The Role of Spinal and Peripheral alpha1 Adrenoceptors in Micturition Reflex in Rats

Jeong, Myung Soo; Lee, Jeong Gu

Abstract

PURPOSE: The role of spinal alpha1 adrenoceptors in normal micturition reflex of rat has not been known clearly yet. The purpose of this study is to elucidate the role of alpha1 adrenoceptor both at the spinal and peripheral level in mediating the micturition reflex which is induced by bladder distension in normal anesthetized rat and to compare the effects of different alpha1 adrenoceptor antagonists against the micturition reflex.
MATERIALS AND METHODS
Wtih eighty female Sprague-Dawley rats(200-250gm) anesthetized with urethane, continuous cystometry was done by infusion of saline at a rate of 0.5ml/min. The following drugs were injected into femoral artery(intraarterial, i.a.) and subarachnoid space(intrathecal, i.t.) at the level of L6-S1 spinal cord segment; phentolamine, prazosin, doxazosin and tamsulosin. Cystometric parameters were analyzed before and after the drug injections; basal pressure(BP), micturition pressure(MP), bladder capacity(BC), micturition volume(MV), frequency and residual volume(RV).
RESULTS
After i.a. injections of prazosin, doxazosin and tamsulosin, MP was significantly decreased. Doxazosin(i.a.), markedly increased MV, BC and RV. MP was more inhibited by doxazosin than prazosin or tamsulosin injection intraarterially. After i.a. injection of phentolamine, decrease in MP and frequency but increase in MV and BC were noted. Phentolamine(i.t.) raised BP and abolished MR followed by overflow incontinence. Prazosin(i.t.) induced marked increases in MV. Tamsulosin(i.t.) caused significant decreases in frequency but increases in BC.
CONCLUSIONS
At spinal level, antagonism of micturition reflex evoked by bladder distension was more prominent by phentolamine. Inhibition of micturition reflex with alpha1 adrenoceptor blockers were greater peripherally. With these results, it could be suggested that micturition reflex evoked by volume-induced bladder distension could be modulated through alpha1 adrenoceptors at both the spinal and peripheral level. In some selected cases, alpha1 adrenoceptor agonist or antagonist can be useful for the management of lower urinary tract dysfunction