Synergic Suppressive Effect of Silodosin and Imidafenacin on Non-Voiding Bladder Contractions in Male Rats with Subacute Bladder Outlet Obstruction

Objectives: To investigate single or combined effect of silodosin, an α1A-adrenoceptor antagonist, and imidafenacin, an antimuscarinic agent, on bladder function in a subacute bladder outlet obstruction (BOO) model of male rats. Methods: Partial BOO was created in male Wistar rats by ligating the urethra with a steel rod. On day 10 after surgery, when frequent voiding was most remarkable on voiding behavior measurement in a metabolic cage, cystometric investigations in a conscious restrained condition were conducted with cumulative intravenous administration of silodosin alone (0.1, 1, 10, and 100 µg/kg), imidafenacin alone (1, 3, and 10 µg/kg), or a combination of the two drugs. Results: When compared with the Sham rats, the BOO rats showed an increase in bladder capacity, residual volume, mean amplitude and the number of non-voiding contractions (NVCs), accompanied with an increase in bladder weight. In the BOO rats, silodosin alone at 100 µg/kg significantly decreased the number of NVCs, whereas imidafenacin alone at 3 and 10 µg/kg significantly decreased both the number and mean amplitude of NVCs. The combination administration with lower doses (silodosin at 10 µg/kg and imidafenacin at 1 µg/kg) significantly suppressed both the number and mean amplitude of NVCs. Conclusions: The present results indicate a suppressive effect of silodosin or imidafenacin alone and a synergic effect of the combination of these two drugs on NVCs in a subacute BOO model of male rats.