Comparison of the effects of β3 -adrenoceptor agonism on urinary bladder function in conscious, anesthetized, and spinal cord injured rats

Effect of β3-adrenoceptor agonist on the micromotion of bilateral major pelvic ganglion-excised rat bladder

AIMS

Micromotion is an autonomous intramural movement of the bladder, and is believed to be an initial step in the generation of urinary urgency. Therefore, controlling micromotion may be a novel target in overactive bladder (OAB) treatment. However, developing micromotion treatment has been limited by the absence of a standardized animal model. We attempted to create a micromotion animal model and investigated the effectiveness of a β₃ -adrenoceptor agonist (CL316,243) on micromotion.

METHODS

Bilateral major pelvic ganglia (MPGs) were excised in 18 male Sprague-Dawley rats, resulting in an almost completely denervated bladder. On postoperative Day 7, cystometry was performed. Rats were divided into three treatment groups: CL316,243; β_3- adrenoceptor antagonist (SR59230A) pretreated CL316,243; and a nonselective antimuscarinic agent (oxybutynin). Changes in micromotion were evaluated after the intra-arterial administration of each agent.

RESULTS

Low-amplitude oscillations in intravesical pressure (micromotion) were observed 1 week after MPGs excision. Micromotion frequency significantly (p = 0.003) decreased (2.17 ± 3.54 times/5 min) with CL316,243 compared with vehicle (6.33 ± 1.97 times/5 min). Micromotion amplitude also decreased with CL316,243 (1.15 ± 1.93 cmH₂ O) compared with vehicle (5.96 ± 5.12 cmH₂ O), approaching conventional significance (p = 0.090). No significant decreases in frequency or amplitude were observed with oxybutynin treatment.

CONCLUSIONS

Systemic administration of the β₃ -adrenoceptor agonist CL316,243 effectively controlled micromotion in bilateral MPGs-excised, almost completely denervated rat bladders. This result indicates that β₃ -adrenoceptor agonist may affect the bladder directly, suggesting that it might be effective for overall OAB, regardless of the presence or level of neurological deficits. Bilateral MPGs-excised rats are considered a plausible micromotion animal model suitable for future research.

The Efficacy and Safety of Mirabegron for the Treatment of Neurogenic Lower Urinary Tract Dysfunction: A Systematic Review and Meta-analysis

Background and Objective: Over the past few years, mirabegron has been increasingly used as a therapeutic option for neurogenic lower urinary tract dysfunction. Here, we carried out a meta-analysis to investigate the efficacy and safety of mirabegron for the treatment of neurogenic lower urinary tract dysfunction.

Methods: We used a range of databases to retrieve randomized controlled trials (RCTs) relating to mirabegron in patients with neurogenic lower urinary tract dysfunction: PubMed, Embase, and Cochrane Library; our strategy conformed to the PICOS (populations, interventions, comparators, outcomes, and study designs) strategy.

Results: Our analyses involved four RCTs involving 245 patients. We found that mirabegron treatment resulted in a significant improvement in bladder compliance [mean difference (MD) = 19.53, 95% confidence interval (CI): 14.19 to 24.87, P < 0.00001], urinary incontinence episodes (MD = −0.78, 95% CI: −0.89 to −0.67, P < 0.00001) and Incontinence Quality of Life (I-QOL) (MD = 8.02, 95% CI: 3.20 to 12.84, P = 0.001). Significant differences were detected in terms of Patient Perception of Bladder Condition (PPBC) (MD = −0.54, 95% CI: −1.46 to 0.39, P = 0.26) and urinary urgency episodes (MD = −0.72, 95% CI: −3.1 to 1.66, P = 0.55). With regard to safety, there were no significant differences between mirabegron and control groups in terms of the incidence of drug-related adverse events [odds ratio (OR): 0.83, 95% CI: 0.43 to 1.59, P = 0.57], arrhythmias (OR: 1.27, 95% CI: 0.37 to 4.38, P = 0.70), hypertension (OR: 0.70, 95% CI: 0.13 to 3.82, P = 0.68), or post-voiding residual volume (MD: 1.62, 95% CI: −9.00 to 12.24, P = 0.77).

Conclusion: Mirabegron is an efficacious and safe treatment for patients with neurogenic lower urinary tract dysfunction.

β3 -Adrenoceptors in the normal and diseased urinary bladder-What are the open questions?

β₃ -Adrenoceptor agonists are used in the treatment of overactive bladder syndrome. Although the relaxant response to adrenergic stimulation in human detrusor smooth muscle cells is mediated mainly via β₃ -adrenoceptors, the plasma concentrations of the therapeutic dose of mirabegron, the only clinically approved β₃ -adrenoceptor agonist, are considerably lower than the EC₅₀ for causing direct relaxation of human detrusor, suggesting a mechanism of action other than direct relaxation of detrusor smooth muscle. However, the site and mechanism of action of β₃ -adrenoceptor agonists in the bladder have not been firmly established. Postulated mechanisms include prejunctional suppression of ACh release from the parasympathetic nerves during the storage phase and inhibition of micro-contractions through β₃ -adrenoceptors on detrusor smooth muscle cells or suburothelial interstitial cells. Implications of possible desensitization of β₃ -adrenoceptors in the bladder upon prolonged agonist exposure and possible causes of rarely observed cardiovascular effects of mirabegron are also discussed. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

A pilot randomized-controlled trial of the urodynamic efficacy of mirabegron for patients with neurogenic lower urinary tract dysfunction

AIMS

To determine the effectiveness of mirabegron in patients with neurogenic lower urinary tract dysfunction.

METHODS

Randomized, double-blind, placebo-controlled study. Canadian patients with spinal cord injury (SCI) or multiple sclerosis (MS) with urinary symptoms and incontinence were recruited. Patients were randomized to mirabegron 25 mg (or an identical placebo) for 2 weeks at which point a dose escalation to mirabegron 50 mg (or an identical placebo) was maintained for 8 weeks. Urodynamics were performed before and after treatment. The primary outcome measure was maximum cystometric capacity (MCC). Intention to treat analysis and ANCOVA models (with adjustment for baseline values) were used and marginal means (MM) are reported; P-value <0.05 was considered significant.

RESULTS

Sixteen (9 SCI and 7 MS) patients were randomized to mirabegron and 16 (10 SCI and 6 MS) to placebo. At study completion, there was no significant difference in MCC between mirabegron and placebo (MM 305 vs 369 mL, P = 0.20). There was no significant difference in volume at first neurogenic detrusor overactivity (NDO, MM 167 vs 137 mL, P = 0.14) and peak pressure of NDO (MM 69 vs 82 cmH₂ O, P = 0.25). There was no significant difference in pad weights or voiding diary parameters. There was a significantly lower symptom burden among those treated with mirabegron (total neurogenic bladder symptom score MM 29 vs 34, P = 0.047).

CONCLUSIONS

Among patients with SCI or MS, we demonstrated non-significant trends towards improvement in some urodynamic parameters with mirabegron 50 mg compared to placebo, and a significantly lower neurogenic bladder symptom burden.

The potential role of unregulated autonomous bladder micromotions in urinary storage and voiding dysfunction; overactive bladder and detrusor underactivity

The isolated bladder shows autonomous micromotions, which increase with bladder distension, generate sensory nerve activity, and are altered in models of urinary dysfunction. Intravesical pressure resulting from autonomous activity putatively reflects three key variables; the extent of micromotion initiation, distances over which micromotions propagate, and overall bladder tone. In vivo, these variables are subordinate to the efferent drive of the central nervous system. In the micturition cycle storage phase, efferent inhibition keeps autonomous activity generally at a low level, where it may signal 'state of fullness', whilst maintaining compliance. In the voiding phase, mass efferent excitation elicits generalised contraction (global motility initiation). In lower urinary tract dysfunction, efferent control of the bladder can be impaired, for example due to peripheral 'patchy' denervation. In this case, loss of efferent inhibition may enable unregulated micromotility, and afferent stimulation, predisposing to urinary urgency. If denervation is relatively slight, the detrimental impact on voiding may be low, as the adjacent innervated areas may be able to initiate micromotility synchronous with the efferent nerve drive, so that even denervated areas can contribute to the voiding contraction. This would become increasingly inefficient the more severe the denervation, such that ability of triggered micromotility to propagate sufficiently to engage the denervated areas in voiding declines, so the voiding contraction increasingly develops the characteristics of underactivity. In summary, reduced peripheral coverage by the dual efferent innervation (inhibitory and excitatory) impairs regulation of micromotility initiation and propagation, potentially allowing emergence of overactive bladder and, with progression, detrusor underactivity.

Urethane anesthesia in acute lower urinary tract studies in the male rat

Urethane is a widely used anesthetic in animal lower urinary tract research. Our objective was to investigate the quality of anesthesia and the correlation between bladder (voiding) contractions, micturition pressure, bladder capacity and urethane dosage and body weight. Urethane was given subcutaneously and/or intraperitoneally (1.0-1.2 g/kg). The bladder was filled with saline and the bladder pressure was recorded continuously. Animals in which the subcutaneous/intraperitoneal ratio was higher needed less urethane. Heavier animals needed less extra urethane. In animals, in which no bladder contractions could be evoked, the total amount of urethane given was similar to that in those that did show contractions. In the animals that did void, the bladder never emptied completely and residual volumes remained. There was no relationship between animal weight or total amount of urethane and mean capacity. Anesthesia lasted up till 14 h, during which bladder (voiding) contractions could be recorded. Considering all results, we conclude that urethane is a well suited anesthetic for acute lower urinary tract physiological research in the intact rat.

Young rats exhibit an age- and sex-dependent bladder response to alpha-antagonists but not beta-agonists

INTRODUCTION

Previous studies have suggested that the onset of alpha- (α) and beta- (β) adrenergic receptor activity is delayed in young animals. The use of alpha1- (α1-) antagonists for dysfunctional voiding, and beta3- (β3-) agonists for overactive bladder in younger children may not be indicated if maturation is required before bladder and urethral adrenergic receptors are active.

OBJECTIVE

To determine the sex- and age-dependent responses of the bladder and external urethral sphincter (EUS) to α- and β-adrenergic agents in neonatal and young adult rats.

MATERIALS AND METHODS

A total of 72 naïve Sprague-Dawley rats (36 female, 36 male) and 15 bladder-reduced (BR) female Sprague-Dawley rats underwent cystometry and EUS electromyography at 3, 6, and 9 weeks of life. Following administration of WAY 100,635 (0.3 mg/kg, serotonergic receptor antagonist), the non-selective α-agonist phenylephrine (0.3 mg/kg), α-antagonist phentolamine (1-3 mg/kg), β-agonist isoprenaline (3 mg/kg) and β-antagonist propranolol (3 mg/kg) were delivered intravenously. The maximum intravesical pressure (IVP), pressure threshold (PT), intermicturition interval (IMI), contraction duration (CD), burst amplitude and burst frequency were compared after each drug.

RESULTS

The α-antagonist phentolamine lowered the IVP in 9-week-old males without lowering the PT. In contrast, the β-agonist isoprenaline lowered the IVP in both males and females of all ages, also without affecting the PT. Isoprenaline was also effective at shortening the CD in females, suggesting more effective bladder emptying. The α-agonist phenylephrine increased the IVP in 3-week-old and 6-week-old females and 3-week-old males, but this effect was blocked by pretreatment with phentolamine. The β-antagonist propranolol increased the PT in both males and females, and shortened the IMI in females, which was consistent with retention. Phenylephrine increased the burst duration in 9-week-old naïve females, while isoprenaline increased the burst amplitude and duration in 9-week-old BR females.

CONCLUSIONS

In the neonatal rat, both α- and β-adrenergic receptors actively regulate bladder function by 3 weeks of life, but the desired effect of decreasing IVP by α-antagonists was delayed until 9 weeks in male rats. In contrast, β-agonists were effective at decreasing IVP in both male and female rats of all ages, which suggests that they are better agents for enhancing bladder emptying in female and young male rats.