Intrathecal morphine slows gastrointestinal transit in rats.

Intrathecal (i.th.) (by direct lumbar puncture) and intraperitoneal (i.p.) administration of morphine (30-100 micrograms/rat) caused a dose-related inhibition of gastrointestinal transit in the rat. Pretreatment with i.th. naloxone (5 micrograms at -5 min) reversed the effects of i.th., but not i.p., morphine. These results suggest that the spinal cord appears to be a target site for the inhibitory effects of morphine on gastrointestinal transit in the rat.