Prejunctional alpha-adrenoceptors regulate nitrergic neurotransmission in the rabbit urethra

We evaluated the effects of prejunctional ol-adrenoceptors on nitric oxide (NO)-mediated urethral relaxation in rabbits using a muscle bath technique and high-performance liquid chromatography coupled with a microdialysis pro cedure. The amount of NO2-/NO3- released during electrical field stimulatio n was measured by an NO2-/NO3- analyzer based on the Griess method. Pretrea tment with phenylephrine (0.01 mu M) acid yohimbine (0.1-10 mu M) significa ntly reduced the relaxation responses induced by electrical field stimulati on. In contrast, pretreatment with clonidine (0.01 mu M) and prazosin (0.01 -1 mu M) enhanced the relaxation responses. Cys-NO-induced relaxations of r abbit urethral smooth muscle were not affected by pretreatment with ol-adre noceptor agonists and antagonists. The amount of NO2-/NO3- released by elec trical field stimulation increased after pretreatment with clonidine (0.01 mu M) and prazosin(0.01-1 mu M), but decreased after pretreatment with phen ylephrine (0.01 mu M) and yohimbine (0.1-10 mu M). The results suggest that the release of NO from nitrergic nerves in the rabbit urethra is reduced a nd increased by stimulation of prejunctional alpha(1)- and alpha(2)-adrenoc eptors, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.