Additive effects of intravenous and intravesical application of vibegron, a β3-adrenoceptor agonist, on bladder function in rats with bladder overactivity

To examine the effects of intravenous and intravesical application of vibegron, a new β₃-adrenoceptor (β₃-AR) agonist, on bladder function in rats with oxotremorine methiodide (oxo-M: a nonselective muscarinic receptor agonist)-induced bladder overactivity. Cystometry was performed in conscious female rats with intravesical instillation of oxo-M (200 μM). In oxo-M-treated rats, vehicle or vibegron (1 and 10 mg/kg) was cumulatively applied intravenously at 30-min intervals. In other groups of rats, oxo-M + vehicle or oxo-M + vibegron (10, 100 μM, and 1 mM) was cumulatively instilled intravesically at 60-min intervals followed by intravenous application of vibegron (10 mg/kg). Expression of β₃-ARs in the bladder was also evaluated using immunohistochemical staining. Intravenous application of vibegron (10 mg/kg) significantly increased bladder capacity (1.3 times) and decreased baseline, threshold, and maximal voiding pressure compared with vehicle. Next, intravesical application of vibegron (1 mM) significantly increased threshold pressure and bladder capacity (1.2 times) compared with vehicle. Combined treatments of intravesical (1 mM) and intravenous (10 mg/kg) application of vibegron induced a significantly larger degree of increases in bladder capacity (1.4 times) compared with vehicle. In addition, β₃-ARs were expressed throughout the rat bladder, mainly in the urothelium. These results suggest that vibegron excreted in urine as an unchanged compound can induce the additive inhibitory effects on bladder overactivity possibly through urothelial β₃-AR activation, which inhibits the afferent limb of micturition reflex rather than the efferent function as evidenced by the increases in threshold pressure and bladder capacity without affecting bladder contractile function after intravesical vibegron application.