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

Effect of tibial nerve stimulation on bladder afferent nerve activity in a rat detrusor overactivity model

OBJECTIVES

To study the post-stimulation effect of tibial nerve stimulation on rat bladder afferent activity, and urodynamic parameters in normal and acetic acid-induced detrusor overactivity conditions.

METHODS

In urethane anesthetized male Wistar rats, the tibial nerve was stimulated for 30 min at 5 Hz, pulse width 200 μs and amplitude approximately threefold the threshold to induce a slight toe movement. The post-stimulation effect was studied by measuring afferent nerve activity of postganglionic pelvic nerve branches and various urodynamic parameters under two different conditions: (i) in physiological saline filling experiments (simulating normal bladder condition); and (ii) in acetic acid irritated bladders (simulating detrusor overactivity).

RESULTS

After 30 min of tibial nerve stimulation in saline filling experiments, the bladder capacity, threshold pressure and afferent nerve activity were not significantly different from the prestimulation measurements. The instillation of 0.5% acetic acid significantly reduced the bladder capacity and increased the afferent nerve activity. Tibial nerve stimulation significantly improved the bladder capacity and suppressed the afferent nerve activity compared with prestimulation acetic acid measurements.

CONCLUSIONS

Tibial nerve stimulation is able to significantly restore the bladder capacity by inhibiting afferent nerve activity in chemically irritated rat bladders. The present study provides important basic electrophysiological evidence to substantiate the clinical use of tibial nerve stimulation for treatment of symptoms related to detrusor overactivity.

Urodynamic effects of oxybutynin and tolterodine in conscious and anesthetized rats under different cystometrographic conditions

Background

Antimuscarinic agents are the most popular treatment for overactive bladder and their efficacy in man is well documented, producing decreased urinary frequency and an increase in bladder capacity. During cystometry in rats, however, the main effect reported after acute treatment with antimuscarinics is a decrease in peak micturition pressure together with little or no effect on bladder capacity. In the present experiments we studied the effects, in rats, of the two most widely used antimuscarinic drugs, namely oxybutynin and tolterodine, utilising several different cystometrographic conditions. The aim was to determine the experimental conditions required to reproduce the clinical pharmacological effects of antimuscarinic agents, as seen in humans, in particular their ability to increase bladder capacity.

Results

Intravenous or oral administration of tolterodine or oxybutynin in conscious rats utilized 1 day after catheter implantation and with saline infusion at constant rate of 0.1 ml/min, gave a dose-dependent decrease of micturition pressure (MP) with no significant change in bladder volume capacity (BVC). When the saline infusion rate into the bladder was decreased to 0.025 ml/min, the effect of oral oxybutynin was similar to that obtained with the higher infusion rate. Also, experiments were performed in rats in which bladders were infused with suramin (3 and 10 μM) in order to block the non-adrenergic, non-cholinergic component of bladder contraction. Under these conditions, oral administration of oxybutynin significantly reduced MP (as observed previously), but again BVC was not significantly changed.

In conscious rats with bladders infused with diluted acetic acid, both tolterodine and oxybutynin administered at the same doses as in animals infused with saline, reduced MP, although the reduction appeared less marked, with no effect on BVC.

In conscious rats utilized 5 days after catheter implantation, a situation where inflammation due to surgery is reduced, the effect of tolterodine (i.v.) and oxybutynin (p.o.) on MP was smaller and similar, respectively, to that observed in rats utilized 1 day after catheter implantation, but the increase of BVC was not statistically significant.

In anesthetized rats, i.v. administration of oxybutynin again induced a significant decrease in MP, although it was of questionable relevance. Both BVC and threshold pressure were not significantly reduced. The number and amplitude of high frequency oscillations in MP were unmodified by treatment.

Finally, in conscious obstructed rats, intravenous oxybutynin did not modify frequency and amplitude of non-voiding contractions or bladder capacity and micturition volume.

Conclusion

Despite the different experimental conditions used, the only effect on cystometrographic parameters of oxybutynin and tolterodine in anesthetized and conscious rats was a decrease in MP, whereas BVC was hardly and non-significantly affected. Therefore, it is difficult to reproduce in rats the cystometrographic increase in BVC as observed in humans after chronic administration of antimuscarinic agents, whereas the acute effects seem more similar.

Experimental model of bladder instability in rabbits

OBJECTIVE

Propose a new experimental model of bladder instability in rabbits after partial bladder obstruction.

MATERIALS AND METHODS

Thirty North Folk male rabbits, weighting 1,700 to 2,820 g (mean: 2,162 g) were studied. The animals were distributed in 2 experimental groups, formed by 15 rabbits each: Group 1 - clinical control. In this group there was no surgical intervention; Group 2 - bladder outlet obstruction. In this group, after anesthetizing the animal, urethral cannulation with Foley catheter 10F was performed and then an adjustable plastic bracelet was passed around the bladder neck. It was then adjusted in order to not constrict the urethra. The following parameters were studied in M1 - pre-operative period; M2 - 4 weeks post-operatively moments: 1)- urine culture; 2)- cystometric study; 3)- serum creatinine and BUN.

RESULTS

Bladder weight was 2.5 times larger in the group with obstruction than in the control group. Cystometric evaluation showed a significant increase in maximal vesical volume in the final moment at Group G2. However, there was no statistically significant difference among the groups studied. There was no statistically significant difference between maximal detrusor pressure and vesical compliance in the different moments or in the studied groups. There was an absence of uninhibited detrusor contractions in all the animals in group 1, and involuntary contractions were detected in 93% of group 2 animals. There was no significant variation in BUN and serum creatinine either among the groups or in the same group.

CONCLUSIONS

We observed in the group with obstruction a bladder weight 2.5 higher than normal bladders. We detected involuntary contractions in 93% of the animals in group 2, establishing this experimental model as appropriate to secondary bladder instability and partial bladder outlet obstruction.

Oxybutynin for diagnosis of infravesical obstruction in boys with urinary incontinence

OBJECTIVES

To investigate whether good suppression of symptoms during anticholinergic therapy in boys with urinary urge incontinence is correlated with anatomic infravesical obstruction.

METHODS

In a prospective study, 65 boys with urge incontinence were treated temporarily with anticholinergics. The effect of therapy was assessed, and a full video-urodynamic evaluation was performed. When obstruction could not be excluded urodynamically, urethrocystoscopy was done to assess the level and severity of obstruction, followed by endoscopic treatment. The effect of oxybutynin on incontinence was compared with the presence or absence of obstruction.

RESULTS

In 49 of 65 boys aged 4 to 14 years with daytime urge incontinence, infravesical obstruction was found. Of the 49 boys, 38 (76%) had a good response to anticholinergic therapy. Of the 16 boys without infravesical obstruction, 12 (75%) did not improve with anticholinergic therapy. When anticholinergic therapy was used as a diagnostic test for infravesical obstruction, we found a positive predictive value and negative predictive value of 90% (95% confidence interval 74% to 96%) and 52% (95% confidence interval 31% to 73%), respectively.

CONCLUSIONS

The effect of anticholinergic therapy on urge incontinence can be used as a diagnostic test to differentiate between anatomic infravesical obstruction and other causes of incontinence in boys.

The overactive bladder: neuropharmacological basis of clinical management

The overactive bladder continues to pose a major challenge to clinicians treating lower urinary tract disorders, not least because our understanding of the pathogenesis of detrusor overactivity is still relatively limited. However, progress in understanding the basis of the overactive bladder is moving steadily forward, accompanied by a growing number of different forms of treatment. New pharmacological treatments and variations in the mode of delivery of older agents offer hope of efficacy with fewer side-effects. Neuromodulation is also offering a viable alternative to surgery in patients unresponsive to medical treatment.

Overactive detrusor

Detrusor overactivity poses a major challenge to physicians from many specialities. Progress in our understanding of the pathogenesis of detrusor overactivity is slow but steady. Advances in treatment continue to be made, both with new agents and new methods of delivering older drugs. Neuromodulation is showing great promise as experience increases, and developments in bladder augmentation offer hope for lower morbidity treatments in future.