Evaluation of mRNAs Encoding Muscarinic Receptor Subtypes in Human Detrusor Muscle

Intracellular signaling pathways of muscarinic acetylcholine receptor-mediated detrusor muscle contractions

Acetylcholine plays an essential role in the regulation of detrusor muscle contractions, and antimuscarinics are widely used in the management of overactive bladder syndrome. However, several adverse effects limit their application and patients' compliance. Thus, this study aimed to further analyze the signal transduction of M2 and M3 receptors in the murine urinary bladder to eventually find more specific therapeutic targets. Experiments were performed on adult male wild-type, M2, M3, M2/M3, or Gαq/11 knockout (KO), and pertussis toxin (PTX)-treated mice. Contraction force and RhoA activity were measured in the urinary bladder smooth muscle (UBSM). Our results indicate that carbamoylcholine (CCh)-induced contractions were associated with increased activity of RhoA and were reduced in the presence of the Rho-associated kinase (ROCK) inhibitor Y-27632 in UBSM. CCh-evoked contractile responses and RhoA activation were markedly reduced in detrusor strips lacking either M2 or M3 receptors and abolished in M2/M3 KO mice. Inhibition of Gαi-coupled signaling by PTX treatment shifted the concentration-response curve of CCh to the right and diminished RhoA activation. CCh-induced contractile responses were markedly decreased in Gαq/11 KO mice; however, RhoA activation was unaffected. In conclusion, cholinergic detrusor contraction and RhoA activation are mediated by both M2 and M3 receptors. Furthermore, whereas both Gαi and Gαq/11 proteins mediate UBSM contraction, the activation at the RhoA-ROCK pathway appears to be linked specifically to Gαi. These findings may aid the identification of more specific therapeutic targets for bladder dysfunctions.NEW & NOTEWORTHY Muscarinic acetylcholine receptors are of utmost importance in physiological regulation of micturition and also in the development of voiding disorders. We demonstrate that the RhoA-Rho-associated kinase (ROCK) pathway plays a crucial role in contractions induced by cholinergic stimulation in detrusor muscle. Activation of RhoA is mediated by both M2 and M3 receptors as well as by Gi but not Gq/11 proteins. The Gi-RhoA-ROCK pathway may provide a novel therapeutic target for overactive voiding disorders.

The role of rhoA/rho-kinase and PKC in the inhibitory effect of L-cysteine/H2S pathway on the carbachol-mediated contraction of mouse bladder smooth muscle

We investigated the role of RhoA/Rho-kinase (ROCK) and PKC in the inhibitory effect of L-cysteine/hydrogen sulfide (H2S) pathway on the carbachol-mediated contraction of mouse bladder smooth muscle. Carbachol (10-8-10-4 M) induced a concentration-dependent contraction in bladder tissues. L-cysteine (H2S precursor; 10-2 M) and exogenous H2S (NaHS; 10-3 M) reduced the contractions evoked by carbachol by ~ 49 and ~ 53%, respectively, relative to control. The inhibitory effect of L-cysteine on contractions to carbachol was reversed by 10-2 M PAG (~ 40%) and 10-3 M AOAA (~ 55%), cystathionine-gamma-lyase (CSE) and cystathionine-β-synthase (CBS) inhibitor, respectively. Y-27632 (10-6 M) and GF 109203X (10-6 M), a specific ROCK and PKC inhibitor, respectively, reduced contractions evoked by carbachol (~ 18 and ~ 24% respectively), and the inhibitory effect of Y-27632 and GF 109203X on contractions was reversed by PAG (~ 29 and ~ 19%, respectively) but not by AOAA. Also, Y-27632 and GF 109203X reduced the inhibitory responses of L-cysteine on the carbachol-induced contractions (~ 38 and ~ 52% respectively), and PAG abolished the inhibitory effect of L-cysteine on the contractions in the presence of Y-27632 (~ 38%). Also, the protein expressions of CSE, CBS, and 3-MST enzymes responsible for endogenous H2S synthesis were detected by Western blot method. H2S level was increased by L-cysteine, Y-27632, and GF 109203X (from 0.12 ± 0.02 to 0.47 ± 0.13, 0.26 ± 0.03, and 0.23 ± 0.06 nmol/mg respectively), and this augmentation in H2S level decreased with PAG (0.17 ± 0.02, 0.15 ± 0.03, and 0.07 ± 0.04 nmol/mg respectively). Furthermore, L-cysteine and NaHS reduced carbachol-induced ROCK-1, pMYPT1, and pMLC20 levels. Inhibitory effects of L-cysteine on ROCK-1, pMYPT1, and pMLC20 levels, but not of NaHS, were reversed by PAG. These results suggest that there is an interaction between L-cysteine/H2S and RhoA/ROCK pathway via inhibition of ROCK-1, pMYPT1, and pMLC20, and the inhibition of RhoA/ROCK and/or PKC signal pathway may be mediated by the CSE-generated H2S in mouse bladder.

The effects of simulated childbirth trauma on the gene expression of neurotransmitter receptors in the bladder of female rats

BACKGROUND/PURPOSE

To investigate the effects of simulated childbirth on the gene expression of parasympathetic muscarinic, purinergic (P2X), and neurokinin receptors of lower urinary tract in rats.

METHODS

In all, twenty-four primiparous pregnant Sprague-Dawley female rats were equally divided into three groups: (1). Control group; 8 rats, (2) intra-vaginal balloon dilation for 2 h group; 8 rats, (3) and for 4 h group; 8 rats. After balloon dilatation for 4 months, all rats were sacrificed. We analyzed the gene expression of parasympathetic muscarinic, purinergic (P2X), and neurokinin receptors by real-time quantitative PCR (q-PCR). We quantified pro-inflammatory cytokines of TNF-α and IL-6 by Enzyme-linked immunosorbent assays (ELISA). The urodynamic parameters and micturition frequency by cystometry (CMG) were recorded.

RESULTS

Our results showed that the balloon dilation significantly increased micturition frequency and modified peak micturition pressure compare to those in the control groups. Balloon dilation significantly decreased voiding interval and bladder volume compared to those in the control groups. Gene expressions of M3 muscarinic, P2X3 purinergic receptors, and significantly increased following balloon dilation for 2 hours and 4 hours than those in the control group. In addition, we found that NK1R and NK3R receptors were significantly decreased after balloon dilation compare to control group. The marked increase of TNF-α and IL-6 were also seen in the 2 balloon groups.

CONCLUSION

The results of our study suggested that birth trauma may impair the function of urinary tract, this being partly related to the changes in the gene expression of the neurotransmitter receptors of the lower urinary tract.

Overactive bladder and bladder pain syndrome/interstitial cystitis in primary Sjögren's syndrome patients: A nationwide population-based study

To investigate the risks of overactive bladder (OAB) and bladder pain syndrome/interstitial cystitis (BPS/IC) in primary Sjögren’s syndrome (pSS) patients. A nationwide, population-based cohort study was conducted using data from Taiwan’s National Health Insurance Research Database. From 2001 to 2010, participants with newly diagnosed pSS were recognized as the study group. In addition, a comparison cohort of non-pSS participants was matched for age, gender, and initial diagnosis date. Risks of developing OAB and BPS/IC in pSS patients of different age, sex, and various therapeutic strategies were calculated. Hazard ratios (HR) and a 95% confidence interval (CI) were analyzed by Cox proportional hazard model. In total, 11,526 pSS patients were recognized. The HRs of OAB and BPS/IC in pSS patients were 1.68 (95% C.I.: 1.48–1.91, p<0.01) and 2.34 (95% C.I.: 1.59–3.44, p<0.01), respectively. The risks of OAB and BPS/IC were significantly increased for pSS patients aged < 65 years (HR: 1.73 and 2.67), female patients (HR: 1.74 and 2.34), and patients requiring treatment for dry eyes and dry mouth (HR: 2.06 and 2.93). pSS patients exhibited an increased risk of OAB and BPS/IC. Female gender, younger age, and severe glandular dysfunction requiring treatments were potential risk factors.

Big-conductance Ca2+-activated K+ channels in physiological and pathophysiological urinary bladder smooth muscle cells

Contraction and relaxation of urinary bladder smooth muscle cells (UBSMCs) represent the important physiological functions of the bladder. Contractile responses in UBSMCs are regulated by a number of ion channels including big-conductance Ca²⁺- activated K⁺ (BK) channels. Great progress has been made in studies of BK channels in UBSMCs. The intent of this review is to summarize recent exciting findings with respect to the functional interactions of BK channels with muscarinic receptors, ryanodine receptors (RyRs) and inositol triphosphate receptors (IP₃Rs) as well as their functional importance under normal and pathophysiological conditions. BK channels are highly expressed in UBSMCs. Activation of muscarinic M₃ receptors inhibits the BK channel activity, facilitates opening of voltage-dependent Ca²⁺ (Ca_V) channels, and thereby enhances excitability and contractility of UBSMCs. Signaling molecules and regulatory mechanisms involving RyRs and IP₃Rs have a significant effect on functions of BK channels and thereby regulate cellular responses in UBSMCs under normal and pathophysiological conditions including overactive bladders. Moreover, BK channels may represent a novel target for the treatment of bladder dysfunctions.

Autonomic consequences of spinal cord injury

Spinal cord injury (SCI) results not only in motor and sensory deficits but also in autonomic dysfunctions. The disruption of connections between higher brain centers and the spinal cord, or the impaired autonomic nervous system itself, manifests a broad range of autonomic abnormalities. This includes compromised cardiovascular, respiratory, urinary, gastrointestinal, thermoregulatory, and sexual activities. These disabilities evoke potentially life-threatening symptoms that severely interfere with the daily living of those with SCI. In particular, high thoracic or cervical SCI often causes disordered hemodynamics due to deregulated sympathetic outflow. Episodic hypertension associated with autonomic dysreflexia develops as a result of massive sympathetic discharge often triggered by unpleasant visceral or sensory stimuli below the injury level. In the pelvic floor, bladder and urethral dysfunctions are classified according to upper motor neuron versus lower motor neuron injuries; this is dependent on the level of lesion. Most impairments of the lower urinary tract manifest in two interrelated complications: bladder storage and emptying. Inadequate or excessive detrusor and sphincter functions as well as detrusor-sphincter dyssynergia are examples of micturition abnormalities stemming from SCI. Gastrointestinal motility disorders in spinal cord injured-individuals are comprised of gastric dilation, delayed gastric emptying, and diminished propulsive transit along the entire gastrointestinal tract. As a critical consequence of SCI, neurogenic bowel dysfunction exhibits constipation and/or incontinence. Thus, it is essential to recognize neural mechanisms and pathophysiology underlying various complications of autonomic dysfunctions after SCI. This overview provides both vital information for better understanding these disorders and guides to pursue novel therapeutic approaches to alleviate secondary complications.

Functional link between muscarinic receptors and large-conductance Ca2+ -activated K+ channels in freshly isolated human detrusor smooth muscle cells

Activation of muscarinic acetylcholine receptors (mAChRs) constitutes the primary mechanism for enhancing excitability and contractility of human detrusor smooth muscle (DSM). Since the large-conductance Ca(2+)-activated K(+) (KCa1.1) channels are key regulators of human DSM function, we investigated whether mAChR activation increases human DSM excitability by inhibiting KCa1.1 channels. We used the mAChR agonist, carbachol, to determine the changes in KCa1.1 channel activity upon mAChR activation in freshly isolated human DSM cells obtained from open bladder surgeries using the perforated whole cell and single KCa1.1 channel patch-clamp recordings. Human DSM cells were collected from 29 patients (23 males and 6 females, average age of 65.9 ± 1.5 years). Carbachol inhibited the amplitude and frequency of KCa1.1 channel-mediated spontaneous transient outward currents and spontaneous transient hyperpolarizations, which are triggered by the release of Ca(2+) from ryanodine receptors. Carbachol also caused membrane potential depolarization, which was not observed in the presence of iberiotoxin, a KCa1.1 channel inhibitor, indicating the critical role of the KCa1.1 channels. The potential direct carbachol effects on KCa1.1 channels were examined under conditions of removing the major cellular Ca(2+) sources for KCa1.1 channel activation with pharmacological inhibitors (thapsigargin, ryanodine, and nifedipine). In the presence of these inhibitors, carbachol did not affect the single KCa1.1 channel open probability and mean KCa1.1 channel conductance (cell-attached configuration) or depolarization-induced whole cell steady-state KCa1.1 currents. The data support the concept that mAChR activation triggers indirect functional KCa1.1 channel inhibition mediated by intracellular Ca(2+), thus increasing the excitability in human DSM cells.

Pharmacotherapy of overactive bladder syndrome

Urinary incontinence is a common and distressing condition that is known to adversely affect quality of life. Overactive bladder (OAB) is the term used to describe the symptom complex of urgency with or without urge incontinence, usually with frequency and nocturia. Drug therapy, in addition to behavioral modification, remains integral in the management of women with OAB, and the development of new drugs, treatment regimens and methods of delivery should improve patient compliance and acceptability. Developments over the last 10 years have led to the launch of several new drugs for the treatment of OAB that may offer greater efficacy while minimizing adverse effects. This article critically reviews the current pharmacological treatment of OAB in addition to providing a rationale for treatment.

Activation of muscarinic M3 receptors inhibits large-conductance voltage- and Ca2+-activated K+ channels in rat urinary bladder smooth muscle cells

Large conductance voltage- and Ca(2+)-activated K(+) (BK) channels are key regulators of detrusor smooth muscle (DSM) contraction and relaxation during urine voiding and storage. Here, we explored whether BK channels are regulated by muscarinic receptors (M-Rs) in native freshly isolated rat DSM cells under physiological conditions using the perforated whole cell patch-clamp technique and pharmacological inhibitors. M-R activation with carbachol (1 μM) initially evoked large transient outward BK currents, followed by inhibition of the spontaneous transient outward BK currents (STBKCs) in DSM cells. Carbachol (1 μM) also inhibited the amplitude and frequency of spontaneous transient hyperpolarizations (STHs) and depolarized the DSM cell membrane potential. Selective inhibition of the muscarinic M3 receptors (M3-Rs) with 4-diphenylacetoxy-N-methylpiperidine (4-DAMP; 0.1 μM), but not muscarinic M2 receptors with methoctramine (1 μM), blocked the carbachol inhibitory effects on STBKCs. Furthermore, blocking the inositol 1,4,5-triphosphate (IP3) receptors with xestospongin-C (1 μM) inhibited the carbachol-induced large transient outward BK currents without affecting carbachol inhibitory effects on STBKCs. Upon pharmacological inhibition of all known cellular sources of Ca(2+) for BK channel activation, carbachol (1 μM) did not affect the voltage-step-induced steady-state BK currents, suggesting that the muscarinic effects in DSM cells are mediated by mobilization of intracellular Ca(2+). In conclusion, our findings provide strong evidence that activation of M3-Rs leads to inhibition of the STBKCs, STHs, and depolarization of DSM cells. Collectively, the data suggest the existence of functional interactions between BK channels and M3-Rs at a cellular level in DSM.

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.

Quantitative Analysis of the Levels of Expression of Muscarinic Receptor Subtype RNA in the Detrusor Muscle of Patients with Overactive Bladder

INTRODUCTION

Antimuscarinic drugs have frequently been used for the treatment for patients with an overactive bladder (OAB) and there have been many studies on the distribution of muscarinic receptor subtypes in the bladder. However, the distribution of muscarinic receptor subtypes in OAB patients has not been well investigated. In this study we investigated the distribution of muscarinic receptor subtypes with mRNA and protein expressions in patients with and without OAB, and investigated both the dome and trigone area.

METHODS

Samples of bladder smooth muscle were obtained from 10 individuals, five patients with OAB and a non-OAB group consisting of five patients who received radical cystectomy.

RESULTS

The M2 receptor was predominant, but there was no significant difference in the level of M2 expression between the groups in the dome area. M5 expression in the dome area was significantly higher in the OAB group than in the non-OAB group. In the trigone area, the level of M2 mRNA expression was the highest in the non-OAB group, and was significantly lower in the OAB group. The levels of M1 and M5 mRNA expression were also observed in samples obtained from the trigone area.

CONCLUSION

The multiformity of the muscarinic receptor subtypes in human bladder smooth muscle was confirmed, and our results suggest that the efficacy of a given pharmacologic therapy differs from patient to patient.

Muscarinic agonists and antagonists: effects on the urinary bladder

Voiding of the bladder is the result of a parasympathetic muscarinic receptor activation of the detrusor smooth muscle. However, the maintenance of continence and a normal bladder micturition cycle involves a complex interaction of cholinergic, adrenergic, nitrergic and peptidergic systems that is currently little understood. The cholinergic component of bladder control involves two systems, acetylcholine (ACh) released from parasympathetic nerves and ACh from non-neuronal cells within the urothelium. The actions of ACh on the bladder depend on the presence of muscarinic receptors that are located on the detrusor smooth muscle, where they cause direct (M₃) and indirect (M₂) contraction; pre-junctional nerve terminals where they increase (M₁) or decrease (M₄) the release of ACh and noradrenaline (NA); sensory nerves where they influence afferent nerve activity; umbrella cells in the urothelium where they stimulate the release of ATP and NO; suburothelial interstitial cells with unknown function; and finally, other unidentified sites in the urothelium from where prostaglandins and inhibitory/relaxatory factors are released. Thus, the actions of muscarinic receptor agonists and antagonists on the bladder may be very complex even when considering only local muscarinic actions. Clinically, muscarinic antagonists remain the mainstay of treatment for the overactive bladder (OAB), while muscarinic agonists have been used to treat hypoactive bladder. The antagonists are effective in treating OAB, but their precise mechanisms and sites of action (detrusor, urothelium, and nerves) have yet to be established. Potentially more selective agents may be developed when the cholinergic systems within the bladder are more fully understood.

Mechanisms of action of sacral neuromodulation

The lower urinary tract dysfunction encompasses voiding, postvoiding, and storage symptoms. Conventional treatment modalities include pharmacotherapy and behavioural therapy. Sacral neuromodulation (SNM) is a safe and minimally invasive treatment modality that has recently gained wide acceptance in the management of urinary urge incontinence, urge frequency, and nonobstructive urinary retention, in particular, among those patients with conditions refractory to conventional methods. We searched multiple electronic databases through June 30, 2009 for eligible studies. We examined published clinical and experimental studies concerning the mechanisms of action of SNM. In the first part of the manuscript, we describe the anatomy and functions of the lower urinary tract including the reflexes involved in its functions and then review the pathophysiology of major types of the lower urinary tract dysfunction. In the second part, we discuss different ways for SNM to control various types of voiding dysfunction. The lower urinary tract dysfunctions affect millions of people worldwide and have a severe impact on their quality of life. SNM offers a safe and minimally invasive modality in the treatment of voiding dysfunctions, especially in patients with conditions refractory to conventional therapies.

Muscarinic acetylcholine receptors in the urinary tract

Muscarinic receptors comprise five cloned subtypes, encoded by five distinct genes, which correspond to pharmacologically defined receptors (M(1)-M(5)). They belong to the family of G-protein-coupled receptors and couple differentially to the G-proteins. Preferentially, the inhibitory muscarinic M(2) and M(4) receptors couple to G(i/o), whereas the excitatory muscarinic M(1), M(3), and M(5) receptors preferentially couple to G(q/11). In general, muscarinic M(1), M(3), and M(5) receptors increase intracellular calcium by mobilizing phosphoinositides that generate inositol 1,4,5-trisphosphate (InsP3) and 1,2-diacylglycerol (DAG), whereas M(2) and M(4) receptors are negatively coupled to adenylyl cyclase. Muscarinic receptors are distributed to all parts of the lower urinary tract. The clinical use of antimuscarinic drugs in the treatment of detrusor overactivity and the overactive bladder syndrome has focused interest on the muscarinic receptors not only of the detrusor, but also of other components of the bladder wall, and these have been widely studied. However, the muscarinic receptors in the urethra, prostate, and ureter, and the effects they mediate in the normal state and in different urinary tract pathologies, have so far not been well characterized. In this review, the expression of and the functional effects mediated by muscarinic receptors in the bladder, urethra, prostate, and ureters, under normal conditions and in different pathologies, are discussed.

Solifenacin: pharmacology and clinical efficacy

While antimuscarinic drug therapy has been proven to be effective in the management of patients with symptoms of overactive bladder syndrome, compliance and persistence with medication is often affected by the bothersome antimuscarinic adverse effects of dry mouth, constipation, somnolence and blurred vision. The development of bladder-selective M3-specific antagonists, such as solifenacin, has introduced the possibility of increasing efficacy while minimizing adverse effects. This article will review the preclinical and clinical data surrounding the development of solifenacin as well as providing an overview of the extensive body of evidence supporting its use in the management of patients with overactive bladder syndrome.

Treatment of overactive bladder in the aging population: focus on darifenacin

Anticholinergics are commonly used in primary and secondary care settings for the treatment of overactive bladder syndrome. The number of anticholinergic drugs available on the market is increasing and various studies, both observational and randomized controlled trials, have evaluated effectiveness of the different preparations available. When anticholinergic therapy is prescribed, there is still uncertainty about which anticholinergic drugs are most effective, at which dose, and by which route of administration. There is also uncertainty about the role of anticholinergic drugs in different patient groups, particularly in the elderly. The rationale for using anticholinergic drugs in the treatment of overactive bladder syndrome is to block the parasympathetic acetylcholine pathway and thus abolish or reduce the intensity of detrusor muscle contraction. There are currently five recognized subtypes of muscarinic receptor; the M₁, M₂, and M₃ subtypes are of interest in bladder activity. Muscarinic receptors are found in other parts of the body, eg, in the gut, salivary glands, tear ducts. Side effects associated with non-selective antimuscarinics can be particularly distressing in the elderly. The development of bladder selective M₃ specific antagonists has the advantage of providing increased efficacy with minimal side effects. Darifenacin is one such preparation. The aim of this review is to assess the pharmacology, interactions and the safety and tolerability of darifenacin in the treatment of overactive bladder in the elderly population with particular reference to clinical trial data available.

Actions of two main metabolites of propiverine (M-1 and M-2) on voltage-dependent L-type Ca2+ currents and Ca2+ transients in murine urinary bladder myocytes

The anticholinergic propiverine (1-methyl-4-piperidyl diphenylpropoxyacetate), which is used for the treatment of overactive bladder syndrome, has functionally active metabolites [M-1 (1-methyl-4-piperidyl diphenylpropoxyacetate N-oxide) and M-2 (1-methyl-4-piperidyl benzilate N-oxide)], but the site of actions of these metabolites is uncertain. Propiverine is rapidly absorbed after oral administration and is extensively biotransformed in the liver, giving rise to several active metabolites (M-1 and M-2). This study determines the effect of M-1 and M-2 on voltage-dependent nifedipine-sensitive inward Ca(2+) currents (I(Ca)) using patch-clamp techniques and fluorescent Ca(2+) imaging [after electrical field stimulation (EFS) and acetylcholine (ACh)] in the murine urinary bladder. In conventional whole-cell recording, propiverine and M-1 but not M-2 inhibited the peak amplitude of I(Ca) in a concentration-dependent manner at a holding potential of -60 mV (propiverine, K(i) = 10 microM; M-1, K(i) = 118 microM). M-1 shifted the steady-state inactivation curve of I(Ca) to the left at -90 mV by 7 mV. Carbachol (CCh) reversibly inhibited I(Ca). This inhibition probably occurred through muscarinic type 3 receptors, coupling with G-proteins, because nanomolar concentrations of 4-diphenylacetoxy-N-methyl-piperidine greatly reduced this inhibition, whereas pirenzepine or 11-([2-[(diethylamino)methyl]-1-piperdinyl]acetyl)-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one (AF-DX 116) at concentrations up to 1 microM was almost ineffective. In the presence of M-2, the CCh-induced inhibition of I(Ca) was blocked. In fluorescent Ca(2+) imaging, M-2 inhibited EFS-induced and ACh-induced Ca(2+) transients. These results suggest that M-1 acts, at least in part, as a Ca(2+) channel antagonist (as it inhibited I(Ca)), whereas M-2 has more direct antimuscarinic actions.

Solifenacin

Pharacologic therapy has been the mainstay of treatment for patients who have overactive bladder. In recent years, a number of new antimuscarinic agents have been introduced. Solifenacin succinate is a new once-daily antimuscarinic agent that is an effective and well-tolerated treatment option for patients who have overactive bladder. Solifenacin increases functional bladder capacity and decreases urgency, frequency, and incontinence. In pharmacokinetic studies, solifenacin demonstrated selectivity for the bladder over the salivary gland; thus, it is likely that the bladder selectivity of this agent is responsible for the low incidence of dry mouth and constipation reported in the clinical trials.

Local Effects of Antimuscarinics

Overactive bladder (OAB) syndrome has been estimated to occur in nearly 17% of the population. The most common drug treatments for OAB are antimuscarinic agents that act to increase bladder capacity and decrease the urge to urinate during the storage phase. An increasing number of studies have focused on te role and mechanism of muscarinic acetylcholine receptors for the regulation of afferent activity during urine storage. Interactions between muscarinic receptors in the urothelium, afferent nerves, or myofibroblasts and locally released acetylcholine might be involved in the emergence of detrusor overactivity and OAB. Therefore, antimuscarinic agents may be effective in treating OAB not only by suppression of muscarinic receptor-mediated detrusor muscle contractions but also by modulation of muscarinic receptor-bladder afferent interactions.

Qualitative and quantitative expression profile of muscarinic receptors in human urothelium and detrusor

PURPOSE

We compared the complete spectrum of receptor subtypes expressed by human detrusor and its primary culture with the expression profile in a human urothelium immortalized cell line, and in fresh urothelium tissue and its primary cell culture.

MATERIALS AND METHODS

The levels of mRNA expressed for receptor subtypes M1 through M5 were determined with reverse transcriptase-polymerase chain reaction and quantitative polymerase chain reaction in total RNA extracted individually from different human bladder specimens, including fresh tissue of human urothelium and detrusor, and their respective primary cultures, as well as from the UROtsa cell line.

RESULTS

All 5 muscarinic receptors were detected in fresh human bladder tissue by reverse transcriptase-polymerase chain reaction RNA. The same was true in separated urothelium and detrusor tissue except for the lack of the M5 receptor transcript. Receptor subtype mRNA expression in the UROtsa cell line paralleled expression in fresh human bladder. Quantitative polymerase chain reaction data further corroborated these results and showed comparable mRNA expression for M2 and M3 in primary detrusor cultures. Primary cultures also had a decreased copy number of receptor genes than native tissue. The decrease was even more pronounced in primary urothelium culture and the UROtsa cell line in the presence of high calcium. M2 and M3 receptors were also detected in urothelium and detrusor by immunoreactivity.

CONCLUSIONS

We identified all 5 existing muscarinic receptor subtypes in detrusor and urothelium, and transcripts levels of M2 and M3 were comparable in detrusor. These results support an alternative site of action in urothelium for anti-muscarinic drugs. Urothelial receptors should be considered in the design of future drugs for overactive bladder.

In vivo demonstration of M3 muscarinic receptor subtype selectivity of darifenacin in mice

A novel muscarinic receptor antagonist, darifenacin, inhibited specific binding of [N-methyl-(3)H]scopolamine ([(3)H]NMS) in the mouse bladder, submaxillary gland and heart in a concentration-dependent manner. The inhibitory effect was most potent in the submaxillary gland, followed by the bladder and heart. In addition, darifenacin inhibited specific [(3)H]NMS binding in the membranes of CHO-K1 cell lines expressing muscarinic M(2) and M(3) receptor subtypes, and the potency was significantly (22-fold) greater at the M(3) than at the M(2) subtype. At 0.5 to 12 h after oral administration of darifenacin, a significant increase in K(d) values for specific [(3)H]NMS binding was seen in the bladder, submaxillary gland and lung of mice, compared with control values. Also, there was a sustained decrease in the B(max) values in the submaxillary gland. These data suggest that muscarinic receptor binding of oral darifenacin is rapid in onset and of a long duration. On the other hand, oral darifenacin exerted only temporary or little binding of muscarinic receptors in the heart and colon. Pilocarpine-induced salivary secretion in mice was continuously suppressed by oral darifenacin. The time-course of suppression coincided well with that for the muscarinic receptor binding in the submaxillary gland. The antagonistic effect of darifenacin against the dose-response curves for pilocarpine appeared to be insurmountable. In conclusion, the present study has shown that oral darifenacin may exert a pronounced and long-lasting binding of muscarinic receptors in tissues expressing the M(3) subtype.

Pharmacological treatment for overactive bladder in women

Urinary incontinence is a common and distressing condition that is known to adversely affect quality of life. Overactive bladder is the term used to describe the symptom complex of urinary frequency and urgency, with or without urge incontinence. Drug therapy, in addition to behavioral modification, remains integral in the management of women with overactive bladder, and the development of new drugs, treatment regimens and methods of delivery should improve patient compliance and acceptability. This article critically reviews the current pharmacological treatment of overactive bladder in addition to providing a rationale for treatment.

Oxybutynin and its new transdermal application for the treatment of overactive bladder

It has long been accepted that antimuscarinic agents are the backbone of the pharmacological treatment of overactive bladder. Oxybutynin has been the gold standard of these medications for years due to its efficacy, but suffers from a lack of selectivity for the bladder, and extensive metabolism and lipophilicity result in significant side-effect issues. The transdermal delivery of oxybutynin turns this disadvantage of lipophilicity into an advantage. This, in turn, bypasses gastrointestinal absorption and metabolism by the cytochrome P450 system and reduces the breakdown into metabolites responsible for many of the side effects, while providing equivalent efficacy to the immediate-release oral formulation.

Human Muscarinic Receptor Binding Characteristics of Antimuscarinic Agents to Treat Overactive Bladder

PURPOSE

We characterized the binding affinities of several antimuscarinic agents in human muscarinic receptors.

MATERIALS AND METHODS

Competitive inhibitory effects of antimuscarinic agents on specific NMS [H] (PerkinElmer Life Sciences, Boston, Massachusetts) binding were examined in human tissue homogenates and in CHO-K1 cell membranes expressing human muscarinic receptor subtypes.

RESULTS

Oxybutynin, propiverine, tolterodine, the respective metabolites DEOB, DPr-P-4(N-->O) and 5-HM, and darifenacin inhibited in concentration dependent fashion specific [(3)H]NMS binding in homogenates of the human bladder and parotid gland as well as in membranes of CHO-K1 cell lines expressing human muscarinic M(1) to M(5) receptor subtypes. Based on inhibition constant values the inhibitory effects of tolterodine, 5-HM and DPr-P-4(N-->O) were 1.4 to 1.7 times greater in the bladder than in the parotid gland, whereas the inhibitory effects of oxybutynin, DEOB, propiverine and darifenacin were 2 to 10 times greater in the parotid gland. Consequently tolterodine, 5-HM and DPr-P-4(N-->O) compared with oxybutynin, DEOB, propiverine and darifenacin were found to show 3 to 4 times greater affinity to muscarinic receptors in the human bladder than in the parotid gland. Tolterodine and 5-HM were 2-fold more potent for inhibiting specific [(3)H]NMS binding at cell membranes expressing the M(2) vs the M(3) subtype. Conversely oxybutynin, DEOB, propiverine, DPr-P-4(N-->O) and darifenacin showed 2 to 22 times higher affinity to the M(3) than to the M(2) subtype.

CONCLUSIONS

Compared with oxybutynin, tolterodine, 5-HM and DPr-P-4(N-->O) may bind more selectively to muscarinic receptors in the human bladder than in the parotid gland.

Solifenacin in the management of the overactive bladder syndrome

Overactive bladder (OAB) is the term used to describe the symptom complex of urinary frequency and urgency, with or without urge incontinence. Whilst antimuscarinic drug therapy has proven to be effective in the management of patients with symptoms of the OAB syndrome, compliance with medication is often affected by the bothersome antimuscarinic adverse effects of dry mouth, constipation, somulence and blurred vision. The development of bladder selective M3 specific antagonists offers the possibility of increasing efficacy whilst minimising adverse effects. At present, there are no M3 specific antagonists currently available, although solifenacin and darifenacin are under development and are due to be registered in 2004-2005. The purpose of this article is to review the pharmacology and clinical trial data available for solifenacin in addition to examining its emerging role in the treatment of the OAB syndrome.

Muscarinic receptor subtypes of the bladder and gastrointestinal tract

The parasympathetic nervous system is responsible for maintaining normal intestinal and bladder function, contracting the smooth muscle by releasing the neurotransmitters acetylcholine (ACh) and ATP and relaxing sphincters by releasing nitric oxide. ACh is the main transmitter released and smooth muscle contraction is mediated via a mixed M2/M3 receptor population; M3 receptors acting via phospholipase C and M2 receptors acting via inhibition of adenylate cyclase. In ileal, colonic, gastric and bladder (detrusor) smooth muscle the density of M2 receptors is far greater than the density of M3 receptors, the M2:M3 ratio being 3:1 in most species including man. Despite the predominance of M2-receptors, direct contraction of intestinal and detrusor smooth muscle is mediated via the M3-receptor subtype and only this subtype is involved in contraction in vitro. Furthermore, knocking out the M3-receptor gene can have severe consequences on intestinal and bladder responses. In some tissues however M2-receptors may mediate an indirect "re-contraction" whereby a reduction in adenylate cyclase activity reverses the relaxation induced by beta-adrenoceptor stimulation. Thus, intestinal and bladder responses to muscarinic agonists are slightly depressed in M2 receptor knockout mice. The role of receptor subtypes in disease is unclear, but an enhancement of M2 receptor mediated responses has been reported to occur in diabetes. Animal models suggest that M2 receptors may play a greater role in some situations such as in the denervated bladder and intestine. In human disease the mechanisms operating are not so clear. Detrusor sensitivity to muscarinic agonists is enhanced in the neurogenic overactive bladder, but there is controversy surrounding the role of M2 receptors and conflicting results have been reported. Thus, the main muscarinic receptor mediating contraction in normal smooth muscle is the M3 receptor, but M2 receptors are also present and possibly may have an enhanced role in disease.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Darifenacin in the treatment of overactive bladder

Antimuscarinic drug therapy has been shown to be effective in the management of patients with symptoms of the overactive bladder syndrome (OAB), but the bothersome antimuscarinic adverse effects of dry mouth, constipation, somnolence and blurred vision often affect compliance with medication. The development of bladder selective M3 specific antagonists offers the possibility of increasing efficacy whilst minimising adverse effects. The M3 specific antagonist solifenacin has recently been marketed, and darifenacin will soon be available. The purpose of this article is to review the pharmacology and clinical trial data available for darifenacin, in addition to examining its role in the treatment of the OBS.

Improving the Tolerability of Anticholinergic Agents in the Treatment of Overactive Bladder

Pharmacological treatment for overactive bladder has centred around the interruption of the detrusor activity that is central to urge and incontinence symptoms. The majority of patients with this disorder are treated with antimuscarinic agents. These drugs have been demonstrated to improve urgency, frequency of micturition and urge incontinence, all of which are primary symptoms of overactive bladder; however, they are also commonly associated with anticholinergic adverse effects, most notably dry mouth. Attempts to increase tolerability have included the development of advanced formulations that regulate release of the active ingredient and the development of pharmacological agents that target the desired bladder receptors more specifically and accurately. Although all agents provide good efficacy, tolerability is greatly affected by the formulation used to deliver the active pharmacological agent, as well as the specificity of the targeted receptors. Clinical trials involving a transdermal formulation of oxybutynin have shown that this delivery method may be associated with a lower incidence of anticholinergic adverse events compared with both the immediate-release and the extended-release oral formulations of traditional agents, as well as the most recently approved agents - trospium chloride, solifenacin and darifenacin. Much is still being learned about the function and specificity of muscarinic receptors, which will support the development of agents with sustained efficacy and enhanced tolerability compared with the available formulations to date. These include the S-isomer of oxybutynin, as well as selective muscarinic M2 receptor antagonists.

CYSTOMETRIC FINDINGS IN MICE LACKING MUSCARINIC M 2 OR M 3 RECEPTORS

PURPOSE

The physiological importance of muscarinic M3 and M2 receptors for bladder function was investigated in vivo using mice lacking M3 or M2 receptors and littermate WT controls.

MATERIALS AND METHODS

Unanesthetized mice of each sex underwent continuous cystometry before and after administration of atropine (1 mg/kg).

RESULTS

Male M3 knockout (KO) mice had longer voiding intervals, and larger micturition volumes and bladder capacity than M2 KO or WT males. There was no significant difference in any cystometric parameters between male M2 KO and WT mice. In females M3 KO and M2 KO mice had longer voiding intervals and larger micturition volumes than WT animals. Atropine had marked inhibitory effects on voiding efficacy in WT and M2 KO mice but it had no effect on any cystometric parameters in M3 KO mice.

CONCLUSIONS

The current results confirm that M3 receptor is the principal muscarinic receptor subtype responsible for bladder contraction and the role of M2 receptors is of minor importance. Functional impairments found in M3 KO mice were milder than those elicited by acute blockade of muscarinic receptors by atropine in WT mice, suggesting that noncholinergic mechanisms can compensate for a chronic loss of M3 receptors.

THIS ARTICLE HAS BEEN RETRACTED Electroporation-mediated muscarinic M3 receptor gene transfer into rat urinary bladder

BACKGROUND

Muscarinic M3 (M3) receptor has been recognized as a major muscarinic receptor for smooth muscle contractions of the urinary bladder. Under the hypothesis that overexpression of M3 receptor in the urinary bladder would enhance urinary bladder contractions, we have transferred the M3 receptor gene into rat bladders using electroporation (EP) and evaluated the functional expression of the transferred gene.

METHODS

Plasmids expressing luciferase, a green fluorescence protein and M3 receptor were injected into the rat bladder and square-wave electric pulses were immediately applied. Two days after gene transfer, we analyzed gene expression. Immunohistochemical staining was performed and the contractile responses from isolated bladder strips, which were induced KCl, carbachol and electrical field stimulation (EFS), were evaluated.

RESULTS

The optimal conditions of electroporation were 8 pulses, 45 voltages, 50 milliseconds/pulses and 1 Hz. Under these conditions, luciferase gene expression was enhanced approximately 300-fold, compared to an injection of DNA only. Regarding immunohistochemistry with an anti-M3 receptor, an increase in immunoactivity was observed in the M3 receptor gene transferred rat bladder, compared to the bladder of the control rat. In rats with the transferred M3 receptor gene, carbachol- and EFS-induced maximum contractile responses of bladder smooth muscle strips significantly increased.

CONCLUSIONS

These findings suggest that an in vivo EP procedure is an useful method for gene transfer into the bladder and that an overexpression of M3 receptor in the rat bladder enhances bladder contractility. This technique may become a new treatment modality for detrusor underactivity.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Functional selectivity of muscarinic receptor antagonists for inhibition of M3-mediated phosphoinositide responses in guinea pig urinary bladder and submandibular salivary gland

Binding and functional affinities of the muscarinic acetylcholine (mACh) receptor antagonists darifenacin, tolterodine, oxybutynin, and atropine were assessed in Chinese hamster ovary (CHO) cells expressing the human recombinant M2 (CHO-m2) or M3 (CHO-m3) receptors, and in guinea pig bladder and submandibular gland. In [N-methyl-3H]scopolamine methyl chloride binding studies in CHO cells, darifenacin displayed selectivity (14.8-fold) for the M3 versus M2 mACh receptor subtype. Oxybutynin was nonselective, whereas atropine and tolterodine were weakly M2-selective (5.1- and 6.6-fold, respectively). Antagonist functional affinity estimates were determined by the inhibition of agonist-induced [3H]inositol phosphate accumulation in CHO-m3 cells and antagonism of the agonist-induced inhibition of forskolin-stimulated cyclic AMP accumulation in CHO-m2 cells. Darifenacin was the most M3-selective antagonist (32.4-fold), whereas oxybutynin, atropine, and tolterodine exhibited lesser selectivity. Functional affinity estimates in guinea pig urinary bladder and submandibular salivary gland using indices of phosphoinositide turnover revealed that oxybutynin, darifenacin, and tolterodine each displayed selectivity for the response in the bladder, relative to that seen in the submandibular gland (9.3-, 7.9-, and 7.4-fold, respectively). In contrast, atropine displayed a similar affinity in both tissues. These data demonstrate that in bladder, compared with submandibular gland from a single species, the mACh receptor antagonists darifenacin, tolterodine, and oxybutynin display selectivity to inhibit agonist-mediated phosphoinositide responses. It is proposed that both responses are mediated via M3 mACh receptor activation and that differential functional affinities displayed by some, but not all, antagonists are indicative of the influence of cell background upon the pharmacology of the M3 mACh receptor.

The M2 muscarinic receptor mediates in vitro bladder contractions from patients with neurogenic bladder dysfunction

Bladder muscle specimens from seven patients with neurogenic bladder dysfunction were analyzed to determine whether the muscarinic receptor subtype mediating contraction shifts from M(3) to the M(2) subtype as found in the denervated, hypertrophied rat bladder. Seven bladder specimens were analyzed from six female and one male patients. Six of the patients had traumatic cervical spinal cord injuries (C(4)-C(7)), and the other patient had an L(1) congenital myelomeningocele. This was compared with results from bladder specimens obtained from eight organ transplant donors. The affinities of three subtype-selective muscarinic receptor antagonists for inhibition of carbachol-induced contractions were determined. The affinity of the M(3) selective antagonists darifenacin or p-fluoro-hexahydrosiladifenadol (p-F-HHSiD) was determined in six of the seven spinal injury patient specimens. The affinity was consistent with M(2)-mediated contractions in four of these six specimens, intermediate between M(2) and M(3) in one specimen, and within the M(3) range in one specimen. The other specimen, tested only with the M(2) selective antagonist methoctramine, showed an M(3) affinity. In the organ donors, the affinity of p-F-HHSiD was within the M(2) range for six of seven specimens, whereas the affinity of darifenacin was within the M(3) range for five of six and intermediate between M(2) and M(3) for the other specimen tested. The affinity of methoctramine in both organ donor specimens tested was within the M(3) range. Whereas normal detrusor contractions are mediated by the M(3) receptor subtype, in patients with neurogenic bladder dysfunction as well as certain organ transplant donors, contractions can be mediated by the M(2) muscarinic receptor subtype.

Muscarinic receptors: What we know

An understanding of muscarinic receptors is tantamount to an understanding of overactive bladder. The M(3) muscarinic receptor subtype is responsible for detrusor smooth muscle contraction and it exerts an exocrine function in the salivary glands. Alterations in the receptor's response to acetylcholine as a result of injury may lead to hypersensitivity and overactivity. The M(2) receptor subtype, which is mainly responsible for cardiac function, is the muscarinic receptor of highest proportion in the detrusor. M(2) also may play a role in detrusor contraction in injury and pathologic states. Muscarinic antagonists are the mainstay of pharmacotherapy for overactive bladder, but those that are available are not tissue specific. Growing knowledge of the nuances of receptor-ligand behavior and interaction between muscarinic receptors subtypes may provide novel targets for future drug development, improve efficacy, and reduce bothersome side effects.

[Pathophysiology of the overactive bladder and its pharmacological treatment]

This paper reviews the possible mechanisms underlying bladder overactivity and discusses the targets for pharmacological treatment of this disorder. Damage to the brain (cerebrovascular disease, etc.) induces bladder overactivity by reducing suprapontine inhibition. Currently, attention has focused on C-fiber bladder afferents that may concern the mechanisms for bladder overactivity resulting from various etiologies such as spinal cord lesions, bladder outlet obstruction and bladder hypersensitivity disorders. With regard to the pathophysiology of idiopathic overactive bladder, both myogenic and neurogenic mechanisms may be involved in involuntary detrusor contraction. Since an intravesical capsaicin or resiniferatoxin was shown to have favorable therapeutic effects, afferent C-fiber neurons become a new target for pharmacological treatment. C-fiber neurons are known to contain tachykinins and other peptides as neurotransmitters. When released, tachykinins can influence via NK receptors bladder activity. In addition, evidences suggest that ATP receptors (P2X3) and prostaglandin receptors in afferent C-fiber neurons may play a role in mediating bladder overactivity. Thus, NK-antagonist, P2X3-antagonist and PG receptor-antagonist may be potential therapeutic drugs in the near future. beta 3-Adrenoceptor agonist is an another candidate drug for the treatment of the overactive bladder. Finally, it is important to notice that in any etiology including an idiopathic one, antimuscarinic drugs can improve bladder overactivity, although dry mouth and constipation are inevitable side-effects.

Muscarinic M2 receptors inhibit Ca2+-activated K+ channels in rat bladder smooth muscle

PURPOSE

To clarify the functional relationship between M2 muscarinic receptor and Ca2+-activated K+ channel, we investigated the effect of carbachol (CCh) on the membrane current of rat bladder smooth muscle cells.

METHODS

Rat bladder single smooth muscle cells were patch clamped with whole-cell configuration.

RESULTS

CCh (10 micro mol/L) transiently induced an outward current in the presence of K+ in the pipette solution. A high Ca2+ concentration in the pipette solution persistently induced an outward current, which was inhibited by CCh. In the presence of M2 inhibitor, AFDX-384, CCh induced the outward current persistently, indicating that M2 was involved in the current inhibition. In pertussis toxin pretreated cells, CCh did not apparently inhibit the outward current. The CCh-induced outward current was inhibited by iberiotoxin, a selective inhibitor of large-conductance Ca2+-activated K+ channels (BKCa).

CONCLUSION

CCh induces BKCa, which is inhibited by M2- and Gi-mediated signal transduction pathway. This M2-mediated pathway may enhance contraction which is initiated by M3-stimulation in rat bladder smooth muscle.

Tolterodine: selectivity for the urinary bladder over the eye (as measured by visual accommodation) in healthy volunteers

OBJECTIVE

Tolterodine exhibits a favourable selectivity for the urinary bladder over salivary glands in vivo, in the anaesthetised cat, whereas oxybutynin shows the opposite selectivity profile in this model. This study further evaluated the selectivity profiles of tolterodine and oxybutynin by comparing the effects on bladder function and visual accommodation in the same individuals.

METHODS

In a double-blind, randomised, four-way crossover study, 16 healthy volunteers received single oral doses of tolterodine 5 mg and oxybutynin 2.5, 5 and 7.5 mg. Voiding parameters were assessed for 12 hours post-dose, along with visual accommodation (near point of vision) at regular intervals.

RESULTS

A dose-dependent increase in maximum bladder capacity was observed for oxybutynin [2.5 mg (+35%), 5 mg (+45%) and 7.5 mg (%)]. The effect of tolterodine 5 mg on bladder capacity was approximately twice (+93%) that seen after oxybutynin 5 mg and the onset of the effect was more rapid with tolterodine. Effects on visual accommodation were also dose-dependent for oxybutynin (maximum changes in near point of vision were 13%, 20% and 29%, respectively). The maximum change observed after tolterodine 5 mg was the same as after oxybutynin 5 mg (i.e. 20%).

CONCLUSIONS

Tolterodine seems to exhibit selectivity for the bladder over the eye. Therefore, these results suggest that the normal dosage of tolterodine (2 mg twice daily) may have less effect on visual accommodation than the equivalent dosage of oxybutynin (5 mg three times daily) in patients with an overactive bladder.

Current and future pharmacological treatment for overactive bladder

PURPOSE

Urinary incontinence and overactive bladder are important and common conditions that have received little general medical attention. We reviewed the magnitude and impact of these conditions, and discuss pharmacotherapy as well as new drugs under investigation.

MATERIALS AND METHODS

The main emphasis of this review is pharmacological therapy for the bladder. We discuss currently available agents, drugs under development and pharmacological targets that would be suitable targets for treating overactive bladder. Drugs such as duloxetine that target not bladder smooth muscle, but rather central nervous system control of the micturition reflex are undergoing clinical trials. We also discuss intravesical therapy and alternative drug delivery methods, such as intravesical capsaicin and botulinum toxin, with special emphasis on approaches to modulate bladder afferent nerve function for preventing overactive bladder.

RESULTS

There are many advantages to advanced drug delivery systems, including long-term therapeutic efficacy, decreased side effects and improved patient compliance. Future speculation such as gene therapy holds great promise for overactive bladder because it is possible to access all genitourinary organs via endoscopy and other minimally invasive techniques that are ideally suited for gene therapy.

CONCLUSIONS

Traditional anticholinergic therapies are limited in their effectiveness. There is great hope for future research regarding voiding dysfunction and urinary incontinence through a focus on afferent nerve intervention for preventing overactive bladder.

Muscarinic receptor subtypes and management of the overactive bladder

Anticholinergic agents are the most widely used therapy for urge incontinence despite exerting adverse effects, such as constipation, tachycardia, and dry mouth, that limit their use. These adverse effects result from a lack of selectivity for the bladder over other organs. Although M2-muscarinic receptors are the predominant cholinoreceptor present in urinary bladder, the smaller population of M3-receptors appears to be the most functionally important and mediates direct contraction of the detrusor muscle. M2-receptors modulate detrusor contraction by several mechanisms and may contribute more to contraction of the bladder in pathologic states, such as bladder denervation or spinal cord injury. Prejunctional inhibitory M2-receptors or M4-receptors and prejunctional facilitatory M1-muscarinic receptors in the bladder have also been reported, but their relevance to the clinical effectiveness of muscarinic antagonists is unknown. In clinical studies, tolterodine, a nonselective muscarinic antagonist, has been reported to be equally effective to oxybutynin but to induce less dry mouth. Controlled-release and intravesical, intravaginal, and rectal administrations of oxybutynin have all been reported to cause fewer adverse effects. Conversely, darifenacin, a new M3-selective antagonist, has been reported to have selectivity for the bladder over the salivary gland in vivo. Whether M3-selective or nonselective muscarinic antagonists will be the most clinically effective for the overactive bladder-preserving the best balance between efficacy and tolerability-has yet to be established, and comparative clinical trials between compounds, such as darifenacin (M3 selective) and tolterodine (nonselective) will be required.

Differential gene expression of cholinergic muscarinic receptor subtypes in male and female normal human urinary bladder

OBJECTIVES

To study the mRNA expression of each muscarinic receptor subtype in bladder areas involved in micturition, such as the bladder dome, neck, and trigone. Our study focused on the analysis of the gene expression of muscarinic receptors in the human male and female urinary bladder. Other than the well-known role of bladder parasympathetic innervation, an extensive study of the muscarinic receptor mRNA distribution in male and female urinary bladder is still lacking.

METHODS

The study was carried out on 5 female (age 56 +/- 10 years) and 5 male (age 70 +/- 9 years) patients. The patients selected for this study did not have any lower urinary tract symptoms, as determined by International Prostate Symptom Score questionnaire. The mRNAs encoding muscarinic receptor subtypes were assessed by reverse transcription-polymerase chain reaction, followed by Southern blot analysis.

RESULTS

Using a molecular approach, we demonstrated the presence of all muscarinic receptor subtypes in the different urinary bladder areas involved in micturition; in particular, our data indicated that mRNAs encoding muscarinic receptors are largely expressed in all examined bladder areas, both in men and women, although with some remarkable differences and a peculiar distribution.

CONCLUSIONS

Our results indicate that the pharmacology of the human bladder may be more complex than previously recognized. Furthermore, the choice to study each biopsy as a single sample and not use a pool of tissues allowed us to point out the individual variability between subjects and sex-related differences in the expression profile of muscarinic receptor subtype mRNAs.