Modulation of noradrenaline release in vivo through prejunctional alpha-adrenoceptors

1. Extensive in vitro studies have suggested that noradrenaline release from sympathetic nerve endings is modulated by alpha 2-adrenoceptors on the terminal varicosities, activation of which by alpha-adrenoceptor agonists or neuronally released noradrenaline leads to inhibition of transmitter release. 2. Studies in intact animals support essentially the physiological operation of this mechanism, whereas human studies have reached mixed conclusions and more information is required.