Effect of the potassium channel opener WAY-133537 on the overactive bladder of spinalized rats

Involvement of TRPM4 in detrusor overactivity following spinal cord transection in mice

Transient receptor potential cation channel subfamily M member 4 (TRPM4) has been shown to play a key role in detrusor contractility under physiological conditions. In this study, we investigated the potential role of TRPM4 in detrusor overactivity following spinal cord transection (SCT) in mice. TRPM4 expression and function were evaluated in bladder tissue with or without the mucosa from spinal intact (SI) and SCT female mice (T8-T9 vertebra; 1-28 days post SCT) using PCR, western blot, immunohistochemistry, and muscle strip contractility techniques. TRPM4 was expressed in the urothelium (UT) and detrusor smooth muscle (DSM) and was upregulated after SCT. Expression levels peaked 3-7 days post SCT in both the UT and DSM. Pharmacological block of TRPM4 with the antagonist, 9-Phenanthrol (30 μM) greatly reduced spontaneous phasic activity that developed after SCT, regardless of the presence or absence of the mucosa. Detrusor overactivity following spinal cord injury leads to incontinence and/or renal impairment and represents a major health problem for which current treatments are not satisfactory. Augmented TRPM4 expression in the bladder after chronic SCT supports the hypothesis that TRPM4 channels play a role in DSM overactivity following SCT. Inhibition of TRPM4 may be beneficial for improving detrusor overactivity in SCI.

Changes in mast cell infiltration: a possible mechanism in detrusor overactivity induced by visceral hypersensitivity

OBJECTIVE

To establish the detrusor overactivity (DO) model induced by visceral hypersensitivity (VH) and investigate the relationship between mast cell (MC) infiltration and DO.

MATERIALS AND METHODS

Sixty rats are divided into 4 groups randomly: Group 1:Baseline group; Group 2: DO group; Group 3: CON group; Group 4: VH group. The colorectal distension (CRD) and abdominal withdral reflex (AWR) scores are performed to evaluate VH. The cystometric investigation and histological test of MC infiltration are assessed.

RESULTS

The threshold pressure of CRD in the VH group is significantly lower than that in the CON group (P<0.001). At the distension pressure ≥20 mmHg, the AWR scores of the VH group are significantly higher than those of the CON group (10 mmHg: P=0.33; 20 mmHg: P=0.028; 40 mmHg: P<0.001; 60 mmHg: P<0.001; 80 mmHg: P<0.001). DO model is successfully established in the VH group (DO rate=100%). Compared with the CON group, the numbers of MC infiltration are significantly increased in the VH group, including submucosa of bladder (P<0.001), mucosa lamina propria/mesentery of small intestine (P<0.001), and mucosa lamina propria/mesentery of large intestine (P<0.001). Furthermore, more MC activation as well as degranulation are observed in the VH group.

CONCLUSIONS

It is indicated that DO model can be established in the VH rats. The MC infiltration may play an important role in DO induced by VH, and may be helpful to understand the mechanisms of DO in VH patients.

Improved model for the establishment and evaluation of detrusor overactivity in female Wistar rats

OBJECTIVE

To improve the model for establishment and evaluation of detrusor overactivity in female Wistar rats.

MATERIALS AND METHODS

We ligated the perineal urethra of female Wistar rats and then performed filling cystometry. The probability of detrusor overactivity, bladder capacity, peak voiding pressure and histological changes were investigated.

RESULTS

Detrusor overactivity ratio of the obstruction group was 32.4%. Bladder capacity increased from 0.273 ± 0.036 mL in control group to 0.89 ± 0.19 mL in detrusor overactivity group (P < 0.001), and peak voiding pressure increased from 45.9 ± 4.1 cm.H2O to 63.5 ± 17.4 cm.H2O (P = 0.007). For obstruction group, compared to no detrusor overactivity rats, detrusor overactivity rats had higher bladder capacity (0.89 ± 0.19 mL versus 0.43 ± 0.09 mL, P < 0.001) and higher peak voiding pressure (63.5 ± 17.4 cm.H2O versus 44.8 ± 6.2 cm.H2O, P = 0.005). Detrusor overactivity rats were classified according to peak voiding pressure (49.2 ± 4.2 cm.H2O versus 80.8 ± 7.1cm.H2O, P < 0.001). Moreover, bladder weight increased significantly in detrusor overactivity rats (P = 0.003, P = 0.028) and detrusor histological hypertrophy was observed.

CONCLUSIONS

Ligating perineal urethra and filling cystometry with intra-urethral cannula approach is a simple and easily reproducible method to establish and evaluate the model of detrusor overactivity in rats.

The timing of established detrusor hyperreflexia in a rat model of neuropathic bladder

BACKGROUND

Proper timing of catheter insertion and the use of a suitable surgical method are essential parts of producing rat models to evaluate neuropathic bladder following spinal cord injury (SCI).

METHODS

Thirty-two female Sprague-Dawley rats were randomly allocated into four groups. Group 1 underwent surgical laminectomy using the classic method. Group 2 underwent SCI 7 d following insertion of the catheter, and group 3 underwent sham operation. For bladder catheterization, a 4.5 Fr catheter was fixed into the bladder and tunneled beneath the skin to reach out at the nape of the neck. Group 4 underwent urodynamic study via bladder catheter prior to surgery and every 10 d following the operation to determine the exact time of establishing neuropathic bladder following spinal shock. The animals' survival rate and bladder wall's histopathologic changes were assessed 30 d following the operation.

RESULTS

Simultaneous suprapubic catheter placement raised the mortality rate in group 1 in comparison with group 2. Repeated urodynamic study in group 4 showed hypertonic behavior in the bladder 10 d after SCI, with significantly increased leak point pressure and bladder capacity; however, the end filling pressure and constant neuropathic bladder on cystometric indices are attained from 20 d after the operation.

CONCLUSIONS

Insertion of a bladder catheter 1 wk prior to SCI provides an applicable route for repeated cystometric studies in rats. The results demonstrate that sustained bladder overactivity is established in rats 20 d after SCI and animals are ready for further experiments on neuropathic bladder dysfunction following this period.

Inhibitory effects of the ATP-sensitive potassium channel openers cromakalim, pinacidil and minoxidil on the carbachol-response curve in porcine detrusor muscle

Aims

ATP-sensitive potassium channels represent promising drug targets for treating specific bladder diseases. The inhibitory effects of ATP-selective potassium channel openers (PCOs) on the carbachol–response curve in porcine detrusor muscle were examined.

Materials and methods

Each of the three substances used in the study represent one prototype of a different class of PCO: cromakalim belongs to the benzopyran series, pinacidil is a cyanoguanidine derivative, and minoxidil represents a pyrimidine derivative. The porcine detrusor muscle represents one of the best models for human detrusor. Experiments were conducted on muscle strips of porcine detrusor muscle suspended in a tissue bath. Concentration–response curves of carbachol were constructed after pretreatment with cromakalim at 10⁻⁷, 10⁻⁶ and 10⁻⁵ M, and with pinacidil and minoxidil at 10⁻⁶, 10^−5.5 and 10⁻⁵ M, respectively. Each muscle strip was only used to examine one concentration of one substance.

Results

Cromakalim had the greatest inhibitory effect, significantly suppressing the carbachol–response curve at 10⁻⁶ and 10⁻⁵ M. Pinacidil showed a significant inhibitory effect at 10^−5.5 and 10⁻⁵ M, which was smaller than that of cromakalim. Minoxidil did not significantly inhibit the contractions at all examined concentrations.

Conclusions

The examined ATP-sensitive PCOs belonging to the benzopyrans and cyanoguanidines significantly suppressed detrusor contractions. The development of derivatives of these prototypes could open new possibilities for the pharmacological treatment of selected bladder diseases.

Phasic activity of urinary bladder smooth muscle in the streptozotocin-induced diabetic rat: effect of potassium channel modulators

Increased phasic activity in the bladder smooth muscle of animal models and patients with detrusor overactivity has been suggested to underlie the pathophysiology of overactive bladder. Potassium (K+) channels are key regulators of bladder smooth muscle tone and thus may play a role in this altered phasic activity. In this study the effects of K+ channel modulators on the phasic activity of bladder strips from the streptozotocin-induced diabetic rat model of bladder dysfunction were investigated. Bladder strips from rats 1 week following streptozotocin administration and age-matched controls were mounted in tissue baths at 37 °C and the effects of K+ channel modulators on resting basal tension or phasic activity induced by a low concentration of carbachol (0.5 μM) were investigated. Activation of BKCa channels by NS1619 had a minor inhibitory effect on carbachol-induced phasic activity of bladder strips from control and diabetic rats, and significantly inhibited amplitude only at 30 μM. Activation of KATP channels by cromakalim inhibited the frequency of carbachol-induced phasic activity of bladder strips, although strips from diabetic rats showed a trend towards being less sensitive to cromakalim. The BKCa channel blocker iberiotoxin was able to induce phasic activity in resting tissues, with diabetic bladder strips demonstrating significantly enhanced phasic activity compared to controls. In contrast, inhibition of SKCa and KATP channels did not induce phasic activity in resting tissues. In conclusion, responses of diabetic rat bladder to BKCa and KATP channel modulators are altered, suggesting altered function and/or expression of channels which may contribute to bladder dysfunction in this model.

Developments in the pharmacotherapy of the overactive bladder

PURPOSE OF REVIEW

The overactive bladder is a common and distressing condition that has a significant impact on the quality of life of many people worldwide. Anticholinergics remain the first line in pharmacotherapy, however the use of these agents is hindered by adverse effects and limited efficacy. Thus there is a need for more effective treatments. Recently, there has been a move towards targeting novel pathways thought to play a role in overactivity. This review aims to provide an insight into the recent developments in pharmacotherapy of the overactive bladder.

RECENT FINDINGS

With recent advances in our understanding of the basic science of the overactive bladder it is becoming clear that the control of bladder functioning is far more complex than previously believed. Peripherally, a prominent role has emerged for the urothelium and the underlying suburothelium in mechanosensory control, and the role of afferent pathways in pathophysiology is increasingly recognized.

SUMMARY

Recent research has highlighted several potential targets for treatment of the overactive bladder, particularly within the mechanosensory pathways. With the exception of botulinum toxin, however, few new therapies have emerged showing clinical benefits. A clearer understanding of the pathophysiology of the bladder will hopefully lead to more effective and tolerated treatments.