Elsevier

Life Sciences

Volume 31, Issues 12–13, September 1982, Pages 1381-1384
Life Sciences

Binding of 3H-β-endorphin in rat brain

https://doi.org/10.1016/0024-3205(82)90386-1Get rights and content

Abstract

The binding of 3H-β-endorphin to rat brain homogenates, reported by several other laboratories, has suggested unique selective β-endorphin binding sites. We now present additional evidence supporting the concept of distinct β-endorphin binding (epsilon) sites in rat brain. In competitive displacement studies, 3H-β-endorphin was inhibited far better by unlabeled β-endorphin than a variety of opiates and enkephalins. Conversely, β-endorphin inhibited the binding of a series of 3H-labeled ligands, including dihydromorphine, ethylketocyclazocine, SKF 10,047, naloxone and D-ala2-D-leu5-enkephalin, far less potently than their corresponding unlabeled drug. Other differences were also found. Compared to 3H-dihydromorphine and 3H-D-ala2-D-leu5-enkephalin in binding, 3H-β-endorphin binding was far less sensitive to the reagent N-ethylmaleimide and more sensitive to the proteolytic enzyme trypsin. The regional distribution for 3H-β-endorphin binding was also distinct from other 3H-ligands tested. This evidence supports the concept of a distinct binding site for β-endorphin which does not correspond to the previously defined opioid binding sites.

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  • No evidence for G-protein-coupled epsilon receptor in the brain of triple opioid receptor knockout mouse

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    Citation Excerpt :

    Interestingly the existence of epsilon sites was suggested in the rat brain also, on the basis of binding studies. [ 3H]β-Endorphin labeling showed a unique regional distribution (Akil et al., 1980; Goodman et al., 1983; Johnson et al., 1982) and distinct sensitivity to bivalent cations (Law et al., 1979) as compared to other tritiated opioid ligands. Later, studies aiming at characterizing the so-called “benzomorphan sites” in rat brain revealed strong similarities with properties of the epsilon receptor described in the rat vas deferens.

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