Background: The k and d opioid receptors were characterized in longitudinal muscle strip of guinea-pig ileum (GPI, K, k), mouse (MVD, d, K, k) and rabbit (LVD, k) vas deferens and rabbit ear artery (ART, d, k) with particular attention to the presence of receptor subtypes.
Material/Methods: For this purpose, type/subtype selective agonist and antagonist were used such as [D-Ala2, D-Leu5]-enkephalin (d agonist) [D-Pen2,5]-enkephalin (d1 agonist), deltorphin II (d2 agonist) naltriben (NTB, d2 antagonist), BOC-YPGFLT(OtBu) (d antagonist) on the one hand and ethylketocyclazocine (EKC, k/(agonist), PD-117 302 (k1 agonist), [Met5]-enkephalin-Arg6, Phe7 (ME-RF, d/k2/(agonist) and its amide ME-RF-NH2, k2/(agonist), naltrexone (NTX, K>d=k antagonist) and norbinaltorphimine (nBNI, k antagonist) on the other hand.
Results/Conclusions: In MVD the Ke of NTB against different (agonists revealed no receptor type heterogeneity. In LVD the Ke of nBNI but not of NTX against EKC versus the ones against ME-RF and ME-RF-NH2 indicated inhomogenous (receptor population. The (receptor antagonist BOC-YPGFLT(OtBu) antagonized the action of ME-RF-NH2 in ART but not in MVD or LVD indicating a special receptor subtype in ART (k, possibly d).

Keywords: isolated organs, k opioid receptors, d opioid receptors, norbinaltorphimine, naltriben, BOC-YPGFLT(OtBu)