The role of spinal and peripheral alpha1- and alpha2-adrenoceptors on bladder activity induced by bladder distension in anaesthetized rat.

OBJECTIVE: To elucidate the effects of alpha1- and alpha2-adrenoceptor antagonists on the micturition reflex induced by bladder distension in the anaesthetized rat at the peripheral and spinal level. Materials and methods Using continuous cystometry in 80 anaesthetized female Sprague-Dawley rats, changes in basal pressure (BaP), micturition pressure (MP), bladder capacity (BC), micturition volume (MV), interval of bladder contraction (frequency) and residual volume (RV) to the selective intra-arterial and intrathecal administration of drugs were monitored and analysed.
RESULTS: The intra-arterial administration of phentolamine, prazosin, doxazosin and tamsulosin significantly decreased the MP; doxazosin increased MV, BC, RV and frequency. MP was inhibited more by intra-arterial doxazosin than by prazosin or tamsulosin. Intrathecal phentolamine increased BaP, BC, RV and decreased MP and MV; tamsulosin decreased frequency and increased BC. Clonidine markedly increased BaP and frequency, whereas MV and BC were significantly lower; yohimbine increased MV, BC and decreased RV. Intra-arterial yohimbine significantly increased MV.
CONCLUSIONS: At the spinal level, the micturition reflex evoked by bladder distension was preferentially suppressed by phentolamine or yohimbine, suggesting the involvement of alpha2-adrenoceptors. In the periphery, alpha1-adrenoceptor blockers preferentially suppressed the reflex. We suggest that both alpha1- and alpha2-adrenoceptors play a role in the distension-evoked micturition reflex in the rat.