relationships can explain, in part, how antagonists work and how selective they can be for each one of the subtypes. However, it is necessary to develop new molecules which antagonize the α1-adrenoceptors or make chemical modifications in these molecules to improve the selectivity, pharmacokinetic profile and/or reduce the adverse effects of known drugs.

Detrusor Overactivity May Be a Prognostic Factor for Better Response to Combination Therapy Over Monotherapy in Male Patients With Benign Prostatic Enlargement and Storage Lower Urinary Tract Symptoms

Purpose

Several trials have shown that in men with overactive bladder (OAB) and benign prostate enlargement (BPE), the combination of an α-blocker with an anticholinergic is superior to α-blocker monotherapy. The purpose of this study is to explore whether urodynamic detrusor overactivity (DO) affects clinical outcomes in men with BPE and OAB.

Methods

This is a post hoc analysis of a prospective, randomized trial, designed to evaluate the changes of morphometric parameters of the prostate following monotherapy or combination therapy in men with BPE-OAB. The initial study recruited men aged ≥50 years, with BPE and predominantly storage lower urinary tract symptoms (LUTS). Patients were randomized to receive tamsulosin monotherapy or a combination of tamsulosin and solifenacin for 26 weeks. All participants completed a 3-day bladder diary and the International Prostate Symptom Score (IPSS), and then underwent pressure-flow and ultrasonographic studies. Data were stratified and analysed based on the urodynamic observation of DO at baseline (DO vs. non-DO). The primary endpoint was the mean change in urgency episodes from baseline. Secondary outcomes were the changes in nocturia, total IPSS, and urodynamic parameters.

Results

Sixty-nine men were initially randomized, but only 60 men were included in this analysis. Urgency episodes significantly improved in men with DO who received combination therapy compared to the DO monotherapy subgroup (P=0.04) or to the non-DO combination treatment subgroup (P=0.038). Nocturia also improved in the DO combination treatment subgroup as compared to the non-DO combination subgroup (P=0.037). The 24-hour frequency and total IPSS significantly improved from baseline without significant differences among the subgroups.

Conclusions

The present study suggests that baseline DO could be a prognostic factor for a better response to combination therapy over monotherapy in men with BPE and storage LUTS.

β-Adrenoceptor regulates contraction and inflammatory cytokine expression of human bladder smooth muscle cells via autophagy under pathological hydrostatic pressure

AIMS

Abnormal intravesical pressure created by partial bladder outlet obstruction (PBOO) triggered the progression from chronic inflammation to fibrosis, initiating structural and functional alterations of bladder. To elucidate the underlying mechanisms of contraction and inflammatory response, we investigated the isolated human bladder smooth muscle cells (hBSMC) under pathological hydrostatic pressure (HP) mimicking the in vivo PBOO condition.

METHODS

hBSMCs were subjected to HP of 200 cm H₂ O to explore the contraction and inflammatory cytokine expression of hBSMC treated with β-adrenoceptors (ADRBs) and/or autophagy signaling pathway agonists and/or antagonists.

RESULTS

We showed that pathological HP induced the release of the proinflammatory cytokines, including monocyte chemotactic protein-1, regulated upon activation normal T cell expressed and secreted factor, and interleukin-6. HP downregulated ADRB2 and ADRB3 expression, which was consistent with the results of the PBOO rat model. ADRB2 or autophagy activation repressed pathological HP-induced proinflammatory cytokine production. ADRB2, ADRB3 or autophagy activation ameliorated the HP-enhanced contraction. The increased contraction and autophagy activity by ADRB2 agonist under HP conditions were reversed by pretreatment with antagonists of adenosine monophosphate-activated protein kinase (AMPK).

CONCLUSION

The present study provides evidence that the ADRB3 agonist suppresses hBSMC contraction under pathological HP conditions. Moreover, the ADRB2 agonist negatively regulates the contraction and inflammatory response of hBSMCs through AMPK/mTOR-mediated autophagy under pathological HP. These findings provide a theoretical basis for potential therapeutic strategies for patients with PBOO.

Expression of bladder α1-adrenoceptor subtype after relief of partial bladder outlet obstruction in a rat model

Purpose

Many patients with benign prostatic hyperplasia require treatment for persistent storage symptoms, even when the obstruction is successfully relieved by surgery. Previous studies identified a characteristic increase in α_1D-adrenoceptor levels in the bladder in a bladder outlet obstruction (BOO) model. Here, we investigated the expression of α₁-adrenoceptor subtypes in the bladder after relief of partial BOO (pBOO) in a rat model.

Materials and Methods

A total of 60 female Sprague–Dawley rats were randomly divided into three groups (sham-operated, pBOO, and pBOO relief groups), and the expression of α₁-adrenoceptor subtypes in the urothelium and detrusor muscle tissues was examined by western blot.

Results

The expression of the α_1D-adrenoceptor was significantly higher in the urothelium and detrusor muscle tissue of the pBOO and pBOO relief groups than in the corresponding tissue of the sham-operated group. Additionally, the α_1A-adrenoceptor was predominant in the sham-operated group but significantly decreased in the urothelium in the pBOO group. No significant differences were found in α_1A-adrenoceptor levels in detrusor muscle or whole bladder.

Conclusions

Our results showed that α_1D-adrenoceptor levels were consistently increased with pBOO, even after relief, suggesting that the α_1D-adrenoceptor might be a cause of persistent storage symptoms after relief of pBOO.

β-Adrenoceptor signaling regulates proliferation and contraction of human bladder smooth muscle cells under pathological hydrostatic pressure

BACKGROUND

Partial bladder outlet obstruction (PBOO) promotes bladder detrusor hyperplasia, increases bladder pressure, and decreases bladder compliance. To extensively explore its underlying mechanism, our study aimed to investigate the effect of pathological hydrostatic pressure on human bladder smooth muscle cell (hBSMC) proliferation and contraction through β-adrenoceptor (ADRB) signaling in vitro.

METHODS

hBSMCs were subjected to pathological hydrostatic pressure (100 cm H₂ O) to investigate the effect of ADRBs on the proliferation and contraction of hBSMCs treated with its agonists and/or antagonists.

RESULTS

Firstly, exposure to 100 cm H₂ O hydrostatic pressure significantly upregulated the expression of α-smooth muscle actin (α-SMA) in hBSMCs at 6 hours, and promoted cell proliferation at 24 hours. When subjected to hydrostatic pressure alone, hBSMCs treated with ADRB2 and ADRB3 agonists for 6 hours inhibited α-SMA expression compared with untreated cells. By contrast, hBSMCs treated with ADRB2 agonists for 24 hours suppressed cell proliferation compared with untreated cells. The two classical pathways of ADRB, protein kinase A (PKA), and exchange factor directly activated by cAMP (EPAC) inhibited the contraction of hBSMCs under hydrostatic pressure via regulating mothers against decapentaplegic homolog 2 (SMAD2) activity. The proliferation of hBSMCs was mainly regulated by the EPAC pathway through extracellular signal-regulated kinase 1/2 (ERK1/2) activity.

CONCLUSION

The contraction of hBSMCs under hydrostatic pressure was regulated by ADRB2 and ADRB3 via the PKA/EPAC-SMAD2 pathway, and the proliferation of hBSMCs was regulated by ADRB2 via the EPAC-ERK1/2 pathway. Compared with ADRB3, ADRB2 played a predominant role under pathological hydrostatic pressure. These findings markedly uncovered the underlying mechanism of ADRBs in PBOO and provided new insights into the efficient treatment of patients with PBOO.

The pharmacology of α1-adrenoceptor subtypes

This review examines the functions of α₁-adrenoceptor subtypes, particularly in terms of contraction of smooth muscle. There are 3 subtypes of α₁-adrenoceptor, α_1A- α_1B- and α_1D-adrenoceptors. Evidence is presented that the postulated α_1L-adrenoceptor is simply the native α_1A-adrenoceptor at which prazosin has low potency. In most isolated tissue studies, smooth muscle contractions to exogenous agonists are mediated particularly by α_1A-, with a lesser role for α_1D-adrenoceptors, but α_1B-adrenoceptors are clearly involved in contractions of some tissues, for example, the spleen. However, nerve-evoked responses are the most crucial physiologically, so that these studies of exogenous agonists may overestimate the importance of α_1A-adrenoceptors. The major α₁-adrenoceptors involved in blood pressure control by sympathetic nerves are the α_1D- and the α_1A-adrenoceptors, mediating peripheral vasoconstrictor actions. As noradrenaline has high potency at α_1D-adrenceptors, these receptors mediate the fastest response and seem to be targets for neurally released noradrenaline especially to low frequency stimulation, with α_1A-adrenoceptors being more important at high frequencies of stimulation. This is true in rodent vas deferens and may be true in vasopressor nerves controlling peripheral resistance and tissue blood flow. The α_lA-adrenoceptor may act mainly through Ca²⁺ entry through L-type channels, whereas the α_1D-adrenoceptor may act mainly through T-type channels and exhaustable Ca²⁺ stores. α₁-Adrenoceptors may also act through non-G-protein linked second messenger systems. In many tissues, multiple subtypes of α-adrenoceptor are present, and this may be regarded as the norm rather than exception, although one receptor subtype is usually predominant.

β3 -Adrenoceptors in the normal and diseased urinary bladder-What are the open questions?

β₃ -Adrenoceptor agonists are used in the treatment of overactive bladder syndrome. Although the relaxant response to adrenergic stimulation in human detrusor smooth muscle cells is mediated mainly via β₃ -adrenoceptors, the plasma concentrations of the therapeutic dose of mirabegron, the only clinically approved β₃ -adrenoceptor agonist, are considerably lower than the EC₅₀ for causing direct relaxation of human detrusor, suggesting a mechanism of action other than direct relaxation of detrusor smooth muscle. However, the site and mechanism of action of β₃ -adrenoceptor agonists in the bladder have not been firmly established. Postulated mechanisms include prejunctional suppression of ACh release from the parasympathetic nerves during the storage phase and inhibition of micro-contractions through β₃ -adrenoceptors on detrusor smooth muscle cells or suburothelial interstitial cells. Implications of possible desensitization of β₃ -adrenoceptors in the bladder upon prolonged agonist exposure and possible causes of rarely observed cardiovascular effects of mirabegron are also discussed. 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.

Decreased Monoamine Oxidase A Expression and Activity in the Bladders of Rats With Partial Outlet Obstruction

OBJECTIVE

To investigate changes in expression and activity of monoamine oxidase A (MAO-A) in rats with partial bladder outlet obstruction (pBOO). Previous studies suggested that monoamines, such as serotonin (5-hydroxytryptamine [5-HT]) and noradrenaline, are involved in bladder hyperactivity secondary to pBOO. However, little is known about the role of MAO-A, an enzyme oxidizing 5-hydroxytryptamine and noradrenalin, in the pathogenesis.

MATERIALS AND METHODS

Female Sprague Dawley rats were subjected to sham or pBOO operations for 7 days, then their bladders were isolated. MAO-A protein levels in the bladder were examined by Western blotting. MAO-A activity was measured by the commercially available MAO-Glo Assay kit. In addition, MAO-A distribution in the bladder was examined by immunohistochemistry.

RESULTS

Weights of the bladders from rats with pBOO were increased about 3.5-fold, compared with those from sham rats. Significant decreases in MAO-A protein and activity levels were observed in whole bladder of rats with pBOO compared with those of sham rats. By immunohistochemistry, it was firstly demonstrated that MAO-A was predominantly expressed in the detrusor layer of the sham rat bladders. The intensity of staining was decreased after pBOO operation.

CONCLUSION

We demonstrated, for the first time, the distribution of MAO-A in the bladder and the pathologic changes in MAO-A protein and activity levels in rats with pBOO. This marked decrease in MAO-A potentially resulting in increased monoamine levels, especially in the detrusor of rat bladder, might be a key factor explaining the mechanism of bladder overactivity associated with pBOO.

Inhibition of cholinergic neurotransmission by β3-adrenoceptors depends on adenosine release and A1-receptor activation in human and rat urinary bladders

The direct detrusor relaxant effect of β₃-adrenoceptor agonists as a primary mechanism to improve overactive bladder symptoms has been questioned. Among other targets, activation of β₃-adrenoceptors downmodulate nerve-evoked acetylcholine (ACh) release, but there is insufficient evidence for the presence of these receptors on bladder cholinergic nerve terminals. Our hypothesis is that adenosine formed from the catabolism of cyclic AMP in the detrusor may act as a retrograde messenger via prejunctional A₁ receptors to explain inhibition of cholinergic activity by β₃-adrenoceptors. Isoprenaline (1 µM) decreased [³H]ACh release from stimulated (10 Hz, 200 pulses) human (-47 ± 5%) and rat (-38 ± 1%) detrusor strips. Mirabegron (0.1 µM, -53 ± 8%) and CL316,243 (1 µM, -37 ± 7%) mimicked isoprenaline (1 µM) inhibition, and their effects were prevented by blocking β₃-adrenoceptors with L748,337 (30 nM) and SR59230A (100 nM), respectively, in human and rat detrusor. Mirabegron and isoprenaline increased extracellular adenosine in the detrusor. Blockage of A₁ receptors with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 100 nM) or the equilibrative nucleoside transporters (ENT) with dipyridamole (0.5 µM) prevented mirabegron and isoprenaline inhibitory effects. Dipyridamole prevented isoprenaline-induced adenosine outflow from the rat detrusor, and this effect was mimicked by the ENT1 inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI, 30 µM). Cystometry recordings in anesthetized rats demonstrated that SR59230A, DPCPX, dipyridamole, and NBTI reversed the decrease in the voiding frequency caused by isoprenaline (0.1-1,000 nM). Data suggest that inhibition of cholinergic neurotransmission by β₃-adrenoceptors results from adenosine release via equilibrative nucleoside transporters and prejunctional A₁-receptor stimulation in human and rat urinary bladder.

Young rats exhibit an age- and sex-dependent bladder response to alpha-antagonists but not beta-agonists

INTRODUCTION

Previous studies have suggested that the onset of alpha- (α) and beta- (β) adrenergic receptor activity is delayed in young animals. The use of alpha1- (α1-) antagonists for dysfunctional voiding, and beta3- (β3-) agonists for overactive bladder in younger children may not be indicated if maturation is required before bladder and urethral adrenergic receptors are active.

OBJECTIVE

To determine the sex- and age-dependent responses of the bladder and external urethral sphincter (EUS) to α- and β-adrenergic agents in neonatal and young adult rats.

MATERIALS AND METHODS

A total of 72 naïve Sprague-Dawley rats (36 female, 36 male) and 15 bladder-reduced (BR) female Sprague-Dawley rats underwent cystometry and EUS electromyography at 3, 6, and 9 weeks of life. Following administration of WAY 100,635 (0.3 mg/kg, serotonergic receptor antagonist), the non-selective α-agonist phenylephrine (0.3 mg/kg), α-antagonist phentolamine (1-3 mg/kg), β-agonist isoprenaline (3 mg/kg) and β-antagonist propranolol (3 mg/kg) were delivered intravenously. The maximum intravesical pressure (IVP), pressure threshold (PT), intermicturition interval (IMI), contraction duration (CD), burst amplitude and burst frequency were compared after each drug.

RESULTS

The α-antagonist phentolamine lowered the IVP in 9-week-old males without lowering the PT. In contrast, the β-agonist isoprenaline lowered the IVP in both males and females of all ages, also without affecting the PT. Isoprenaline was also effective at shortening the CD in females, suggesting more effective bladder emptying. The α-agonist phenylephrine increased the IVP in 3-week-old and 6-week-old females and 3-week-old males, but this effect was blocked by pretreatment with phentolamine. The β-antagonist propranolol increased the PT in both males and females, and shortened the IMI in females, which was consistent with retention. Phenylephrine increased the burst duration in 9-week-old naïve females, while isoprenaline increased the burst amplitude and duration in 9-week-old BR females.

CONCLUSIONS

In the neonatal rat, both α- and β-adrenergic receptors actively regulate bladder function by 3 weeks of life, but the desired effect of decreasing IVP by α-antagonists was delayed until 9 weeks in male rats. In contrast, β-agonists were effective at decreasing IVP in both male and female rats of all ages, which suggests that they are better agents for enhancing bladder emptying in female and young male rats.

β3-Adrenoceptor agonists for overactive bladder syndrome: Role of translational pharmacology in a repositioning clinical drug development project

β3-Adrenoceptor agonists were originally considered as a promising drug class for the treatment of obesity and/or type 2 diabetes. When these development efforts failed, they were repositioned for the treatment of the overactive bladder syndrome. Based on the example of the β3-adrenoceptor agonist mirabegron, but also taking into consideration evidence obtained with ritobegron and solabegron, we discuss challenges facing a translational pharmacology program accompanying clinical drug development for a first-in-class molecule. Challenges included generic ones such as ligand selectivity, species differences and drug target gene polymorphisms. Challenges that are more specific included changing concepts of the underlying pathophysiology of the target condition while clinical development was under way; moreover, a paucity of public domain tools for the study of the drug target and aspects of receptor agonists as drugs had to be addressed. Nonetheless, a successful first-in-class launch was accomplished. Looking back at this translational pharmacology program, we conclude that a specifically tailored and highly flexible approach is required. However, several of the lessons learned may also be applicable to translational pharmacology programs in other indications.

Non-uniform changes in membrane receptors in the rat urinary bladder following outlet obstruction

The aim of the present study was to investigate the expression and distribution of membrane receptors after bladder outlet obstruction (BOO). Partial bladder outlet obstruction (BOO) was induced in female rats and bladders were harvested after either 10 days or 6 weeks of BOO. The expression of different receptors was surveyed by microarrays and corroborated by immunohistochemistry and western blotting. A microarray experiment identified 10 membrane receptors that were differentially expressed compared to sham-operated rats including both upregulated and downregulated receptors. Four of these were selected for functional experiments on the basis of magnitude of change and relevance to bladder physiology. At 6 weeks of BOO, maximal contraction was reduced for neuromedin B and vasopressin (AVP), consistent with reductions of receptor mRNA levels. Glycine receptor-induced contraction on the other hand was increased and receptor mRNA expression was accordingly upregulated. Maximal relaxation by the β3-adrenergic receptor agonist CL316243 was reduced as was the receptor mRNA level. Immunohistochemistry supported reduced expression of neuromedin B receptors, V1a receptors and β3-adrenergic receptors, but glycine receptor expression appeared unchanged. Western blotting confirmed repression of V1a receptors and induction of glycine receptors in BOO. mRNA for vasopressin was detectable in the bladder, suggesting local AVP production. We conclude that changes in receptor expression following bladder outlet obstruction are non-uniform. Some receptors are upregulated, conferring increased responsiveness to agonist, whereas others are downregulated, leading to decreased agonist-induced responses. This study might help to select pharmacological agents that are effective in modulating lower urinary tract symptoms in BOO.

Bladder smooth muscle strip contractility as a method to evaluate lower urinary tract pharmacology

We describe an in vitro method to measure bladder smooth muscle contractility, and its use for investigating physiological and pharmacological properties of the smooth muscle as well as changes induced by pathology. This method provides critical information for understanding bladder function while overcoming major methodological difficulties encountered in in vivo experiments, such as surgical and pharmacological manipulations that affect stability and survival of the preparations, the use of human tissue, and/or the use of expensive chemicals. It also provides a way to investigate the properties of each bladder component (i.e. smooth muscle, mucosa, nerves) in healthy and pathological conditions. The urinary bladder is removed from an anesthetized animal, placed in Krebs solution and cut into strips. Strips are placed into a chamber filled with warm Krebs solution. One end is attached to an isometric tension transducer to measure contraction force, the other end is attached to a fixed rod. Tissue is stimulated by directly adding compounds to the bath or by electric field stimulation electrodes that activate nerves, similar to triggering bladder contractions in vivo. We demonstrate the use of this method to evaluate spontaneous smooth muscle contractility during development and after an experimental spinal cord injury, the nature of neurotransmission (transmitters and receptors involved), factors involved in modulation of smooth muscle activity, the role of individual bladder components, and species and organ differences in response to pharmacological agents. Additionally, it could be used for investigating intracellular pathways involved in contraction and/or relaxation of the smooth muscle, drug structure-activity relationships and evaluation of transmitter release. The in vitro smooth muscle contractility method has been used extensively for over 50 years, and has provided data that significantly contributed to our understanding of bladder function as well as to pharmaceutical development of compounds currently used clinically for bladder management.

The pharmacological rationale for combining muscarinic receptor antagonists and β-adrenoceptor agonists in the treatment of airway and bladder disease

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Muscarinic receptors increase smooth muscle tone in airways and urinary bladder.

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β-Adrenoceptors relax smooth muscle tone and oppose muscarinic contraction.

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Opposition involves transmitter release, signal transduction and receptor expression.

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This supports the combined use of muscarinic antagonists and β-adrenoceptor agonists.

Muscarinic receptor antagonists and β-adrenoceptor agonists are used in the treatment of obstructive airway disease and overactive bladder syndrome. Here we review the pharmacological rationale for their combination. Muscarinic receptors and β-adrenoceptors are physiological antagonists for smooth muscle tone in airways and bladder. Muscarinic agonism may attenuate β-adrenoceptor-mediated relaxation more than other contractile stimuli. Chronic treatment with one drug class may regulate expression of the target receptor but also that of the opposing receptor. Prejunctional β₂-adrenoceptors can enhance neuronal acetylcholine release. Moreover, at least in the airways, muscarinic receptors and β-adrenoceptors are expressed in different locations, indicating that only a combined modulation of both systems may cause dilatation along the entire bronchial tree. While all of these factors contribute to a rationale for a combination of muscarinic receptor antagonists and β-adrenoceptor agonists, the full value of such combination as compared to monotherapy can only be determined in clinical studies.

Do β-adrenoceptor agonists induce homologous or heterologous desensitization in rat urinary bladder?

β3-Adrenoceptor agonists have recently been introduced for the symptomatic treatment of the overactive bladder syndrome. As such treatment is not curative, long-term treatment is anticipated to be required. As the susceptibility of β3-adrenoceptors to undergo agonist-induced desensitization is cell type- and tissue-dependent, we have explored whether pre-treatment with a β-adrenoceptor agonist will attenuate subsequent relaxation responses to freshly added agonist using rat urinary bladder as a model. We have used the prototypical β-adrenoceptor agonist isoprenaline, the β2-selective fenoterol and the β3-selective CL 316,243 and mirabegron as well as the receptor-independent bladder relaxant forskolin. We show that a 6-h pre-treatment with agonist can significantly reduce subsequent relaxation against KCl-induced smooth muscle tone, but agonist-induced desensitization was also observed with longer pre-treatments or against passive tension. The agonist-induced desensitization was prominent for the β2 component of rat bladder relaxation but much weaker or even absent for the β3 component. Moreover, β-adrenoceptor agonist pre-treatment reduced contractile responses to the muscarinic agonist carbachol and the receptor-independent stimulus KCl. Taken together these data do not support the hypothesis that the long-term clinical efficacy of β3-adrenoceptor agonists in the treatment of the overactive bladder syndrome will be limited by receptor desensitization. Rather they raise the possibility that such treatment may not only cause smooth muscle relaxation but also may attenuate hyper-contractility of the bladder.

Changes in the function and expression of T-type and N-type calcium channels in the rat bladder after bladder outlet obstruction

PURPOSE

We evaluated possible changes in the function and expression of T-type and N-type Ca(2+) channels in the bladder of rats with bladder outlet obstruction.

MATERIALS AND METHODS

Female Sprague Dawley® rats were divided into a group with bladder outlet obstruction created by partial urethral ligation and a sham operated group. Six weeks postoperatively we determined the mRNA expression of T-type and N-type Ca(2+) channels in the bladder, dorsal root ganglion and spinal cord. We also cystometrically investigated expression by intravenous administration of the T-Ca blocker RQ-00311610 or the N-type Ca(2+) channel blocker ω-conotoxin GVIA. We then performed in vitro functional studies of detrusor strips using these blockers.

RESULTS

mRNA expression of T-type Ca(2+) channels in the bladder detrusor and mucosa layers, and the spinal cord dorsal horn, and N-type Ca(2+) channels in the whole bladder and detrusor layer, and the spinal cord dorsal horn was greater in the obstructed group than the sham operated group. In obstructed rats bladder capacity and voided volume increased after RQ-00311610 administration but the number of nonvoiding contractions decreased after ω-conotoxin GVIA administration. Detrusor strips from obstructed rats showed weaker contractile responses to electrical field stimulation, particularly in regard to the purinergic component. ω-Conotoxin GVIA suppressed electrical field stimulation induced contractions only in the detrusor of obstructed rats, especially the cholinergic component.

CONCLUSIONS

Blocking T-type Ca(2+) channels increased bladder capacity while N-type Ca(2+) channel blockade inhibited nonvoiding contractions in rats with bladder outlet obstruction. Decreased bladder efferent neurotransmission occurred after bladder outlet obstruction, predominantly in its purinergic component and detrusor contractions via cholinergic neurotransmission were activated in a compensatory manner, probably via N-type Ca(2+) channel up-regulation.

Phenotypic switching induced by damaged matrix is associated with DNA methyltransferase 3A (DNMT3A) activity and nuclear localization in smooth muscle cells (SMC)

Extracellular matrix changes are often crucial inciting events for fibroproliferative disease. Epigenetic changes, specifically DNA methylation, are critical factors underlying differentiated phenotypes. We examined the dependency of matrix-induced fibroproliferation and SMC phenotype on DNA methyltransferases. The cooperativity of matrix with growth factors, cell density and hypoxia was also examined. Primary rat visceral SMC of early passage (0–2) were plated on native collagen or damaged/heat-denatured collagen. Hypoxia was induced with 3% O₂ (balanced 5% CO₂ and 95% N₂) over 48 hours. Inhibitors were applied 2–3 hours after cells were plated on matrix, or immediately before hypoxia. Cells were fixed and stained for DNMT3A and smooth muscle actin (SMA) or smooth muscle myosin heavy chain. Illumina 450 K array of CpG sites was performed on bisulfite-converted DNA from smooth muscle cells on damaged matrix vs native collagen. Matrix exquisitely regulates DNMT3A localization and expression, and influences differentiation in SMCs exposed to denatured matrix +/− hypoxia. Analysis of DNA methylation signatures showed that Matrix caused significant DNA methylation alterations in a discrete number of CpG sites proximal to genes related to SMC differentiation. Matrix has a profound effect on the regulation of SMC phenotype, which is associated with altered expression, localization of DNMTs and discrete changes DNA methylation.

Correlation Between Bladder Mucosal Alpha-1D/Alpha-1A Adrenoceptor mRNA Ratio and Lower Urinary Tract Function in Benign Prostatic Obstruction Patients

OBJECTIVES

Alpha-1 adrenoceptor (AR) antagonists are commonly used as therapeutic agents for patients with benign prostatic obstruction (BPO). Our objective was to investigate the correlation between the ratio of bladder mucosal alpha-1D/alpha-1A adrenoceptor mRNA and lower urinary tract function in BPO patients.

METHODS

In 20 BPO patients, the expression level of alpha-1 AR mRNAs in the bladder mucosal biopsies was investigated by reverse transcriptase polymerase chain reaction. The subjects were divided into two groups. In Group 1, the ratio of alpha-1D mRNA to alpha-1A mRNA was greater than one. In Group 2, the ratio was less than one. We determined the correlation by Schäfer nomogram between Group 1 and Group 2 patients and lower urinary tract function as determined by a video urodynamic study.

RESULTS

Two patients were excluded due to inability to void. Another was excluded because the alpha-1D/alpha-1A mRNA ratio was one. On the Schäfer nomogram, six of nine Group 1 cases had obstructions less than IV and normal or weak detrusor contractility. For Group 2, six of eight cases had obstructions more than IV and normal or strong detrusor contractility.

CONCLUSION

Patients with higher levels of alpha-1D AR mRNA were distinct from those with higher alpha-1A AR mRNA levels with regard to obstruction and detrusor activity. The results suggest that the Schäfer nomogram might be useful in determining which alpha-1 AR antagonists are better for BPO patients suffering from storage symptoms.

5-Hydroxytryptamine-induced bladder hyperactivity via the 5-HT2A receptor in partial bladder outlet obstruction in rats

We investigated the effects of partial bladder outlet obstruction (BOO) on the function and gene expression of 5-hydroxytryptamine (5-HT) receptor subtypes in rat bladder. Isometric contractions of the isolated bladders from sham-operated control and BOO rats were examined. The contractile responses to 5-HT were significantly increased in BOO rat bladder strips, while the responses to KCl, carbachol, or phenylephrine were not different from the control. The 5-HT-induced hypercontraction in BOO rat bladder strips was inhibited by ketanserin, a 5-HT(2A) receptor antagonist. The contractile responses to 5-HT in bladder strips were not affected by urothelium removal from the intact bladder. The gene expression of 5-HT receptor subtypes in the bladders was analyzed by RT-PCR. The mRNA expression of the 5-HT(2A), 5-HT(2B), 5-HT(2C), 5-HT(4), and 5-HT(7) receptors was detected in both the control and BOO rat bladders. Quantitative RT-PCR analysis showed there was a significant increase of 5-HT(2A) receptor mRNA in the BOO rat bladder compared with the control bladder. On the other hand, the gene expression of the 5-HT(4) receptor was not changed in the BOO rat bladder. These results suggest that the increased contractile responses to 5-HT in BOO rat bladder may be partly caused by 5-HT(2A) receptor upregulation in the detrusor smooth muscles.

Autonomic nervous control of the urinary bladder

The autonomic nervous system plays an important role in the regulation of the urinary bladder function. Under physiological circumstances, noradrenaline, acting mainly on β(3) -adrenoceptors in the detrusor and on α(1) (A) -adrenoceptors in the bladder outflow tract, promotes urine storage, whereas neuronally released acetylcholine acting mainly on M(3) receptors promotes bladder emptying. Under pathophysiological conditions, however, this system may change in several ways. Firstly, there may be plasticity at the levels of innervation and receptor expression and function. Secondly, non-neuronal acetylcholine synthesis and release from the urothelium may occur during the storage phase, leading to a concomitant exposure of detrusor smooth muscle, urothelium and afferent nerves to acetylcholine and noradrenaline. This can cause interactions between the adrenergic and cholinergic system, which have been studied mostly at the post-junctional smooth muscle level until now. The implications of such plasticity are being discussed.

Male lower urinary tract symptoms and α1D-adrenoceptors

Historically, α(1)-adrenoceptors have been classified into three subtypes (α(1)(A), α(1)(B) and α(1)(D)) that are widely distributed in various organs. Research on the α(1)(D)-adrenoceptors in the bladder, urethra and prostate has focused on the relationship between expression levels and symptoms of bladder outlet obstruction, and the implications and functional roles of α(1)(D)-adrenoceptors subtypes in these organs. The α(1)(D)-adrenoceptor messenger ribonucleic acid and protein seem to be increased in obstructed bladders or small capacity bladders. In contrast, α(1)(D)-adrenoceptor subtype knock-out mice have been found to have a prolonged voiding interval. Interestingly, an α(1)(D)-adrenoceptor antagonist was found to inhibit the facilitation of afferent nerve activity for the micturition reflex induced by intravesical infusion of acetic acid. Clinically, patients who felt urgency at low filling volumes and had a small bladder capacity were found to have more α(1)(D)-adrenoceptor messenger ribonucleic acid in their bladder mucosa than patients who felt urgency at high filling volumes and had a large bladder capacity. An α(1)(D)-adrenoceptor antagonist was found to increase the first desired volume and the maximum desired volume while decreasing detrusor overactivity in pressure flow studies. Thus, α(1)(D)-adrenoceptors in the lower urinary tract might play an important role in the pathophysiology of lower urinary tract disorders.

Modulation of alpha 1 adrenergic receptors on urinary bladder in rat spinal cord injury model

Purpose

Whereas many studies have focused on the vesical changes of the α1 adrenergic receptor (AR) subtypes in partial outlet obstruction, few studies have addressed the modulation of the α1 AR subtypes after spinal cord injury (SCI). Therefore, we studied the modulation of the α1 ARs in urinary bladder in a rat SCI model.

Methods

Four weeks after a SCI, the whole vesical bodies from eight female Sprague-Dawley rats and from eight controls were harvested. The total RNA was extracted from the samples and was used to prepare cDNA. We developed standard plasmid constructs of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and three α1 ARs (α1a, α1b, and α1d) to convert the cycle threshold (Ct) values from real-time polymerase chain reaction (RT-PCR) into subtype mRNA concentrations. The detected Ct values of 16 samples from RT-PCR were interpolated into the standard plasmid curves.

Results

All serially diluted standard samples showed very good linearity. The mRNA expression of GAPDH was higher in the SCI group, whereas the mRNA expression of all α1 ARs was lower in the SCI group than in the control animals. The α1a, α1b, and α1d mRNA expression in the controls was 81.7%, 3.3%, and 15.1%, respectively, whereas the α1a, α1b, and α1d mRNA expression in the SCI group was 33.5%, 5.2%, and 60.9%, respectively.

Conclusions

SCI moderates the α1 AR mRNA subtypes in the urinary bladder. The relatively increased α1d or decreased α1a AR mRNA expression may be a therapeutic candidate for controlling the symptoms of neurogenic bladder after SCI.

Effects of Spinal and Peripheral Injection of α1A or α1D Adrenoceptor Antagonists on Bladder Activity in Rat Models with or without Bladder Outlet Obstruction

PURPOSE

Antagonists of α1-adrenergic receptors (α1ARs) relax prostate smooth muscle and relieve voiding and storage symptoms. Recently, increased expression of α1ARs with change of its subtype expression has been proved in bladder outlet obstruction (BOO). To search for the evidence of changes in α1ARs subtype expression and activity in the peripheral and spinal routes, the effects of spinal and peripheral administration of tamsulosin (an α1A/D-selective AR), naftopidil (an α1A/D-selective AR), and doxazosin (non-selective AR) on bladder activity were investigated in a rat model with or without BOO.

METHODS

A total of 65 female Sprague-Dawley rats were divided into the BOO surgery group (n=47) and the sham surgery group (n=18). After 6 weeks, cystometry was assessed before and after intrathecal and intra-arterial administrations of tamsulosin, naftopidil, and doxazosin.

RESULTS

After intra-arterial administrations of all three drugs, bladder capacity (BC) was increased and maximal intravesical pressure (Pmax) was decreased in both BOO and the sham rat models (P<0.05). After intrathecal administration of all three drugs, BC was increased and Pmax was decreased in only the BOO group. The episodes of involuntary contraction in the BOO rat models were decreased by intra-arterial administration (P=0.031). The increase of BC after intrathercal and intra-arterial administrations of α1ARs was significantly greater in the BOO group than in the sham group (P=0.023, P=0.041). In the BOO group, the increase of BC and decrease in Pmax were greater by intra-arterial administration than by intrathecal administration (P=0.035). There were no significant differences of the degrees of changes in the cystometric parameters among the three different α1ARs.

CONCLUSIONS

Up-regulations of the α1ARs in BOO were observed by the greater increases of BC after α1AR antagonist administrations in the BOO group than in the sham group. However, there were no subtype differences of the α1ARs in functional parameters of bladder activity. In addition, α1ARs also act on the lumbosacral cord which implies that the sensitivity of α1ARs is increased in pathologic models such as BOO. Further evaluation including differential expression of α1ARs in BOO models are need.

Urothelial beta-3 adrenergic receptors in the rat bladder

AIMS

To investigate the distribution of beta-3 adrenergic receptors (β(3)ARs) in the rat bladder and to examine the contribution of urothelial β(3)ARs to agonist-induced suppression of bladder reflexes and relaxation of smooth muscle.

METHODS

Bladder tissue was collected from 8- to 10-month old female SD rats. In some samples, the urothelium was surgically separated from the smooth muscle. The expression and localization of βAR mRNA and β(3)AR protein were determined using RT-PCR and immunohistochemistry. Contractile responses to the specific β(3)AR agonists TAK-677 and BRL37344 were measured in bladder strips with or without the urothelium. The contribution of urothelial β(3)ARs to the micturition reflex was assessed in continuous cystometry in urethane anesthetized rats using intravesical delivery of β(3)AR agonists.

RESULTS

RT-PCR detected mRNA of all βARs in urothelium and smooth muscle. Immunostaining detected β(3)ARs throughout the urothelium, in the smooth muscle, myofibroblast-like cells, and in the peripheral nerves. Ovariectomy did not change the distribution of β(3)ARs in any bladder structure. Intravesical administration of TAK-677 and BRL37344 (1-5 × 10(-4) M) decreased voiding frequency and amplitude of bladder contractions. In bladder strips in vitro both β(3)AR agonists (10(-12) to 10(-4) M) relaxed the smooth muscle in a concentration-dependent manner to the same extent in strips with and without the urothelium.

CONCLUSIONS

In addition to their presence in bladder smooth muscle, β(3)ARs are present in the urothelium where their activation may alter reflex voiding via release of factor(s) that act on non-myocyte structures including the afferent and/or efferent nerves to influence bladder contractility.

Beta3-adrenoceptors in the rat sacral spinal cord and their functional relevance in micturition under normal conditions and in a model of partial urethral obstruction

AIMS

Beta3-adrenoceptor selective agonists are evaluated as a new treatment for patients with lower urinary tract symptoms . It is believed that β3-AR selective agonists exert their effects via a peripheral site of action. However, β3-ARs have been found in brain tissue. This study examined whether β3-ARs are present in rat sacral spinal cord, and whether there are differences in β3-AR expression between normal and partial urethral obstruction (PUO) animals, and furthermore assessed the functional relevance of spinal β3-ARs for micturition.

METHODS

Thirty-eight male Sprague-Dawley rats underwent either PUO or sham-operation. Two weeks after operation, half of the animals were used for histomorphological analysis. Remaining animals were used for functional experiments, where a β3-AR selective agonist, BRL 37344, was given intrathecally. Bladder function was assessed by continuous cystometry in non-anesthetized animals before and after drug administration.

RESULTS

Beta3-ARs were found in sacral spinal cord segments with an accumulation in the ventral horn. There was a significant increase of β3-AR expression in obstructed rats. In functional experiments obstructed rats showed increased bladder weight, micturition frequency, spontaneous activity, and bladder pressures (all P < 0.05) compared to controls. Intrathecally administered BRL 37344 showed no effect in non-obstructed rats. In obstructed rats intrathecal BRL 37344 significantly reduced bladder pressures, spontaneous activity, and micturition frequency (all P < 0.05).

CONCLUSIONS

Beta3-ARs are present in rat sacral spinal cord, and are significantly up-regulated after PUO. Besides their well-established peripheral site of action in the treatment of voiding dysfunction, β3-AR selective agonists might exert relevant effects at a central nervous site of action.

β-adrenoceptor agonist effects in experimental models of bladder dysfunction

β-adrenoceptor stimulation can enhance the storage function of the urinary bladder by acting on detrusor smooth muscle tone, mediator release from the urothelium and/or afferent nerve activity. In humans this may occur predominantly if not exclusively via the β₃-subtype. The effects of β-adrenoceptor agonists including several β₃-selective agonists have been studied in vitro and in vivo, in healthy animals of both genders and various age groups and in a wide range of animal (mostly rat) models of genetic or acquired bladder dysfunction. Such models included bladder irritation by intravesical instillation of acetic acid or prostaglandin E₂, bladder outlet obstruction, stroke, diabetes, spontaneously hypertensive rats, and NO synthase inhibition. Across all of these models β-adrenoceptor agonists had effects consistent with improved bladder storage function. β₃-adrenoceptor effects are resistant to agonist-induced desensitization in many cell types, but whether this also applies to the human bladder is unknown. The efficacy of β-adrenoceptor agonists appears to be largely unaffected by common polymorphisms of the β₃-adrenoceptor gene. Taken together these findings suggest that β₃-adrenoceptor agonists may become useful drugs for the treatment of bladder storage dysfunction, a view supported by recent phase III clinical studies for one such agent, mirabegron.

β-Adrenergic Receptor Subtypes in the Urinary Tract

Within the urinary tract, β-adrenergic receptors (AR) are found largely on smooth muscle cells but are also present, at least in the bladder, in the urothelium and on afferent nerves. Our understanding of β-AR subtype expression and function is hampered by a lack of well-validated tools, particularly with regard to β(3)-AR. Moreover, the β-AR subtypes involved in a specific function may differ between species. In the ureter, β-AR can modulate pacemaker activity and smooth muscle tone involving multiple subtypes. In the human bladder, β-AR promote urine storage. Bladder smooth muscle relaxation primarily involves β(3)-AR, and the agonists selective for this subtype are in clinical development to treat bladder dysfunction. While prostate and urethra also express β-AR, the overall physiological role in these tissues remains unclear.

Changes in Awake Cystometry and Expression of Bladder β-adrenoceptors after Partial Bladder Outlet Obstruction in Male Rats

PURPOSE

To explore possible changes in awake cystometry and expression of beta-adrenoceptors (ARs) as a cause for bladder dysfunction in a male rat model of partial bladder outlet obstruction (pBOO).

MATERIALS AND METHODS

Awake cystometry was performed in rats with pBOO (16) and sham-operated rats (16), 8 weeks after the operation. The expression of mRNA and protein of β-ARs was assessed by real-time PCR and western blot.

RESULTS

The bladders with pBOO (1030mg) were increased compared to those in control rats (230mg). In the cystometric studies, the maximum intravesical pressure significantly increased in the pBOO group compared to control group rats (p=0.001). The time to reach maximal intravesical pressure during micturition in the pBOO group was significantly longer than the sham group (p=0.003). The frequency of non-void contraction in the pBOO group was significantly more than the sham group (p=0.006). The mRNA expressions of β2- and 3-ARs were increased insignificantly in pBOO group compared to sham group. The data of pBOO group expressed as folds of corresponding expression in sham group were 1.28 and 1.46 respectively in β2- and 3-ARs. Compared to the sham groups, the density of 60Kda protein band recognized by β2-AR antibodies and the density of 45Kda protein band recognized by β3-AR antibodies were higher in the bladder from pBOO group rats.

CONCLUSION

PBOO of male rats increase the maximal intravesical pressure and contraction time during micturition and the frequency of non-void contraction as well as weight of bladder. The expression of β2- and 3-ARs subtypes was increased insignificantly compared to sham operated group. This study demonstrates that the changes of cystometric or non-void contraction parameters in pBOO is one of the pathophysiologic processes potentially associated with the alterations of bladder β-ARs.

Can [I]-Iodocyanopindolol Label β(3)-Adrenoceptors in Rat Urinary Bladder?

β₃-Adrenoceptors have been demonstrated to mediate urinary bladder smooth muscle relaxation but proof of their expression at the protein level has been missing because of lack of suitable antibodies or radioligands. As among various available radioligands [¹²⁵I]-iodocyanopindolol ([¹²⁵I]-ICYP) exhibited the smallest problems in labeling cloned human β₃-adrenoceptors in previous studies, we have explored its suitability to label β₃-adrenoceptors in rat urinary bladder in saturation and competition radioligand binding experiments. Rat lung was used as an internal control and exhibited all characteristics expected from this tissue with regard to β1/β2-adrenoceptor labeling. Saturation and competition binding studies with [¹²⁵I]-ICYP in rat bladder yielded saturable binding sites with an affinity compatible with β₃-adrenoceptors. In competition experiments various agonists and antagonists largely exhibited a profile compatible with a population consisting largely of β₃-adrenoceptors. However, the binding competition properties of ICI 118,551 and SR 59,230A were not easily explained by the idea of labeling a homogeneous β₃-adrenoceptor population but interpretation of the data was limited by a high degree of non-specific binding in [¹²⁵I]-ICYP concentrations required to label the receptors. We conclude that [¹²⁵I]-ICYP can be used to label tissue β₃-adrenoceptors but results obtained with this ligand have to be interpreted with caution.

The forefront for novel therapeutic agents based on the pathophysiology of lower urinary tract dysfunction: alpha-blockers in the treatment of male voiding dysfunction - how do they work and why do they differ in tolerability?

alpha(1)-Adrenoceptor antagonists are the mainstay of medical treatment of male voiding dysfunction which typically is attributed to benign prostatic hyperplasia. While original concepts have assumed that they relieve voiding dysfunction by relaxing prostatic smooth muscle, newer data indicate that their therapeutic effects at least partly occur independent of prostatic relaxation, perhaps involving direct effects on blood vessels, urothelium, afferent nerves, and/or smooth muscle of the urinary bladder. The adverse event profiles differ among alpha(1)-adrenoceptor antagonists, with tamsulosin having a particularly good cardiovascular tolerability. While this was originally attributed to its selectivity for alpha(1A)-adrenoceptors, it appears that alfuzosin which lacks subtype-selectivity, has a very similar tolerability. In contrast, doxazosin and terazosin, which are chemically and pharmacologically more closely related to alfuzosin than to tamsulosin, appear to have more side effects attributable to the cardiovascular system. More recent data indicate that tolerability differences between alpha(1)-adrenoceptor antagonists may at least partly relate to pharmacokinetic rather than to pharmacodynamic differences. Taken together, these data emphasize the idea that concepts about drug efficacy and tolerability despite being highly plausible may not necessarily be true and always require thorough experimental testing.