Dopamine regulates canine plasma beta-endorphin-immunoreactivity levels

Intravenous administration of the dopamine antagonists domperidone and metoclopramide elevates canine plasma beta-endorphin immunoreactivity. Pretreatment with dopamine, but not dexamethasone, inhibits this effect. Sephadex G-50 chromatography shows that this response is due to beta-endorphin-like peptides, not beta-lipotropin. These findings indicate that pituitary beta-endorphin secretion is tonically inhibited by dopamine and suggest that the intermediate lobe is the source of this secretion.