Effects of Combination Treatment of Alpha 1-Adrenergic Receptor Antagonists on Voiding Dysfunction: Study on Target Organs in Overactive Bladder Rats

PURPOSE: Overactive bladder (OAB) causes urinary urgency, usually accompanied by frequency and nocturia. Alpha 1-adrenergic receptor (α(1)-AR) antagonists are known to improve lower urinary tract symptoms associated with OAB. The α(1)-AR antagonists constitute a variety of drugs according to the receptor subtype affinity. This study investigated the efficacy of tamsulosin, naftopidil, and a combination of the two on OAB rats. METHODS: The OAB rat model was induced by an intraperitoneal injection of cyclophosphamide for 14 days. The experimental groups were divided into 5 groups: control group, OAB-induction group, OAB-induction and tamsulosin monotherapy group, OAB-induction and naftopidil monotherapy group, and OAB-induction and tamsulosin-naftopidil combination therapy group. For the drug-treated groups, each drug was administrated for 14 days after the OAB induction. Cystometry for urodynamic evaluation and immunohistochemical stain for c-Fos and nerve growth factor (NGF) expressions in the central micturition centers were performed. RESULTS: Increased contraction pressure and time with enhanced c-Fos and NGF expressions in the central micturition centers were found in the OAB rats. Tamsulosin suppressed contraction pressure and time while inhibiting c-Fos and NGF expressions. Naftopidil showed no significant effect and combination therapy showed less of an effect on contraction pressure and time. Naftopidil and combination therapy exerted no significant effect on the c-Fos and NGF expressions. CONCLUSIONS: Tamsulosin showed the most prominent efficacy for the treatment of OAB compared to the naftopidil and combination. The combination of tamsulosin with naftopidil showed no synergistic effects on OAB; however, further studies of addon therapy might provide opportunities to find a new modality.