Release of dopamine from tuberoinfundibular neurons into pituitary stalk blood after prolactin or haloperidol administration.

The effects of PRL or haloperidol on the release of dopamine from tuberoinfundibular neurons were assessed by measuring the concentrations of dopamine in hypophysial portal plasma. The mean concentration of dopamine in portal plasma of male rats which had received an intracerebroventricular injection of PRL or a sc injection of haloperidol on the day before the collection of pituitary stalk blood was approximately 5 times that in stalk plasma of vehicle-treated control rats. The haloperidol-induced increase in the concentration of dopamine in pituitary stalk plasma appeared to be PRL mediated, since this effect of haloperidol was significantly attenuated in rats which had been pretreated with antiserum to PRL. These observations are consistent with the view that the mechanisms involved in the release of dopamine from tuberoinfundibular neurons are regulated, in part, by PRL. Moreover, in view of the inhibitory effect of dopamine on PRL-secretion, a PRL-induced increase in the release of dopamine from tuberoinfundibular neurons into hypophysial portal blood may be one mechanism by which PRL regulates its own secretion.