Influence of atropine and isoprenaline on detrusor hyperactivity in children with neurogenic bladder

Management of overactive bladder syndrome

Overactive bladder (OAB) syndrome is the term used to describe the symptom complex of urinary urgency with or without urge incontinence, usually with frequency and nocturia. Drug treatment continues to have an important role in the management of women with OAB. Other treatment options include conservative management with lifestyle interventions, modification of fluid intake, and physiotherapy including bladder retraining. Surgery remains the last resort in the treatment and is usually reserved for intractable detrusor overactivity, as it is associated with significant morbidity. This article reviews the management of the overactive bladder with specific focus on newer developments in the medical treatment of OAB in women.

Oxybutynin and its new transdermal application for the treatment of overactive bladder

It has long been accepted that antimuscarinic agents are the backbone of the pharmacological treatment of overactive bladder. Oxybutynin has been the gold standard of these medications for years due to its efficacy, but suffers from a lack of selectivity for the bladder, and extensive metabolism and lipophilicity result in significant side-effect issues. The transdermal delivery of oxybutynin turns this disadvantage of lipophilicity into an advantage. This, in turn, bypasses gastrointestinal absorption and metabolism by the cytochrome P450 system and reduces the breakdown into metabolites responsible for many of the side effects, while providing equivalent efficacy to the immediate-release oral formulation.

Potential therapeutic targets for the treatment of detrusor overactivity

Current treatments for the overactive detrusor are poorly tolerated and can exert significant adverse effects. Possible targets for the development of new treatments are considered. Potential targets in four locations are examined: detrusor smooth muscle, urothelium, peripheral nerves and the CNS. In the detrusor, the role of various muscarinic receptor subtypes is discussed and beta-adrenoceptor agonists, phosphodiesterase inhibitors and potassium channel openers, all of which inhibit detrusor contractility, are considered for drug development. In the urothelium, a number of substances are released that affect bladder function including ATP, acetylcholine and an inhibitory factor that has yet to be identified. All three systems have the potential to be novel targets for drug development. Other possible therapeutic targets are the mechanisms influencing transmitter release in the bladder, for example, prejunctional 5-hydroxytryptamine (5-HT) 4 receptors. Finally, targets within the CNS and spinal cord are considered, including opioid receptors, 5-HT receptors and alpha-adrenoceptors.

Recent developments in the management of detrusor overactivity

PURPOSE OF REVIEW

Detrusor overactivity is a relatively common yet embarrassing symptom complex with significant impact on quality of life. The mainstay of current pharmacological treatment involves use of muscarinic receptor antagonists, but their therapeutic efficacy is limited by their troublesome side effects resulting in the non-continuance of treatment in a significant number of patients. Therefore, the development of new drugs can proceed by targeting alternative pathways affecting detrusor overactivity. In this article, the pharmacological basis for the current therapeutic alternatives for managing detrusor overactivity and possible future developments are discussed.

RECENT FINDINGS

It is clear that far from being a passive container for urine, the urothelium is a crucial part of the bladder. Its functions are complex, dynamic and important, and only now becoming understood. The release of ATP from urothelium in response to distension and its action on P2X receptors resulting in activating both motor and sensory neurons is being increasingly recognised. In the normal bladder, muscarinic receptor stimulation produces the main part of detrusor contraction. However, in functionally abnormal bladders, a non-cholinergic activation via the purinergic receptors may occur. The central nervous mechanisms controlling the micturition reflex have also recently attracted attention.

SUMMARY

Recent research has suggested that several transmitters may modulate voiding. However, few drugs with clinical benefits have been developed so far. Present treatments for overactive bladders have significant non-compliance rates. Hopefully, future research will lead to drugs with greater therapeutic benefits and better tolerance.

Treatment of overactive bladder: other drug mechanisms

The well-known side effects of antimuscarinic drugs have focused interest on other ways of treating overactive bladder. Targets for pharmacologic intervention may be found in the central nervous system (CNS) or peripherally. Several CNS transmitter systems can modulate voiding, but few drugs with a defined CNS site of action have been demonstrated to be clinically useful. The mechanism of action of imipramine, which may be effective in the treatment of overactive bladder, has not yet been clarified. Like imipramine, duloxetine is an inhibitor of serotonin (5-HT) and norepinephrine reuptake. Duloxetine has shown some promise in the treatment of urinary incontinence, but, as with the selective serotonin reuptake inhibitors, its effectiveness in the treatment of overactive bladder has not been proven. Drugs affecting norepinephrine, dopamine or gamma-aminobutyric acid (GABA) receptors and mechanisms may be useful. There is also evidence for a central site of action of alpha(1)-adrenoceptor (AR) antagonists. Traditionally, drugs for the treatment of overactive bladder have had a peripheral site of action. Drugs acting on ARs or membrane channels, as well as prostaglandin synthase inhibitors and several other agents, have been used with moderate success. However, recent developments may lead to more effective drugs, including potassium channel openers, prostaglandins, selective and nonselective inhibitors of cyclooxygenase and those acting on the beta(3)-ARs in the human detrusor. Drugs that reduce afferent activity represent an attractive therapeutic approach, and transmitters of afferent nerves and their receptors are possible targets for pharmacologic interventions.

Drug therapy for urinary incontinence

Drugs used for treatment of urinary incontinence may act on the central nervous system (CNS) or peripherally. Few drugs with a defined CNS site of action are available for treatment of urine storage disorders; most of those currently used have a peripheral site of action. To treat bladder overactivity associated with urgency and urge incontinence, antimuscarinic drugs, alpha-adrenoceptor antagonists, beta-adrenoceptor agonists, prostaglandin synthesis inhibitors, and several other agents most often developed for non-urological indications, are employed. Current treatment is based on the use of antimuscarinic drugs, and oxybutynin is, despite a high incidence of side-effects, the gold standard. Pharmacological treatment of stress incontinence has had limited success, and only alpha-adrenoceptor agonists, with and without combination with oestrogens have had a documented effect. New drugs, specifically directed at treatment of urine storage disorders, are desirable.

Pharmacokinetics and effects of intravesical oxybutynin on the paediatric neurogenic bladder

OBJECTIVE

To evaluate the pharmacokinetics of both oxybutynin and its active metabolite, N-desethyl oxybutynin (NDO), when the drug is instilled directly into the bladder in children with myelodysplasia and neurogenic bladder disturbance, in whom it may improve continence and decrease the risk of upper urinary tract deterioration.

PATIENTS AND METHODS

The study comprised 13 children (five girls and eight boys, mean age 9.3 years, range 1-15) with neurogenic bladders who were treated using clean intermittent catheterization and intravesical instillation of a sterile, pharmacy-produced solution of oxybutynin. Steady-state minimum plasma levels of oxybutynin and NDO, together with their effect on urodynamic variables and incontinence, were evaluated. The dose (0.04-0.17 mg/kg, mean 0.1 mg/kg) was instilled twice daily.

RESULTS

The effects of the drug on incontinence and urodynamic variables were pronounced, improving both in most cases. Minimum plasma levels were < 0.3-7.2 ng/mL for oxybutynin and 0.8-14 ng/mL for NDO. The ratio of oxybutynin to NDO was 0.29-0.83 (mean 0.47).

CONCLUSION

There was no clear relationship between minimum plasma levels of the drug or NDO and their clinical effects; however, the combination of oxybutynin and NDO seemed to be more strongly correlated with the clinical effects.

Effect of choline ester analogues, noradrenaline and nifedipine on normal and hypertrophied human urinary bladder detrusor muscle

1. Acetylcholine, bethanechol, carbachol and propionylcholine were all agonists of normal human detrusor smooth muscle. The order of potency was found to be carbachol > acetylcholine > bethanachol > propionylcholine. 2. In hypertrophied detrusor smooth muscle carbachol was more potent than acetylcholine, but hypertrophied detrusor preparations were less sensitive to carbachol than normal detrusor smooth muscle. 3. Noradrenaline had no direct effect on either normal or hypertrophied detrusor muscle, but it had a reversible inhibitory effect on the spontaneous contractile activity of normal detrusor preparations. Hypertrophied detrusor preparations usually lacked such spontaneous activity. 4. In calcium-free saline, agonist-induced responses of both normal and hypertrophied detrusor muscle were dramatically reduced indicating that choline ester activity in the muscles was strongly dependent upon extracellular calcium. 5. Nifedipine at 10(-5) mol l-1 inhibited acetylcholine responses and K(+)-induced contractures of both normal and hypertrophied detrusor muscles. Acetylcholine-induced responses of normal detrusor preparations were much more sensitive to inhibition by nifedipine than were the responses of hypertrophied detrusor muscle. 6. The properties and densities of both the muscarinic cholinoreceptors and calcium channels appear to have been altered by the hypertrophic response secondary to benign prostatic hyperplasia.

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.

Alpha-adrenoceptor function before and after chemical sympathectomy in human and feline detrusor muscles

Isolated bladder segments from man and cat were treated with 6-hydroxydopamine (6-OHDA) in vitro. Chemical sympathectomy was evaluated with fluorescence microscopy and found to be very similar to the effect of 6-OHDA administered in vivo to cats. Isometric smooth muscle contractile responses were induced by field stimulation (FS). The amplitude of the responses increased after denervation. The effects of alpha-adrenoceptor agonists and antagonists on the FS-induced contractile responses were compared before and after treatment with 6-OHDA. The reduction in the contractile responses after the addition of noradrenaline to the feline bladder strips was more pronounced after treatment. Phentolamine induced an increase in contractile responses before treatment, an effect not seen afterwards in human bladder strips but which persisted in feline bladder strips. Selective alpha-adrenoceptor agonists did not alter the contractile responses in denervated strips. It is suggested that the function of the alpha-adrenoceptors in the detrusor is to inhibit neuronally mediated contractile responses of smooth muscle.

Effect of phenylpropanolamine on incontinence in children with neurogenic bladders. A double-blind crossover study

In children with myelodysplasia and a low-level spinal cord lesion (low lumbar-sacral), detrusor hyperactivity together with dyssynergic urethral function forms the main pathophysiological basis for incontinence. Pharmacological treatment of incontinence due to neurogenic bladder dysfunction has been tried, mainly with anticholinergics and alpha-adrenoceptor antagonists. In this study, the effects of the alpha-adrenoceptor agonist phenylpropanolamine on urodynamic parameters and incontinence were investigated in 10 patients. Effects on incontinence were evaluated in a double-blind crossover trial. Plasma concentrations of phenylpropanolamine were measured by means of gas chromatography-mass spectrometry. Phenylpropanolamine reduced detrusor hyperactivity and improved continence, but the effect was not so pronounced as to make the patients continent.

Influence of adrenergic agonists and antagonists on urethral pressure, bladder pressure and detrusor hyperactivity in children with myelodysplasia

In children with myelodysplasia and a low lumbar or sacral level of spinal cord lesions detrusor hyperactivity with pressure fluctuations is an almost constant phenomenon contributing to incontinence. In thirteen children with this type of dysfunction the effect of adrenergic agonists and antagonists on bladder and urethral pressures were studied by means of intravesical and urethral pressure recordings during the normal bladder-filling phase. Intravenous infusion of noradrenaline during the bladder-filling phase slightly reduced detrusor hyperactivity and the urethral pressure was increased. Following i.m. injection of the alpha-adrenergic antagonist phentolamine both the intravesical and proximal urethral pressures were reduced to about the same extent and the detrusor hyperactivity decreased. It is concluded that noradrenaline mainly changed urethral pressure while alpha-adrenergic blockade caused decreased tone in both the detrusor and the urethra as well as decreased detrusor hyperactivity.

The effect of noradrenaline on the contractile response of the urinary bladder. An in vitro study in man and cat

In this study, bladder muscle strips from the detrusor of man and cat were used to evaluate the modulating effects of adrenergic agonist and antagonists on the field stimulation induced contractile response. Noradrenaline (NA) inhibited and phentolamine enhanced the contraction in a dose-dependent manner. Propranolol did not influence the field stimulation response. When a study of the combined effect of adrenergic drug influence was performed, the NA-induced inhibition was partly reversed by propranolol but a further increase of the contractile response compared to the control was seen, when phentolamine was added. No species differences were found. The conclusion drawn from these results is, that the inhibiting effect of NA on the contractile response is mediated via alpha- and beta-adrenergic receptors. The former could be located on the short parasympathetic intramural neurons while the latter probably are located on muscle cells.

Correlation of detrusor vesicae activity to radiologic findings in childhood myelodysplasia

In selected cases of childhood myelodysplasia associated with incontinence oral anticholinergics, e.g. atropine, may significantly improve the results of continence training programs. At present, the differentiation of patients who may benefit from this kind of pharmacotherapy from those who do not respond calls for laborious recordings of the intravesical pressure. Urography and micturition cystourethrography routinely used for the morphologic evaluation of the urinary tract were compared with the pressure tracings. No useful correlation between findings was obtained, thus excluding the possibility to replace the pressure studies by the much simpler radiologic examinations.

Continence training of children with neurogenic bladder and detrusor hyperactivity: effect of atropine

Recording of the intravesical pressure throughout the filling phase in children with low lumbar and high sacral levels of myelodysplasia showed detrusor hyperactivity which could be inhibited by anticholinergic medication in a dose-dependent manner under experimental conditions. Atropine as treatment for urinary incontinence during everyday activity was remarkably effective when given parenterally. Orally administered atropine was associated with 50-100% improvement of incontinence in six of 9 patients and 35-45% in the remaining three patients. Successful treatment with anticholinergic drugs requires careful selection of patients, including recording of the filling-phase intravesical pressure. Only in patients with detrusor hyperactivity is a good result of such treatment to be expected.

Observations on the internal sphincter mechanism during the filling phase in children with hyperactive neurogenic bladder

The internal sphincter mechanism in the urinary bladder was investigated in three groups of children. Two groups had neurogenic bladder, one of them with and one without detrusor hyperactivity. The third group had no myelodysplasia and normal detrusor activity in the filling phase. In this group the sphincter contractions were sustained at high pressure level, with superimposed waves of substantial amplitude. Myelodysplasia of segments below L3 was associated with hyperactivity of the detrusor. The general sphincter pattern in this condition was the same as in the normal group, but the behavior of the sphincter was not synchronized with the pressure fluctuations in the bladder. In the children with low thoracic or high lumbar level of lesion ther was no detrusor hyperactivity. Their sphincter mechanism could be characterized as passive, with low mean pressure and low amplitude of superimposed waves. When detrusor hyperactivity is present, it seems to be the main factor in leakage from neurogenic bladder. In the absence of detrusor hyperactivity in neurogenic bladder, passivity of the internal urethral sphincter due to dissociation from the spinal centers is proposed as the explanation of incontinence.