ALTERATIONS IN CHOLINERGIC AND PURINERGIC SIGNALING IN A MODEL OF THE OBSTRUCTED BLADDER

Purinergic signalling in the urinary bladder - When function becomes dysfunction

Knowledge of the participation of ATP and related purines in urinary tract physiology has been established over the last five decades through the work of many independent groups, inspired by, and building on the pioneering studies of Professor Geoffrey Burnstock and his coworkers. As part of a series of reviews in this tribute edition, the present article summarises our current understanding of purines and purinergic signalling in modulating and regulating urinary tract function. Purinergic mechanisms underlying the origin of bladder pain; sensations of bladder filling and urinary tract motility; and regulation of detrusor smooth muscle contraction are described, encompassing the relevant history of discovery and consolidation of knowledge as methodologies and pharmacological tools have developed. We consider normal physiology, including development and ageing and then move to pathophysiology, discussing the causal and consequential contribution of purinergic signalling mechanism and their constituent components (receptors, signal transduction, effector molecules) to bladder dysfunction.

Nerve transfer for restoration of lower motor neuron-lesioned bladder function. Part 1: attenuation of purinergic bladder smooth muscle contractions

This study determined the effect of pelvic organ decentralization and reinnervation 1 yr later on the contribution of muscarinic and purinergic receptors to ex vivo, nerve-evoked, bladder smooth muscle contractions. Nineteen canines underwent decentralization by bilateral transection of all coccygeal and sacral (S) spinal roots, dorsal roots of lumbar (L)7, and hypogastric nerves. After exclusions, 8 were reinnervated 12 mo postdecentralization with obturator-to-pelvic and sciatic-to-pudendal nerve transfers then euthanized 8-12 mo later. Four served as long-term decentralized only animals. Controls included six sham-operated and three unoperated animals. Detrusor muscle was assessed for contractile responses to potassium chloride (KCl) and electric field stimulation (EFS) before and after purinergic receptor desensitization with α, β-methylene adenosine triphosphate (α,β-mATP), muscarinic receptor antagonism with atropine, or sodium channel blockade with tetrodotoxin. Atropine inhibition of EFS-induced contractions increased in decentralized and reinnervated animals compared with controls. Maximal contractile responses to α,β-mATP did not differ between groups. In strips from decentralized and reinnervated animals, the contractile response to EFS was enhanced at lower frequencies compared with normal controls. The observation of increased blockade of nerve-evoked contractions by muscarinic antagonist with no change in responsiveness to purinergic agonist suggests either decreased ATP release or increased ecto-ATPase activity in detrusor muscle as a consequence of the long-term decentralization. The reduction in the frequency required to produce maximum contraction following decentralization may be due to enhanced nerve sensitivity to EFS or a change in the effectiveness of the neurotransmission.

Electroacupuncture Alleviates Bladder Overactivity via Inhabiting Bladder P2X3 Receptor

Electroacupuncture (EA) has been widely applied for overactive bladder, but the mechanism of its action remains to be clarified. This study was aimed to investigate EA regulating the effect of purinergic signaling in the OAB of rats. Electroacupuncture (continuous wave, 30 Hz, 1 mA) was applied to stimulate the Ciliao point (BL32) and the Huiyang point (BL35) of rats. Results showed that when the P2X₃ receptor in bladder peripheral level and the spinal cord central level was involved in the bladder micturition reflex of the afferent signaling, intravenous administration P2X₃ antagonist AF-353 can significantly inhibit urination in naive rats and OAB of rats and increase bladder volume and micturition pressure. EA stimulation alleviated bladder overactivity significantly and after the P2X₃ receptor was blocked, the EA effect was weakened. EA stimulation can effectively reduce the P2X₃ mRNA and protein expression in OAB of rats, spinal cord (L6-S1), and DRG (L6-S1) and can significantly reduce the number of positive P2X₃ cells in OAB of rats, spinal cord (L6-S1), and DRG (L6-S1). These findings suggest that EA stimulation could alleviate bladder overactivity, and the function is closely related to the inhabited P2X₃ receptor in the bladder.

Characterisation of nerve-mediated ATP release from bladder detrusor muscle and its pathological implications

BACKGROUND AND PURPOSE

This study aims to characterise the molecular mechanisms that determine variability of atropine resistance of nerve-mediated contractions in human and guinea pig detrusor smooth muscle.

EXPERIMENTAL APPROACH

Atropine resistance of nerve-mediated contractions and the role of P2X1 receptors, were assessed in isolated preparations from guinea pigs and also humans with or without overactive bladder syndrome, from which the mucosa was removed. Nerve-mediated ATP release was measured directly with amperometric ATP-sensitive electrodes. Ecto-ATPase activity of guinea pig and human detrusor samples was measured in vitro by measuring the concentration-dependent rate of ATP breakdown. The transcription of ecto-ATPase subtypes in human samples was measured by qPCR.

KEY RESULTS

Atropine resistance was greatest in guinea pig detrusor, absent in human tissue from normally functioning bladders, and intermediate in human overactive bladder. Greater atropine resistance correlated with reduction of contractions by the ATP-diphosphohydrolase apyrase, directly implicating ATP in their generation. E-NTPDase-1 was the most abundantly transcribed ecto-ATPase of those tested, and transcription was reduced in tissue from human overactive, compared to normal, bladders. E-NTPDase-1 enzymic activity was inversely related to the magnitude of atropine resistance. Nerve-mediated ATP release was continually measured and varied with stimulation frequency over the range of 1-16 Hz.

CONCLUSION AND IMPLICATIONS

Atropine resistance in nerve-mediated detrusor contractions is due to ATP release and its magnitude is inversely related to E-NTPDase-1 activity. ATP is released under different stimulation conditions compared with ACh, implying different routes for their release.

Development of a P2X1-purinoceptor mediated contractile response in the aged mouse prostate gland through slowing down of ATP breakdown

AIMS

An age-related increase in prostatic smooth muscle tone is partly responsible for the lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH). Changes in the effectors of prostatic smooth muscle contraction with age may play a role in the development of these symptoms. Using a mouse model of prostate contractility, this study investigated the effect of age on the different components of contractility in the prostate gland.

METHODS

The isometric force developed in response to electrical field stimulation or exogenously applied agonists by mouse prostates mounted in organ baths, was evaluated to determine the effect of age on contractile mechanisms. Changes with age in the rate of ATP breakdown and levels of the P2rx1 gene and P2X1-purinoceptor expression in mouse prostate were measured by a modified luciferin-luciferase assay, RT-PCR and western blot, respectively.

RESULTS

Nerve mediated contractile responses containing a component elicited by P2X1-purinoceptors were observed in prostates taken from aged mice, but not in prostates taken from young adult mice. Furthermore, the potency of the endogenous purinoceptor agonist ATP was 50-fold greater in aged mice, whereas the potency of its stable analogue α,β-metATP was unchanged. An age-related decrease in ATP metabolism was also observed.

CONCLUSIONS

With age, a purinergic contractile response to nerve stimulation develops in the mouse prostate gland due to a decrease in the rate of ATP breakdown. This may contribute to the increase in muscular tone observed in BPH and suggests that P2X1-purinoceptors are an additional target for the treatment of BPH.

Extracellular UDP enhances P2X-mediated bladder smooth muscle contractility via P2Y(6) activation of the phospholipase C/inositol trisphosphate pathway

Bladder dysfunction characterized by abnormal bladder smooth muscle (BSM) contractions is pivotal to the disease process in overactive bladder, urge incontinence, and spinal cord injury. Purinergic signaling comprises one key pathway in modulating BSM contractility, but molecular mechanisms remain unclear. Here we demonstrate, using myography, that activation of P2Y6 by either UDP or a specific agonist (MRS 2693) induced a sustained increase in BSM tone (up to 2 mN) in a concentration-dependent manner. Notably, activation of P2Y6 enhanced ATP-mediated BSM contractile force by up to 45%, indicating synergistic interactions between P2X and P2Y signaling. P2Y6-activated responses were abolished by phospholipase C (PLC) and inositol trisphosphate (IP3) receptor antagonists U73122 and xestospongin C, demonstrating involvement of the PLC/IP3 signal pathway. Mice null for Entpd1, an ectonucleotidase on BSM, demonstrated increased force generation on P2Y6 activation (150%). Thus, in vivo perturbations to purinergic signaling resulted in altered P2Y6 activity and bladder contractility. We conclude that UDP, acting on P2Y6, regulates BSM tone and in doing so selectively maximizes P2X1-mediated contraction forces. This novel neurotransmitter pathway may play an important role in urinary voiding disorders characterized by abnormal bladder motility.

ATP inhibits Ins(1,4,5)P3-evoked Ca2+ release in smooth muscle via P2Y1 receptors

Adenosine 5′-triphosphate (ATP) mediates a variety of biological functions following nerve-evoked release, via activation of either G-protein-coupled P2Y- or ligand-gated P2X receptors. In smooth muscle, ATP, acting via P2Y receptors (P2YR), may act as an inhibitory neurotransmitter. The underlying mechanism(s) remain unclear, but have been proposed to involve the production of inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃] by phospholipase C (PLC), to evoke Ca²⁺ release from the internal store and stimulation of Ca²⁺-activated potassium (K_Ca) channels to cause membrane hyperpolarization. This mechanism requires Ca²⁺ release from the store. However, in the present study, ATP evoked transient Ca²⁺ increases in only ~10% of voltage-clamped single smooth muscle cells. These results do not support activation of K_Ca as the major mechanism underlying inhibition of smooth muscle activity. Interestingly, ATP inhibited Ins(1,4,5)P₃-evoked Ca²⁺ release in cells that did not show a Ca²⁺ rise in response to purinergic activation. The reduction in Ins(1,4,5)P₃-evoked Ca²⁺ release was not mimicked by adenosine and therefore, cannot be explained by hydrolysis of ATP to adenosine. The reduction in Ins(1,4,5)P₃-evoked Ca²⁺ release was, however, also observed with its primary metabolite, ADP, and blocked by the P2Y₁R antagonist, MRS2179, and the G protein inhibitor, GDPβS, but not by PLC inhibition. The present study demonstrates a novel inhibitory effect of P2Y₁R activation on Ins(1,4,5)P₃-evoked Ca²⁺ release, such that purinergic stimulation acts to prevent Ins(1,4,5)P₃-mediated increases in excitability in smooth muscle and promote relaxation.

A possible role of the cholinergic and purinergic receptor interaction in the regulation of the rat urinary bladder function

The contractile activation of the upper (dome) and lower (base) parts of the urinary bladder show some differences. Cellular mechanisms that might be responsible for cholinergic effects blocking non-adrenergic non-cholinergic contractions in the base of the rat urinary bladder were investigated. Smooth muscle cells were thus freshly isolated or cultured both from the dome and the base of the rat urinary bladder and the contribution from cholinergic and purinergic pathways to their Ca(2+) homeostasis was examined. The expression of nicotinic acetylcholine (nAChR) and P2X2 purinergic receptors on the cultured cells and on tissue sections was investigated. The ATP-evoked Ca(2+) transients in rat smooth muscle cells did not show any desensitization. However, when ATP was administered together with carbamylcholine (CCh), the latter essentially prevented ATP from evoking Ca(2+) transients in smooth muscle cells from the base (suppression to 12 ± 2.5% of control, n = 57; p < 0.01), but not from the dome (99 ± 5% of control, n = 52; p > 0.05) of the rat urinary bladder. While atropine was unable to modify (6 ± 3% of control, n = 14; p < 0.05), α-bungarotoxin (118 ± 12% of control, n = 20; p > 0.05) blocked the inhibitory effects of CCh. Additionally, α7 subunits of nAChR and P2X2 purinergic receptors were identified using immunocytochemistry, immunohistochemistry, and Western blot in cultured urinary bladder smooth muscle cells, in urinary bladder sections, and in urinary bladder muscle strips, respectively, suggesting that the activation of nAChR modifies the action of ATP.

Functional, morphological and molecular characterization of bladder dysfunction in streptozotocin-induced diabetic mice: evidence of a role for L-type voltage-operated Ca2+ channels

BACKGROUND AND PURPOSE

Diabetic cystopathy is one of the most common and incapacitating complications of diabetes mellitus. This study aimed to evaluate the functional, structural and molecular alterations of detrusor smooth muscle (DSM) in streptozotocin-induced diabetic mice, focusing on the contribution of Ca(2+) influx through L-type voltage-operated Ca(2+) channels (L-VOCC).

EXPERIMENTAL APPROACH

Male C57BL/6 mice were injected with streptozotocin (125 mg·kg(-1) ). Four weeks later, contractile responses to carbachol, α,β-methylene ATP, KCl, extracellular Ca(2+) and electrical-field stimulation were measured in urothelium-intact DSM strips. Cystometry and histomorphometry were performed, and mRNA expression for muscarinic M(2) /M(3) receptors, purine P2X1 receptors and L-VOCC in the bladder was determined.

KEY RESULTS

Diabetic mice exhibited higher bladder capacity, frequency, non-void contractions and post-void pressure. Increased bladder weight, wall thickness, bladder volume and neural tissue were observed in diabetic bladders. Carbachol, α,β-methylene ATP, KCl, extracellular Ca(2+) and electrical-field stimulation all produced greater DSM contractions in diabetic mice. The L-VOCC blocker nifedipine almost completely reversed the enhanced DSM contractions in bladders from diabetic animals. The Rho-kinase inhibitor Y27632 had no effect on the enhanced carbachol contractions in the diabetic group. Expression of mRNA for muscarinic M(3) receptors and L-VOCC were greater in the bladders of diabetic mice, whereas levels of M(2) and P2X1 receptors remained unchanged.

CONCLUSIONS AND IMPLICATIONS

Diabetic mice exhibit features of urinary bladder dysfunction, as characterized by overactive DSM and decreased voiding efficiency. Functional and molecular data suggest that overactive DSM in diabetes is the result of enhanced extracellular Ca(2+) influx through L-VOCC.

Role of Purinergic Signaling in Voiding Dysfunction

Purinergic signaling is a term that relates to adenosine triphosphate binding to its receptor (purinergic receptors such as P2X and P2Y subtypes). This pathway has been implicated in bladder functional disorders related to interstitial cystitis/painful bladder syndrome, neurogenic bladder secondary to spinal cord injury, lower urinary tract symptoms, diabetes, and aging. Purinergic signaling occurs at multiple sites, including the central nervous system, peripheral motor and sensory nerves, detrusor smooth muscle, and bladder urothelium. Future pharmacologic agents to treat bladder functional disorders may be able to target purinergic signaling at one or more of these sites.

Comparison of mechanical and electrical activity and interstitial cells of Cajal in urinary bladders from wild-type and W/Wv mice

BACKGROUND AND PURPOSE

W/W(v) and wild-type murine bladders were studied to determine whether the W/W(v) phenotype, which causes a reduction in, but not abolition of, tyrosine kinase activity, is a useful tool to study the function of bladder interstitial cells of Cajal (ICC).

EXPERIMENTAL APPROACH

Immunohistochemistry, tension recordings and microelectrode recordings of membrane potential were performed on wild-type and mutant bladders.

KEY RESULTS

Wild-type and W/W(v) detrusors contained c-Kit- and vimentin-immunopositive cells in comparable quantities, distribution and morphology. Electrical field stimulation evoked tetrodotoxin-sensitive contractions in wild-type and W/W(v) detrusor strips. Atropine reduced wild-type responses by 50% whereas a 25% reduction occurred in W/W(v) strips. The atropine-insensitive component was blocked by pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid in both tissue types. Wild-type and W/W(v) detrusors had similar resting membrane potentials of -48 mV. Spontaneous electrical activity in both tissue types comprised action potentials and unitary potentials. Action potentials were nifedipine-sensitive whereas unitary potentials were not. Excitatory junction potentials were evoked by single pulses in both tissues. These were reduced by atropine in wild-type tissues but not in W/W(v) preparations. The atropine-insensitive component was abolished by pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid in both preparations.

CONCLUSIONS AND IMPLICATIONS

Bladders from W/W(v) mice contain c-Kit- and vimentin-immunopositive ICC. There are similarities in the electrical and contractile properties of W/W(v) and wild-type detrusors. However, significant differences were found in the pharmacology of the responses to neurogenic stimulation with an apparent up-regulation of the purinergic component. These findings indicate that the W/W(v) strain may not be the best model to study ICC function in the bladder.

A functional study of purinergic signalling in the normal and pathological rabbit corpus cavernosum

OBJECTIVE

To examine rabbit cavernosal smooth muscle (CSM) relaxation to ATP, ADP and UTP in normal rabbits and in models of conditions that predispose to erectile dysfunction (ED), diabetes mellitus (DM; induced for 6 months) and bladder outlet obstruction (BOO, 6 weeks after surgery).

MATERIALS AND METHODS

Concentration-response curves (CRCs) were constructed to ATP, ADP and UTP on CSM from control rabbits in the absence and presence of antagonists. In addition, CRCs were constructed to ATP in CSM from rabbits with DM and BOO.

RESULTS

ATP and UTP caused equipotent, dose-dependent relaxations of pre-contracted normal rabbit CSM; ADP was more potent. Relaxation was inhibited by Reactive Blue 2, but not by suramin, 8-p-sulfophenyltheophylline or L-N(G)-nitroarginine methyl ester. In rabbits with DM and those with partial BOO, ATP-mediated CSM relaxation was less than in control rabbits. Pharmacological profiling suggests that purine-induced CSM relaxation might be mediated by P2Y(1) and P2Y(4) receptors in the rabbit.

CONCLUSIONS

In healthy rabbits, ATP released from nerves appears to produce relaxation of CSM via P2Y(4) receptors on smooth muscle, while ADP, acting on P2Y(1) receptors on endothelial cells, produces relaxation via nitric oxide. Alterations in CSM purinergic signalling might be implicated in the pathophysiology of ED associated with DM and BOO. Characterization of purinergic signalling in CSM might highlight new therapeutic targets for treating ED.

Age-related changes of P2X(1) receptor mRNA in the bladder detrusor from men with and without bladder outlet obstruction

The urinary bladder purinergic system is reported to change with age and with bladder dysfunction. Here, we examined the expression of purinergic P2X(1) receptors in detrusor and mucosa (urothelium+lamina propria) from male control bladder and investigated age-related P2X(1) receptor mRNA expression in control and obstructed detrusor. Biopsy specimens were obtained at cystoscopy from control patients (n=46, age range 30-86years) and patients diagnosed with outlet obstruction (n=29, 46-88years). Calponin expression (measured by RT-PCR) was similar in control and obstructed detrusor and did not change with age. Quantitative competitive RT-PCR was used to measure P2X(1) receptor and GAPDH mRNA in control and obstructed detrusor. P2X(1) receptor mRNA expression was 9-fold (p<0.0001) higher in the detrusor than in the mucosa. Expression of mRNA for the internal control GAPDH remained stable with age and across control and obstructed detrusor. No difference in P2X(1) receptor expression was observed between control and obstructed detrusor (p=0.35). However, an age-related decrease in P2X(1) mRNA expression was observed in control (n=27; p=0.0054; Spearman coefficient r=-0.520) but not obstructed detrusor (n=19; p=0.093; r=-0.396). Downregulation of P2X(1) mRNA expression might occur as a result of an increased component of neural ATP release in the aging bladder.

Methods and results of urethrolysis

Although occurring with somewhat less frequency now than historically reported, outlet obstruction after incontinence surgery continues to be a source of postoperative patient dissatisfaction and therapeutic dilemma. Several techniques have been described that fall under the rubric of urethrolysis, including sling incision, sling lysis with explantation, and formal vaginal or retropubic urethrolysis (incision and disruption of bladder neck and urethral fibrosis). Surgical approaches have included vaginal, retropubic, or combined techniques with or without the use of adjunctive steps such as graft interposition. However, evidence emanating from reports of these varied techniques has been incomplete due to variability in outcomes presentation, lack of longevity of follow-up, or problematic study design. Nonetheless, the bulk of clinical evidence supports the efficacy of urethrolysis as an intervention for outlet obstruction after stress incontinence surgery. However, persistent irritative bladder symptoms remain bothersome for some women and, in addition, the recurrence of stress incontinence also may complicate the technique of urethrolysis. Management of these potential adverse outcomes also has been inconsistent, with some authorities routinely performing repeat incontinence surgery at the time of urethrolysis and others preferring to assess continence status after convalescence from urethrolysis. The differences among the types of urethrolysis and the results of each type are reviewed in this article in light of evolving definitions of outlet obstruction, diagnosis, and definition in women.

The purinergic component of human vas deferens contraction

OBJECTIVE

To examine purinergic signaling in human vas deferens.

DESIGN

To study contractile responses of the scrotal vas deferens.

SETTING

Research department of a university teaching hospital.

PATIENT(S)

Undergoing vasectomy or orchidectomy (aged 27-88 years, n = 14).

INTERVENTION(S)

Vasectomy or orchidectomy.

MAIN OUTCOME MEASURE(S)

Strips of vas deferens were suspended in an organ bath and subjected to electrical stimulation to establish frequency-response curves. These stimulations were repeated in the presence of pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, P2 receptor antagonist), prazosin (adrenergic alpha1 antagonist), and tetrodotoxin. Concentration-response curves were constructed to noradrenaline and the P2X agonists ATP and alpha,beta-methylene ATP (alpha,beta-meATP). The P2X receptor subtype distribution was assessed by immunohistochemistry using specific antibodies.

RESULT(S)

The response at 32 Hz in the presence of PPADS was reduced by 40% and in the presence of prazosin by 80%. Noradrenaline caused concentration-dependent contractions (EC50 = 11.8 microM). Contractions to ATP and alpha,beta-meATP (EC50 = 6.27 microM) suggested that the functional receptor was P2X1 and/or P2X3. However, immunohistochemistry demonstrated P2X1, but not P2X3, receptor immunoreactivity on the smooth muscle cells.

CONCLUSION(S)

This study demonstrated that ATP is a co-transmitter with noradrenaline in the contraction of the human vas deferens predominantly acting through the P2X1 receptor.

Animal models in urological disease and sexual dysfunction

There are several conditions associated with dysfunction of the lower urinary tract or which result in a reduction in the ability to engage in satisfactory sexual function and result in significant bother to sufferers, partners and/or carers. This review describes some of the animal models that may be used to discover safe and effective medicines with which to treat them. While alpha adrenoceptor antagonists and 5-alpha-reductase inhibitors deliver improvement in symptom relief in benign prostatic hyperplasia sufferers, the availability of efficacious and well-tolerated medicines to treat incontinence is less well served. Stress urinary incontinence (SUI) has no approved medical therapy in the United States and overactive bladder (OAB) therapy is limited to treatment with muscarinic antagonists (anti-muscarinics). SUI and OAB are characterised by high prevalence, a growing ageing population and a strong desire from sufferers and physicians for more effective treatment options. High patient numbers with low presentation rates characterizes sexual dysfunction in men and women. The introduction of Viagra in 1998 for treating male erectile dysfunction and the success of the phosphodiesterase type 5 inhibitor class (PDE5 inhibitor) have indicated the willingness of sufferers to seek treatment when an effective alternative to injections and devices is available. The main value of preclinical models in discovering new medicines is to predict clinical outcomes. This translation can be established relatively easily in areas of medicine where there are a large number of drugs with different underlying pharmacological mechanisms in clinical usage. However, apart from, for example, the use of PDE5 inhibitors to treat male erectile dysfunction and the use of anti-muscarinics to treat OAB, this clinical information is limited. Therefore, current confidence in existing preclinical models is based on our understanding of the biochemical, physiological, pathophysiological and psychological mechanisms underlying the conditions in humans and how they are reflected in preclinical models. Confidence in both the models used and the pharmacological data generated is reinforced if different models of related aspects of the same disorder generate confirmatory data. However, these models will only be fully validated in retrospect once the pharmacological agents they have helped identify are tested in humans.

Management of refractory urinary urge incontinence following urogynecological surgery with sacral neuromodulation

AIMS

We sought to explore our patient outcomes utilizing sacral neuromodulation in the management of refractory urinary urge incontinence following urogynecological surgical procedures.

METHODS

A total of 25 women with urinary urge incontinence following urogynecological surgery were selected for SNS therapy and retrospectively analyzed. All patients completed a comprehensive urological evaluation. Clinical data was recorded to determine outcomes and identify parameters that would be predictive of response to neuromodulation. Outcomes were determined via subjective patient questionnaire and graded as follows: significant response (> or =80% improvement), moderate response (> or =50% and <80% improvement), and poor response (<50% response).

RESULTS

Nineteen patients had a previous pubovaginal sling (10 with concomitant pelvic prolapse repair), 3 a previous retropubic suspension, and 3 a transperitoneal vesicovaginal fistula repair. Urethrolysis was performed in 4 patients to alleviate bladder outlet obstruction prior to sacral neuromodulation. Mean patient age was 59.8 years and length of follow-up was 7.2 months. Twenty-two women (88%) had the IPG placed during a Stage 2 procedure. Twenty patients maintained at least a 50% improvement in clinical symptoms at last follow-up and 6 patients were continent. Overall, the number of pads/day improved from 4.2 to 1.1 (P < 0.001). There were no significant differences in response to neuromodulation based upon age, duration of symptoms, type of surgery, or urodynamic parameters.

CONCLUSION

Sacral neuromodulation appears to be an effective therapy in patients with refractory urge incontinence following urogynecological surgery. Larger prospective studies with longer follow-up are needed to assess the durability of this therapeutic modality.

Neocuproine, a copper (I) chelator, potentiates purinergic component of vas deferens contractions elicited by electrical field stimulation

Effects of the specific copper (I) chelator, neocuproine, on the purinergic and adrenergic components of nerve-evoked contractions were investigated in the prostatic rat vas deferens. Electrical field stimulation (EFS; 4 Hz) induced bimodal contractions of vas deferens tissue in the presence of alpha1-adrenoceptor antagonist prazosin (to isolate the purinergic component) or purinoceptor antagonist suramin (to isolate the adrenergic component). Neocuproine significantly potentiated the purinergic component of the contractile responses to EFS. However, the same agent failed to elicit any significant effect on the adrenergic component of nerve-evoked contractions. The copper (II) chelator cuprizone could not affect the purinergic component of contractions. The potentiating effect of neocuproine which was reversible after washout of the drug, did not occur following the application of the pre-prepared neocuproine-copper (I) complex. A nitric oxide synthase inhibitor, L-nitroarginine; a cyclooxygenase inhibitor, indomethacin or an alpha2-adrenoceptor antagonist, yohimbine, failed to alter the responses to neocuproine on the purinergic component of the contraction to EFS. Neocuproine did not elicit any significant effect on preparations in which the purinergic receptors were desensitized with alpha,beta-methylene ATP. In conclusion, our results suggest that neocuproine potentiates the purinergic component of rat vas deferens contractions elicited by EFS, presumably by facilitating purinergic neurotransmission and that copper (I)-sensitive mechanisms can modulate purinergic transmission in this tissue.

Urodynamic properties and neurotransmitter dependence of urinary bladder contractility in the BK channel deletion model of overactive bladder

Overactive bladder and incontinence are major medical issues, which lack effective therapy. Previously, we showed (Meredith AL, Thornloe KS, Werner ME, Nelson MT, and Aldrich RW. J Biol Chem 279: 36746-36752, 2004) that the gene mSlo1 encodes large-conductance Ca2+-activated K+ (BK) channels of urinary bladder smooth muscle (UBSM) and that ablation of mSlo1 leads to enhanced myogenic and nerve-mediated contractility and increased urination frequency. Here, we examine the in vivo urodynamic consequences and neurotransmitter dependence in the absence of the BK channel. The sensitivity of contractility to nerve stimulation was greatly enhanced in UBSM strips from Slo-/- mice. The stimulation frequency required to obtain a 50% maximal contraction was 8.3 +/- 0.9 and 19.1 +/- 1.8 Hz in Slo-/- and Slo+/+ mice, respectively. This enhancement is at least partially due to alterations in UBSM excitability, as muscarinic-induced Slo-/- contractility is elevated in the absence of neuronal activity. Muscarinic-induced Slo-/- contractility was mimicked by blocking BK channels with iberiotoxin (IBTX) in Slo+/+ strips, whereas IBTX had no effect on Slo-/- strips. IBTX also enhanced purinergic contractions of Slo+/+ UBSM but was without effect on purinergic contractions of Slo-/- strips. In vivo bladder pressure and urine output measurements (cystometry) were performed on conscious, freely moving mice. Slo-/- mice exhibited increased bladder pressures, pronounced pressure oscillations, and urine dripping. Our results indicate that the BK channel in UBSM has a very significant role in urinary function and dysfunction and as such likely represents an important therapeutic target.

Alterations in neurogenically mediated contractile responses of urinary bladder in rats with diabetes

Diabetic bladder dysfunction (DBD) is among the most common and bothersome complications of diabetes mellitus. Autonomic neuropathy has been counted as the cause of DBD. In the present study, we compared the alterations in the neurogenically mediated contractile responses of urinary bladder in rats with streptozocin-induced diabetes, 5% sucrose-induced diuresis, and age-matched controls. Male Sprague-Dawley rats were divided into three groups: 9-wk diabetic rats, diuretic rats, and age-matched controls. Micturition and morphometric characteristics were evaluated using metabolic cage and gross examination of the bladder. Bladder detrusor muscle strips were exposed to either periodic electrical field stimulation (EFS) or to EFS in the presence of atropine, alpha,beta-methylene adrenasine 5'-triphosphate, or tetrodotoxin. The proportions of cholinergic, purinergic, and residual nonadrenergic-noncholinergic (NANC) components of contractile response were compared among the three groups of animals. Diabetes caused a significant reduction of body weight compared with diuresis and controls, although the bladders of diabetic and diuretic rats weighed more than the controls. Both diabetes and diuresis caused significant increase in fluid intake, urine output, and bladder size. Diabetes and diuresis caused similarly increased response to EFS and reduced response to cholinergic component compared with controls. However, the purinergic response was significantly smaller in diuretic bladder strips compared with controls but not in diabetic rats. A residual NANC of unknown origin increased significantly but differently in diabetics and diuretics compared with controls. In conclusion, neurogenically mediated bladder contraction is altered in the diabetic rat. Diabetic-related changes do not parallel diuretic-induced changes, indicating that the pathogenesis of DBD needs further exploration.

Effect of neocuproine, a copper(i) chelator, on rat bladder function

The effects of a specific copper(I)-chelator, neocuproine (NC), and a selective copper(II)-chelator, cuprizone, on nonadrenergic-noncholinergic transmitter mechanisms in the rat urinary bladder were studied by measuring nerve-evoked contractions of bladder strips and voiding function under urethane anesthesia. After blocking cholinergic and adrenergic transmission with atropine and guanethidine, electrical field stimulation induced bimodal contractions of bladder strips. An initial, transient contraction that was blocked by the purinergic antagonist, suramin, was significantly enhanced by NC (20 and 200 microM applied sequentially) but not affected by cuprizone. The facilitating effect, which was blocked by suramin and reversible after washout of the drug, did not occur following administration of neocuproine-copper(I) complex (NC-Cu). NC (20 microM) significantly increased the second, more sustained contraction, whereas 200 microM decreased this response. These effects of NC on the sustained contractions were not elicited by NC-Cu and not blocked by suramin. The nitric oxide synthase inhibitor, l-nitroarginine, did not alter the responses to NC. NC (20 microM) elicited a marked increase in basal tone of the strips. This effect was less prominent after the second application of 200 microMNC or with NC-Cu treatment or in the presence of suramin. In anesthetized rats, during continuous infusion cystometry, intravesical infusion of 50 microM NC but not NC-Cu or cuprizone significantly decreased the intercontraction interval (ICI) without changing contraction amplitude. The ICI returned to normal after washout of NC. Suramin blocked this effect. These results indicate that NC enhances bladder activity by facilitating purinergic excitatory responses and that copper(I)-sensitive mechanisms tonically inhibit purinergic transmission in the bladder.

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.

Partial bladder outlet obstruction abolishes the receptor- and G protein-dependent increase in calcium sensitivity in rabbit bladder smooth muscle

Partial bladder outlet obstruction (PBOO) alters the function of the whole bladder and produces specific alterations in the contractility of the bladder smooth muscle cell. The goal of this study was to test the hypothesis that PBOO affects smooth muscle contraction at the level of the receptor- and G protein-dependent increase in myofilament Ca2+ sensitivity. To address this question, we used alpha-toxin-permeabilized strips of bladder smooth muscle from control animals and animals subjected to 2 wk of PBOO. Increasing free [Ca2+] increased force in permeabilized strips from control animals; the addition of 10 microM carbachol and 10 microM GTP increased both the Ca2+ sensitivity of the contractions and the maximal levels of force attained. In contrast, although increases in [Ca2+] increased force in permeabilized strips from PBOO animals, the addition of carbachol and GTP had no additional effects. Myosin light chain phosphorylation levels increased with [Ca2+], and although they tended to be higher in strips from PBOO animals, they did not reach statistical significance. Assessment of G protein activity from both animal models suggests this is not a site responsible for the loss of carbachol and GTP enhancement of myofilament Ca2+ sensitivity. The addition of phorbol dibutyrate increased the Ca2+ sensitivity of force development in strips from both animal models, suggesting that an alteration in PKC signaling is not involved. Our results are consistent with the hypothesis that PBOO decreases receptor-mediated myofilament calcium sensitization and that the site of action is downstream from either the G proteins or PKC.

Effects of intravenous and infravesical administration of suramin, terazosin and BMY 7378 on bladder instability in conscious rats with bladder outlet obstruction

OBJECTIVE

To evaluate the effect of the nonselective purinergic antagonist suramin and the alpha1-adrenergic antagonists, terazosin and BMY 7378, given intravenously or infused directly into the bladder during cystometry in conscious rats with bladder outlet obstruction induced by urethral ligation.

MATERIALS AND METHODS

Cystometry was performed in conscious female rats recording bladder volume capacity (BVC), evaluated as the amount of saline infused between two voiding cycles, and micturition volume (MV). Changes in frequency and amplitude of spontaneous non-voiding bladder contractions (NVC) were also recorded. The effects of the intravenous administration of suramin (100 mg/kg), BMY 7378 (1 mg/kg), and terazosin (0.3 mg/kg) on NVC, BVC and MV were evaluated in obstructed rats with bladder infusion of saline. The effects of infravesical infusion of suramin (3-10 micromol/L), terazosin (1 micromol/L) and BMY 7378 (10 micromol/L) were also evaluated and compared with values observed in control rats during saline infusion into the bladder.

RESULTS

Intravenous injection with suramin had no effects on NVC, BVC and MV, but suramin infused into the bladder induced a consistent reduction in the amplitude of NVC (significantly different from matched control animals) with a tendency to reduce their frequency. BVC and MV were slightly but significantly decreased by infravesical infusion of suramin. In contrast, BMY 7378 and terazosin, given intravenously, were extremely potent at inhibiting the frequency and amplitude of the NVC, but were inactive on NVC when infused into bladder.

CONCLUSIONS

These findings confirm a role for alpha1-adrenergic receptors in bladder instability caused by bladder outlet obstruction. In addition, a purinergic neurotransmitter, presumably ATP, is shown to be involved.

Overactive bladder--pharmacological aspects

The micturition reflex can be initiated by contraction or distension of detrusor smooth muscle cells, or by signals from the urothelium. It has been shown that bladder distension causes release of ATP from the urothelium, and that ATP can activate P2X3 receptors on suburothelial afferent nerve terminals to evoke a neural discharge. However, most probably the activation of afferent fibres during bladder filling involves not only ATP, but a cascade of inhibitory and stimulatory transmitters/mediators. These mechanisms may be targets for future drugs. Both in the normal and functionally disturbed bladder, muscarinic receptor stimulation produces the main part of detrusor contraction, but evidence is accumulating that in disease states, such as neurogenic bladders, outflow obstruction, idiopathic detrusor instability, interstitial cystitis, and also in the ageing bladder, a non-cholinergic activation via purinergic receptors may occur. If this component of activation is responsible not only for part of the bladder contractions, but also for the symptoms of the overactive bladder, it should be considered an important target for therapeutic interventions. Drags blocking different P2X receptor subtypes, or counteracting bladder contraction via other mechanisms, e.g. beta3-adrenoceptor stimulation, may be developed for treatment of the overactive bladder.

Categorización de receptores α1-adrenérgicos en el detrusor de pacientes con hbp obstructiva. estudio inicial en modelo animal de experimentación

INTRODUCTION

The action of alpha 1-adrenergic receptor antagonists in ameliorating irritation and obstruction in patients with bladder outlet obstruction (due to Benign Prostatic Hyperplasia-BPH) has been demonstrated. Although it is well known that alpha 1-a receptors are responsible for prostate smooth muscle relaxation, the mechanism by which irritative bladder symptoms are improved is unknown. Different alpha 1 receptor subtypes may be involved. The objective of this study is to investigate the changes in the alpha-adrenergic receptor populations in the obstructed detrusor, and to determine which subtype is proportionally increased in this situation (bladder outlet obstruction).

MATERIAL AND METHODS

This was an in vivo study in an experimental model: male NZ (New Zealand) rabbits. The bladder neck of one group of rabbits was obstructed surgically using the technique proposed by Levin et al. Subsequent to bladder catherization with a 8Fr catheter, the bladder neck was exposed by means of a low medial abdominal incision. The bladder neck was tied with a 2/0 silk thread below the ureteral orifices. The catheter was taken out at the end of the intervention. The rabbits were sacrificed after 4 weeks using intracardiac pentothal and cystectomy was performed. A control group that did not undergo bladder obstruction were also sacrificed at this time, for the comparative study. Part of the detrusor was used for a pathological study and the rest for a physio-pharmacological study in which the organ was placed in a bath of adrenoceptor agonists (phenylephrine and noradrenaline) and antagonists WB101, AH11101A and BMY7378 (antagonists of the alpha 1a, b, d, respectively).

RESULTS

The findings of the pathological study show that the bladder wall was thicker in the rabbits that underwent bladder obstruction. The physio-pharmacological studies demonstrate that the detrusor response to the selective alpha-1 adrenergic agonist was greater in the rabbits that underwent bladder obstruction, however detrusor contractility was decreased (KPSS). With bladder obstruction the alpha 1d receptors were increased.

DISCUSSION AND CONCLUSIONS

Receptor-binding studies (Malloy et al) aim to differentiate the alpha-adrenoreceptor populations. These studies identify and quantitate the different receptor subtypes in tissue without taking into account their activity. The isometric and physio-pharmacological tests evaluate active receptors, i.e. those that respond to agonist and antagonist stimuli. This enables detrusor activity to be evaluated accurately. The results obtained in this investigational study support the hypothesis that there is a high statistically significant increase in the alpha 1 adrenergic receptors in the obstructed detrusor. Furthermore, in agreement with previous molecular studies, during prostate obstruction alpha 1d is the predominate sub-population in the bladder. These findings may have patho-physiological, clinical and pharmacological implications. If this hypothesis which has been demonstrated in an experimental model, is also demonstrated in studies in humans, pharmacological development should not only be focussed on selective alpha 1a receptor antagonists (prostate) but also on those of alpha 1d, for relieving symptoms in patients with bladder outlet obstruction (BPH and prostatism).

Pharmacologic perspective on the physiology of the lower urinary tract

Myogenic activity, distention of the detrusor, and signals from the urothelium may initiate voiding. In the bladder, afferent nerves have been identified not only in the detrusor, but also suburothelially, where they form a plexus that lies immediately beneath the epithelial lining. Extracellular adenosine triphosphate (ATP) has been found to mediate excitation of small-diameter sensory neurons via P2X3 receptors, and it has been shown that bladder distention causes release of ATP from the urothelium. In turn, ATP can activate P2X3 receptors on suburothelial afferent nerve terminals to evoke a neural discharge. However, most probably, not only ATP but also a cascade of inhibitory and stimulatory transmitters and mediators are involved in the transduction mechanisms underlying the activation of afferent fibers during bladder filling. These mechanisms may be targets for future drugs. The central nervous control of micturition involves many transmitter systems, which may be suitable targets for pharmacologic intervention. gamma-Aminobutyric acid, dopamine, enkephalin, serotonin, and noradrenaline receptors and mechanisms are known to influence micturition, and potentially, drugs that affect these systems could be developed for clinical use. However, a selective action on the lower urinary tract may be difficult to obtain. Most drugs currently used for treatment of detrusor overactivity have a peripheral site of action, mainly the efferent (cholinergic) neurotransmission and/or the detrusor muscle itself. In the normal bladder, muscarinic receptor stimulation produces the main part of detrusor contraction, but evidence is accumulating that in disease states, such as neurogenic bladders, outflow obstruction, idiopathic detrusor instability, and interstitial cystitis, as well as in the aging bladder, a noncholinergic activation via purinergic receptors may occur. If this component of activation is responsible not only for part of the bladder contractions, but also for the symptoms of the overactive bladder, it should be considered an important target for therapeutic interventions.

De novo urge syndrome and detrusor instability after anti-incontinence surgery: current concepts, evaluation, and treatment

The onset of de novo irritative voiding symptoms after anti-incontinence surgery for stress urinary incontinence is troubling to both patient and physician alike. At present, mechanisms responsible for the development of these symptoms are incompletely elucidated. Although bladder outlet obstruction may certainly be a cause, correct diagnosis and treatment of this condition in its more insidious manifestation may be difficult. In addition, alternative etiologic factors related to surgical technique during outlet enhancing surgery may play a role, prompting a rethinking of these procedures. In this discussion, we review changes in voiding physiology and mechanisms for voiding dysfunction after anti-incontinence surgery, emphasizing de novo urge syndrome and detrusor instability. In addition, we present our approach to the evaluation, diagnosis, and treatment of these challenging patients.