Haloperidol treatment increases the biosynthesis and release of endorphins in guinea-pig ileum

Guinea-pigs treated acutely (5 mg kg-1 i.p.) and chronically (2 or 5 mg kg-1 day-1 for 4 days) with haloperidol, show an increase of the inhibitory response produced by electrical stimulation at 10 Hz of the ileum myenteric plexus-longitudinal muscle (MPLM) preparation. The response can be reversed by the specific narcotic antagonist naloxone (5 X 10(-7) M), which suggests that the increase in the response produced by haloperidol is mediated by release of endorphins. When haloperidol-treated guinea-pigs received cycloheximide (24 and 12 h before death), there was a substantial decrease in the response indicating that the biosynthesis and release of endorphins are increased by haloperidol.