Atropine resistance of transmurally stimulated isolated human bladder muscle

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.

Effect of age on the responses of rat bladder detrusor strips to adenosine triphosphate

OBJECTIVE

To assess age-related changes in bladder function using the contractile responses to ATP of detrusor strips from rats of various ages. Materials and methods Urinary bladders were obtained from male Wistar rats aged 9 weeks (young), 24 weeks (adult) and 24 months (aged). Contractions of urinary bladder muscle strips to ATP were measured isometrically. The size of the initial phasic response and the secondary contractile response that developed after washing out ATP (postwashout contraction) were measured. The magnitudes of the ATP-induced phasic and postwashout contraction were compared among the age groups. During the contractions, prostanoid concentrations in the organ-bath medium were measured using an enzyme immunoassay.

RESULTS

The ATP-induced postwashout contraction did not occur after stimulation with KCl or acetylcholine, but was induced by alpha,beta-methylene ATP. Both the phasic and postwashout contractions were concentration-dependent. Although the phasic contraction did not change progressively with age, the magnitude and duration of the postwashout contraction increased substantially with age. Nicardipine (a calcium antagonist) slightly inhibited both contractions. Suramin (a nonselective P2-receptor antagonist) did not significantly inhibit the phasic contraction, but reduced the postwashout contraction. PPADS (a selective P2X receptor antagonist) did not inhibit either contraction. Indomethacin (a prostaglandin synthesis inhibitor) had no effect on the phasic contraction but almost completely blocked the postwashout contraction when added before ATP stimulation, but was less effective when added after ATP. The prostaglandin E2 concentration in the organ bath increased during the postwashout contraction.

CONCLUSIONS

These findings suggest that the ATP-induced postwashout contraction is not directly mediated by P2x purinoceptors, but results from the synthesis of prostaglandins, especially E2, which is a sensory autacoid. The age-linked increase in postwashout contraction may be involved in the changes in sensory and voiding mechanisms seen in the aged urinary bladder.

Mechanisms of excitatory neuromuscular transmission in the guinea-pig urinary bladder

1. In smooth muscle of the guinea-pig bladder, either membrane potential recordings or [Ca2+]i measurements were made simultaneously with isometric tension recordings. 2. Single transmural stimuli initiated excitatory junction potentials (EJPs) which triggered action potentials, transient increases in [Ca2+]i and associated contractions. These responses were abolished by alpha, beta-methylene ATP, suggesting that they resulted from the activation of purinoceptors by neurally released ATP. 3. Nifedipine abolished action potentials leaving the underlying EJPs and reduced the amplitude of both nerve-evoked increases in [Ca2+]i and associated contractions. The subsequent co-application of caffeine and ryanodine inhibited the residual responses without inhibiting EJPs. These results indicate that stimulation of purinoceptors activates both Ca2+ influx through L-type Ca2+ channels and Ca2+ release from intracellular Ca2+ stores. 4. In the presence of alpha, beta-methylene ATP, trains of stimuli failed to initiate EJPs but increased the frequency of action potentials. Trains of stimuli also initiated oscillatory increases in [Ca2+]i and associated contractions. These responses were abolished by hyoscine, indicating that they resulted from the activation of muscarinic receptors by neurally released ACh. 5. Oscillatory increases in [Ca2+]i and associated contractions were inhibited by either nifedipine or caffeine, indicating that the stimulation of muscarinic receptors activates both Ca2+ influx through L-type Ca2+ channels and Ca2+ release from intracellular Ca2+ stores.

Urinary incontinence: anatomy, physiology and pathophysiology

Urinary continence in the female depends on urine being stored in a receptive bladder closed by a competent sphincter mechanism. Incontinence can result from a failure of storage, i.e. detrusor instability or a failure of the sphincter mechanism leading to stress incontinence. In addition there is a complex neural control which co-ordinates urethral and bladder function to alter from storage to voiding at socially acceptable times. Although the majority achieve continence early in childhood, there are a number of insults brought to bear on the continence mechanism other than advancing age. The most notable of these is childbirth with resultant neuromuscular damage to the pelvic floor. The onset of the menopause with oestrogen deprivation and increased risk of urinary tract infection can further compromise bladder function. Restoration of continence in those affected involves a thorough knowledge of normal functioning anatomy and physiology of the lower urinary tract as only through improved understanding of disease mechanisms can rational treatment be applied.

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.

Evaluation of the role of neurolinins and urecholine hypersensitivity in an animal model of infravesical outflow obstruction

OBJECTIVES

To determine whether detrusor muscle strips from a male rat with infravesical outflow obstruction model demonstrate supersensitivity to parasympathomimetic and neurokinin NK-1 and NK-2 selective agonists.

METHODS

Bladder instability developed after 6 weeks of partial urethral obstruction. The micturition frequency and voided volume were determined in unanesthetized animals. Detrusor hypertrophy was confirmed by evaluation of bladder weight. In vitro organ bath was used to compare the affinity and maximal activity of bethanechol and neurokinin NK-1 and NK-2 selective agonists on strips from the detrusor muscle of sham and obstructed rats. Bethanechol, N-Ac[Arg6, Sar9, Met(O2)]-SP(6-11), and [beta-Ala8]-NKA(4-10) were used to characterize cholinergic muscarinic, neurokinin NK-1 and NK-2 receptors. Results. No significant differences in affinities and maximal responses were found using 10-mg detrusor muscle strips with each of the three agonists.

CONCLUSIONS

Bladder instability produced by outlet obstruction does not involve changes in the affinity or maximal activity of cholinergic muscarinic, neurokinin NK-1 and NK-2 receptors. Furthermore, detrusor supersensitivity to neurokinins or bethanechol was not seen. This suggests that bladder instability is not due to an increased affinity or maximal response to neurokinins or parasympathomimetics.

Inhibitory effects of propiverine, atropine and oxybutynin on bladder instability in rats with infravesical outlet obstruction

OBJECTIVE

To compare the inhibitory effects of propiverine HCl(BUP-4) with those of atropine and oxybutynin on the detrusor instability induced by partial obstruction of the bladder neck of female rats.

MATERIALS AND METHODS

Partial obstruction was created using partial ligation of the proximal urethra in 20 female Sprague-Dawley rats. Both the obstructed rats and a control group of 15 rats were evaluated cystometrically about 6 weeks later and the values compared both baseline and after injection with BUP-4, atropine or oxybutynin. During cystometry, the bladder capacity (BC), residual volume (RV), compliance and frequency of spontaneous activity (SA) were determined.

RESULTS

The BC, RV and frequency of SA were significantly increased, and compliance markedly decreased, in obstructed compared with normal rats. The micturition pressure was significantly decreased only after injection with BUP-4 in both normal and obstructed rats. For both, the BC was increased significantly after injection with atropine or BUP-4 (P < 0.05), with the increase greater after BUP-4 than after atropine in both groups (P < 0.01). After injecting BUP-4, the RV was significantly increased in both groups (P < 0.05); atropine increased the RV only in normal rats (P < 0.01) and oxybutynin had no significant effect on RV. Increases in compliance after the administration of each drug were significant only in obstructed rats (P < 0.01) and were markedly higher after oxybutynin (780%) than after the other drugs (180-250%). The frequencies and amplitude of SA after injection with each drug were significantly lower only in obstructed rats, but in these rats, there were no significant differences in this reduction after injecting oxybutynin or BUP-4, whereas they were significantly greater after injecting oxybutynin than after atropine.

CONCLUSION

Partial bladder outlet obstruction successfully created a hyperactive (unstable) bladder, typified by increased BC, RV, frequency of SA and a marked decrease in compliance. The greater BC, lower MP and frequency and amplitude of SA were prominent after the administration of BUP-4. Thus it is suggested that BUP-4 effectively inhibited bladder instability in rats induced by infravesical outlet obstruction and was more effective than oxybutynin in increasing BC.

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.

Change in bladder contractility associated with bladder overactivity in rats with cerebral infarction

PURPOSE

To evaluate the contractile properties of overactive bladder from rats in the chronic stage of experimental cerebral infarction.

MATERIALS AND METHODS

Cystometry was performed in conscious male S-D rats after inducing occlusion of the left middle cerebral artery. Bladder muscle strips were evaluated for force development in response to field stimulation, acetylcholine and KCl. By measuring the contractile response to field stimulation after adding atropine and alpha,beta-methylene-ATP, contributions of cholinergic and purinergic transmission were determined.

RESULTS

Bladder capacity of cerebral-infarcted rats was <50% of the capacity of sham-operated rats and significantly less than that of sham-operated rats even 4 months after surgery. There was no significant difference in bladder weight between sham-operated rats and cerebral-infarcted rats. No differences in the contractile response of detrusor strips to field stimulation and acetylcholine, or in the relative contribution of cholinergic and purinergic transmission to the contractile response, were observed over time or between strips from sham-operated rats and cerebral-infarcted rats. KCl induced significantly less contraction in strips from 4 month infarcted rats than in strips from 4 month sham-operated rats, 2 week infarcted rats and 2 month infarcted rats.

CONCLUSIONS

This animal model will be useful for chronic studies on the mechanism of detrusor hyperactivity (DH).

The overactive bladder: pharmacologic basis of drug treatment

OBJECTIVES

To provide an overview of the basis for drug treatment of the overactive bladder.

METHODS

Published information is evaluated.

RESULTS

The causes of bladder overactivity are not known, but theoretically, increased afferent activity, decreased inhibitory control in the central nervous system (CNS) or peripheral ganglia, and increased sensitivity of the detrusor to efferent stimulation may be involved. Several CNS transmitters can modulate voiding, but few useful drugs with a defined CNS site of action have been developed. Drugs that stimulate gamma-aminobutyric acid receptors are used clinically. Potentially, drugs affecting opioid, 5-hydroxytryptamine, norepinephrine, dopamine, and glutamatergic receptors and mechanisms can be developed, but a selective action on the lower urinary tract may be difficult to obtain. Traditionally, drugs used for treatment of bladder overactivity have had a peripheral site of action, mainly efferent neurotransmission or the detrusor itself. Antimuscarinic drugs, beta-adrenoceptor agonists, alpha-adrenoceptor antagonists, drugs affecting membrane channels, prostaglandin synthetase inhibitors, and several other agents have been used with limited success. New information on the alpha-adrenoceptor and muscarinic receptor subtypes in the human detrusor has emerged and may be the basis for the development of new compounds with effects on bladder overactivity. Decreasing afferent activity seems an attractive therapeutic approach, and drugs affecting afferent nerves by causing release of tachykinins, such as capsaicin and analogs, as well as agents blocking tachykinin receptors, may be of therapeutic interest.

CONCLUSIONS

New drugs, specifically designed for the treatment of bladder overactivity, are desirable.

A myogenic basis for the overactive bladder

OBJECTIVES

This article summarizes evidence supporting the conclusion that the spontaneous rises in pressure that occur in the overactive bladder, particularly in detrusor instability (DI), regardless of etiology, are myogenic.

METHODS

The evidence quoted has been obtained by several groups of investigators and includes electrophysiologic studies of detrusor myocytes, tension studies of strips of smooth muscle, in vivo experiments on animal models, and light and electron microscopic studies of the structure of the bladder wall.

RESULTS

The results of these studies demonstrate changes in the properties, structure, and innervation of the detrusor. These changes are consistent with the hypothesis that partial denervation of the detrusor may be responsible for altering the properties of the smooth muscle, leading to increased excitability and increased ability of activity to spread between cells, resulting in coordinated myogenic contractions of the whole detrusor.

CONCLUSIONS

It is suggested that alterations in the properties of the detrusor myocytes are a necessary prerequisite for the production of the unstable pressure rises seen in DI of any origin.

Anticholinergic and calcium antagonistic activities of NS-21 contribute to the inhibition of rat urinary bladder contractions

1. Pharmacological characteristics of NS-21 and its main metabolite, RCC-36, in the inhibition of rat urinary bladder contractions were investigated both in vitro and in vivo. 2. NS-21 and RCC-36 inhibited muscarinic receptor bindings to rat bladder membranes with [3H]3-quinuclidinyl bezilate (pKi 6.19 and 7.24, respectively), whereas they failed to inhibit the following receptor bindings: adrenergic (alpha 1, alpha 2 and beta), dopaminergic (D1 and D2), adenosine (A1 and A2), histaminergic (H1) and opioid (mu, delta and kappa) receptors. 3. NS-21 and RCC-36 suppressed carbachol-induced contractions of isolated rat detrusor strips in competitive (pA2 6.80 and 7.93, respectively) and noncompetitive (pD'2 5.93 and 5.77, respectively) manners. 4. NS-21 and RCC-36 inhibited CaCl2-induced contractions of rat detrusor strips in the presence of 100 mM K+ (pIC50 6.54 and 5.76, respectively), as well as the 100 mM K(+)-induced 45Ca influx into the isolated bladder strips at > or = 1 microM. 5. Electrical stimulation of the peripheral end of the pelvic nerve in anesthetized rats induced bladder contractions composed of two phases: an initial phasic contraction that was weakly suppressed by atropine, and a tonic contraction that was strongly suppressed by atropine. NS-21 suppressed both contractions to the same degree (ID50 2.65 and 2.19 mg/kg, i.v., respectively). RCC-36 suppressed the tonic contraction (ID50 1.20 mg/kg, i.v.) more markedly than the initial contraction (ID50 7.43 mg/kg, i.v.). 6. These results suggest that NS-21 and RCC-36 suppressed bladder contractions owing to their anticholinergic and calcium antagonistic activities.

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.

Effect of ischemia and partial outflow obstruction on rat bladder function

We investigated the effects of ischemia induced by ligation of the bilateral internal iliac arteries following partial outlet obstruction on changes in detrusor function in rat. Rats were divided into three groups: sham-operated control rats, rats with partial outlet obstruction, and rats with obstruction+ischemia. Bladder function was studied by the in vitro organ bath technique 7 days after surgery. The weight of the bladder was significantly increased in both the obstruction and obstruction+ischemia groups. The obstruction+ischemia group exhibited a greater increase in weight. The passive length-tension relationship of detrusor muscle strips showed that tissue elasticity was decreased and the active length-tension relationship demonstrated that the peak response was observed at a shorter tissue length in the obstruction+ischemia group compared with the other two groups. There was no difference in the passive and active length-tension relationships between the control group and the obstruction group. The contractile response to various kinds of stimulation (field stimulation, bethanechol, ATP, and KCl) increased in the obstruction group and decreased in the obstruction+ischemia group. These findings suggest that partial outflow obstruction alone increased bladder contractility in response to stimuli. However, ischemia reduced the contractility and elasticity of the bladder wall.

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.

Neurophysiology of micturition and continence

This article reviews the neuroanatomy, neurophysiology, and neuropharmacology involved in micturition and continence. Knowledge of these topics helps the clinician diagnose and treat voiding disorders that are caused by disease, trauma, drugs, and aging.

Urinary bladder function and drug development

Disorders of the bladder are extremely common and are becoming more so in an ageing population. Recently, our understanding of lower urinary tract physiology and pathology has also increased. Here, Douglas Ferguson and Nim Christopher summarize this new knowledge of lower urinary tract function, the changes in innervation that occur with age and the common disease states, and discuss how it is being used to develop new drug treatments for bladder disorders.

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.

Characterization and autoradiographic localization of [3H] alpha, beta-methylene adenosine 5'-triphosphate binding sites in human urinary bladder

OBJECTIVES

To characterize [3H] alpha, beta-methylene adenosine 5'-triphosphate ([3H] alpha, beta-MeATP, a radioligand for P2x-purinoceptors) binding sites in the washed homogenates and membrane preparations of human urinary bladder and, using autoradiography, to localize [3H] alpha, beta-MeATP binding sites in human bladder.

MATERIALS AND METHODS

Specimens were obtained from the fundus of the urinary bladder of male patients aged 56-79 years. The washed homogenates or membrane preparations of the bladder specimens were incubated with [3H] alpha, beta-MeATP and the bound and free radioligand separated by filtration. For autoradiography, cryostat sections were incubated with 10 nM [3H] alpha, beta-MeATP, washed, dried and exposed for 2 weeks to emulsion-coated coverslips. In both experiments, 100 microM beta, gamma-methylene ATP was used to determine non-specific binding.

RESULTS

Six of 16 specimens in the binding assay and three of seven specimens in the localization study showed specific [3H] alpha, beta-MeATP binding. The binding process was saturable and the specific binding sites were composed of a high- and low-affinity component. The specific binding to membrane preparations was reduced in the presence of Mg2+ in the incubation medium. Competitive displacement experiments showed that the order of potency of the unlabelled ligands to displace the [3H] alpha, beta-MeATP binding was alpha, beta-methylene ATP > beta, gamma-methylene ATP > suramin > 2-methylthio ATP > ATP > ADP >> adenosine, which indicates that the binding sites are, or are linked to, P2x-purinoceptors. Autoradiography showed that the specific [3H] alpha, beta-MeATP binding sites were located only over the smooth muscle of the bladder.

CONCLUSIONS

The results suggest that P2x-purinoceptors exist in human urinary bladder, although at a lower density than reported for rodent urinary bladder.

Changes in rat bladder function following exposure to pain and water stimuli

Changes in rat bladder function following the exposure to physical stress were studied in vitro. Rats were divided into two stress groups and two control groups and maintained for 6 months under specific conditions. The stress groups, consisting of animals subjected to water or pain stress and control groups were kept in cages floored with wooden chips or wire net. The body weight of the stressed groups was significantly lower than that of the controls. Gastric ulcer occurred in none of the groups. The detrusor response of the water group to acetylcholine was significantly greater than that of the two control groups. In the pain group, the contractile response was induced by norepinephrine. In the other three groups, however, norepinephrine evoked a relaxation of muscle strips. The contractile response of the bladder to both serotonin (5-hydroxytryptamine) and ATP (adenosine 5'-triphosphate) did not differ between the four groups.

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.

Post-irradiation bladder dysfunction: muscle strip findings

Strips of rat detrusor muscle were studied in an organ bath 6 months after X-irradiation at doses of 15 and 25 Gy; cystometric studies in these animals had shown a persistent and significant reduction in compliance. The organ bath study demonstrated an increase in the purinergic sensitivity of irradiated detrusor muscle as compared with control. This was significant: p < 0.0145 for the 25 Gy dose group (n = 8) and p < 0.0456 for the 15 Gy group (n = 8) at an alpha,beta-methylene-ATP concentration of 10(-4) M (Mann-Whitney U-Test). There was no difference in sensitivity to cholinergic or noradrenergic stimulation, or to electrical stimulation of the transmural nerves. The finding of purinergic hypersensitivity in irradiated muscle, coupled with ultrastructural evidence of a neural injury, raises the interesting possibility that a denervation supersensitivity phenomenon may contribute to the pathophysiology of post-irradiation bladder dysfunction.

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.

Rabbit as a model of urinary bladder function

Micturition is a complex neuromuscular process. Although control mechanisms have been identified at several levels of the central nervous system and spinal cord, the final pathway in the control of micturition is the autonomic innervation of the urinary bladder and related structures. Following this line of reasoning further, micturition is ultimately dependent on the ability of the urinary bladder to both contract and generate intravesical pressure, and to modify its shape in such a way as to efficiently expel its contents without leaving a high residual volume. In order to understand the various elements of micturition, a wide variety of both in vivo and in vitro animal models has been developed. In many cases, animal models have been utilized to describe the effect of specific experimental pathologies on the lower urinary tract. The current review of the use of the rabbit in urological research is not meant to be a comprehensive treatise on the topic, but should provide a rational description of the how this species can be utilized to study both normal and pathological function.

Guinea pig as an animal model for the study of urinary bladder function in the normal and obstructed state

The guinea pig has become an excellent model for the study of mechanical and electrical mechanisms regulating bladder function in the normal and obstructed state. Much preliminary work has been done on the in vitro behavior of the detrusor smooth muscle. The tissue has permitted electrophysiological studies by sucrose gap, microelectrode, and patch clamp technique. Excellent urodynamic studies can be performed under anesthesia. A recent model of bladder obstruction has resulted in a source of tissue which is suitable for electrophysiological analysis of the muscle. Low-cost and simple animal care requirements permit large-scale studies correlating urodynamic, structural, biochemical, contractile, and electrophysiological changes in response to 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.

Age-related changes in the response of the rat urinary bladder to neurotransmitters

The effect of age on the contractile response of the rat urinary bladder to various neurotransmitters was studied using in vitro detrusor strips isolated from female Wistar rats. The contractile responses to 8 neurotransmitters were determined for rat urinary bladders isolated from 3 age groups: 24, 16, and 6 months old. The results can be summarized as follows: 1) There was no age-dependent change in the maximum response to KCl. 2) The contractile response to norepinephrine, adenosine 5'-triphosphate (ATP), and serotonin increased with age. 3) The relaxation response to isoproterenol was significantly less in 24-month-old rats than in the other 2 age groups. 4) There were no age related changes in the responses to acetylcholine, prostaglandin F2 alpha, and angiotensin II. 5) Vasoactive intestinal polypeptide (VIP) failed to induce any response in the rat bladders of any group. 6) There were no significant differences in the ED50s for the 5 neurotransmitters among the 3 age groups. In summary, significant differences in the response to adrenergic, purinergic, and serotonergic stimulation were found as a function of age, whereas no age related changes in the response to cholinergic or generalized depolarization with KCl were found.

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.

Loss of sensory neuropeptides in the obstructed human bladder

This is the first investigation of alterations in the innervation of the obstructed human bladder by nerves containing neuropeptides. The patient groups studied were those with stable detrusor function, those with unstable detrusor function, and those presenting with acute retention of urine. Specimens of bladder tissue were taken from the lateral wall of the bladder below the peritoneal reflection. A total of 23 patients was studied (control, n = 4; acute retention, n = 5; stable obstruction, n = 5; unstable obstruction, n = 9). Substance P, calcitonin gene-related peptide and vasoactive intestinal polypeptide levels in the bladder were quantified by immunoassay. The density of innervation of the bladder detrusor by nerves containing these neurotransmitters and by those containing neuropeptide Y and somatostatin was assessed using both semiquantitative and quantitative immunohistochemical techniques. A reduction in the density of innervation by vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P and somatostatin-immunoreactive but not neuropeptide Y-immunoreactive nerve fibres was shown in the obstructed bladder. These findings, combined with the significant reduction in substance P content of the obstructed bladder and in particular of the acute retention bladder, indicate that there may be an afferent nerve dysfunction resulting from prostatic bladder outflow obstruction.

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.

Involvement of opioid mechanisms in peripheral motor control of detrusor muscle

Isometric recordings of mechanical activity in muscle strips from rat and human detrusor were performed and the effect of mu- and delta-opioid receptor stimulation and blockade on detrusor contraction induced by electrical field stimulation was tested. Stimulation of the opioid mu-receptor with morphine (10(-13)-10(-4) M) and DAGO (10(-13)-10(-6) M) had no significant effect on electrical field stimulation except at one concentration of morphine (10(-6) M). Naloxone (10(-10)-10(-5) M) caused a significant facilitation of the electrical field stimulation-induced contraction, which was counteracted by morphine (10(-8) M) and the delta-agonist DPDPE (10(-8) M) in both rat and human detrusor. Addition of atropine (10(-6) M) or hexamethonium chloride (10(-6) M) or spantide (10(-6) M) did not alter the facilitating effect of naloxone in the rat detrusor. Hexamethonium (10(-5) M) decreased the facilitating effect of naloxone on electrical field stimulation-induced contractions in the human detrusor, indicating involvement of ganglionic mechanisms. In human detrusor about 15% of the contractile response was found to be atropine-resistant (10(-6) M) and one third of this was found to be resistant to tetrodotoxin (1.5 x 10(-6) M). The atropine resistant-response in human detrusor was facilitated by naloxone to the same extent as the atropine-sensitive part. Adrenergic blockade per se, achieved with phentolamine mesylate (10(-6) M) and propranolol (10(-6) M), caused a significant facilitation of the electrical field stimulation-induced contraction in the rat detrusor but did not affect the facilitating effect of naloxone (10(-13)-10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)

A pharmacological in vitro study of the mouse urinary bladder at the time of acute change in bladder reservoir function after irradiation

Mouse urinary bladder strips were investigated as to whether the acute change in bladder reservoir function seen after irradiation might be due to major changes in basic nerve and smooth muscle functions. The release mechanism of acetylcholine, cholinergic and non-cholinergic nerve activation explored by indomethacin and potassium channel activation were investigated. It was concluded that the normal mouse bladder is partly cholinergically and partly non-cholinergically innervated. The role of acetylcholine is of the same importance as in other rodents. However, it was not possible to distinguish any difference between normal and irradiated mouse bladders in respect to nerve and smooth muscle function.