[Mode of action of trimebutine: involvement if opioid receptors]

Several studies in dogs, cats, rabbits and humans have suggested that the motility-stimulating properties of trimebutine (TMB) are mediated by peripheral opiate receptors. The present work deals with the capacity of the drug and its N-desmethyl metabolite (NDTMB) to displace mu, delta and kappa specific ligands from their receptors using guinea-pig whole brain membranes and ileum myenteric plexus synaptosomes membranes. The activity of both compounds on the twitch response induced by transmural stimulation of the guinea-pig ileum and of the mouse and rabbit vas deferens was also investigated. These preparations have been claimed to be specific for the mu, delta and kappa receptor subtypes respectively. TMB (0.2 to 1.8 microM) and NDTMB (0.3 to 6 microM) displayed a good affinity for all receptor subtypes in brain and myenteric plexus preparations. The decreasing order of IC50 (50 per cent inhibitory concentration)'S of TMB ranged from 0.75 microM in the guinea-pig ileum to 7.1 and 39 microM in the vas deferens of the rabbit and the mouse respectively. These results indicate that TMB and NDTMB possess mu, delta as well as kappa agonistic properties without true specificity for one or the other of these subtypes. They also confirm that activation of peripheral mu, delta and kappa opiate receptors mediate the gastrointestinal motility effect of TMB.