Inhibitory effects of CL316243, a beta 3-adrenoceptor agonist, on the myogenic activities and on the mechanosensitive afferent activities in the obstructed rat bladder

Watanabe D1, Aizawa N1, Suzuki M2, Kume H2, Igawa Y1

Research Type

Basic Science / Translational

Abstract Category

Pharmacology

Abstract 233
Autonomic Pharmacology
Scientific Podium Short Oral Session 12
Wednesday 4th September 2019
17:15 - 17:22
Hall H2
Animal Study Bladder Outlet Obstruction Physiology
1.Department of Continence Medicine, The University of Tokyo Graduated School of Medicine, Tokyo, Japan, 2.Department of Urology, The University of Tokyo Graduated School of Medicine, Tokyo, Japan
Presenter
D

Daiji Watanabe

Links

Abstract

Hypothesis / aims of study
It has been reported that β3-adrenoceptor (β3-AR) agonists can inhibit non-voiding contractions (NVCs) of the hypertrophied bladder in rats with bladder outlet obstruction (BOO) [1]. Moreover, bladder myogenic microcontractions may link to the single-unit mechanosensitive afferent activities (SAAs) of Aδ-fiber, and β3-AR agonists inhibit the afferent activities through the suppression of the microcontractions in normal rats [2]. In addition, SAAs of Aδ- and C-fibers were intermittently enhanced by propagation of bladder myogenic microcontractions in BOO rats [3]. In this study, we investigated the effects of CL316243, a β3-AR agonist, on the myogenic activities and on the SAAs of the bladder in BOO rats.
Study design, materials and methods
Female Sprague-Dawley rats weighing 190 to 210 gm were used. The proximal urethra was tightly ligated with a steel rod (1.1 mm in diameter), then the rod was removed. This ligation was kept before the experiments. Six weeks after the surgery, cystometry (CMG) and SAAs measurements were performed. Continuous CMG measurements were performed under an awake and free-moving condition. A PE-50 catheter with a cuff was implanted into the bladder a day before the measurements. Saline was instilled into the bladder at a rate of 20 mL/h. CMG recordings were repeated three times both before and after the intravenous (i.v.) administration of CL316243 (10 μg/kg). The following parameters were averaged and analyzed before and after CL316243-administration: voided volume (VV), residual volume (RV), intercontraction interval (ICI), basal pressure (BP), threshold pressure (TP), the maximum pressure (MP) during a micturition, and the number of NVCs. NVCs were defined as bladder contractions without micturition, of which amplitude was greater than 2 cmH2O.
SAAs measurements were performed under a urethane-anesthetized condition (1.0 g/kg, intraperitoneally). Bilateral L6 dorsal roots were transected via a laminectomy. The fine filaments were dissected from the left L6 dorsal roots and placed across a bipolar electrode for monitoring SAAs. Nerve fibers primarily originating from the bladder were identified by electrical stimulation of the left pelvic nerve and by bladder distension. Nerves with conduction velocities (CV) more than 2.5 m/second were designated as Aδ-fibers and those with CV less than 2.5 m/second as C-fibers. The bladder was emptied and saline instilled until the intravesical pressure reached 30 cmH2O. The bladder was kept under an isovolumetric condition, allowed to stabilize for 5 min, and then CL316243 (10 μg/kg, i.v.) was administered i.v. and recording was performed for 5 min. Mean bladder pressure, number of microcontractions and SAAs were analyzed before and after CL316243-administration. All data are expressed as mean ±SEM. Both results between before and after administration were analyzed using an unpaired Student’s t-test. P-values <0.05 were considered statistically significant.
Results
In continuous CMG, 9 rats were used. After the administration of CL316243, the MP and the number of NVCs were decreased, while other parameters did not change (Table 1). In SAA measurements, 10 rats were used and totally 16 SAAs (Aδ-fibers: n=9, C-fibers: n=7) were isolated. CL316243 significantly decreased the mean intravesical pressure and the number of microcontractions. SAAs of Aδ-fibers, but not C-fibers, were also decreased after CL316243-administration (Fig. 1).
Interpretation of results
As harmonized with a previous study [1], CL316243 decreased NVCs. Also similarly in the SAAs measurements, bladder microcontractions were decreased after CL316243-administration. These present results suggest that CL316243 can inhibit bladder myogenic activities in BOO rats. In addition, the present SAAs measurements showed an inhibitory effect of CL316243 on the Aδ-fibers, but not on the C-fibers, suggesting that CL316243 can inhibit the SAAs of Aδ-fibers at least partly due to suppressing bladder myogenic activities in BOO rats like as in normal rats.
Concluding message
The present results suggest that β3-AR agonists inhibit the SAAs of Aδ-fiber at least partly due to suppressing bladder myogenic activities in female BOO rats. These results may give us a possible mechanism involved in the inhibitory action of β3-AR agonists on OAB associated with BOO.
Figure 1 Table 1. CMG parameters before and after CL316243-administration during continuous CMG measurements (N=9)
Figure 2 Figure 1. A: Representative traces of intravesical pressure and mechanosensitive SAAs of Aδ-fibers under an isovolumetric condition. B: Each parameter analyzed for 3 minutes interval
References
  1. Woods M, Carson N, Norton NW, Sheldon JH, & Argentieri TM (2001). Efficacy of the beta 3-adrenergic receptor agonist CL-316243 on experimental bladder hyperreflexia and detrusor instability in the rat. J Urol 166: 1142-1147.
  2. Aizawa N, Homma Y, & Igawa Y (2012). Effects of mirabegron, a novel beta3-adrenoceptor agonist, on primary bladder afferent activity and bladder microcontractions in rats compared with the effects of oxybutynin. Eur Urol 62: 1165-1173.
  3. Aizawa N, Ichihara K, Fukuhara H, Fujimura T, Andersson KE, Homma Y, et al. (2017). Characteristics of the mechanosensitive bladder afferent activities in relation with microcontractions in male rats with bladder outlet obstruction. Scientific reports 7: 7646.
Disclosures
<span class="text-strong">Funding</span> None <span class="text-strong">Clinical Trial</span> No <span class="text-strong">Subjects</span> Animal <span class="text-strong">Species</span> Rat <span class="text-strong">Ethics Committee</span> Animal Ethics Committee, The University of Tokyo Graduate School of Medicine