The Journal of pharmacology and experimental therapeutics
-
J. Pharmacol. Exp. Ther. · Jan 1986
Independent central and peripheral mediation of morphine-induced inhibition of gastrointestinal transit in rats.
The individual contributions of central (brain) and peripheral (enteric) sites in the mediation of the systemic actions of opioids are not well established. In this study, we made use of naltrexone methobromide, a quaternary analog of naltrexone, to separate the central and peripheral components of the slowing action of morphine on gastrointestinal transit in rats. It was established that i.c.v., but not s.c., administration of quaternary naltrexone antagonized morphine-induced analgesia in the radiant-heat tail-flick assay in rats. ⋯ Distinct and independent central and peripheral systems appear to mediate morphine-induced inhibition of gastrointestinal transit in rats. However, the receptors are probably of the same type. Peripherally selective antagonists such as quaternary naltrexone may be useful in reversing morphine-induced inhibition of gastrointestinal transit without affecting analgesia.