Noradrenergic stimulation of supraoptic neuronal activity and vasopressin release in vitro: mediation by an alpha 1-receptor

Abstract

Using the isolated rat hypothalamoneurohypophysial system, the effects of noradrenaline (NA) and some adrenoceptor agonists on vasopressin (VP) release and supraoptic neuronal activity were assessed in vitro. Extracellular action potentials driven antidromically by neural stalk stimulation were recorded while fractions of the perifusate were collected every minute for radioimmunoassay of VP. NA and the alpha 1-agonist phenylephrine stimulated VP release and elicited bursts in tuberal supraoptic neurons, whereas isoprenaline (a beta-agonist) and clonidine (an alpha 2-agonist) did not. The peak rate of VP release was reached shortly after the onset of burst discharge. when intraburst firing rate was highest, and both effects were dose-dependent when tested to different concentrations of phenylephrine. Thus VP secreting neurons are excited to release VP by alpha 1-adrenoceptor activation.