Atropine blockade of nerve-mediated stimulation of the human detrusor

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.

Inhibition of Female and Male Human Detrusor Smooth Muscle Contraction by the Rac Inhibitors EHT1864 and NSC23766

Introduction

Lower urinary tract symptoms (LUTS) due to overactive bladder (OAB) are caused by spontaneous detrusor contractions. Medical treatment with muscarinic receptor antagonists or β₃-adrenoceptor agonists aims to inhibit detrusor contractions, but overall results are unsatisfactory. Consequently, improved understanding of bladder smooth muscle contraction and identification of novel compounds for its inhibition are needed to develop alternative options. A role of the GTPase Rac1 for smooth muscle contraction has been reported from the prostate, but is unknown in the human detrusor. Here, we examined effects of the Rac inhibitors NSC23766, which may also antagonize muscarinic receptors, and EHT1864 on contraction of human detrusor tissues.

Methods

Female and male human detrusor tissues were obtained from radical cystectomy. Effects of NSC23766 (100 µM) and EHT1864 (100 µM) on detrusor contractions were studied in an organ bath.

Results

Electric field stimulation induced frequency-dependent contractions of detrusor tissues, which were inhibited by NSC23766 and EHT1864. Carbachol induced concentration-dependent contractions. Concentration response curves for carbachol were shifted to the right by NSC23766, reflected by increased EC₅₀ values, but unchanged E_max values. EHT1864 reduced carbachol-induced contractions, resulting in reduced E_max values for carbachol. The thromboxane analog U46619 induced concentration-dependent contractions, which remained unchanged by NSC23766, but were reduced by EHT1864.

Conclusions

NSC23766 and EHT1864 inhibit female and male human detrusor contractions. NSC23766, but not EHT1864 competitively antagonizes muscarinic receptors. In addition to neurogenic and cholinergic contractions, EHT1864 inhibits thromboxane A₂-induced detrusor contractions. The latter may be promising, as the origin of spontaneous detrusor contractions in OAB is noncholinergic. In vivo, both compounds may improve OAB-related LUTS.

Purinergic signalling in the urinary tract in health and disease

Purinergic signalling is involved in a number of physiological and pathophysiological activities in the lower urinary tract. In the bladder of laboratory animals there is parasympathetic excitatory cotransmission with the purinergic and cholinergic components being approximately equal, acting via P2X1 and muscarinic receptors, respectively. Purinergic mechanosensory transduction occurs where ATP, released from urothelial cells during distension of bladder and ureter, acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex, via low threshold fibres, and nociception, via high threshold fibres. In human bladder the purinergic component of parasympathetic cotransmission is less than 3 %, but in pathological conditions, such as interstitial cystitis, obstructed and neuropathic bladder, the purinergic component is increased to 40 %. Other pathological conditions of the bladder have been shown to involve purinoceptor-mediated activities, including multiple sclerosis, ischaemia, diabetes, cancer and bacterial infections. In the ureter, P2X7 receptors have been implicated in inflammation and fibrosis. Purinergic therapeutic strategies are being explored that hopefully will be developed and bring benefit and relief to many patients with urinary tract disorders.

Muscarinic agonists and antagonists: effects on the urinary bladder

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

Urinary incontinence: classification and pharmacological therapy

Pharmacological therapy has been developed which can have significant impact in the management of many forms of urinary incontinence and voiding dysfunction. In general the clinical laboratory studies which have supported or challenged the efficacy of many of the commonly prescribed drugs for voiding dysfunction are often difficult to interpret and contradictory. The available clinical studies often do not demonstrate a lack of bias. Nor do they include an adequate number of subjects, use appropriate and sensitive methods of evaluation, employ double-blind placebo-controlled design, or appear statistically valid. Although the contribution of laboratory research has been of unquestionable value in the development of our current knowledge of lower urinary tract pharmacology it is difficult to interpret the results of in vitro pharmacological studies because of the array of experimental models used and the need to extrapolate to in vivo activity. This paper utilizes a functional scheme which classifies agents by their effects on urinary storage and emptying. The purpose of this review is to promote discussion of the application of uropharmacological investigation to the development of newer, more efficacious forms of drug therapy.

Aging impairs neurogenic contraction in guinea pig urinary bladder: role of oxidative stress and melatonin

The incidence of urinary bladder disturbances increases with age, and free radical accumulation has been proposed as a causal factor. Here we investigated the association between changes in bladder neuromuscular function and oxidative stress in aging and the possible benefits of melatonin treatment. Neuromuscular function was assessed by electrical field stimulation (EFS) of isolated guinea pig detrusor strips from adult and aged female guinea pigs. A group of adult and aged animals were treated with 2.5 mg·kg−1·day−1 melatonin for 28 days. Neurotransmitter blockers were used to dissect pharmacologically the EFS-elicited contractile response. EFS induced a neurogenic and frequency-dependent contraction that was impaired by aging. This impairment is in part related to a decrease in detrusor myogenic contractility. Age also decreased the sensitivity of the contraction to pharmacological blockade of purinergic and sensitive fibers but increased the effect of blockade of nitrergic and adrenergic nerves. The density of cholinergic and nitrergic nerves remained unaltered, but aging modified afferent fibers. These changes were associated with an increased level of markers for oxidative stress. Melatonin treatment normalized oxidative levels and counteracted the aging-associated changes in bladder neuromuscular function. In conclusion, these results show that aging modifies neurogenic contraction and the functional profile of the urinary bladder plexus and simultaneously increases the oxidative damage to the organ. Melatonin reduces oxidative stress and improves the age-induced changes in bladder neuromuscular function, which could be of importance in reducing the impact of age-related bladder disorders.

In vitro characterization of parasympathetic and sympathetic responses in cyclophosphamide-induced cystitis in the rat

In cyclophosphamide-induced cystitis in the rat, detrusor function is impaired and the expression and effects of muscarinic receptors altered. Whether or not the neuronal transmission may be affected by cystitis was presently investigated. Responses of urinary strip preparations from control and cyclophosphamide-pretreated rats to electrical field stimulation and to agonists were assessed in the absence and presence of muscarinic, adrenergic and purinergic receptor antagonists. Generally, atropine reduced contractions, but in contrast to controls, it also reduced responses to low electrical field stimulation intensity (1-5 Hz) in inflamed preparations. In both types, purinoceptor desensitization with alpha,beta-methylene adenosine-5'-triphosphate (alpha,beta-meATP) caused further reductions at low frequencies (<10 Hz). The muscarinic receptor antagonists atropine, 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) ('M(1)/M(3)/M(5)-selective'), methoctramine ('M(2)-selective') and pirenzepine ('M(1)-selective') antagonized the tonic component of the electrical field stimulation-evoked contractile response more potently than the phasic component. 4-DAMP inhibited the tonic contractions in controls more potently than methoctramine and pirenzepine. In inflamed preparations, the muscarinic receptor antagonism on the phasic component of the electrical field stimulation-evoked contraction was decreased and the pirenzepine and 4-DAMP antagonism on the tonic component was much less efficient than in controls. In contrast to controls, methoctramine increased -- instead of decreased -- the tonic responses at high frequencies. While contractions to carbachol and ATP were the same in inflamed and in control strips when related to a reference potassium response, isoprenaline-induced relaxations were smaller in inflamed strips. Thus, in cystitis substantial changes of the efferent functional responses occur. While postjunctional beta-adrenoceptor-mediated relaxations are reduced, effects by prejunctional inhibitory muscarinic receptors may be increased.

A standardised mini pig model for in vivo investigations of anticholinergic effects on bladder function and salivation

PURPOSE

The objective was to validate an in vivo model for evaluation of pharmacological effects on bladder function taking the most predominant anticholinergic side effect (hyposalivation) into account. Therefore, two anticholinergic properties (propiverine hydrochloride and tolterodine-L(+)-tartrate) were used to test the in vivo model. Sacral anterior root stimulation (SARS) was performed to induce reproducible and standardized bladder contractions. To evaluate hyposalivation standardised salivavary flow measurements by stimulating the lingual nerve was performed in addition to SARS.

MATERIALS AND METHODS

10 male mini pigs were anaesthetised. The carotid artery was cannulated for blood pressure measurement and the jugular vein for administration of propiverine 0.4 mg kg(-1) b.w. and tolterodine 0.06 mg kg(-1) b.w. For stimulation-induced salivary flow measurements both lingual nerves were exposed and a cuff electrode was placed around the nerves. The bladder was exposed and a cystostomy catheter was inserted to performed cystometrographic measurements during SARS.

RESULTS

In all experiments, for each animal reproducible intravesical pressure values (pves) and salivary flow rates were elicited during electrostimulation before administration of the drug. Bladder pressure: After administration of propiverine, neurostimulation-induced rise in pves had fallen by 60% from the initial value. After administration of tolterodine pves had fallen by about 50%. After additional administration of atropine pves decreased to about 15% of the initial value for both drugs. Salivation: After propiverine salivary flow had fallen by 61%. Inhibition of salivary flow under tolterodine was about 56%. Additional administration of atropine led in both drugs to a nearly complete blockade of salivation. Heart rate (HR) and blood pressure (BP): Directly following intravenous administration of both drugs, a short-term and reversible period of mild but significant fluctuations in HR was observed. There was also a slight but non-significant rise in blood pressure.

CONCLUSIONS

This model allows comparative investigations of various drugs with bladder inhibitory properties in terms of acute efficacy and side effects.

Purinoceptors as therapeutic targets for lower urinary tract dysfunction

Lower urinary tract symptoms (LUTS) are present in many common urological syndromes. However, their current suboptimal management by muscarinic and alpha(1)-adrenoceptor antagonists leaves a significant opportunity for the discovery and development of superior medicines. As potential targets for such therapeutics, purinoceptors have emerged over the last two decades from investigations that have established a prominent role for ATP in the regulation of urinary bladder function under normal and pathophysiological conditions. In particular, evidence suggests that ATP signaling via P2X(1) receptors participates in the efferent control of detrusor smooth muscle excitability, and that this function may be heightened in disease and aging. ATP also appears to be involved in bladder sensation, via activation of P2X(3) and P2X(2/3) receptors on sensory afferent neurons, both within the bladder itself and possibly at central synapses. Such findings are based on results from classical pharmacological and localization studies in non-human and human tissues, knockout mice, and studies using recently identified pharmacological antagonists--some of which possess attributes that offer the potential for optimization into candidate drug molecules. Based on recent advances in this field, it is clearly possible that the development of selective antagonists for these receptors will occur that could lead to therapies offering better relief of sensory and motor symptoms for patients, while minimizing the systemic side effects that limit current medicines.

Decreased expression of G protein-coupled receptor kinases in the detrusor smooth muscle of human urinary bladder with outlet obstruction

AIM

We examine the expression of mRNA of G protein-coupled receptor kinase (GRK) subtypes and muscarinic acetylcholine receptor (M) subtypes in the detrusor smooth muscle of the human urinary bladder. Furthermore, we confirm the presence and the localization of GRK proteins in the detrusor smooth muscle of the obstructed bladder in comparison with the control bladder.

METHODS

Detrusor smooth muscle tissues of the human urinary bladder were obtained from 12 male patients; 6 patients did not have bladder outlet obstruction, and the other 6 patients had bladder outlet obstruction. Portions of the dome or anterior wall of the urinary bladder were used for the present study. Reverse transcription/polymerase chain reaction for GRK2, M2 and M3 was performed using total RNA extracted from human urinary bladder detrusor. Antibodies to GRK2, GRK3 and GRK4 were used to confirm the presence of the protein product in the human urinary bladder using immunohistochemical staining and the western blotting technique.

RESULTS

All complementary DNA (cDNA) transcribed from three different mRNA (M2, M3 and GRK2) were successfully amplified and size-fractionated. The expression of GRK2 protein was strong in the human bladder detrusor, but was significantly weakened by western blotting in obstructed bladder in comparison with control bladder.

CONCLUSIONS

Failure in desensitization mechanisms of muscarinic acetylcholine receptors might be related to storage symptom elicited by overactivity in obstructed bladder with benign prostatic hyperplasia.

Distribution of neuropeptide Y-containing nerves in the neurogenic and non-neurogenic detrusor

OBJECTIVE

To evaluate the role of neuropeptide Y in the detrusor of patients with neurogenic detrusor overactivity (NDO), as it has an important role in the neural regulation of the lower urinary tract by exerting differential effects on the release of cholinergic and adrenergic transmitters via autoinhibition and heterosynaptic interactions.

MATERIALS AND METHODS

Detrusor biopsies were obtained from 38 patients; 31 had video-urodynamically verified NDO, caused by meningomyelocele in 17 or spinal cord injury in 14. Seven had stress urinary incontinence (SUI) and this group served as a control. All specimens were fixed, paraffin wax-embedded, sectioned and stained with a monoclonal antibody against neuropeptide Y and a general nerve marker protein-gene-product 9.5 (PGP 9.5). The number of PGP 9.5- and neuropeptide Y-containing nerves was quantified by a standardized evaluation using image-analysis software.

RESULTS

The median (range) number of neuropeptide Y-containing nerves in the neurogenic detrusor, at 0.273 (0.126-0.639) per muscle cell nucleus (MCN), was significantly lower (P = 0.014) than that in patients with SUI, at 0.383 (0.267-0.728). In the neurogenic detrusor the number of PGP 9.5-positive nerves, at 0.278 (0.054-0.641)/MCN was also lower (P = 0.111) than in patients with SUI, at 0.368 (0.258-0.497). The ratio of neuropeptide Y to PGP 9.5 counts per biopsy did not differ between the groups (P = 0.628).

CONCLUSIONS

The number of PGP 9.5-positive nerves was not significantly and the number of neuropeptide Y-containing nerves was significantly reduced in patients with NDO. This may have been caused by transynaptic nerve degeneration of the detrusor, as described by in patients with spinal cord injury. As neuropeptide Y inhibits the contractile response of the detrusor the reduction of neuropeptide Y-containing nerves may play a role in the development and persistence of DO.

A Role for the P2X Receptor in Urinary Tract Physiology and in the Pathophysiology of Urinary Dysfunction

OBJECTIVE

We provide a historical perspective of the P2X receptor class in bladder physiology and the pathophysiology of urinary dysfunction.

METHODS

A literature search was performed using the MEDLINE database.

RESULTS

Evidence suggests that P2X receptors serve a combined function in sensory and motor activity of human bladder. P2X receptors mediate excitation of sensory neurons and evoke muscle contraction in response to ATP release. Anatomical and functional defects in the P2X receptor signaling are associated with a variety of urologic diseases.

CONCLUSION

Current research underscores the importance of P2X receptors in urologic physiology. Potential applications exist in relation to the diagnosis and treatment of urinary dysfunction. However, the detailed mechanism of P2X receptor function in bladder physiology and in urinary tract disease remains unknown and warrants further investigation.

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

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

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.

The tachykinin NK-2 receptor antagonist SR48968 does not block noncholinergic contractions in unstable human bladder

Concentration-response curves to acetylcholine, and responses to electrical field stimulation (EFS) were compared in detrusor muscle strips, from control patients and those with idiopathic detrusor instability (IDI). Responses were similar in both groups. However, atropine abolished responses to EFS in 80% of control but only 33% of IDI patients (P>0.05), with the residual atropine-resistant response in most IDI patients abolished by tetrodotoxin. The post-atropine residual response was unaffected by the tachykinin NK-2 receptor antagonist SR48968. Despite the known existence of NK-2 receptors in the human detrusor, there was no evidence for tachykinin contribution to EFS-induced contractions.

P2X receptors and their role in female idiopathic detrusor instability

PURPOSE

It is clear from previous studies that adenosine triphosphate is released as a contractile co-transmitter with acetylcholine from parasympathetic nerves supplying the mammalian bladder but the physiological significance of ligand gated purinergic P2X receptors in human bladder innervation has not been adequately investigated. We examined the role of these receptors in female patients with idiopathic detrusor instability.

MATERIALS AND METHODS

Female patients with idiopathic detrusor instability were recruited for cystoscopy and bladder biopsy with ethics approval. Control tissue was obtained from age and sex matched patients with a urodynamically proved stable bladder. We obtained 4 bladder biopsies per patient from the posterior wall. Samples were analyzed in an organ bath for functional studies of the detrusor muscle to assess the purinergic contribution to its contraction. In addition, we performed quantitative analysis using reverse transcriptase-polymerase chain reaction and immunohistochemical localization of P2X receptors.

RESULTS

In patients with idiopathic detrusor instability detrusor P2X2 receptors were significantly elevated, while other P2X receptor subtypes were significantly decreased. A purinergic component of nerve mediated contractions was not detected in control female bladder biopsy specimens but there was a significant component in unstable bladder specimens. It was particularly prominent at stimulation frequencies of 2 to 16 Hz. which are likely to be most relevant physiologically. Approximately 50% of nerve mediated contractions were purinergic in idiopathic detrusor instability cases.

CONCLUSIONS

In patients with idiopathic detrusor instability there is abnormal purinergic transmission in the bladder, which may explain symptoms. This pathway may be a novel target for the pharmacological treatment of overactive bladder.

The minor population of M3-receptors mediate contraction of human detrusor muscle in vitro

1 The objective was to determine the role of muscarinic receptor subtypes in mediating contraction of the human detrusor smooth muscle in vitro. 2 Contractile responses of human detrusor muscle strips to carbachol were obtained in the absence and presence of a range of muscarinic antagonists (pirenzepine, methoctramine, 4-diphenylacetoxy-N-methyl piperidine methiodide (4-DAMP), tropicamide, oxybutynin and tolterodine). Affinity estimates (pKB values) were calculated for the antagonists and correlated with values at the cloned muscarinic receptor subtypes quoted in the literature. 3 Pirenzepine, methoctramine and tropicamide drugs that have high affinities at M1, M2 and M4-receptors, respectively, all had low affinities on the human detrusor (pKB values of 6.8, 6.9 and 6.5, respectively), whilst the M3-selective antagonist 4-DAMP had a high affinity (9.5). Schild plots for all four antagonists had slopes of unity indicating an action at a single receptor. Oxybutynin and tolterodine also acted as competitive antagonists with affinity estimates of 7.6 and 8.1, respectively. 4 When the antagonist affinities obtained on the bladder were plotted against the values published for these antagonists at the cloned muscarinic receptor subtypes, the best correlations were obtained for the m3- and m5-muscarinic receptor subtypes. 5 These data suggest that direct contractile responses of the human detrusor muscle to muscarinic receptor stimulation in vitro are mediated solely via the M3-muscarinic receptor subtype with no contribution from the major M2-receptor population.

Age-related changes in cholinergic and purinergic neurotransmission in human isolated bladder smooth muscles

We evaluated the correlation among age, cholinergic and purinergic neurotransmissions in the electrical field stimulation-induced contractions in human isolated urinary bladder smooth muscles, using the muscle bath technique. Human bladder specimens were divided into three groups (G1, under 50years; G2, 51-70years; G3, over 70years old), and each muscle strip was suspended in a thermostatically controlled organ bath filled with oxygenated Krebs-Henseleit solution, connected to an isometric force displacement transducer, and an isometric tension development was recorded. The contractile responses induced by KCl, carbachol, adenosine triphosphate (ATP) and electrical field stimulation, and the effects of atropine and alpha, beta methylene ATP on electrical field stimulation-induced contractions were observed. The contractile response to KCl and concentration-response curves for carbachol and ATP, and frequency-response curves for electrical field stimulation were not significantly different among the three groups. The atropine sensitive and resistant parts of contraction induced by electrical field stimulation were decreased and increased with age, respectively. There are significant positive and negative correlations between age and the purinergic, and age and the cholinergic neurotransmissions in human isolated bladder smooth muscles, respectively. The age-related changes in neurotransmissions may contribute to the changes in bladder function in the elderly.

P2X receptor expression in mouse urinary bladder and the requirement of P2X(1) receptors for functional P2X receptor responses in the mouse urinary bladder smooth muscle

1. We have used subtype selective P2X receptor antibodies to determine the expression of P2X(1 - 7) receptor subunits in the mouse urinary bladder. In addition we have compared P2X receptor mediated responses in normal and P2X(1) receptor deficient mice to determine the contribution of the P2X(1) receptor to the mouse bladder smooth muscle P2X receptor phenotype. 2. P2X(1) receptor immunoreactivity was restricted to smooth muscle of the bladder and arteries and was predominantly associated with the extracellular membrane. Diffuse P2X(2) and P2X(4) receptor immunoreactivity not associated with the extracellular membrane was detected in the smooth muscle and epithelial layers. Immunoreactivity for the P2X(7) receptor was associated with the innermost epithelial layers and some diffuse staining was seen in the smooth muscle layer. P2X(3), P2X(5) and P2X(6) receptor immunoreactivity was not detected. 3. P2X receptor mediated inward currents and contractions were abolished in bladder smooth muscle from P2X(1) receptor deficient mice. In normal bladder nerve stimulation evoked contractions with P2X and muscarinic acetylcholine (mACh) receptor mediated components. In bladder from the P2X(1) receptor deficient mouse the contraction was mediated solely by mACh receptors. Contractions to carbachol were unaffected in P2X(1) receptor deficient mice demonstrating that there had been no compensatory effect on mACh receptors. 4. These results indicate that homomeric P2X(1) receptors underlie the bladder smooth muscle P2X receptor phenotype and suggest that mouse bladder from P2X(1) receptor deficient and normal animals may be models of human bladder function in normal and diseased states.

Structural and functional denervation of human detrusor after spinal cord injury

The bladder receives an extensive nerve supply that is predominantly cholinergic, but several putative transmitters are present, some of which are colocalized. Previous studies have shown increased levels of sensory nerves, reduced inhibitory transmitters, and structural and functional changes in the excitatory input in unstable bladder conditions. The present study compared the end-organ nerve supply to the bladder in spinal cord injury (SCI) with uninjured controls. Acetylcholinesterase histochemistry and double-label immunofluorescence were used to investigate neurotransmitter content, with confocal laser scanning microscopy to assess colocalization. Organ bath studies provided functional correlates for the structural changes in the excitatory innervation. Control samples had dense innervation of the detrusor containing a diverse range of transmitters. Hyperreflexic SCI samples showed patchy denervation, and areflexic SCI samples were diffusely denervated. Vasoactive intestinal polypeptide-, neuropeptide Y-, neuronal nitric oxide synthase-, and galanin-immunoreactive nerve fibers were reduced from frequent or moderately frequent to infrequent or very infrequent in SCI. Calcitonin gene-related peptide-immunoreactive fibers were infrequent in controls and SCI samples. Patterns of colocalization were unchanged, but significantly fewer fibers expressed more than one transmitter. The subepithelial plexus was markedly reduced and several of the smaller coarse nerve trunks showed no immunoreactivity to the transmitters assessed. There was no reduction in sensitivity to electrical field stimulation of intrinsic nerves in SCI, but the maximum force generated by each milligram of bladder tissue and the peak force as a proportion of the maximum carbachol contraction were significantly reduced and the responses were protracted. There was no significant functional atropine-resistant neuromuscular transmission in controls or SCI. The reported findings have clinical implications in the management of chronic SCI and development of new treatments.

Simultaneous recording of mechanical and intracellular electrical activity in human urinary bladder smooth muscle

OBJECTIVE

To elucidate the role of the membrane potential in human detrusor smooth muscle contraction, by simultaneously recording mechanical and intracellular electrical activity in muscle strips. Materials and methods The agonists acetylcholine and carbachol were applied to induce a contraction on muscarinic receptor stimulation; to block the response, atropine was added to the bath. The Ca2+ necessary for activating the contractile machinery can be recruited via two pathways: release from intracellular stores or influx from the extracellular matrix. High potassium was applied to induce Ca2+ influx through voltage-sensitive Ca2+ channels.

RESULTS

There were significant changes in the force when agonist, antagonist and high potassium was administered. However, there were significant changes in membrane potential only when KCl was applied to the bath and not with muscarinic agonist or antagonist application. Activity in the form of spike potentials did not change significantly on applying any of the test substances.

CONCLUSION

The present results indicate that the Ca2+ mobilized on M3 receptor stimulation originates primarily from intracellular stores, with no systematic changes in membrane potential. Atropine only caused a relaxation in muscle previously contracted by M3-receptor agonist stimulation; it had no effect on relaxed muscle strips.

Inhibition of the contractile response of the rat detrusor muscle by the beta(2)-adrenoceptor agonist clenbuterol

The action of clenbuterol, beta(2)-adrenoceptor agonist, on the contractile response of isolated rat detrusor muscle strips was investigated in vitro. Clenbuterol (10(-5) M) inhibited the detrusor muscle frequency response (1-40 Hz, p<0.02) with a more pronounced effect at 1 Hz than 40 Hz. Clenbuterol (10(-6) M) significantly inhibited the contractile response to exogenous ATP (10(-4) to 10(-2) M, p<0.05) but not to carbachol (10(-9) to 10(-4) M). The presence of 10(-5) M ICI 118, 551, beta(2)-adrenoceptor antagonist, shifted significantly the clenbuterol dose-response to 1 Hz electrical field stimulation (EC(50) 3.4x10(-6) M (+/-2.2x10(-6) M) for clenbuterol alone, to 4.1x10(-4) M (+/-8.8 x10(-5) M), P<0.05). In conclusion, clenbuterol inhibits electrical field and ATP-stimulated contractions of detrusor muscle. Reversal of the clenbuterol inhibition of detrusor muscle contraction by ICI 118, 551 shows that clenbuterol is probably acting through postsynaptic beta(2)-adrenoceptors, which modulate the response to ATP released from purinergic nerves.

Intracellular recording of spontaneous electrical activity in human urinary bladder smooth muscle strips

We studied the spontaneous electrical activity of human urinary bladder smooth muscle strips, with the eventual aim of uncovering the mechanism underlying the clinical syndrome of the unstable bladder. Intracellular microelectrodes were used to record the membrane potentials of detrusor cells in muscle bundles originating from biopsy samples. Spontaneous spike-shaped potential fluctuations were analysed automatically. The membrane potential at the start of the potential change (V(start)), amplitude, duration at 10% of the amplitude (d(10%)), and upstroke velocity (DeltaV/Deltat) were estimated and statistically analysed. The mean resting membrane potential of the detrusor strip cells was -42 mV (SD: 9 mV). Different types of spontaneous activity could be recorded. On successive impalements within one preparation, the type of activity varied from one single spike-shaped potential to extensive bursts and was not correlated to the resting membrane potential. There was a large variation in size and shape of the spike-shaped potentials between the biopsy samples and even within one cell. The results provide the first description of spontaneous electrical activity in human detrusor smooth muscle strips. This activity is asynchronous, which could aid to maintain a low pressure in the bladder. Most likely, this spontaneous detrusor activity is myogenic in origin.

Evidence for purinergic neurotransmission in the urinary bladder of pithed rats

The purpose of this study was to investigate the contribution of adenosine-5'-triphosphate (ATP) to segmental (L6-S2) spinal electrical stimulation evoked increases in intra-vesical pressure in pithed rats. Exogenous ATP and substance P produced dose-dependent increases in intra-vesical pressure (ED10 mmHg (dose required to elicit 10 mmHg increase in intra-vesical pressure)= 1.7 mg/kg and 1.1 microg/kg, i.v., respectively). Desensitisation (or antagonism) of P2x purinoceptors with alpha,beta-methylene ATP (alpha,beta-meATP; 30 microg/kg per min, i.v.) or pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 10 mg/kg, i.v.) significantly (p < 0.05) antagonized the intra-vesical pressure responses to ATP (> 8 and 3.6-fold increase in ED10 mmHg, respectively) but had no significant effect on intra-vesical pressure responses to substance P. Spinal stimulation evoked frequency-dependent increases in intra-vesical pressure (EF20 mmHg (frequency required to produce 20 mmHg increase in intra-vesical pressure) = 3.4 Hz). Blockade of muscarinic cholinoceptors and adrenoceptors with atropine (3 mg/kg, i.v.), propranolol (3 mg/kg, i.v.) and phentolamine (10 mg/kg, i.v.) produced marginal attenuation of the intra-vesical pressure responses to spinal stimulation indicating a major non-adrenergic non-cholinergic (NANC) component in the overall response. The NANC responses were significantly (p < 0.05) antagonized by alpha,beta-meATP (30 microg/kg per min, i.v.) and PPADS (10 mg/kg, i.v.) (> 2.6-fold increase in EF20 mmHg), consistent with involvement of a purinergic neurotransmitter, presumably ATP. Comparative studies in young (4-6 months) and old (21-23 months) Fischer rats revealed no age-dependent changes in the relative contribution of the cholinergic and purinergic systems, with the latter being the dominant one. These findings suggest that purinergic neurotransmission, presumably mediated by ATP acting via P2x purinoceptors, represents a major component of excitatory innervation to the urinary bladder in pithed rats.

Pharmacologic actions of temiverine (p-INN) and its active metabolite, RCC-36, on isolated human urinary bladder muscle

BACKGROUND

Temiverine (p-INN) is a newly synthesized drug that is expected to have anticholinergic action. We investigated the pharmacologic actions of temiverine and its active metabolite, RCC-36, on isolated human bladder.

METHODS

Effects of temiverine and RCC-36 on the detrusor contractions induced by acetylcholine, potassium chloride (KCl), calcium chloride (CaCl2), and electric field stimulation were evaluated using the muscle-bath technique, and compared with the effects of atropine and oxybutynin.

RESULTS

Atropine (10(-9) to 10(-6) mol/L), oxybutynin (10(-8) to 10(-5) mol/L), temiverine (10(-8) to 10(-5) mol/L), and RCC-36 (10(-8) to 3 x 10(-6) mol/L) caused a parallel shift to the right of the concentration-response curves to acetylcholine stimulation. The rank order of pA2 value was atropine > oxybutynin = RCC-36 > temiverine. Atropine did not suppress the maximum contractile response to acetylcholine, but the other drugs significantly suppressed this at the higher concentrations. Each drug caused a concentration-dependent inhibition of KCl (80 mmol/L)-, and CaCl2 (5 mmol/L)-induced contractile responses. Rank order of maximum inhibition was RCC-36 = temiverine > oxybutynin > atropine. Each drug caused a concentration-dependent inhibition of electric field-induced contraction with or without 10(-6) mol/L atropine pretreatment. Maximum inhibitions of temiverine and RCC-36 were significantly greater than that of oxybutynin.

CONCLUSION

Atropine, oxybutynin, temiverine, and RCC-36 have different efficacies and potencies of anticholinergic and calcium antagonistic activity on isolated human detrusor muscles. Furthermore, temiverine and RCC-36 have significant inhibitory actions toward the atropine-resistant part of contractions, which may be related to the calcium antagonistic actions of these compounds.

Smooth muscle of the bladder in the normal and the diseased state: pathophysiology, diagnosis and treatment

The smooth muscle of the normal bladder wall must have some specific properties. It must be very compliant and able to reorganise itself during filling and emptying to accommodate the change in volume without generating any intravesical pressure, but whilst maintaining the normal shape of the bladder. It must be capable of synchronous activation to generate intravesical pressure at any length to allow voiding. The cells achieve this through spontaneous electrical activity combined with poor electrical coupling between cells, and a dense excitatory innervation. In the diseased state, alterations of the smooth muscle may lead to failure to store or failure to empty properly. The diseased states discussed are bladder instability and diabetic neuropathy. Bladder instability is characterised urodynamically by uninhibitable rises in pressure during filling, and is seen idiopathically and in association with bladder outflow obstruction and neuropathy. In diabetic neuropathy, many of the smooth muscle changes are a consequence of diuresis, but there is evidence for alterations in the sensory arm of the micturition reflex. In the unstable bladder, additional alterations of the smooth muscle are seen, which are probably caused by the patchy denervation that occurs. The causes of this denervation are not fully established. Nonsurgical treatment of instability is not yet satisfactory; neuromodulation has some promise, but is expensive, and the mechanisms poorly understood. Pharmacological treatment is largely through muscarinic receptor blockade. Drugs to reduce the excitability of the smooth muscle are being sought, since they may represent a better pharmacological option.

Current pharmacological treatment of bladder hyperactivity

Bladder hyperactivity is a serious pathology with a high clinical incidence. Various drugs have been used to try to inhibit involuntary detrusorial contractions and to increase bladder capacity. The authors describe the properties, action mechanism, clinical use and side effects of the main drugs analysed. Most of the data regarding drug influence on the vesico-urethral apparatus are obtained from “in vitro” or “in-vivo” studies on animals and therefore cannot always be related to the clinical effects that would occur in man. It is still difficult to find an “ideal” drug with high detrusor selectivity, due to both the lack of knowledge on neuro-mediators and the difficulty in identifying receptors and “action sites”.

Acute effects of unilateral pelvic ganglionectomy on urinary bladder function in vivo in the male rat

Mean and maximal micturition volumes following a standardized water intake were determined before and up to three days after unilateral pelvic ganglionectomy or sham operation in adult male rats. Sham operation did not change the volumes. Unilateral ganglionectomy on the other hand decreased significantly both mean and maximal micturition volumes (and thus increased micturition frequency). The effect was most pronounced 1 day after ganglionectomy, but was still significant after 3 days. Cystometrograms were recorded without and with atropine (1 mg/kg) before operation and 1, 2 or 3 days after sham-operation or ganglionectomy. Micturition pressure decreased to about 50% 1 day after ganglionectomy and remained at this level. Atropine decreased micturition pressure in the controls to about 55% of the initial. The atropine resistant pressure response in the ganglionectomized rats amounted to 90% after 1 day, and was still above 70% after 3 days. The sham-operated controls had no residual urine without or with atropine. The unilaterally ganglionectomized animals had no residual urine in the absence of atropine, but after administration of the drug the animals rapidly developed a significant residual urine.

Electrical and mechanical responses produced by nerve stimulation in detrusor smooth muscle of the guinea-pig

In smooth muscles of the guinea-pig bladder, intramural nerve stimulation generated an excitatory junctional potential (e.j.p.), action potential and twitch contraction. Nicardipine inhibited the action potential but not the e.j.p. The e.j.p. amplitude was reduced by suramin, or desensitization of the ATP receptor with receptor agonists. The amplitude of the twitch contraction was reduced by atropine, and the remainder was blocked by nicardipine. In the presence of maximally effective concentrations of atropine, the threshold concentration of acetylcholine required to produce contraction was about 10(-7) M, whereas acetylcholine concentrations greater than 10(-6) M were required to cause depolarization. It is concluded that nerve stimulation releases acetylcholine and ATP, and the former produces contraction without change in the membrane potential, while the latter generates the e.j.p. which triggers an action potential and thus elicits contractions.

Length density and total length of acetylcholinesterase positive nerves related to cystometry and in vitro studies of muscle strips in mini-pig urinary bladder after chronic outflow obstruction and recovery from obstruction

Chronic partial bladder outlet obstruction was created in mini-pigs by implanting a 6-7 mm ring around the proximal urethra. After a median obstruction period of 63 days, the ring was removed and after a median recovery period of 60 days the animals were sacrificed. At each occasion stepwise cystometry, measurement of residual urine, muscle strips studies with electrical and carbachol stimulation, and stereological estimations of length density and total length of acetylcholinesterase positive nerves were performed. The results can be summarized as follows: (1) unchanged sensitivity of muscle strips to carbachol, but markedly decreased contractility and rate of contraction to carbachol, (2) no evidence of detrusor instability, but severely decompensated bladders in two pigs, (3) a significant increase in residual volume, (4) a pronounced decrease in length density and total length of acetylcholinesterase positive nerves, and (5) at field stimulation strips from some pigs showed increased sensitivity and contractility with high atropine and TTX resistance, while strips from the other pigs revealed decreased sensitivity and markedly decreased contractility to electrical stimulation. In general, most of the changes were markedly, though incompletely, reversed after recovery. Light and electron microscopy of muscle strips showed no histological or ultrastructural changes during the experiments or after storing 1 day at 4 degrees C.

Urodynamic and other effects of tolterodine: a novel antimuscarinic drug for the treatment of detrusor overactivity

Tolterodine, a novel compound intended for treatment of urgency and urge incontinence, has been characterized as a potent muscarinic receptor antagonist in pharmacological in vitro and in vivo studies. In cats, tolerodine was shown to reduce bladder pressure at doses significantly lower than those affecting salivation. To predict clinical effectiveness, an open pilot study was performed in healthy male volunteers. Efficacy was measured by cystometry and by spontaneously reported effects after administration of a single oral dose of tolterodine, 6.4 mg, given as a water solution. Tolterodine had distinct inhibitory effects on urinary bladder function, both at 1 and 5 hours post-dose. At 1 hour, but not at 5 hours post-dose tolterodine also significantly reduced stimulated salvation. In addition to the objectively demonstrated changes in urodynamic parameters, most volunteers experienced voiding difficulties. No significant changes in blood pressure, heart rate, or near point of accommodation were registered. Tolterodine, in the dosage used, was both objectively and subjectively shown to exert a marked inhibitory effect on micturition in healthy subjects, and the data suggest a more pronounced effect on bladder function than on salivation.

Inhibition in the human urinary bladder by gamma-amino-butyric acid

OBJECTIVE

To investigate the effects of gamma-amino-butyric acid (GABA) on detrusor activity in man to determine whether it has any inhibitory effect on detrusor contraction. The inhibitory neurotransmitter GABA has been found in mammalian urinary bladders and the effects of GABA on detrusor activity in the rabbit bladder has previously been described [1].

MATERIALS AND METHODS

Human detrusor muscle strips, obtained at cystectomy, were made to contract by electrical stimulation of their autonomic nerves or by the addition of carbachol in a superfusion apparatus. GABA and its analogues were added to the superfusion chamber and any changes in the responses were measured.

RESULTS

The electrically evoked nerve-mediated contractions in human bladder muscle were exclusively cholinergic. GABA inhibited nerve-mediated contractions in human detrusor muscle-strips by the activation of the GABAB receptor, since baclofen (a GABAB receptor agonist) produced similar inhibition and muscimol (a GABAA receptor agonist) did not. There was no inhibition of carbachol-mediated contractions by GABA.

CONCLUSION

This in vitro study shows that GABA has a peripherally mediated inhibitory effect on excitatory neurotransmission in human detrusor muscle. The site of action is on the post-ganglionic nerves and appears to be mediated via the GABAB receptor.

The pathophysiological changes in the bladder obstructed by benign prostatic hyperplasia

None of the hypotheses to explain the genesis of obstructed detrusor instability covered in this report provide a satisfactory explanation, by themselves, for the condition. While symptoms associated with prostatic obstruction are a common cause of patient referral to a urologist, all therapeutic advances so far have been directed towards the relief of bladder outflow resistance. It is possible that pharmacotherapy, for example, with drugs which stabilize muscle cell membranes and autonomically active drugs such as alpha 1-antagonists, possibly combined with anticholinergics, will have a therapeutic role in the treatment of obstructive detrusor instability. Further studies of obstructed human bladder are necessary to investigate the importance of changes in receptor density, affinity and distribution, agonist release and degradation and subsequently the ultrastructural and physiological alterations following the relief of obstruction.

Evidence for purinergic neurotransmission in human urinary bladder affected by interstitial cystitis

Detrusor specimens were obtained from 5 patients affected by interstitial cystitis (IC) and 5 patients with bladder carcinoma (controls). Muscle strips were prepared for in vitro pharmacological studies. In all detrusor strips taken from IC patients, an important portion of the electrically-induced contraction was atropine-resistant. In contrast, atropine-resistance was never observed in control detrusors. H1 and H2 antagonists did not affect noncholinergic contractile response which, conversely, was abolished following desensitization to alpha, beta methylene ATP (APCPP). Detrusor muscle from patients affected by IC exhibited an increase in sensitivity to APCPP and a decrease in sensitivity to acetylcholine with respect to control detrusor. Taken together these results are consistent with the presence of a purinergic neurotransmission in parasympathetic nerve terminals of the urinary bladder affected by IC, probably as a consequence of alterations in the innervation and/or electrical coupling between smooth muscle cells. The sensitivity of IC detrusor muscle to histamine was much lower than that of control detrusor, suggesting a desensitization of histamine receptors present in the bladder wall of IC patients.

Response of isolated human neurogenic detrusor smooth muscle to intramural nerve stimulation

The effect of intramural nerve stimulation of isolated strips of human detrusor was investigated and compared with the response of isolated detrusor strips of control bladders. All patients with neurogenic bladder underwent ileocystoplasty in order to resolve intractable incontinence and/or vesicoureteric reflux due to low compliance or severe detrusor uninhibited contractions. The response of isolated strips of neurogenic bladder to field stimulation was significantly greater than the response of isolated strips of control bladders. Tetrodotoxin virtually eliminated the response to field stimulation for both groups. Atropine (10(-6)M) almost completely inhibited the response of control bladder strips to field stimulation (4% of the response remaining), whereas the responses of the strips from neurogenic bladders were inhibited by approximately 70%. Low dose KCl (5 and 10 mM) significantly enhanced the detrusor contractility of control bladders, whereas the response of neurogenic bladders was unchanged. The responses of both groups were significantly inhibited in the presence of 20 mM KCl. The dose response curves and the ED50 values for KCl were similar for both neurogenic and control bladders. The rate of reduction of the response to field stimulation in the presence of zero calcium medium was significantly smaller for the isolated strips of neurogenic bladders than for the control bladders.

Response of the human neurogenic bladder to KCl, carbachol, ATP and CaCl2

The in vitro pharmacological responses of the human neurogenic bladder to KCl, carbachol, ATP and CaCl2 have been analysed. The contractility (contractile strength and ED50) of neurogenic bladders was significantly increased when treated with carbachol, ATP and CaCl2. In contrast, there was no apparent difference in the responsiveness of neurogenic bladders when treated with KCl. There was no apparent correlation between pharmacological responsiveness and clinical parameters, such as gender, age or cystometric data, in the neurogenic bladders.

Partial mediation by nitric oxide of the relaxation of human isolated detrusor strips in response to electrical field stimulation

1. A method for reproducing relaxation of human isolated detrusor smooth muscle in vitro in response to electrical field stimulation is described. 2. The parameters of stimulation associated with relaxation were those which would be expected to give a largely nerve-mediated response: the relaxations were not reduced by tetrodotoxin (3 x 10(-7) M) and were therefore not dependent on voltage sensitive sodium channels. 3. The relaxations were decreased (mean 74.1%) by nitro L-arginine (NOARG, 10(-5) M). 4. Methylene blue (10(-5) M), an inhibitor of soluble guanylate cyclase, abolished the relaxations. 5. These results indicate that there may be a relaxation mechanism in the human bladder which is at least partly mediated via the production of nitric oxide.

The effect of in vivo oestrogen pretreatment on the contractile response of rat isolated detrusor muscle

1. The effect of oestradiol pretreatment was investigated on the response of rat isolated detrusor muscle to cholinergic, electrical and 5-hydroxytryptamine (5-HT) stimulation with and without diethylstilbestrol (DES) (2 microM) in the organ bath. 2. Virgin female Wistar rats were injected subcutaneously for 8 days with oestradiol benzoate 150 micrograms kg-1. Control rats received no injections or injection only with the vehicle, ethyl oleate. 3. Detrusor muscle from treated rats showed a decreased sensitivity to acetylcholine (ACh) and carbachol-induced contractile responses. The dose-response curves to these agonists showed a 44% reduction in maximum contractile response for ACh (P < 0.001), and a 38% reduction in maximum contractile response for carbachol (P < 0.05). The addition of 2 microM DES to the bathing medium further significantly reduced the maximum contractile response by 56 and 57% of control respectively. 4. Electrically stimulated detrusor muscle from treated rats showed a significant 49% reduction in the maximum contractile response (P < 0.001). The addition of 2 microM DES to the bathing medium further significantly reduced the maximum contractile response by 66% of control. The tetrodotoxin resistant responses were smaller in pretreated rats, suggesting a reduced sensitivity of the smooth muscle to direct electrical stimulation. 5. The response to 5-HT stimulation by detrusor muscle samples from oestradiol-treated rats showed a non-significant reduction in maximum contractile response, but the addition of 2 microM DES to the bath chamber resulted in a 67% reduction in the response (P < 0.001). 6. Oestradiol pretreatment did not affect the potassium dose-response curve.7. Oestradiol pretreatment reduced the rat detrusor muscle sensitivity to the blocking effect of atropine on the response to electrical field stimulation. Pretreatment also reduced the potentiating effect of physostigmine on the same response.8. These results suggest that oestradiol pretreatment had a modulating effect on cholinergic responses.The addition of oestrogen to the tissue environment enhances this inhibitory effect.

The Cholinergic and Purinergic Components of Detrusor Contractility in a Whole Rabbit Bladder Model

Whole rabbit bladders were suspended in a bath chamber and stimulated with ATP, bethanechol, electrical field stimulation, and bethanechol + ATP. Detrusor pressure and fluid expelled by the bladder were recorded, synchronized, and digitized. Detrusor work and power were calculated with a computer program. Maximum work was 61.4 +/- 28.7, 83.3 +/- 17.0, 85.0 +/- 15.0, 90.8 +/- 13.1 cm. H2O, ml. for ATP, bethanechol, electrical and bethanechol + ATP, respectively. Maximum power generated by ATP was 4.8 +/- 3.0 cm. H2O, ml./sec and was approximately 66% of that generated by bethanechol, and 50% of that generated by electrical stimulation, and bethanechol + ATP. ATP cannot empty the bladder with moderate outlet resistance while bethanechol and electrical stimulation can. Our results suggest that ATP is able to generate detrusor power and achieve work in bladder emptying. However, ATP generated power and work is considerably less than that of electrical stimulation or bethanechol alone. ATP mediated contraction is not inhibited by atropine or tetrodotoxin but is inhibited by P2 purinoceptor desensitization, suggesting a functional role of purine receptors on detrusor smooth muscle. Since ATP generated pressure is more rapid than with bethanechol alone, we support the hypothesis that ATP may be important in the initiation of micturition.

Contractions induced by angiotensin I, angiotensin II and bradykinin in isolated smooth muscle from the human detrusor

In isolated human detrusor preparations angiotensin (At)II 10(-9)-10(-5) M caused concentration-dependent contractions. The contractile effect was immediate, and had an amplitude which at the highest concentration used, 10(-5) M, reached 103 +/- 16% of the mean contraction produced by K+ 124 mM (27.6 +/- 1.4 mN). The AtII effect was completely blocked by saralasin 10(-6) M, but was not affected by pre-treatment of the preparations with captopril or enalaprilate. There was a marked tachyphylaxis to the actions of the peptide. AtI (10(-8)-10(-5) M) also caused contractions which were rapidly developing, and subject to a marked tachyphylaxis. At a concentration of 10(-5) M, the mean amplitude was 66 +/- 9% of the K(+)-induced contraction. The contractions were blocked by saralasin 10(-6) M, but not by captopril or enalaprilate 10(-5) M. In contrast, contractions produced by AtI in rabbit mesenteric arteries were practically abolished by the angiotensin converting enzyme (ACE) inhibitors. The contractions induced by both AtI and AtII were practically abolished after pre-treatment in a nominally calcium-free Krebs solution. However, blockade of L-type calcium channels by nifedipine 10(-6) M reduced the responses to both AtI 10(-6) M (by 38 +/- 4%) and AtII 10(-6) M (by 39 +/- 7%), but never abolished the contractions. Bradykinin (Bk; 3 x 10(-8)-10(-5) M) had a contractile effect in detrusor preparations which varied widely between strips. At a concentration of 3 x 10(-6) M, a maximum was reached amounting to 30 +/- 10% of the K(+)-induced contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

The direct effects of diethylstilboestrol and nifedipine on the contractile responses of isolated human and rat detrusor muscles

We have studied the direct effect of 2 mumol.l-1 diethylstilboestrol on isolated rat and human detrusor muscles. Diethylstilboestrol significantly reduced the amplitude of the contractile response of rat detrusor muscle to stimulation with acetylcholine, carbachol, electrical field stimulation, and 5-hydroxytryptamine. In isolated human bladder it also significantly reduced contractions stimulated with acetylcholine, carbachol, and electrical field stimulation. In depolarized rat detrusor muscle stimulated with different concentrations of calcium ions, the contractile responses were significantly reduced by the addition of diethylstilboestrol. Diethylstilboestrol also significantly reduced the amplitude of contractile response to potassium chloride. The inhibitory action of diethylstilboestrol was enhanced by the reduction of extracellular calcium ions, the maximum contractile response to acetylcholine, carbachol, and electrical field stimulation being reduced by a further 32%, 23%, and 45% respectively. Diethylstilboestrol did not have a significant effect on carbachol-induced contractions in depolarized rat detrusor muscle suspended in a calcium-free environment. Diethylstilboestrol was effective in blocking rat and human detrusor muscle contraction. The likely mechanism is a reduction of the influx of calcium ions into the cell during contraction rather than an effect on intracellular calcium release. These results give support for treating incontinent patients with drugs that block calcium ion uptake, and may suggest a further beneficial effect of oestrogen therapy in postmenopausal women.