Dissociation of presynaptic alpha 2-adrenoceptors following prazosin administration: presynaptic effect of prazosin.

Evidence has been obtained that prazosin possesses a presynaptic alpha 2-adrenoceptor blocking action in the rat was deferens preparation stimulated at 1 Hz. In the presence of prazosin yohimbine failed to affect the presynaptic alpha 2-adrenoceptor stimulatory effect of 1-noradrenaline while the effect of xylazine was almost completely abolished. It is therefore suggested that there are two kinetically different prejunctional alpha 2-adrenoceptor sites.