Histamine-induced prolactin release and activity of tuberoinfundibular dopaminergic neurons in male rats.

The role of tuberoinfundibular dopamine (DA) in the histamine-induced rise of plasma prolactin was studied in male rats. Right lateral ventricle (icv) histamine injection (30 micrograms/rat) caused a significant rise of plasma prolactin at 15 and 30 min; at 60 min values returned to basal levels. Histamine does not modified steady-state DA concentrations. For turnover evaluation, histamine was icv injected immediately or 30 min after the tyrosine hydroxylase inhibitor alpha-methyltyrosine (250 mg/kg i.p.) and DA concentration in the median eminence was measured at 0, 1 and 2 hours after the inhibitor injection. Rate constants of DA decline and DA synthesis rates were found similar in both controls (cerebrospinal fluid) and histamine-injected rats. These results indicate that the stimulatory action of histamine on prolactin release might not be associated to DA. It would be due mainly to its action on prolactin-releasing factors and to a minor extent, to changes in the dopaminergic system.