Evidence for a single functional opioid delta receptor subtype in the mouse isolated vas deferens

The identification of opioid delta receptor subtypes in mouse brain led to the investigation of the nature of the opioid delta receptors in the mouse isolated vas deferens in vitro. Noncumulative concentration-effect curves were constructed for DPDPE (delta 1 agonist) and [D-Ala2, Glu4]deltorphin (delta 2 agonist) in control tissues, or in tissues which had been incubated with either [D-Ala2, Leu5, Cys6] enkephalin (DALCE) (noncompetitive delta 1 antagonist) or 5'-naltrindole isothiocyanate (5'-NTII) (noncompetitive delta 2 antagonist). Incubation of the tissues with DALCE, under either oxygenated or nonoxygenated conditions, did not alter the concentration-effect curves for either agonist. In contrast, incubation of the tissues with 5'-NTII resulted in a significant rightward displacement of the concentration-effect curves of both DPDPE and [D-Ala2, Glu4] deltorphin. Additionally, naltriben, a selective and competitive delta 2 antagonist, showed no significant difference in its ability to antagonize a fixed, submaximal concentration of either DPDPE or [D-Ala2, Glu4]deltorphin. Furthermore, there was no significant difference in the affinity of naloxone (i.e., pA2) at the receptor(s) acted upon by either DPDPE or [D-Ala2, Glu4]deltorphin. Tolerance to DPDPE or [D-Ala2, Glu4]deltorphin was produced by incubation of the tissues with these agonists; construction of the [D-Ala2, Glu4]deltorphin concentration-effect curve in DPDPE-tolerant tissues demonstrated cross-tolerance between these agonists and, conversely, construction of DPDPE concentration-effect curves in [D-Ala2, Glu4]deltorphin-tolerant tissues revealed cross-tolerance between these agonists.(ABSTRACT TRUNCATED AT 250 WORDS)