title: Specificity of opioids towards the mu-, delta- and epsilon-opiate receptors.
abstract: The potency of a number of opioid agonists have been determined on three different bioassays, the isolated guinea-pig ileum (GPI), the mouse vas deferens (MVD) and the rat vas deferens (RVD). With the exception of beta-endorphin, compounds with opioid activity on the GPI and the MVD exhibited considerably less or no activity on the RVD; the opiate receptor in this latter tissue being thus characterized as beta-endorphin selective ('epsilon-receptor'). A system of classification of opioids according to their relative relative affinities for particular opiate receptor types is given.
mesh_terms: D000818:Animals; D001681:Biological Assay; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects*; D008297:Male; D051379:Mice; D009294:Narcotics / Q000494:pharmacology*; D009928:Organ Specificity; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects*; D013045:Species Specificity; D014649:Vas Deferens / Q000187:drug effects*
chemical_list: D009294:Narcotics; D011957:Receptors, Opioid