The effects of α_1A adrenoceptor antagonists on the urethral perfusion pressure of female rat

Purpose: This study was performed to identify the effects of the α_1A adrenoceptor antagonist on the urethral perfusion pressure (UPP), and also to assess its therapeutic potentials for female bladder outlet obstruction (BOO). Materials and methods: A cannula was placed in the femoral artery for drug administration and systemic blood pressure monitoring in each female rat. The UPP and vesical pressure (Pves) were monitored using a triple-lumen catheter. Tamsulosin (group I), doxazosin (group II) and phentolamin (group III) were injected into female rats via the femoral cannula. Tamsulosin was also injected to male rats (group IV) for comparison with Group I. Results: After administration of tamsulosin in group I, the frequency was significantly decreased and the duration of minimal urethral relaxation with high frequency oscillations (Dhfo) was significantly prolonged. None of the parameters were significantly different compared with groups II and III, with the exception of the mean arterial blood pressure (MAP). The changes of MAP after tamsulosin were significantly lower than those after doxazosin and phentolamin. In the male rats (group IV), prior to the administration of tamsulosin, the UPP and Pves curves were similar to those of the female rats, but the maximal Pves was significantly higher than in group I. After the administration of tamsulosin to group IV, the prolongation of the frequency and Dhfo were significant. Conclusions: In the female rat urethra, the α_1A adrenergic receptor may be a functional subtype. The α _1A adrenoceptor antagonist was found to prolong the Dhfo and decrease the frequency of involuntary bladder contraction. It might be possible that the α_1A adrenoceptor antagonist improves not only the obstructive symptoms, but the bladder irritative symptoms also, by prolonging the Dhfo and frequency of an involuntary bladder contraction.