Domperidone elevates rat plasma beta-endorphin-immunoreactivity when administered peripherally but not intracerebroventricularly.

Domperidone, a dopamine receptor antagonist which apparently does not penetrate the blood-brain barrier in rats was administered to adult males. Domperidone 500 micrograms and 100 micrograms, given through intracarotid cannula, significantly elevated plasma beta-endorphin-immunoreactivity (beta-EP-I) at +15 min. To show that only a peripheral site(s) of action is implicated, domperidone was given to rats by cannulae implanted into both lateral ventricles. Plasma beta-EP-I was unaffected by this route of administration. These results suggest that plasma beta-EP-I is tonically inhibited by dopamine acting at site(s) outside of the blood-brain barrier.