Objectives: We examined the effects of alpha1-adrenoceptor antagonist (tamsulosin hydrochloride) and antimuscarinic agent (solifenacin succinate) alone or in combination on the urinary adenosine triphosphate (ATP) level and cystometric parameters before and after bladder stimulation.
Methods: Female rats were administered tamsulosin hydrochloride (0.5 or 3 µg/kg/h) and/or solifenacin succinate (20 or 100 µg/kg/h) via a subcutaneously implanted osmotic minipump. Rats receiving distilled water were used as control. After 2 weeks, continuous cystometry with physiological saline or 0.1% acetic acid solution was performed. Urinary ATP level was also measured before and after stimulation by 0.1% acetic acid solution.
Results: During cystometry with bladder stimulation, the interval between voiding became shorter and the maximum voiding pressure (MVP) became higher in the control group. In the high-dose tamsulosin and solifenacin groups, the inhibition of urinary frequency was observed. The MVP also became higher in the high-dose tamsulosin group, but such a change was not seen in the high-dose solifenacin group. In case of low-dose administration, either agent alone did not inhibit the increase of urinary frequency and MVP due to bladder stimulation. However, co-administration of these ineffective low doses of tamsulosin and solifenacin resulted in the inhibition of urinary frequency. The high-dose or low-dose solifenacin group and the co-administration group showed similar inhibition of the increase of urinary ATP after bladder stimulation.
Conclusion: Tamsulosin may have a different effect on the bladder and/or the neuronal pathways that is unrelated to ATP, so the combination of tamsulosin and solifenacin may synergistically inhibit urinary frequency after bladder stimulation.