Evidence for Functional δ-Opiate Receptors in the Rat Intestine

Abstract

Abstract The selective δ-opiate agonists d-Ser2, Leu5, Thr6-enkephalin (DSLET), d-Ala2, d-Leu5-enkephalin and d-Pen2, d-Pen5-enkephalin caused inhibition of the cholinergic contraction produced by transmural stimulation of the rat isolated jejunum. Dynorphin A, which is an agonist at both κ- and δ-opioid receptors also inhibited the cholinergic contraction, as did leu- and met-enkephalin. The selective μ-receptor agonist d-Ala2-NMe-Phe4, Gly-ol5-enkephalin was the least potent of all peptides tested. In general, the order of potency of the peptides was similar to that reported for the δ-receptor-rich mouse vas deferens with potency values similar to those recorded previously for the hamster vas deferens. The selective δ-opioid antagonist naltrindole caused parallel shifts to the concentration-effect curve to DSLET giving a pA2 value of 10·15. The results indicate that the previously identified δ-binding sites in the rat jejunum may correspond to functional δ-opiate receptors involved in attenuating acetylcholine release.