Elsevier

Neuroscience Letters

Volume 215, Issue 1, 30 August 1996, Pages 65-69
Neuroscience Letters

Binding of Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2) and related peptides to μ1 and μ2 opiate receptors

https://doi.org/10.1016/S0304-3940(96)12928-1Get rights and content

Abstract

Two endogenous brain peptides (Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2) and Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2)), a cyclized analog and two fragments of Tyr-W-MIF-1, and hemorphin (Tyr-Pro-Trp-Thr) were tested for binding to μ1 and μ2 opiate receptors. All these peptides bound to both μ1 and μ2 sites in assays optimized to discriminate these subtypes of the μ opiate receptor in membranes from bovine thalamus. The cyclized analog of Tyr-W-MIF-1, previously shown to have potency near that of Tyr-d-Ala-Gly-N-MePhe-Gly-ol (DAMGO) and morphine in producing analgesia after intracerebroventricular (i.c.v.) injection, bound to μ1 and μ2 sites with affinities similar to those of (DAMGO). Tyr-W-MIF-1, previously shown to induce analgesia after i.c.v. injection but with much higher potency after intrathecal (i.t.) injection, also bound to both μ1 and μ2 sites with an affinity between that of morphiceptin and hemorphin. Although the highest ratios of Ki's for μ2/μ1 were shown by hemorphin, Tyr-MIF-1, and Tyr-W-MIF-1, none of the compounds were significantly different in selectivity. The results indicate that the relatively lower potency of Tyr-W-MIF-1 after i.c.v., compared with i.t. injection, is not due to a lack of binding to μ1 sites. They suggest that it has relatively high efficacy at μ2, but low efficacy at μ1 sites, a possibility that might explain some of the novel properties of these peptides.

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