Reversal of tolerance to the antitransit effects of morphine during acute intestinal inflammation in mice
Article first published online: 3 FEB 2009
1997 British Pharmacological Society
British Journal of Pharmacology
Volume 122, Issue 6, pages 1216–1222, November 1997
How to Cite
Pol, O. and Puig, M. M. (1997), Reversal of tolerance to the antitransit effects of morphine during acute intestinal inflammation in mice. British Journal of Pharmacology, 122: 1216–1222. doi: 10.1038/sj.bjp.0701472
- Issue published online: 3 FEB 2009
- Article first published online: 3 FEB 2009
- (Received March 12, 1997, Revised June 26, 1997, Accepted July 31, 1997)
- Morphine tolerance;
- gastrointestinal transit;
- intestinal inflammation;
- cholecystokinin-A receptor antagonist;
- N-methyl-D-aspartate receptor channel blocker
- 1The aim of investigation was to establish and compare the reversibility of tolerance to the antitransit effects of morphine by three different procedures: (a) acute inflammation of the gut, (b) lorglumide a cholecystokininA (CCKA) receptor antagonist, or (c) MK-801, an N-methyl-D-aspartate (NMDA) receptor ion channel blocker. The type of interaction between morphine and lorglumide or MK-801 on the inhibition of gastrointestinal transit (GIT) in naive animals was also evaluated.
- 2Male Swiss CD-1 mice were implanted with 75 mg of morphine base or placebo pellets. Gastrointestinal transit was assessed with a charcoal meal and results expressed as % inhibition of GIT. Inflammation was induced by the intragastric (p.o.) administration of croton oil (CO), while controls received castor oil (CA) or saline (SS). Morphine was administered by subcutaneous (s.c.) or intracerebroventricular (i.c.v.) injection, to naive and tolerant animals treated with CO, CA or SS. Dose-response curves for s.c. morphine were also perforrmed in naive and tolerant mice receiving 5.2 or 7.4 nmol (s.c.) lorglumide or MK-801, respectively.
- 3The ED50 values for inhibition of GIT by s.c. morphine were: 45.9±2.7 and 250.1±3.1 nmol in naive and tolerant animals, respectively, demonstrating a five fold decrease in the potency of morphine. In naive animals, inflammation (CO) decreased the ED50 of morphine three times (14.4±2.2 nmol). However, no tolerance to s.c. morphine (ED50 16.4±2.6 nmol) was manifested during intestinal inflammation. After i.c.v. administration, a similar degree of tolerance to morphine was observed (4.8 fold decrease in potency). Intestinal inflammation had no effect on the ED50 values of i.c.v. morphine in naive and tolerant animals, showing that reversal of tolerance is related to local mechanism/s. Mean values for intestinal pH were 6.9±0.04 and 6.2±0.04 in SS and CO treated mice, respectively. In addition, morphine was 74 times more potent by the i.c.v. than by the s.c. route (naive-SS).
- 4Morphine and lorglumide interacted synergistically in naive animals; in addition, the administration of lorglumide reversed tolerance to s.c. morphine. No interaction (additivity) was observed in naive animals when morphine and MK-801 were administered in combination. However, the drug completely reversed tolerance to the antitransit effects of morphine.
- 5The present investigation shows that acute inflammation of the gut reverses tolerance to the antitransit effects of s.c. morphine by a peripheral mechanism. Qualitatively similar results were obtained after the administration of lorglumide or MK-801. Our results suggest that a local decrease in pH could play an important role during inflammation, while antagonism of endogenous compensatory systems would explain the reversal of tolerance induced by lorglumide or MK-801.
British Journal of Pharmacology (1997) 122, 1216–1222; doi:10.1038/sj.bjp.0701472