Evidence for lack of modulation of mu-opioid agonist action by delta-opioid agonists in the mouse vas deferens and guinea-pig ileum.
1. There is evidence from in vivo studies for an interaction of mu- and delta-opioid ligands. In the present work this concept has been investigated using the mouse vas deferens and guinea-pig ileum myenteric plexus-longitudinal preparations. 2. In field stimulated vasa deferentia of the mouse, co-administration of sub-effective concentrations of the delta-opioid agonist [D-Pen2,D-Pen5]enkephalin (DPDPE) and [Met5]- or [Leu5]enkephalin had no effect on the dose-response curves of the mu-agonists [D-Ala2,MePhe4, Gly-ol5]enkephalin (DAMGO) and morphine. Similarly, the delta-opioid agonists did not alter the potency of morphine and DAMGO when added at different times prior to the mu-opioid agonists, or when EC50 concentrations of delta-opioid ligands were co-administered. Compounds with preferred activity for the putative delta 1-(DPDPE) or delta 2-([D-Ala2,Glu4]deltorphin II (Delt II)) opioid receptors were ineffective in this respect. 3. The guinea-pig ileum contains delta-opioid receptors. No function of these receptors in mediating blockage of field-stimulated contractions was observed with ligands having affinity for the putative delta 1 or delta 2 subtypes nor were the agonists able to modulate responses to mu-opioid ligands in this tissue. 4. The results demonstrate the modulation of mu-opioid agonists by delta-opioid agonists does not occur in the isolated peripheral tissues examined. Thus the findings do not support the concept of a functional coupling of opioid receptors, though the results may be explained by differences between opioid systems in the brain and peripheral tissues examined.
Elliott
J
J
Department of Chemistry, Loughborough University of Technology, Leics.
Traynor
J R
JR
D000818:Animals; D004558:Electric Stimulation; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009197:Myenteric Plexus / Q000187:drug effects / Q000502:physiology; D017465:Receptors, Opioid, delta / Q000819:agonists*; D017450:Receptors, Opioid, mu / Q000819:agonists*; D014649:Vas Deferens / Q000187:drug effects / Q000502:physiology
D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu