Pharmacologic perspective on the physiology of the lower urinary tract

Therapeutic effects of the putative P2X3/P2X2/3 antagonist A-317491 on cyclophosphamide-induced cystitis in rats

It is suggested that ATP and purinergic P2X receptors are involved in overactive bladder. In this study, we investigated the effect of the recently developed P2X3 and P2X2/3 receptor antagonist A-317491 on cyclophosphamide (CYP)-induced cystitis to determine whether a P2X receptor antagonist could be beneficial for the treatment of bladder overactivity induced by CYP. Female Sprague-Dawley (SD) rats were given 150 mg/kg CYP (i.p.). When the micturition activity was observed for 24 h in a conscious and unrestrained condition, CYP-treated rats exhibited increased urinary frequency. Two days after CYP injection, cystometry was performed in conscious rats, in which the bladder was continuously infused with saline (5 ml/h). In CYP-treated rats, non-voiding contractions were interposed between micturitions, suggestive of hyper-reflexia. Intravenous administration of A-317491 (20 or 50 mg/kg) or pyridoxal phosphate-6-azo (benzene-2,4-disulfonic acid) tetrasodium (PPADS; a nonselective purinergic receptor antagonist, 10 mg/kg) prolonged the interval of voiding contraction and reduced the non-voiding contractions. On the other hand, oxybutynin (1 mg/kg), a muscarinic receptor antagonist, did not affect the frequency of non-voiding or voiding contractions in CYP-treated rats. A-317491 at the higher dose decreased the amplitude of voiding contractions, but increased the micturition volume. The residual urine in the bladder increased after treatment with CYP; A-317491 and PPADS reduced this, whereas oxybutynin had no effect. These data suggest that A-317491 is effective at improving the signs of CYP-induced cystitis and that the P2X3 or P2X2/3 receptor pathway is involved in bladder overactivity observed during CYP-induced cystitis.

Increased expression of transient receptor potential vanilloid subfamily 1 in the bladder predicts the response to intravesical instillations of resiniferatoxin in patients with refractory idiopathic detrusor overactivity

OBJECTIVES

To investigate the correlation of transient receptor potential vanilloid subfamily 1 (TRPV1) mRNA expression levels and the clinical outcome of intravesical resiniferatoxin treatment in patients with idiopathic detrusor overactivity (IDO), as such treatment with vanilloids can be effective for DO.

PATIENTS AND METHODS

In all, 28 patients with IDO refractory to anticholinergics were enrolled and treated with four weekly intravesical instillations of 10 nm resiniferatoxin. Eleven patients having ureteroscopic surgery served as controls. Two bladder wall biopsies were taken from the posterior wall by rigid cystoscopy. TRPV1 expression in the bladder wall samples was determined by individual quantitative reverse transcription-polymerase chain reaction, and immunohistochemical staining. Responders to the therapy were defined as those with an improvement in an urgency scale by >/=1, and with improved general satisfaction. Baseline TRPV1 expression was compared between responders, nonresponders and controls.

RESULTS

At 3 months, 14 patients (50%) were responders and in the other 14 the treatment failed (nonresponders). Bladder biopsies were available in seven responders and 11 nonresponders. Transcript levels before treatment correlated significantly with the therapeutic effect of resiniferatoxin (P = 0.004), with higher TRPV1 mRNA expression in responders (median 1.50, range 0.89-2.78) than nonresponders (0.74, 0.34-1.32). Responders also had higher TRPV1 expression levels than a control group (P = 0.067), but the TRPV1 transcript levels of nonresponders were not significantly different from those of the control (P = 0.367).

CONCLUSION

Successful intravesical resiniferatoxin treatment is closely associated with the over-expression of TRPV1 in the bladder mucosa and submucosa in patients with IDO.

Comparative pharmacological analysis of Rho-kinase inhibitors and identification of molecular components of Ca2+ sensitization in the rat lower urinary tract

We aimed to compare the expression and function of molecular components of the RhoA/Rho-kinase signaling pathway in the contractile responses of detrusor, trigonal and urethral smooth muscle, using selective Rho-kinase inhibitors. Contractility studies and molecular approaches were employed to demonstrate the expression patterns and functional activity of the RhoA/Rho-kinase signaling pathway in the lower urinary tract. Frequency-response curves (1-32 Hz) and concentration-response curves (CRC) to carbachol (CCh, 0.01-30 microM), phenylephrine (PE, 0.01-300 microM) and endothelin-1 (ET-1, 0.01-100 nM) were significantly attenuated (p<0.01) following incubation with the Rho-kinase inhibitors H-1152 (0.1-1 microM), Y-27632 (1-10 microM) or HA-1077 (10 microM). Addition of Rho-kinase inhibitors also markedly reduced (p<0.01) the contractions evoked by either KCl (80 mM) or alpha,beta-methylene ATP (alpha,beta-mATP, 10 microM). Among the Rho-kinase inhibitors tested, H-1152 was approximately 9-16 times more potent than Y-27632 or HA-1077. In addition, basal tone of detrusor and trigonal strips was reduced following addition of Y-27632 (10 microM), H-1152 (1 microM) and HA-1077 (10 microM). The expression of RhoA, RhoGDI, leukemia-associated RhoGEF (LARG) and p115RhoGEF was similar among the detrusor, trigone and urethra, whereas Rho-kinase alpha, Rho-kinase beta and PDZ-RhoGEF protein levels were significantly lower in the urethra. Components of the RhoA/Rho-kinase signaling are expressed in detrusor, trigonal and urethral smooth muscle and dynamically regulate contraction and tone. Manipulation of RhoGEF expression may provide further understanding of mechanisms involving Ca(2+) sensitization in the lower urinary tract.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Mechanisms of disease: involvement of the urothelium in bladder dysfunction

Although the urinary bladder urothelium has classically been thought of as a passive barrier to ions and solutes, a number of novel properties have been recently attributed to urothelial cells. Studies have revealed that the urothelium is involved in sensory mechanisms (i.e. the ability to express a number of sensor molecules or respond to thermal, mechanical and chemical stimuli) and can release chemical mediators. Localization of afferent nerves next to the urothelium suggests that urothelial cells could be targets for neurotransmitters released from bladder nerves or that chemicals released by urothelial cells could alter afferent nerve excitability. Taken together, these and other findings highlighted in this article suggest a sensory function for the urothelium. Elucidation of mechanisms that influence urothelial function might provide insights into the pathology of bladder dysfunction.

The effects of ovariectomy and estrogen replacement on acetylcholine release from nerve fibres and passive stretch-induced acetylcholine release in female rat bladder

AIMS

The present study investigated the effects of ovariectomy and estrogen replacement on the release of acetylcholine (Ach) from cholinergic neurons as well as on the tetrodotoxin (TTX)-insensitive stretch-induced Ach release in isolated rat detrusor. In addition, the above effects on rat micturition characteristics were also studied.

METHODS

Thirty female rats randomly received a sham operation, ovariectomy, or ovariectomy plus estrogen replacement. Using metabolic cages, micturition parameters were recorded. Then, in vitro functional experiments that included the measurements of nerve-mediated detrusor muscle contraction, Ach release from nerve fibres, and stretch-induced TTX-insensitive Ach release were performed. Ach release was measured using microdialysis and high-performance liquid chromatography.

RESULTS

Ovariectomized rats showed a significant decrease in voided volume and significant increase in 24-hr frequency of voiding. Ovariectomy caused the significant increase in both TTX-insensitive basal Ach release and TTX-insensitive stretch-induced Ach release. On the other hand, ovariectomy caused a significant decrease in Ach release from nerve fibres, resulting in the decrease in the contractile responses of detrusor muscle to electrical nerve stimulation. Estrogen replacement restored these alterations induced by ovariectomy.

CONCLUSIONS

Our findings showed that as a results of estrogen deficiency, Ach release from nerve fibres decreased, suggesting that this reduction of Ach released from cholinergic nerves may cause the decrease in detrusor contractility. Furthermore, this study also demonstrated that stretch-induced TTX-insensitive Ach release was increased by ovariectomy. This may be a contributing factor to the development of overactive bladder in elderly women.

The bladder epithelium and overactive bladder: What we know

Although the urothelium has been traditionally thought of as a passive barrier between urine and detrusor muscle, new studies have shown that the urothelium is a highly specialized structure involved in antigen presentation, micturition reflex, metabolic secretion, inflammatory regulation, and sensory afferent functioning. Data from several laboratories have shown that the urothelium can respond to thermal, mechanical, and chemical stimuli. The earlier findings (activation of urothelial transient receptor potential channel vanilloid 1 producing the second messenger nitric oxide, which in turn triggers suburothelial sensory nerves) demonstrate how the urothelium acts as a transducer, releasing chemicals that target adjacent bladder cells and sensory neurons. We now know that bladder urothelium acts also as a transducer whereby afferent neurons, via urothelial mechanoafferent transduction, are involved in the micturition process and the pathogenesis of bladder disorders. This paper highlights the important role that the urothelium has in bladder pathophysiology.

Current trends in the evaluation and management of female urinary incontinence

Despite its common occurrence and often seemingly obvious causes, female urinary incontinence requires a thorough and thoughtful evaluation for its proper diagnosis and treatment. With rare exceptions, urinary incontinence is the result of failure of the sphincter mechanism to resist bladder pressures encountered during daily activities. This may be the result of sphincter failure, overactivity of the bladder detrusor muscle or both. In uncomplicated cases, the diagnosis is usually based on an evaluation in the office. Urodynamic and cystoscopic study may be helpful in complex, resistant and recurring cases of urinary incontinence of any cause. Most cases of incontinence may be classified as stress, urge or mixed urinary incontinence. Treatment of stress urinary incontinence focuses on supplementing the urethral continence mechanisms, particularly the urethral supports and periurethral striated muscle function. The current paradigm for the treatment of urge incontinence centres on pharmacologic therapy, primarily by correcting detrusor overactivity with antimuscarinic drugs. Other therapies aimed at altering sensorimotor function may be used in resistant cases. The treatment of mixed urinary incontinence requires consideration of the contribution of each of its components. With proper diagnosis, effective treatment is possible for most patients.

The role of alpha-blockers in the management of lower urinary tract symptoms in prostate cancer patients treated with radiation therapy

OBJECTIVE

Radiation therapy (RT) is commonly used for the treatment of prostate cancer, either via brachytherapy or external beam, and is often accompanied by dose-related obstructive and irritative lower urinary tract symptoms (LUTS). This review will analyze the current state of knowledge of LUTS secondary to RT for prostate cancer and review treatment options for this complication.

METHODS

A review of the literature.

RESULTS

Radiation-induced effects in the lower urinary tract that result in LUTS include injury to peripheral neurons, interstitial fibrosis of the bladder, and loss of muscle fibers in the muscularis propria. LUTS are associated with a diminished quality of life and impaired sexual function. Numerous nonrandomized studies and one randomized study support the proposition that the occurrence of LUTS secondary to RT is effectively mitigated by alpha1-adrenoreceptor blockade.

CONCLUSIONS

Basic and clinical science studies as well as clinical guidelines relevant for LUTS secondary to RT suggest that the routine use of alpha1-adrenoreceptor antagonists should be considered in patients treated with RT, either prophylactically or at the earliest sign of LUTS.

Interstitial cells of Cajal in the murine gallbladder

OBJECTIVE

The presence of interstitial cells of Cajal (ICC) has been described throughout the digestive tract. In this study, we investigated whether ICC also exist in the gallbladder wall of CD1 mice.

MATERIAL AND METHODS

Immunofluorescent confocal microscopy was used to identify the morphology and distribution of ICC in either whole-mount flat preparations or enzyme-dispersed cells from the gallbladder of CD1 mice. Methylene blue staining and transmission electron microscopy were performed to detect the presence of ICC, and reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were used to confirm the expressions of ICC-specific marker c-kit in the gallbladder tissues.

RESULTS

The presence of c-kit-positive cells was demonstrated in both the gallbladder wall and the enzyme-dispersed cells. The ICC were distributed throughout the wall of the gallbladder and organized into a network. Under transmission electron microscopy, ICC were characterized by their well-developed perinuclear endoplasmic reticulum, abundant mitochondria, free ribosomes and intermediate filaments, and distinctive caveolae and lack of myosin filaments. The expressions of ICC-specific marker c-kit were also confirmed in the gallbladder tissue.

CONCLUSION

The murine gallbladder wall contains ICC.

Purinergic P2 receptors as targets for novel analgesics

Following hints in the early literature about adenosine 5'-triphosphate (ATP) injections producing pain, an ion-channel nucleotide receptor was cloned in 1995, P2X3 subtype, which was shown to be localized predominantly on small nociceptive sensory nerves. Since then, there has been an increasing number of papers exploring the role of P2X3 homomultimer and P2X2/3 heteromultimer receptors on sensory nerves in a wide range of organs, including skin, tongue, tooth pulp, intestine, bladder, and ureter that mediate the initiation of pain. Purinergic mechanosensory transduction has been proposed for visceral pain, where ATP released from epithelial cells lining the bladder, ureter, and intestine during distension acts on P2X3 and P2X2/3, and possibly P2Y, receptors on subepithelial sensory nerve fibers to send messages to the pain centers in the brain as well as initiating local reflexes. P1, P2X, and P2Y receptors also appear to be involved in nociceptive neural pathways in the spinal cord. P2X4 receptors on spinal microglia have been implicated in allodynia. The involvement of purinergic signaling in long-term neuropathic pain and inflammation as well as acute pain is discussed as well as the development of P2 receptor antagonists as novel analgesics.

Non-neuronal cholinergic system in human bladder urothelium

OBJECTIVES

To evaluate the non-neuronal cholinergic system in the isolated human bladder. Recently, several reports have demonstrated that non-nerve-evoked acetylcholine (ACh) release may contribute to various pathophysiologic conditions.

METHODS

Human bladders were obtained from 15 patients. Bladder strips with or without urothelium were suspended in an organ bath filled with Krebs-Henseleit solution. ACh release was measured using microdialysis and high-performance liquid chromatography. The contribution of urothelium to non-nerve-evoked ACh release was tested, and the effects of age and elevation of the resting tension (0 to 40 mN) on ACh release were also evaluated. Furthermore, choline acetyltransferase (ChAT) immunohistochemical staining of bladder was performed.

RESULTS

Immunohistochemistry showed marked ChAT-positive staining in the urothelium and suburothelial region. Tetrodotoxin-insensitive non-nerve-evoked ACh release occurred and was significantly greater in strips with than without urothelium. The non-nerve-evoked ACh release from strips with urothelium increased with age, and the positive correlation between age and release was significant. Stretching of the strips caused increases in non-nerve-evoked ACh release that was significantly greater in strips with than without urothelium. The stretch-induced release of non-nerve-evoked ACh increased with age.

CONCLUSIONS

These data have demonstrated that a non-neuronal cholinergic system is present in the human bladder and that the urothelium/suburothelium partially releases ACh. We found a significant age-related and stretch-induced increase in non-nerve-evoked ACh release. This suggests that the non-neuronal cholinergic system may contribute to the physiology and pathophysiology of human bladder function.

The overactive bladder: review of current pharmacotherapy in adults. Part 1: pathophysiology and anticholinergic therapy

Overactive bladder is a syndrome characterised by urinary urgency, with or without urge incontinence, and usually with frequency and nocturia. It affects millions of people of all ages worldwide and causes significant morbidity, especially in terms of health-related quality of life. It poses a huge economic burden on health resources. Managing such patients involves a thorough history, physical examination and the use of pertinent investigations before the initiation of treatment. Therapy consists of lifestyle changes, bladder training, anticholinergics, second-line agents such as resiniferatoxin instillation or botulinum toxin injections into the bladder in refractory cases and, finally, in intractable cases, surgery. In the first part of this review of pharmacotherapy for the treatment of this condition, the focus is on the pathophysiological factors potentially involved in overactive bladder and covers the wide range of currently available first-line anticholinergic agents. Treatment algorithms are suggested on the basis of current literature.

The emergence of new drugs for overactive bladder

Overactive bladder is a common and distressing problem. Standard therapy is directed towards modifying the detrusor motor sensitivity and response via anticholinergic medication. Currently available medications are reviewed and alternative targets for treatment are presented.

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.

Peptidergic sensory and parasympathetic fiber sprouting in the mucosa of the rat urinary bladder in a chronic model of cyclophosphamide-induced cystitis

In this study, we used a well-established animal model to investigate changes in the peptidergic and parasympathetic innervation of the bladder following chronic bladder inflammation. Adult female Sprague-Dawley rats were injected with either 70 mg/kg cyclophosphamide diluted in saline, i.p., once every 3 days or saline. After 10 days, all animals were tested for urinary frequency and number of low volume voids, as well as symptoms of spontaneous pain. At the end of 12 days, all animals were perfused with histological fixatives and the urinary bladders processed for immunofluorescence using antibodies against calcitonin gene-related peptide and the vesicular acetylcholine transporter as markers, respectively, of peptidergic primary afferent fibers and parasympathetic efferent fibers. We show that animals treated with cyclophosphamide had inflamed bladders and displayed high urinary frequency as well as some indicators of spontaneous pain, such as piloerection and a rounded-back posture. Furthermore, they had a significant increase in the density of both parasympathetic and peptidergic sensory fibers in the bladder mucosa and an increase in peptidergic sensory fibers in the detrusor muscle. Based on these results, we suggest that peripheral sprouting of parasympathetic and peptidergic fibers could be a mechanism responsible for sensitization of the bladder, leading to urinary symptoms. Since we observed that the parasympathetic and peptidergic fibers often wrapped around one another and that their varicosities were very close, these two fiber populations may be interacting with each other to lead to and maintain sensitization. Future studies are required to establish the role of this fiber sprouting in bladder symptoms.

Peptidergic sensory and parasympathetic fiber sprouting in the mucosa of the rat urinary bladder in a chronic model of cyclophosphamide-induced cystitis

In this study, we used a well-established animal model to investigate changes in the peptidergic and parasympathetic innervation of the bladder following chronic bladder inflammation. Adult female Sprague-Dawley rats were injected with either 70 mg/kg cyclophosphamide diluted in saline, i.p., once every 3 days or saline. After 10 days, all animals were tested for urinary frequency and number of low volume voids, as well as symptoms of spontaneous pain. At the end of 12 days, all animals were perfused with histological fixatives and the urinary bladders processed for immunofluorescence using antibodies against calcitonin gene-related peptide and the vesicular acetylcholine transporter as markers, respectively, of peptidergic primary afferent fibers and parasympathetic efferent fibers. We show that animals treated with cyclophosphamide had inflamed bladders and displayed high urinary frequency as well as some indicators of spontaneous pain, such as piloerection and a rounded-back posture. Furthermore, they had a significant increase in the density of both parasympathetic and peptidergic sensory fibers in the bladder mucosa and an increase in peptidergic sensory fibers in the detrusor muscle. Based on these results, we suggest that peripheral sprouting of parasympathetic and peptidergic fibers could be a mechanism responsible for sensitization of the bladder, leading to urinary symptoms. Since we observed that the parasympathetic and peptidergic fibers often wrapped around one another and that their varicosities were very close, these two fiber populations may be interacting with each other to lead to and maintain sensitization. Future studies are required to establish the role of this fiber sprouting in bladder symptoms.

Activation of α 1D Adrenergic Receptors in the Rat Urothelium Facilitates the Micturition Reflex

PURPOSE

Previous studies have revealed that the activation of alpha(1) adrenergic receptors in urothelial cells releases neurotransmitters. We determined if alpha(1D) adrenergic receptors are expressed in the urothelium of the rat bladder and if inhibition of these receptors affects reflex voiding.

MATERIALS AND METHODS

Female Wistar rats were used in the experiments. Receptor expression was evaluated by Western blot. The effects of receptor activation were studied using cystometrograms, measurement of adenosine triphosphate concentrations in the bladder lumen and afferent nerve recording. The alpha(1D) antagonist naftopidil (0.75 to 1.66 mg/kg) was administered intravenously into the external jugular vein.

RESULTS

The expression of alpha(1D) adrenergic receptors was detected in urothelial tissue with Western blot and immunohistochemistry. The alpha(1D) receptor antagonist naftopidil prolonged the intercontraction interval during continuous infusion cystometrograms in conscious rats (143% of the control value) and suppressed the excitatory effect of intravesical infusion of acetic acid (0.1%) on the intercontraction interval (220%). Naftopidil inhibited the bladder afferent nerve activity induced by bladder distention (32.0%) and acetic acid infusion (30.4%), and decreased adenosine triphosphate levels in the bladder perfusate during bladder distention (36.6%).

CONCLUSIONS

Endogenous catecholamines appear to act on alpha(1D) receptors in the urothelium to facilitate mechanosensitive bladder afferent nerve activity and reflex voiding.

Effects of M274773, a neurokinin-2 receptor antagonist, on bladder function in chronically spinalized rats

PURPOSE

Increased afferent nerve activity may have an important role in the pathogenesis of neurogenic detrusor overactivity. We tested the efficacy of the neuokinin-2 receptor antagonist M274773 ((S)-N-[2-(3,4-Dichlorophenyl)-4-[4-(2-oxoperhydro-pyrimidin-l-yl) piperidino]butyl]-N-methylbenzamide dihydrochloride) on neurogenic detrusor overactivity after spinal cord injury in rats.

MATERIALS AND METHODS

Included in this study were 48 adult Sprague-Dawley rats (Charles River, Montreal, Quebec, Canada). Six animals served as normal controls, while 32 underwent spinal cord transection at the 10th thoracic vertebra. Two weeks after spinal cord injury 6 animals underwent filling cystometrography to confirm neurogenic detrusor overactivity, while another 12 served as paraplegic controls. The remaining 24 paraplegic animals were used to test the drug and they were divided into 2 equal groups of 12. Group 1 received the drug at a dose of 0.3 mg/kg daily, while group 2 received a dose of 0.6 mg/kg daily. Each paraplegic control and treatment group was further subdivided into 2 subgroups of 6 rats each. In subgroup 1 filling cystometrography was done 3 weeks after spinal cord injury, while in subgroup 2 it was done 4 weeks after spinal cord injury.

RESULTS

Three weeks after spinal cord injury neurogenic detrusor overactivity developed in all paraplegic control animals with a mean bladder capacity +/- SD of 0.7 +/- 0.2 ml and a mean voiding pressure of 59 +/- 14.2 cm H2O. Neurogenic detrusor overactivity resolved in 50% and 83% of the animals that received M274773 for 1 week at doses of 0.3 and 0.6 mg/kg daily, respectively. Mean cystometric bladder capacity was 1.2 +/- 0.5 vs 1.3 +/- 0.4 ml and mean voiding pressure was 46.1 +/- 10.8 vs 40 +/- 9.9 cm H2O in animals that received 0.3 vs 0.6 mg/kg daily, respectively. The drug produced better urodynamic results when given for 2 weeks rather than 1 week.

CONCLUSIONS

M274773 is effective for neurogenic detrusor overactivity after spinal cord injury in the rat. It may provide an alternative clinical treatment option for neurogenic detrusor overactivity and urgency/frequency syndrome. This new neurokinin-2 selective antagonist has time and dose response effects, which further suggests the potential for clinical application.

beta-NAD is a novel nucleotide released on stimulation of nerve terminals in human urinary bladder detrusor muscle

Endogenous nucleotides with extracellular functions may be involved in the complex neural control of human urinary bladder (HUB). Using HPLC techniques with fluorescence detection, we observed that in addition to ATP and its metabolites ADP, AMP and adenosine, electrical field stimulation (EFS; 4-16 Hz, 0.1 ms, 15 V, 60 s) of HUB detrusor smooth muscle coreleases novel nucleotide factors, which produce etheno-1N(6)-ADP-ribose (eADPR) on etheno-derivatization at high temperature. A detailed HPLC fraction analysis determined that nicotinamide adenine dinucleotide (beta-NAD+; 7.0 +/- 0.7 fmol/mg tissue) is the primary nucleotide that contributes to the formation of eADPR. The tissue superfusates collected during EFS also contained the beta-NAD+ metabolite ADPR (0.35 +/- 0.2 fmol/mg tissue) but not cyclic ADPR (cADPR). HUB failed to degrade nicotinamide guanine dinucleotide (NGD+), a specific substrate of ADP ribosyl cyclase, suggesting that the activity of this enzyme in the HUB is negligible. The EFS-evoked release of beta-NAD+ was frequency dependent and is reduced in the presence of tetrodotoxin (TTX; 0.3 micromol/l), omega-conotoxin GVIA (50 nmol/l), and botulinum neurotoxin A (BoNT/A; 100 nmol/l), but remained unchanged in the presence of guanethidine (3 micromol/l), omega-agatoxin IVA (50 nmol/l), or charbachol (1 micromol/l). Capsaicin (10 micromol/l) increased both the resting and EFS-evoked overflow of beta-NAD+. Exogenous beta-NAD+ (1 micromol/l) reduced both the frequency and amplitude of spontaneous contractions. In conclusion, we detected nerve-evoked overflow of beta-NAD+ and ADPR in HUB. The beta-NAD(+)/ADPR system may constitute a novel inhibitory extracellular nucleotide mechanism of neural control of the human bladder.

Decreased phosphatase activity, increased Ca2+ sensitivity, and myosin light chain phosphorylation in urinary bladder smooth muscle of newborn mice

Developmental changes in the regulation of smooth muscle contraction were examined in urinary bladder smooth muscle from mice. Maximal active stress was lower in newborn tissue compared with adult, and it was correlated with a lower content of actin and myosin. Sensitivity to extracellular Ca²⁺ during high-K⁺ contraction, was higher in newborn compared with 3-wk-old and adult bladder strips. Concentrations at half maximal tension (EC₅₀) were 0.57 ± 0.01, 1.14 ± 0.12, and 1.31 ± 0.08 mM. Force of the newborn tissue was inhibited by ∼45% by the nonmuscle myosin inhibitor Blebbistatin, whereas adult tissue was not affected. The calcium sensitivity in newborn tissue was not affected by Blebbistatin, suggesting that nonmuscle myosin is not a primary cause for increased calcium sensitivity. The relation between intracellular [Ca²⁺] and force was shifted toward lower [Ca²⁺] in the newborn bladders. This increased Ca²⁺ sensitivity was also found in permeabilized muscles (EC₅₀: 6.10 ± 0.07, 5.77 ± 0.08, and 5.55 ± 0.02 pCa units, in newborn, 3-wk-old, and adult tissues). It was associated with an increased myosin light chain phosphorylation and a decreased rate of dephosphorylation. No difference was observed in the myosin light chain phosphorylation rate, whereas the rate of myosin light chain phosphatase–induced relaxation was about twofold slower in the newborn tissue. The decreased rate was associated with a lower expression of the phosphatase regulatory subunit MYPT-1 in newborn tissue. The results show that myosin light chain phosphatase activity can be developmentally regulated in mammalian urinary bladders. The resultant alterations in Ca²⁺ sensitivity may be of importance for the nervous and myogenic control of the newborn bladders.

Morphology and localization of interstitial cells in the guinea pig bladder: structural relationships with smooth muscle and neurons

PURPOSE

In the current study we examined the location of interstitial cell of Cajal (ICC)-like cells in the guinea pig bladder wall and studied their structural interactions with nerves and smooth muscle cells.

MATERIALS AND METHODS

Whole mount samples and cryosections of bladder tissue were labeled with primary and fluorescent secondary antibodies, and imaged using confocal and multiphoton microscopy.

RESULTS

Kit positive ICC-like cells were located below the urothelium, in the lamina propria region and throughout the detrusor. In the suburothelium they had a stellate morphology and appeared to network. They made connections with nerves, as shown by double labeling experiments with anti-kit and anti-protein gene product 9.5. A network of vimentin positive cells was also found, of which many but not all were kit positive. In the detrusor kit positive cells were most often seen at the edge of smooth muscle bundles. They were elongated with lateral branches, running in parallel with the bundles and closely associated with intramural nerves. Another population of kit positive cells was seen in the detrusor between muscle bundles. These cells had a more stellate-like morphology and made connections with each other. Kit positive cells were seen tracking nerve bundles and close to intramural ganglia. Vimentin positive cells were present in the detrusor, of which some were also kit positive.

CONCLUSIONS

There are several populations of ICC-like cells throughout the guinea pig bladder wall. They differ in morphology and orientation but all make connections with intramural nerves and in the detrusor they are closely associated with smooth muscle cells.

Trospium chloride in the management of overactive bladder

Trospium chloride is an orally active, quaternary ammonium compound with antimuscarinic activity. It binds specifically and with high affinity to muscarinic receptors M(1), M(2) and M(3), but not nicotinic, cholinergic receptors. It is hydrophilic and does not cross the normal blood-brain barrier in significant amounts and, therefore, has minimal central anticholinergic activity. Peak plasma trospium chloride concentrations are attained approximately 5-6 hours after oral administration, which should occur before meals as concurrent food ingestion significantly reduces trospium bioavailability. Trospium chloride undergoes negligible metabolism by the hepatic cytochrome P450 system; few metabolic drug interactions are known. While trospium chloride dosage adjustments based on age or sex appear unwarranted, such adjustments may be needed in patients with severe renal impairment. Direct comparative studies in patients with overactive bladder indicate that trospium chloride is at least as effective as oxybutynin and tolterodine. Placebo-controlled studies have also confirmed the efficacy of trospium chloride in terms of improved urodynamic parameters; small-scale, noncomparative studies have documented significant trospium chloride-induced improvements in patients with reflex neurogenic bladder, postoperative bladder irritation and radiation-induced cystitis; and observational studies including >10,000 patients have also revealed favourable findings for trospium chloride, including a marked decrease in incontinence episodes and substantial improvement in health-related quality of life. Trospium chloride is generally well tolerated, and significantly more so than immediate-release oxybutynin. The most frequent adverse events, occurring in >1% of trospium chloride-treated patients, are dry mouth, dyspepsia, constipation, abdominal pain and nausea. Available for many years in several countries outside North America, trospium chloride is likely to develop an important role in the management of overactive bladder following its approval in the US on 28 May 2004.

Loxoprofen inhibits facilitated micturition reflex induced by acetic acid urinary bladder infusion of the rats

Prostaglandins (PGs) are well known as one of the chemical mediators of inflammation. Nonsteroidal anti-inflammatory drugs (NSAIDs), PG synthesis inhibitors, are used for anti-nociception and/or anti-inflammation. We examine the effect of loxoprofen, an NSAID, on micturiton in acetic acid-induced bladder inflammation of the rats. In cystometrogram study with saline infusion into the urinary bladder, loxoprofen did not alter the interval of bladder contraction (IC, 107% of the control). IC was shortened by acetic acid infusion (65% of the control) and loxoprofen prolonged the IC (162% of acetic acid infused period). This prolonged IC was approximately same as the control. Loxoprofen did not alter the threshold pressure and the maximal voiding pressure. These data suggest that PGE2 might not play a part of normal micturition and may play a part of the micturition reflex during acetic acid infusion. That is, loxoprofen might be useful for pathological hyperreflex of the micturition.

Effect of periurethral denervation on smooth muscles of the lower urinary tract

OBJECTIVE

This study was undertaken to determine the effect of periurethral denervation on contractile function of the smooth muscle of the lower urinary tract of the female rat.

STUDY DESIGN

Periurethral nerve transection or sham operation was performed in 35 young female rats. Contractile function of the bladder dome and base was determined as a function of time after surgery. Statistical analysis was conducted by Student t test.

RESULTS

Periurethral denervation resulted in impaired contractile responses to electrical field stimulation in the bladder base (nerve-transected 45 +/- 11 g/cm 2 ; sham 84 +/- 10 g/cm 2 , P < .05) and dome (nerve-transected 179 +/- 16 g/cm 2 ; sham 334 +/- 29 g/cm 2 , P < .05) 2 weeks after nerve transection. The ability to respond to potassium chloride and the muscarinic agonist, carbachol, and the rates of contraction and relaxation, however, remained intact. Baseline phasic contractile activity was increased significantly in bladders from nerve-transected animals. Maximal field-stimulated contractions of the longitudinal urethra smooth muscle were not altered by periurethral denervation (sham 21 +/- 6 g/cm 2 , nerve-transected 19 +/- 5 g/cm 2 , P = .4). Compromised nerve-mediated contractions of the bladder dome and base improved significantly by 21 days.

CONCLUSION

Periurethral nerve transection results in transient impairment of neurogenic contractile responses in the bladder base and dome, though the intrinsic ability of the bladder to contract remains intact. This compromised response of the dome, in conjunction with previous results demonstrating impaired urethral smooth muscle relaxation, suggests that transection of periurethral neurons may have complex effects on the entire lower urinary tract.

Mechanisms of neurokinin A- and substance P-induced contractions in rat detrusor smooth musclein vitro

OBJECTIVE

To investigate the mechanisms of neurokinin A- and substance P-induced contractions of rat urinary bladder smooth muscle, and to compare them with those of the muscarinic agonist carbachol.

MATERIALS AND METHODS

Rat urinary bladder strips were suspended under 1 g of tension in a physiological buffer at 37 degrees C, gassed with 95% O(2)/5% CO(2). Mechanical activity was recorded isometrically during exposure to neurokinin A and substance P.

RESULTS

Both agents produced concentration-dependent contractions of smooth muscle strips which were unaffected by tetrodotoxin (1 micro mol/L), peptidase inhibitors (captopril, thiorphan and bestatin; 1 micro mol/L each) or piroxicam (10 micro mol/L). The rank order of potency of agonists was neurokinin A > substance P > carbachol. Contractile responses to neurokinin A and substance P, like the contractile responses to carbachol, were abolished in a nominally Ca(2+)-free medium and significantly reduced by nifedipine (1 micro mol/L). SKF-96365 (60 micro mol/L), an inhibitor of receptor-mediated Ca(2+) entry, abolished the nifedipine-resistant response to substance P and carbachol, and significantly attenuated the response to neurokinin A. Depleting intracellular Ca(2+) stores with thapsigargin (1 micro mol/L) significantly attenuated neurokinin A-induced contractions but had no effect on substance P- or carbachol- induced contractions. The Rho-kinase inhibitor, Y-27632 (10 micro mol/L), significantly reduced both phasic and tonic components of the contractile responses to neurokinin A, substance P and carbachol.

CONCLUSION

The contractile responses induced by tachykinins in rat urinary bladder smooth muscle strips involve a direct action on smooth muscle and are not modulated by peptidases or prostanoids. Neurokinin A and substance P, like carbachol-induced contractions, depend on extracellular Ca(2+) influx largely through voltage-operated and partly through receptor-operated Ca(2+) channels. Intracellular Ca(2+) release contributes to the contractile response to neurokinin A but appears to have no involvement in substance P- and carbachol-induced contractions. Rho-kinase activation contributes to contractions induced by substance P, neurokinin A and carbachol.

The role of the rhabdosphincter in female rat voiding

OBJECTIVES

To obtain information on the mechanisms of female rat micturition using a model in which pressure was measured in the bladder and distal part of the urethra corresponding to the location of the rhabdosphincter, providing information on the role of the sphincter in opening and closing the urethral lumen.

MATERIALS AND METHODS

A micturition reflex was induced in adult anaesthetized (chloral hydrate and urethane) female rats by filling the bladder with saline. Bladder pressure (BP), urethral pressure (UP), electromyography (EMG) of the middle part of the rhabdosphincter, and urinary flow rate in the distal urethra were simultaneously recorded.

RESULTS

There were four phases of the micturition contraction, the second characterized by intraluminal pressure high-frequency oscillations (IPHFOs) of BP. When a non-oscillatory micturition contraction started, the BP increased and exceeded UP for the rest of the micturition contraction. Even though the BP increased during this first phase, the urethral lumen stayed closed. Its opening was indicated by a simultaneous decrease in BP and increase of UP as the fluid flowed from the bladder to the urethra. When the rhabdosphincter closed, as indicated by an EMG-burst of the muscle, the UP declined, bladder pressure increased and the flow ceased. Because of momentary contractions of the rhabdosphincter, the UP and urine flow rate had the same periodicity as the IPHFOs of BP.

CONCLUSIONS

The simultaneous recording of the BP, UP, EMG of the rhabdosphincter and urinary flow rate showed the sequence of events during micturition. The rhabdosphincter acts as an 'on-off' switch, causing interruptions in the urinary flow rate.

Many diseases may reflect dysfunctions of autonomic balance attributable to evolutionary displacement

We hypothesize that many ailments are attributable to dysfunctions of autonomic balance. The autonomic system is a primitive, highly-adaptive response system that allows differential allocation of biologic effort under varying conditions. The autonomic system, however, can execute a response that is inappropriate for the system stressor due to evolutionary displacement. Evolutionary displacement is a situation in which a trait that evolved as an adaptive response to certain conditions now faces a new set of conditions. Modern human evolution since the Pleistocene era is characterized by substantial evolutionary displacement, brought on in large part by the accelerating ability of humans to change their own environment. In the setting of evolutionary displacement, previously adaptive systems such as the autonomic system can be rendered unhelpful or even counterproductive. Emergence of chronic conditions, maladaptation of the trauma response, and extension of human lifespan are examples of evolutionary displacements that can induce inappropriate sympathetic bias in hosts. We postulate that many diseases are manifestations of this general phenomenon. Implications for existing and future therapeutic strategies are discussed.

Conditions of aging as manifestations of sympathetic bias unmasked by loss of parasympathetic function

We propose a unifying hypothesis that many clinical consequences of aging are pleiotropic manifestations of the loss of parasympathetic function that occurs during post-reproductive senescence. The loss of parasympathetic function unmasks the baseline sympathetic bias inherent in the end-organs, resulting in the familiar signs of aging including tachycardia, constipation, insomnia, erectile dysfunction, fluid retention, and systemic inflammation. These consequences in turn may contribute to many of the common diseases associated with aging including type-2 diabetes, Alzheimer's, atherosclerosis, and cancer. Maintenance and restoration of parasympathetic function may enable upstream control over the deleterious aspects of inherent end-organ adrenergic bias.

The autonomous bladder: a view of the origin of bladder overactivity and sensory urge

Incontinence and the generation of excessive sensory urges are common problems that can seriously influence the quality of life of both men and women. The underlying causes have in some instances been associated with uncontrolled bladder activity. However, the mechanisms generating such activity are still poorly understood and pharmacological tools to control it remain relatively ineffective. There are no effective treatments for bladder overactivity possibly because the bladder mechanisms are not understand or targeted. The purpose of this short review is to raise questions and re-visit ideas from some older possibly forgotten and neglected publications, but which may shed new light on this problem.

Role of Capsaicin-Sensitive Nerve Fibers in Uterine Contractility in the Rat1

The possible participation of capsaicin-sensitive sensory nerves in the modulation of neurogenic contractions was studied in nonpregnant and term pregnant rat uteri. Neurogenic contractions were elicited by electric field stimulation (40 V, 1-70 Hz, 0.6 msec) in intact uteri and uteri that were previously exposed to capsaicin in vitro. In capsaicin pretreated preparations obtained both from nonpregnant and term pregnant rats, a dose-dependent increase in the amplitude of uterine contractions was detected. Prior systemic treatment of the rats with capsaicin (130 mg/kg, s.c.) abolished the effect of in vitro capsaicin administration on the amplitude of neurogenic contractions. Use of a specific antagonist of calcitonin gene-related peptide revealed that depletion of this peptide, which normally elicits uterine smooth muscle relaxation, may be responsible for the increased responsiveness of the uterus to low-frequency stimulation. Experiments on the localization of calcitonin gene-related peptide in uterine tissue specimens exposed to capsaicin revealed dose-dependent depletion of calcitonin-gene related peptide-immunoreactive nerves innervating blood vessels and the myometrium. The findings indicate that capsaicin-sensitive afferent nerves, by the release of sensory neuropeptides, significantly contribute to the modulation of uterine contractility both in nonpregnant and term pregnant rats. It is suggested that uterine sensory nerve activation may be part of a trigger mechanism leading to preterm contractions evoked by, for example, inflammation.