Properties and localization of β-endorphin receptor in rat brain

Stereospecific high-affinity binding sites for βh-[³H]endorphin could be demonstrated in the P₂ pellet of rat brain homogenate. Scatchard analysis of the binding data revealed binding sites with Kd values of 0.81 and 6.8 nM and density of 120 and 240 fmol/mg of protein. Distribution of βh[³H]endorphin binding in various brain regions parallels that of opiate receptor: striatum > thalamus > amygdala > hypothalamus, septum > cortex > midbrain, brainstem. Similar to their effect on ³H-labeled agonist binding, Na⁺ and other monovalent cations, GTP, trypsin, chymotrypsin, phospholipase A₂, and N-ethylmaleimide all inhibited the specific binding of βh[³H]endorphin. In contrast to their action on alkaloid and enkephalin binding, Ca²⁺, Mg²⁺, and Mn²⁺ also inhibited βh-[³H]endorphin binding. These data suggest a difference between βh-endorphin and alkaloid/enkephalin binding sites.