Dopaminergic agents differentially alter β-endorphin processing patterns in the rat pituitary neurointermediate lobe

We have established the content and molecular species of immunoreactive β-endorphin (ir-β-END) and immunoreactive N-acetyl-endorphin (ir-Nac-END) in rat neurointermediate lobe by specific radioimmunoassay (RIA) and high-performance liquid chromatography after chronic administration of dopamine (DA) agonists and antagonists. The DA agonist, bromocriptine, reduces tissue levels of all major immunoreactive species, in particular the C-terminally shortened N-acetylated forms. The DA antagonist, haloperidol, proportionally increases all immunoreactive forms, except Nac-β-END_1–27, thus altering the relative abundance of this species. These data indicate that DA is involved in the control of both tissue levels and processing of β-END-like peptides in the rat neurointermediate lobe.