Alpha 1-adrenergic receptor activation releases vasopressin and oxytocin from perfused rat hypothalamic explants.

Norepinephrine and the alpha-agonist phenylephrine in concentrations of 10(-5) to 10(-3) M prompted the release of radioimmunoassayable vasopressin (up to 150 pg/min) and oxytocin (up to 20 pg/min) from intraarterially perfused explants of rat basal forebrain. Drug effects were markedly reduced or abolished in the presence of the non-specific alpha-antagonists phentolamine and phenoxybenzamine, and the specific alpha 1-antagonist prazosin. In concert with recent in vivo and in vitro electrophysiological observations, these data imply that endogenous noradrenergic pathways to magnocellular neurosecretory cells are excitatory, mediated through activation of their alpha 1-receptors, thereby enhancing the release of both vasopressin and oxytocin in the neurohypophysis.