Morphine no longer blocks gastrointestinal transit but retains antinociceptive action in diallylnormorphine-pretreated rats

Diallylnormorphine (DANM) the quaternary N-allyl derivative of nalorphine, administered to rats, 8 mg/kg i.p., 20 min before i.v. injection of the potent opiate buprenorphine (1 μg/kg, tritrium-labeled), reduced in vivo binding of the latter (63% of controls at 30 min) in small intestine longitudinal muscle including myenteric plexus, but not in cerebrum. Naloxone, 1 mg/kg s.c., had the same effect of buprenorphine binding in the two sites (52 and 54% of controls respectively). The marked slowing in the transit of a forced charcoal meal through the small intestine of rats given 10 mg/kg morphine i.v. was prevented to comparable extents by DANM and naloxone; the latter also abolished the delay in hot plate reaction induced in these animals by morphine which, however, retained considerable antinociceptive effect in DANM-pretreated rats.