Effect of alpha 1-adrenoceptor antagonists on urinary bladder function in urethane-anesthetized rats

1. We investigated the effects of selective alpha 1-adrenoceptor antagonists on rhythmic bladder contraction and cystometrograms as representative of urinary bladder function in urethane-anesthetized rats. 2. The selective alpha 1-adrenoceptor antagonists tamsulosin (0.03-3 micrograms/kg IV), prazosin (0.03-3 micrograms/ kg IV) and bunazosin (0.03-3 micrograms/kg IV) exerted little effect on the amplitude and frequency of rhythmic bladder contraction in anesthetized rats. In contrast, the antipollakiuria agent flavoxate (5 and 10 mg/kg IV) induced a dose-dependent disappearance in frequency without affecting the amplitude of the contractions. 3. Tamsulosin (1 and 3 micrograms/kg IV), prazosin (1 and 3 micrograms/kg IV), and bunazosin (1 and 3 micrograms/kg IV) exerted no effect on the cystometrogram, either. However, flavoxate (5 and 10 mg/kg IV) raised the micturition threshold pressure and prolonged the time to micturition. 4. These results suggest that the alpha 1-adrenoceptor plays little role in urinary bladder contraction in anesthetized rats.