Vascular alpha 2-adrenoceptors can mediate nerve stimulation-evoked contractions

It is now established that alpha 2-adrenoceptors can be present on vascular smooth muscle as targets for exogenous agonists, but some controversy exists as to whether these vascular alpha 2-receptors may also be the target for neurally released noradrenaline. In human saphenous vein we have found evidence that the alpha 2-antagonist yohimbine in low concentrations (0.01 mumol/l) can significantly inhibit stimulation-evoked contractions, whereas the alpha 1-antagonist prazosin is more than ten times less potent. It is concluded that, at least in some tissues, neuro-effector transmission can be mediated by vascular alpha 2-adrenoceptors.