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  • Title: Beta-endorphin: a highly selective endogenous opioid agonist for presynaptic mu opioid receptors.
    Author: Schoffelmeer AN, Warden G, Hogenboom F, Mulder AH.
    Journal: J Pharmacol Exp Ther; 1991 Jul 01; 258(1):237-42. PubMed ID: 1677039.
    Abstract:
    In the presence of physiological cations (in Krebs-4-(2-hydroxyethyl)-1- piperazineethanesulfonic acid buffer) at 37 degrees C the Ki value's of beta-endorphin for mu- and delta-opioid receptor binding sites in rat neocortical membranes, labeled with [3H][D-Ala2,MePhe4,Gly- ol5]enkephalin (DAMGO) and [3H][D-Ala2-D-Leu5]enkephalin (in the presence of unlabeled DAMGO), respectively, amounted to about 9 and 22 nM. Surprisingly, a very different selectivity pattern for the endogenous opioid peptide was found when the affinity of beta-endorphin for functional presynaptic opioid receptors was examined. Thus, beta-endorphin strongly inhibited the electrically evoked release of [3H]NE from rat neocortical slices with an IC50 value of about 0.5 nM, whereas [14C] acetylcholine release from neostriatal slices was inhibited with an IC50 value of about 100 nM. On the other hand, the electrically evoked release of [3H]dopamine from striatal slices was not affected by beta-endorphin. The inhibitory effects of DAMGO and beta-endorphin on [3H]NE release from neocortical slices were equally well antagonized by naloxone. Moreover, 10 nM of the highly selective mu-opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen- Thr-NH2 antagonized competitively the inhibitory effect of beta-endorphin on [3H]NE release.(ABSTRACT TRUNCATED AT 250 WORDS)
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