Stress, dopaminergic blockade and median eminence-neurointermediate lobe catecholamine depletion: effects on hypothalamic, pituitary and plasma immunoreactive beta-endorphin.

We have compared immunoreactive beta-endorphin (ir-beta EP) levels in plasma, hypothalamus, anterior pituitary and neurointermediate lobe of adult female Sprague-Dawley rats, in studies in which levels of catecholamines were manipulated. Whole-brain catecholamines were manipulated by intraperitoneal haloperidol and/or bromocriptine; median eminence and neurointermediate lobe catecholamines were manipulated specifically and differentially by intravenous 6-hydroxydopamine (6-OHDA), with and without pretreatment with intraperitoneal desipramine; changes in amine neurons were assessed by fluorescence histochemistry. Haloperidol and 6-OHDA administration produced a selective reduction of neurointermediate lobe ir-beta EP, to levels equivalent to those seen with prolonged stress; the haloperidol effect was blocked by bromocriptine and the 6-OHDA effect by desipramine. Specific depletion of catecholamine nerve terminals in the median eminence and the neurointermediate lobe was associated with elevated plasma ir-beta EP, with no changes in pituitary or hypothalamic levels. These studies confirm and extend previous reports documenting that ir-beta EP levels in different tissues are modulated by different neural stimuli.