Effects of α-adrenoceptor agents on norepinephrine release from vas deferens of several species including man

Unlike the situation with the vas deferens of rats, guinea-pigs, rabbits an dogs, neither phentolamine nor yohimbine enhanced electrically-evoked release of [ 3H]norepinephrine from the in vitro human vas deferens. However, clonidine produced, by a phentolamine-sensitive mechanism, a concentration-related inhibition of release inthe human vas deferens. The results indicate that, even though presynaptic α-adrenoceptors exist, a negative feedback regulation of release by norepinephrine, which occurs in the vas deferens of the other species, may not be functionally important in the vas deferens of the human.