Specific protection of the binding sites of D-Ala 2 -D-Leu 5 - enkephalin (δ-receptors) and dihydromorphine (μ-receptors)

Abstract

Phenoxybenzamine causes a long-lasting inactivation of the opiate receptors of the $\mu $- and $\delta $-type in homogenates of guinea-pig brain. This effect is selectively prevented when, before exposure to phenoxybenzamine, the homogenate is pre-incubated with ligands of high affinity for either of the two binding sites, i.e. dihydromorphine for the $\mu $-receptor and Tyr-D-Ala-Gly-Phe-D-Leu for the $\delta $-receptor. In contrast, Tyr-D-Ala-Gly-Phe-L-Leu amide, which has high affinities for both binding sites, protects both receptor sites.