Cross-protection of mu and delta opioid receptors in the mouse vas deferens

Opioid receptors in the C57/BL mouse vas deferens can be irreversibly blocked by pre-treatment with beta-chlornaltrexamine. Pre-incubation with the highly selective delta-receptor antagonist ICI 174864 concentration-dependently protected delta-receptors from inactivation, but the same concentrations similarly protected mu receptors. Pre-incubation with selective mu-receptor agonist, [D-Ala2, MePhe4, Gly(ol)5]enkephalin, also protected both mu and delta receptors to the same degree. Neither ligand protected k-opioid receptors. The results suggest that there may be a structural interaction between mu and delta receptors in the mouse vas deferens.