The hypothalamic supraoptic nucleus (SON) contains both vasopressin-secreting (AVP) and oxytocin-secreting (OT) magnocellular neurons which release their respective hormones from the posterior pituitary gland into the systemic circulation. A direct relationship has been demonstrated in earlier physiological studies between the excitability of SON neurons and hormone release from the neurohypophysis. Catecholamines have been shown to activate SON neurons, thereby increasing the action potential frequency to the neural lobe. The present study examined the ability of catecholamines to evoke release of vasopressin and/or oxytocin from the neural lobe of an intraarterially perfused preparation of rat hypothalamo-neurohypophysis.Experiments were carried out on male Long-Evans rats. Drugs (noradrenaline, dopamine, D1 and D2 dopamine receptor agonists) were delivered both into the perfusion medium and directly over the SON. Fractions of effluent medium were collected from the area of the neurohypophysis and tested for hormone release using a selective radioimmunoassay. Noradrenaline (NA) in concentrations of 10spβ5 to 10spβ4 M stimulated AVP release from neural lobe. The alphasb1-adrenergic receptor antagonist, prazosin (50 nM in perfusion experiments; 1muM in local injection experiments) blocked the noradrenaline-stimulated release. Dopamine (10spβ4 to 10spβ3 M), D1 (SKF 38393, 0.5 mM) and D2 (QNP 0.5 mM) dopamine receptor agonists also increased the release of AVP. In the presence of prazosin, DA, QNP and SKF 38393 still evoked AVP release. Therefore, it is proposed that both noradrenaline and dopamine stimulate the release of AVP in this preparation; the responses to dopamine appear to be mediated by both D1 and D2 dopamine receptors, presumably located at the level of the cell somata/dendrites, possibly also on axon terminals in the neural lobe