A myogenic basis for the overactive bladder

Update on the management of overactive bladder: patient considerations and adherence

Overactive bladder (OAB) is a common condition that causes a profound impact on an individual’s overall health and quality of life. Muscarinic receptor antagonists are the mainstay of oral pharmacotherapy for OAB. Although all of the medications in this class are significantly more effective than placebo, they are also associated with more adverse events that may limit their overall use. Although newer preparations of these medications have sought to improve tolerability and efficacy through alternative routes of delivery and once-daily dosing, improved adherence to treatment and treatment persistence continue to be an ongoing challenge. An improved understanding of the factors involved in persistence of medical OAB therapy is imperative in efforts to optimize therapeutic benefits in this chronic and potentially morbid condition.

Influence of age and bladder dysfunction on the contractile properties of isolated human detrusor smooth muscle

OBJECTIVE

To test the hypothesis that the in vitro contractile properties of human detrusor smooth muscle are dependent on the age, gender and lower urinary tract pathology of the patient.

MATERIALS AND METHODS

Contractions were elicited in isolated human detrusor smooth muscle preparations by nerve-mediated electrical field stimulation, agonist application (carbachol, α,β-methylene ATP and high-K solutions) or direct muscle electrical stimulation. Biopsies (n = 227) were obtained from four groups of patients with: stable bladders (control), bladder outlet obstruction (BOO), idiopathic (IDO), or neurogenic (NDO) detrusor overactivity.

RESULTS

The magnitude of nerve-mediated contractions declined as a function of patients' age in each of the BOO, IDO and NDO groups but not in the control group. Contractions elicited by direct muscle activation (10 µM carbachol or electrical stimulation with 20 ms pulses in the presence of 1 µM tetrodotoxin) did not vary with patient age. Carbachol contractions were significantly smaller in samples from NDO bladders. Atropine resistance was more prevalent in the pathology groups compared with the control group and was greatest in the IDO group. There was no influence of age in the prevalence or magnitude of atropine-resistant contractions in any group. Muscle excitability to direct electrical stimulation was similar in all groups.

CONCLUSIONS

In the human bladder there is no evidence for a decline of detrusor smooth muscle contractility or excitability as a function of age, nor any gender difference or presence of pathology. In the pathology groups there was evidence for a decline of functional innervation with age.

Fesoterodine for overactive bladder: A review of the literature

BACKGROUND

Overactive bladder (OAB) is a chronic condition affecting both men and women, with prevalence increasing with age. Antimuscarinics form the cornerstone of treatment of OAB. Fesoterodine, a nonselective muscarinic-receptor antagonist, was approved by the US Food and Drug Administration in late 2008 for once daily, oral administration in the treatment of OAB to relieve the symptoms of urinary urge incontinence, urgency, and frequency.

OBJECTIVE

The aim of this review was to provide an overview of the mechanism of action of and clinical trial data for fesoterodine, and to discuss the present status of fesoterodine in the management of OAB.

METHODS

The MEDLINE and Google Scholar databases were searched (June 1, 1999-December 1, 2009) using the terms fesoterodine, overactive bladder, and muscarinic antagonists. Full-text articles in English were selected for reference, and articles presenting the mechanism of action, pharmacokinetics, and data from clinical trials were included. The parameters measured were tolerability, efficacy, and health-related quality of life (HRQoL). Trials involving animals and Phase I studies were excluded.

RESULTS

The initial literature search yielded 48 papers. A total of 20 articles fulfilled the inclusion criteria. In two 12-week, randomized, multicenter, Phase III clinical trials involving patients with increased micturition frequency and urgency and/or urinary urge incontinence (n = 836 and 1132 in each trial), both fesoterodine 4 and 8 mg were associated with significantly improved symptoms of OAB (frequency of micturition, urgency, and urge incontinence) compared with placebo (P < 0.05). In a post hoc analysis of pooled data of the Phase III trials, HRQoL improved significantly with both doses. In a 12-week, Phase Illb trial, fesoterodine 4 and 8 mg led to treatment satisfaction in ∼80% of patients (of 516 enrolled) who were initially unsatisfied with their previous treatment.

CONCLUSION

A review of the literature suggests that fesoterodine is an efficacious and well-tolerated treatment option for patients with OAB.

New insights into molecular targets for urinary incontinence

Urinary incontinence (UI) is a disease affecting quality of life of 200 million patients worldwide. It is characterized by involuntary loss of urine. The factors involved are cystitis, detrusor hyperreflexia, spinal injury, benign prostatic hyperplasia, etc. The surge in the number of reviews on this subject indicates the amount of research devoted to this field. The prevalence is increasing at an alarming rate but unfortunately, only a few medications are currently available for this condition. There are peripheral as well as central targets including cholinergic, vanilloid, prostaglandin, kinin, calcium channel, cannabinoid, serotonin, and GABA-receptors, which act by different mechanisms to treat different types of incontinence. Drugs acting on the central nervous system (CNS) increase urinary bladder capacity, volume, or pressure threshold for micturition reflex activation while peripherally acting drugs decrease the amplitude of micturition contraction and residual volume. Anticholinergic drugs specifically M3 receptor antagonists are the first choice but have frequent side effects such as dry mouth, CNS disturbances, etc. Therefore, there is a need to understand the biochemical pathways that control urinary dysfunction to determine the potential to which they can be exploited in the treatment of this condition. This article reviews the central and peripheral molecular targets and the potential therapeutic approaches to the treatment of UI.

Hyperosmolarity alters micturition: a comparison of urinary bladder motor activity in hyperosmolar and cyclophosphamide-induced models of overactive bladder

Hyperosmolar factors induce the neurogenic inflammatory response, leading to bladder overactivity (OAB). The aim of the study was to compare the bladder motor activity in a hyperosmolar and acute cyclophosphamide (CYP)-induced model of OAB. Furthermore, we set our sights on defining the most physiological model of OAB in experimental practice. Forty-two female rats were divided randomly into 5 groups. All animals underwent cystometry with the usage of isotonic saline or saline of increasing concentration. Acute chemical cystitis was induced by CYP to elicit OAB. The following cystometric parameters were analyzed: basal pressure, threshold pressure, micturition voiding pressure, intercontraction interval, compliance, functional bladder capacity, motility index, and detrusor overactivity index. CYP and hypertonic saline solutions induced OAB. Having been compared with CYP OAB, none of the rats infused with hypertonic solution exhibited macroscopic signs of bladder inflammation. The comparison of CYP and hyperosmolar models of OAB revealed that the greatest similarity existed between the 2080 mOsm/L OAB model and the acute CYP-induced model. We postulate that the 2080 mOsm/L model of OAB can be established as being a less invasive and more physiological model when compared with the CYP-induced OAB model. Additionally, it may also be a more reliable experimental tool for evaluating novel therapeutics for OAB as compared with CYP-induced models.

Intravesical PGE2 Administration in Conscious Rats as an Experimental Model of Detrusor Overactivity Observed by Simultaneous Registrations of Intravesical and Intraabdominal Pressures

PURPOSE

The urodynamic effects of intravesical PGE2 instillation on bladder function and detrusor overactivity (DO) during the filling phase were investigated in rats by measuring intraabdominal and intravesical pressures simultaneously.

MATERIALS AND METHODS

Continuous cystometry was performed inconscious, female and male Sprague- Dawley rats. We investigated pressure-, volume-, and DO-related parameters.

RESULTS

Intravesical instillation of PGE2 increased all pressure-related parameters and decreased volume-related ones, compared to the control cystometric ones. However, among the total number of intravesical pressure rises (IVPRs) above 2 cmH(2)O during the filling phase, only 33% in female rats and 38% in male rats after PGE2 instillation were identified as true DO during the filling phase.

CONCLUSIONS

Our findings suggest that the rat model with intravesical PGE2 is inappropriate for observing the effects of some drugs or mechanisms on DO, because only approximately 30% of IVPRs were confirmed as true DO. However, this model of intravesical PGE2 instillation has some advantages for the observation of changes in pressure and volume parameters rather than in DO-related ones.

The overactive bladder

Urinary urgency and the associated symptoms which comprise overactive bladder are prevalent amongst the general population and adversely affect quality of life. Disease management consists of a sequential series of options starting with behavioural and lifestyle techniques, pharmacological management (antimuscarinics) and, in severe cases, surgical treatment (urinary diversion, neuromodulation, augmentation cystoplasty and detrusor myectomy). There is increasing recognition of pathophysiological mechanisms in the urothelium, interstitial cells and afferent neurons allowing the importance of peripheral integrative interaction to be identified. The hierarchy of the central nervous system control adds additional complexity to understanding the oflower urinary tract function. Some newer methods of treatment include Botulinum toxin A intramural injections, oral beta-3 adrenergic agonists and rho-kinase inhibitors. The lack of a disease generating hypothesis, the lack of animal models for disease and the subjective nature of the central symptom (urgency) still pose considerable theoretical and scientific hurdles that need to be overcome in the treatment of this condition.

Effects of mechanical stretch on interstitial cells of Cajal in guinea pig bladder

OBJECTIVES

C-kit positive interstitial cells of Cajal (ICCs) play an important role in the regulation of the smooth muscle motility. In this study, we investigated the mechanical sensitivity of ICCs in guinea pig bladder and their possible relationship with detrusor overactivity (DO).

METHODS

Stretch load was performed in vivo in DO models produced by 4 wk of partial bladder outlet obstruction (PBOO). Number and morphology of ICCs were examined using a specific ICC marker, c-kit, immunochemistry staining. The spontaneous and stretch-induced calcium transients (SICT) of ICCs were investigated in cells cultured onto flexible silicone membranes preloaded with the Ca(2+) indicator fluo-4AM in vitro.

RESULTS

C-kit positive ICCs were mainly located along and between bladder smooth muscle bundles. ICCs in DO bladders displayed more lateral branching with mutual connections. The number of c-kit positive bladder ICCs was increased in the DO group compared with the control group (n = 50, P < 0.05). Cultured ICCs from DO bladders showed spontaneous calcium waves with higher frequency and lower amplitude than those from control bladders (n = 15, P < 0.05). Significant SICT were detected in cultured bladder ICCs. SICT generated in ICCs from DO were more likely to transfer to adjacent smooth muscle cells through cell membrane connection than ICCs from control bladders.

CONCLUSIONS

Long-term overload tension following PBOO caused changes in morphology, quantity and spontaneous calcium transients of ICCs in guinea pig bladder. Mechanical sensitivity and interaction with SMC of ICCs may contribute to the mechanosensitive conductances in bladder regulation, and may play a role in the pathogenesis of DO.

A noninvasive evaluation of autonomic nervous system dysfunction in women with an overactive bladder

OBJECTIVE

To verify the hypothesis that a connection exists between overactive bladder (OAB) syndrome and a bladder-specific dysfunction of the autonomic nervous system (ANS).

METHOD

An electrocardiogram recorded heartbeat cycles from the onset of urinary urgency to 5 minutes after voiding in 33 women with an overactive bladder and 176 controls. Power spectral density (PSD) analysis allowed to quantify heart rate variability (HRV), which is in relation to ANS function. Three-dimensional spectrograms and multiscale entropy graphs were used to display HRV values.

RESULTS

The differences between patients and controls were all significant in the time and frequency domains of HRV (P<0.05), which suggests disturbances in bladder-specific ANS activity in women with OAB.

CONCLUSION

By quantifying HRV data, PSD analysis provides a simple, noninvasive method of assessing disturbances in ANS activity and monitoring treatment in women with OAB. It can also be used to evaluate other neuronal conditions.

Medical management of overactive bladder

Overactive bladder (OAB), as defined by the International Continence Society, is characterized by a symptom complex including urinary urgency with or without urge incontinence, usually associated with frequency and nocturia. OAB syndrome has an incidence reported from six European countries ranging between 12-17%, while in the United States; a study conducted by the National Overactive Bladder Evaluation program found the incidence at 17%. In Asia, the prevalence of OAB is reported at 53.1%. In about 75%, OAB symptoms are due to idiopathic detrusor activity; neurological disease, bladder outflow obstruction (BOO) intrinsic bladder pathology and other chronic pelvic floor disorders are implicated in the others. OAB can be diagnosed easily and managed effectively with both non-pharmacological and pharmacological therapies. The first-line treatments are lifestyle interventions, bladder training, pelvic floor muscle exercises and anticholinergic drugs. Antimuscarinics are the drug class of choice for OAB symptoms; with proven efficacy, and adverse event profiles that differ somewhat.

Is the beneficial effect of antimuscarinics related to motor or sensory changes in the bladder?

INTRODUCTION AND HYPOTHESIS

The aim of the study was to assess the sensory and motor effects of antimuscarinic treatment on the bladder in women with overactive bladder, detrusor overactivity demonstrated on urodynamics and a mean bladder wall thickness (BWT) greater than 5 mm.

METHODS

Fifty-eight women underwent treatment with antimuscarinics in 12 weeks. Before treatment and at 1, 2, 6 and 12 weeks of treatment, women completed the patient perception of bladder condition (PPBC) single-item global questionnaire, indicated the severity of their urgency on a visual analogue scale (VAS) and underwent transvaginal ultrasound to determine mean bladder wall thickness (BWT).

RESULTS

PPBC and VAS scores for urgency declined throughout the treatment course whereas mean BWT declined during the first 6 weeks of treatment and then reached a plateau after falling to below 5 mm.

CONCLUSION

The mechanism of action of antimuscarinics appears to be a complex interaction of sensory and motor components.

Detrusor myocyte activity and afferent signaling

AIMS

To discuss (1) mechanisms involved in the generation and control of myocyte contractions and consequent afferent nerve activity and (2) these mechanisms as targets for drugs aimed for treatment of overactive bladder (OAB) symptoms and detrusor overactivity (DO).

METHODS

Literature review of myocyte activation, bladder afferent nerves, mediators in the bladder, and translational aspects of the findings.

RESULTS

During bladder filling, there is normally no parasympathetic outflow from the spinal cord. Despite this, the bladder develops tone during filling and also exhibits non-synchronized local contractions and relaxations that are caused by a basal myogenic mechanical activity that may be reinforced by release of, for example, acetylcholine from non-neuronal and/or neuronal sources or local mediators, such as prostaglandins and endothelins. It is suggested that these spontaneous contractions are able to generate activity in afferent nerves ("afferent noise") that may contribute to DO and OAB.

CONCLUSIONS

Spontaneous bladder myocyte contractions and factors that are able to modulate them, as well as the consequent afferent nerve activity, may be targets for drugs meant for treatment of OAB/DO.

Antimuscarinics and overactive bladder: other mechanism of action

Antimuscarinics are considered first-line treatment for patients with overactive bladder (OAB). However, the mechanism by which antimuscarinics improve the symptoms of OAB remains to be elucidated. Animal studies suggest that antimuscarinics may exert an inhibitory effect on afferent nerves without an effect on detrusor contraction. A release of acetylcholine from the urothelium has been demonstrated in isolated human bladder. In addition, muscarinic receptors (MRs) were found in the urothelium and suburothelial myofibroblasts, suggesting a role for MR mechanisms in urothelial sensory function. Acetylcholine released during the storage phase could be expected to enhance the myogenic contractile activity of the detrusor, which can generate afferent signals. It is suggested that antimuscarinics may decrease bladder afferent activity by blocking MR in the above sites, thereby improving OAB symptoms.

Bladder afferent signaling: recent findings

PURPOSE

Much current research on lower urinary tract physiology focuses on afferent mechanisms. The main goals are to define and control the signaling pathways by which afferent information is generated and conveyed to the central nervous system. We summarize recent research on bladder afferent mechanisms.

MATERIALS AND METHODS

We systematically reviewed the literature by searching PubMed up to June 2009 with focus on the last 5 years.

RESULTS

At least 2 signaling pathways can be identified, including the urothelial and the myogenic pathway. The urothelial pathway is a functional unit consisting of the urothelium, interstitial cells and afferent nerves in the lamina propria. Signaling occurs via muscle-mucosal mechanoreceptors, mucosal mechanoreceptors and chemoreceptors. The myogenic pathway is activated via in-series mechanoreceptors responding to distention and via spontaneous contractile activity in units of myocytes generating afferent noise.

CONCLUSIONS

To control dysfunctional micturition we must know more about all components involved in normal micturition control, including how afferent information is handled by the central nervous system.

Rhythmic contraction generates adjustable passive stiffness in rabbit detrusor

The length-tension (L-T) relationships in airway and vascular smooth muscles have been shown to adapt with length changes over time. Our prior studies have shown that the active and passive L-T relationships in rabbit detrusor smooth muscle (DSM) can adapt and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that is a function of strain and activation history. The present study demonstrates that passive tension due to APS can represent a substantial fraction of total tension over a broad length range. Our previous studies have shown that maximal KCl-induced contractions at short muscle lengths generate APS that is revealed by increased pseudo-steady-state passive tension at longer lengths compared with previous measurements at those lengths. The objective of the present study was to determine the mechanisms involved in APS generation. Increasing the number of KCl-induced contractions or the duration of a contraction increased the amount of APS generated. Furthermore, a fraction of APS was restored in calcium-free solution and was sensitive to the general serine and threonine protein kinase inhibitor staurosporine. Most importantly, rhythmic contraction (RC) generated APS, and because RC occurs spontaneously in human bladder, a physiological role for RC was potentially identified.

Urinary urgency - translating the evidence base into daily clinical practice

AIM

To consider the currently available knowledge and understanding of the symptom of urgency.

MATERIALS & METHODS

Each faculty member reviewed the literature base of a different aspect of urgency and along with their personal clinical experience provided a base of evidence for discussion.

RESULTS

This overview summarises relevant published literature and the current clinical experience of the authors.

DISCUSSION

Whilst the mechanisms producing the sensation of urgency are still not fully understood and we are working within a definition that may complicate measurement and treatment, our pressing need is to effectively manage our patients for whom the practical nature of urgency can be all too apparent.

CONCLUSION

Health care professionals have an important role to play today in helping to alleviate the widespread problem of urgency and its consequences.

BK channel activation by NS11021 decreases excitability and contractility of urinary bladder smooth muscle

Large-conductance Ca(2+)-activated potassium (BK) channels play an important role in regulating the function and activity of urinary bladder smooth muscle (UBSM), and the loss of BK channel function has been shown to increase UBSM excitability and contractility. However, it is not known whether activation of BK channels has the converse effect of reducing UBSM excitability and contractility. Here, we have sought to investigate this possibility by using the novel BK channel opener NS11021. NS11021 (3 microM) caused an approximately threefold increase in both single BK channel open probability (P(o)) and whole cell BK channel currents. The frequency of spontaneous action potentials in UBSM strips was reduced by NS11021 from a control value of 20.9 + or - 5.9 to 10.9 + or - 3.7 per minute. NS11021 also reduced the force of UBSM spontaneous phasic contractions by approximately 50%, and this force reduction was blocked by pretreatment with the BK channel blocker iberiotoxin. NS11021 (3 microM) had no effect on contractions evoked by nerve stimulation. These findings indicate that activating BK channels reduces the force of UBSM spontaneous phasic contractions, principally through decreasing the frequency of spontaneous action potentials.

Perspectives on overactive bladder in the elderly population

INTRODUCTION

Overactive bladder (OAB) represents a disruption in the storage function of the lower urinary tract. This bothersome condition occurs more commonly in the elderly. Since population forecasts predict a worldwide increase in the proportion of people aged over 65 years, it is reasonable to expect that the healthcare burden associated with OAB will also increase. The pathophysiology of OAB in the elderly is thought to be multifactorial, with an abnormality occurring in the nervous supply and/or the structure/function of the urothelium or bladder smooth muscle, leading to bladder hypersensitivity, abnormalities in bladder sensation (urgency) and involuntary detrusor contraction.

METHODS

A review of some of the key aspects relating to management of this growing population was undertaken.

RESULTS

The potential for an elderly patient to present with a number of concomitant conditions means that careful characterization of their overall status is required before deciding on the most appropriate management option for their urinary tract pathology. Lifestyle interventions and pharmacological agents have shown success in treating OAB in the elderly, but as this patient group often has many concomitant conditions they are more likely to be seen by a non-urology specialist.

CONCLUSIONS

It is therefore important to raise awareness of the condition and an appreciation of its impact among healthcare professionals to ensure the most appropriate care.

The medical management of urinary incontinence

Urinary incontinence is the involuntary leakage of urine; it affects millions of people worldwide, causing significant detrimental effects on their quality of life. Direct expenses, such as containment products, long-term drug prescriptions and surgery, complemented by indirect costs, such as reduced employment productivity, result in overall expenditure running to billions of dollars. Stress urinary incontinence (SUI) occurs on physical exertion, and results from weakness of the bladder outlet. Urgency urinary incontinence (UUI) results from inability to resist a sudden compelling desire to pass urine, arising as a consequence of bladder dysfunction. Clinical evaluation clarifies the underlying mechanisms and excludes diseases causing similar symptoms. Urodynamic studies to measure bladder and abdominal pressures and deduce the bladder and outlet function are undertaken when invasive treatments are being considered or when the nature of the incontinence is not entirely clear. Initial management of SUI involves pelvic floor muscle exercise training; if insufficient symptom improvement results, surgical measures are needed. UUI treatment commences with advice on suitable fluid intake and measures to improve ability to defer voiding, followed by antimuscarinic drugs. Refractory UUI is a difficult problem, currently managed with a range of surgical interventions, including bladder injections of botulinum-A neurotoxin, augmentation cystoplasty and nerve stimulation methods. New treatment options are needed, because of the risk of impeding voiding function, resulting in urinary retention. Persistent leakage is controlled with containment products, such as pads, or collection devices, such as catheters.

Modification of rat detrusor muscle contraction by ascorbic acid and citric acid involving enhanced neurotransmitter release and Ca2+ influx

AIMS

Consumption of carbonated soft drinks is independently associated with the development of overactive bladder (OR 1.41, 95% Cl 1.02-1.95). We have shown previously that artificial sweeteners, present in carbonated soft drinks, enhanced detrusor muscle contraction. Other constituents of soft drinks are preservatives and antioxidants, we evaluated the effects of two of these, ascorbic acid and citric acid, on the contractile response of isolated rat bladder muscle strips.

METHODS

Detrusor muscle strips were suspended in a perfusion organ bath. We determined the effect of ascorbic acid and citric acid on the contractile responses to electrical field stimulation (EFS) in the absence and presence of atropine, carbachol, alpha, beta methylene ATP, potassium and calcium.

RESULTS

Ascorbic acid and citric acid (10(-7) M to 10(-3) M) enhanced the contractile response to 10 Hz EFS compared to control (P < 0.01). The frequency and amplitude of spontaneous bladder contractions were enhanced in the presence of ascorbic acid and citric acid by 14%, 21%, 21%, and 11% respectively. Ascorbic acid 10(-4) M significantly increased the atropine resistant response to EFS 5 Hz by 37% (P < 0.01) and inhibited contraction in response to carbachol 10(-4) M by 24%, (P < 0.05). Both ascorbic acid 10(-4) M and citric acid 10(-5) M significantly enhanced maximum contractile responses to alpha, beta methylene ATP, KCI and calcium compared to control.

CONCLUSIONS

Ascorbic acid and citric acid augmented bladder muscle contraction possibly by enhanced Ca(2+) influx. Presynaptic neurotransmitter release was enhanced by ascorbic acid. Carbonated beverages containing preservatives may aggravate symptoms of OAB.

Partial bladder outlet obstruction reduces the tissue antioxidant capacity and muscle nerve density of the guinea pig bladder

AIMS

Reactive nitrogen and oxygen species (RNOS) likely play a role in the development of bladder dysfunction related to bladder outlet obstruction. Antioxidants protect against these free radicals. The aim of our study was to investigate the effect of bladder outlet obstruction on the endogenous antioxidant status of the bladder and to correlate this to bladder structure and function.

METHODS

In 16 guinea pigs either a partial outlet obstruction or a sham operation was induced. The contractile responses of detrusor strips to electrical field stimulation (EFS), acetylcholine, potassium, and ATP were monitored 4 weeks after the operation. The nerve density in bladder tissue was determined by using the non-specific nerve marker PGP 9.5. Separate antioxidants and the total antioxidant status were assessed using the trolox equivalent antioxidant capacity (TEAC) test.

RESULTS

Contractile responses of detrusor strips to EFS were for the greater part based on neurogenic stimulation. The nerve-mediated responses in strips from obstructed bladders were lower compared to the sham group. Obstructed bladders showed a patchy denervation and the nerve density was significantly lower compared to the sham group. The total antioxidant capacity, the glutathione and the glutathione reductase (GR) levels significantly decreased in obstructed bladders compared to the sham group.

CONCLUSION

This study demonstrates that the antioxidant status of guinea pig bladders exposed to outlet obstruction decreased which might be associated with the observed reduction in nerve density. The results strengthen the hypothesis that oxidative stress is involved in the pathophysiology of bladder dysfunction related to obstructed bladders. Neurourol. Urodynam. 28:461-467, 2009. (c) 2008 Wiley-Liss, Inc.

A refocus on the bladder as the originator of storage lower urinary tract symptoms: a systematic review of the latest literature

CONTEXT

The focus of clinical understanding and management of male storage lower urinary tract symptoms (LUTS) has shifted from the prostate to the bladder. This is mirrored by an increasing body of experimental evidence suggesting that the bladder is the central organ in the pathogenesis of LUTS.

OBJECTIVE

A systematic review of the literature available on pathophysiologic aspects of storage LUTS.

EVIDENCE ACQUISITION

Medline was searched for the period ending December 2008 for studies on human and animal tissue exploring possible functional and structural alterations underlying bladder dysfunction. Further studies were chosen on the basis of manual searches of reference lists and review papers.

EVIDENCE SYNTHESIS

Numerous recent publications on LUTS pathophysiology were identified. They were grouped into studies exploring abnormalities on urothelial/suburothelial, muscular, or central levels.

CONCLUSIONS

Studies revealed both structural and functional alterations in bladders from patients with LUTS symptoms or animals with experimentally induced bladder dysfunction. In particular, the urothelium and the suburothelial space, containing afferent nerve fibres and interstitial cells, have been found to form a functional unit that is essential in the process of bladder function. Various imbalances within this suburothelial complex have been identified as significant contributors to the generation of storage LUTS, along with potential abnormalities of central function.

Effects of 17beta-oestradiol on rat detrusor smooth muscle contractility

The aim of this study was to investigate the effect of 17β-oestradiol (E₂) on detrusor smooth muscle contractility and its possible neuroprotective role against ischaemic-like condition, which could arise during overactive bladder disease. The effect of E₂ was investigated on rat detrusor muscle strips stimulated with carbachol, KCl and electrically, in the absence or presence of a selective oestrogen receptor antagonist (ICI 182,780) and, by using confocal Ca²⁺ imaging technique, measuring the amplitude (ΔF/F₀) and the frequency of spontaneous whole cell Ca²⁺ flashes. Moreover, the effect of 1 and 2 h of anoxia–glucopenia and reperfusion (A-G/R), in the absence or presence of the hormone, was evaluated in rat detrusor strips perfused with Krebs solution which underwent electrical field stimulation to stimulate intrinsic nerves; the amplitude and the frequency of Ca²⁺ flashes were also measured. 17β-Oestradiol exhibited antispasmogenic activity assessed on detrusor strips depolarized with 60 mm KCl at two different Ca²⁺ concentrations. 17β-Oestradiol at the highest concentration tested (30 μm) significantly decreased detrusor contractions induced by all the stimuli applied. In addition, the amplitude and the frequency of spontaneous Ca²⁺ flashes were significantly decreased in the presence of E₂ (10 and 30 μm) compared with control detrusor strips. In strips subjected to A-G/R, a significant increase in the amplitude of both spontaneous and evoked flashes was observed. 17β-Oestradiol was found to increase the recovery of detrusor strips subjected to A-G/R. The ability of E₂ to suppress contraction in control conditions may explain its ability to aid recovery following A-G/R.

Basic fibroblast growth factor causes urinary bladder overactivity through gap junction generation in the smooth muscle

Overactive bladder is a highly prevalent clinical condition that is often caused by bladder outlet obstruction (BOO). Increased coupling of bladder smooth muscle cells (BSMC) via gap junctions has been hypothesized as a mechanism for myogenic bladder overactivity in BOO, although little is known about the regulatory system underlying such changes. Here, we report the involvement of basic fibroblast growth factor (bFGF) and connexin 43, a bladder gap junction protein, in bladder overactivity. BOO created by urethral constriction in rats resulted in elevated bFGF and connexin 43 levels in the bladder urothelium and muscle layer, respectively, and muscle strips from these bladders were more sensitive than those from sham-operated controls to a cholinergic agonist. In vitro bFGF treatment increased connexin 43 expression in cultured rat BSMC via the ERK 1/2 pathway. This finding was supported by another in vivo model, where bFGF released from gelatin hydrogels fixed on rat bladder walls caused connexin 43 upregulation and gap junction formation in the muscle layer. Bladder muscle strips in this model showed increased sensitivity to a cholinergic agonist that was blocked by inhibition of gap junction function with alpha-glycyrrhetinic acid. Cystometric analyses of this model showed typical features of detrusor overactivity such as significantly increased micturition frequency and decreased bladder capacity. These findings suggest that bFGF from the urothelium could induce bladder hypersensitivity to acetylcholine via gap junction generation in the smooth muscle, thereby contributing to the myogenic overactivity of obstructed bladders.

Spontaneous release of acetylcholine from autonomic nerves in the bladder

BACKGROUND AND PURPOSE

Bladder contractility is regulated by intrinsic myogenic mechanisms interacting with autonomic nerves. In this study, we have investigated the physiological role of spontaneous release of acetylcholine in guinea pig and rat bladders.

EXPERIMENTAL APPROACH

Conventional isotonic or pressure transducers were used to record contractile activity of guinea pig and rat bladders.

KEY RESULTS

Hyoscine (3 micromol x L(-1)), but not tetrodotoxin (TTX, 1 micromol x L(-1)), reduced basal tension, distension-evoked contractile activity and physostigmine (1 micromol x L(-1))-evoked contractions of the whole guinea pig bladder and muscle strips in vitro. omega-Conotoxin GVIA (0.3 micromol x L(-1)) did not affect physostigmine-induced contractions when given either alone or in combination with omega-agatoxin IVA (0.1 micromol x L(-1)) and SNX 482 (0.3 micromol x L(-1)). After 5 days in organotypic culture, when extrinsic nerves had significantly degenerated, the ability of physostigmine to induce contractions was reduced in the dorso-medial strips, but not in lateral strips (which have around 15 times more intramural neurones). Most muscle strips from adult rats lacked intramural neurones. After 5 days in culture, physostigmine-induced or electrical field stimulation-induced contractions of the rat bladder strips were greatly reduced. In anaesthetized rats, topical application of physostigmine (5-500 nmol) on the bladder produced a TTX-resistant tonic contraction that was abolished by atropine (4.4 micromol x kg(-1) i.v.).

CONCLUSIONS AND IMPLICATIONS

The data indicate that there is spontaneous TTX-resistant release of acetylcholine from autonomic cholinergic extrinsic and intrinsic nerves, which significantly affects bladder contractility. This release is resistant to blockade of N, P/Q and R type Ca(2+) channels.

Role of K+ channels in regulating spontaneous activity in detrusor smooth muscle in situ in the mouse bladder

PURPOSE

We investigated the functional role of K(+) channels for regulating spontaneous activity in mouse bladder detrusor smooth muscle.

MATERIALS AND METHODS

The effects of different K(+) channels blockers on spontaneous changes in membrane potential and intracellular Ca(2+) dynamics were examined using intracellular recording techniques and Ca(2+) imaging with fluo-4 fluorescence, respectively.

RESULTS

Detrusor smooth muscle generated spontaneous action potentials and Ca(2+) transients. Iberiotoxin (0.1 microM), charybdotoxin (0.1 microM) or tetraethylammonium (1 mM) increased the amplitude of action potentials and prolonged their repolarizing phase without inhibiting their after-hyperpolarization. Tetraethylammonium (10 mM) but not stromatoxin (0.1 microM) suppressed after-hyperpolarization and further increased the amplitude and half duration of action potentials. Apamin (0.1 microM) increased the frequency of action potentials but had no effect on their configuration. Spontaneous Ca(2+) transients were generated in individual detrusor smooth muscle cells and occasionally propagated to neighboring cells to form intercellular Ca(2+) waves. Transmural nerve stimulations invariably initiated synchronous Ca(2+) transients within and across muscle bundles. Charybdotoxin (0.1 microM) increased the amplitude of spontaneous Ca(2+) transients, while the subsequent application of tetraethylammonium (10 mM) increased their half duration. In addition, tetraethylammonium increased the synchronicity of Ca(2+) transients in muscle bundles.

CONCLUSIONS

These results suggest that large and intermediate conductance Ca(2+) activated K(+) channels contribute to action potential repolarization and restrict the excitability of detrusor smooth muscle in the mouse bladder. In addition, the activation of voltage dependent K(+) channels is involved in repolarization and after-hyperpolarization, and it has a fundamental role in stabilizing detrusor smooth muscle excitability.

Potential for control of detrusor smooth muscle spontaneous rhythmic contraction by cyclooxygenase products released by interstitial cells of Cajal

Interstitial cells of Cajal (ICCs) have been identified as pacemaker cells in the upper urinary tract and urethra, but the role of ICCs in the bladder remains to be determined. We tested the hypotheses that ICCs express cyclooxygenase (COX), and that COX products (prostaglandins), are the cause of spontaneous rhythmic contraction (SRC) of isolated strips of rabbit bladder free of urothelium. SRC was abolished by 10 μM indomethacin and ibuprofen (non-selective COX inhibitors). SRC was concentration-dependently inhibited by selective COX-1 (SC-560 and FR-122047) and COX-2 inhibitors (NS-398 and LM-1685), and by SC-51089, a selective antagonist for the PGE-2 receptor (EP) and ICI-192,605 and SQ-29,548, selective antagonists for thromboxane receptors (TP). The partial agonist/antagonist of the PGF-2α receptor (FP), AL-8810, inhibited SRC by ∼50%. Maximum inhibition was ∼90% by SC-51089, ∼80–85% by the COX inhibitors and ∼70% by TP receptor antagonists. In the presence of ibuprofen to abolish SRC, PGE-2, sulprostone, misoprostol, PGF-2α and U-46619 (thromboxane mimetic) caused rhythmic contractions that mimicked SRC. Fluorescence immunohistochemistry coupled with confocal laser scanning microscopy revealed that c-Kit and vimentin co-localized to interstitial cells surrounding detrusor smooth muscle bundles, indicating the presence of extensive ICCs in rabbit bladder. Co-localization of COX-1 and vimentin, and COX-2 and vimentin by ICCs supports the hypothesis that ICCs were the predominant cell type in rabbit bladder expressing both COX isoforms. These data together suggest that ICCs appear to be an important source of prostaglandins that likely play a role in regulation of SRC. Additional studies on prostaglandin-dependent SRC may generate opportunities for the application of novel treatments for disorders leading to overactive bladder.

In vivo and in vitro pharmacological characterization of SVT-40776, a novel M3 muscarinic receptor antagonist, for the treatment of overactive bladder

BACKGROUND AND PURPOSE

Highly selective M(3) muscarinic receptor antagonists may represent a better treatment for overactive bladder syndrome, diminishing side effects. Cardiac side effects of non-selective antimuscarinics have been associated with activity at M(2) receptors as these receptors are mainly responsible for muscarinic receptor-dependent bradycardia. We have investigated a novel antimuscarinic, SVT-40776, highly selective for M(3) over M(2) receptors (Ki = 0.19 nmol.L(-1) for M(3) receptor affinity). This study reports the functional activity of SVT-40776 in the bladder, relative to its activity in atria.

EXPERIMENTAL APPROACH

In vitro and ex vivo (oral dosing) inhibition of mouse detrusor and atrial contractile responses to carbachol were used to study the functional activity of SVT-40776. The in vivo efficacy of SVT-40776 was characterized by suppression of isovolumetric spontaneous bladder contractions in anaesthetized guinea pigs after intravenous administration.

KEY RESULTS

SVT-40776 was the most potent in inhibiting carbachol-induced bladder contractions of the anti-cholinergic agents tested, without affecting atrial contractions over the same range of concentrations. SVT-40776 exhibited the highest urinary versus cardiac selectivity (199-fold). In the guinea pig in vivo model, SVT-40776 inhibited 25% of spontaneous bladder contractions at a very low dose (6.97 microg.kg(-1) i.v), without affecting arterial blood pressure.

CONCLUSIONS AND IMPLICATIONS

SVT-40776 is a potent inhibitor of M(3) receptor-related detrusor contractile activity. The absence of effects on isolated atria preparations represents an interesting characteristic and suggests that SVT-40776 may lack unwanted cardiac effects; a feature especially relevant in a compound intended to treat mainly elderly patients.

Emerging drugs for treatment of overactive bladder and detrusor overactivity

BACKGROUND

Overactive bladder (OAB) signifies the presence of urinary urgency and can have major effects on quality of life and social functioning. Standard antimuscarinic drugs have good initial response rates but substantial adverse effects and long-term compliance problems.

OBJECTIVES

To review the complexities of the mechanisms underlying OAB and the current drugs available for treating its symptoms.

METHODS

The literature was reviewed to define current therapies and drugs in clinical trials. Articles were identified by means of a computerised PubMed and Cochrane Library search (using the following keywords: overactive bladder, detrusor overactivity, urgency and bladder), supported by a search of the PharmaProjects database.

CONCLUSIONS

New drug classes, such as beta-3 adrenergic agonists, may work by reducing contractility or excitability of bladder muscle. Moderation of afferent activity may allow improved OAB symptoms, with lower risk of affecting voiding function. Agents acting on the CNS could influence OAB favourably, but target selection and adverse effects are an issue. The recognition of the functional contribution of the urothelium and the diversity of nerve transmitters has sparked interest in both peripheral and central modulation of OAB pathophysiology.

Altered distribution of interstitial cells in the guinea pig bladder following bladder outlet obstruction

AIMS

We investigated the effects of bladder outlet obstruction (BOO) on the distribution of interstitial cells (ICs) in the guinea-pig bladder.

METHODS

Bladder overactivity of BOO animals was validated with urodynamic studies. Immunohistochemical analyses for Kit and vimentin as markers for ICs were performed on both BOO and control bladders. Morphological and functional properties of detrusor smooth muscle (DSM) were examined with alpha-smooth muscle actin staining and intracellular recording, respectively. Electron microscopy was also carried out to characterize ultrastructural morphology of ICs.

RESULTS

Two weeks after surgery, BOO animals showed an increased voiding frequency and a reduced voiding volume. Filling cystometry demonstrated a frequent incidence of non-voiding contractions, a reduced interval between voiding contractions and an increased voiding pressure in BOO bladders. In BOO bladders, the thickness of suburothelial and subserosal connective tissue layers was increased, whilst that of detrusor smooth muscle (DSM) layer was less affected. Population of Kit or vimentin immunoreactive ICs was increased in subserosal layers, and their distribution was altered in suburotherial layer in BOO bladders. Neither alpha-actin immunoreactivity nor spontaneous electrical activity of DSM was altered in BOO bladders. ICs were characterized by their numerous mitochondria and caveolae, and had a close contact with each other and with neighboring DSM or nerves.

CONCLUSIONS

These results demonstrated the increased population of ICs in the BOO guinea-pig model for the first time, and suggest that the altered distribution of ICs may contribute to the pathophysiology of bladder overactivity.

The neural control of micturition

Micturition, or urination, occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. The neural circuitry that controls this process is complex and highly distributed: it involves pathways at many levels of the brain, the spinal cord and the peripheral nervous system and is mediated by multiple neurotransmitters. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary or reflex micturition, leading to urinary incontinence. This is a major health problem, especially in those with neurological impairment. Here we review the neural control of micturition and how disruption of this control leads to abnormal storage and release of urine.