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The neuroendocrine and behavioral effects of Tyr-d-Ala-Gly-Phe-d-Nle-Arg-Phe (DADN), a more stable derivative of the endogenous opiate Met-enkephalin related peptide Met 5 -enkephalin-Arg 6 -Phe 7 were investigated in mice. The behavioral experiments consisted of monitoring the horizontal (square crossing) and vertical (rearing) locomotion in the open field system. To evaluate...
As part of ongoing work aimed at generating proteolytically stable, readily applicable, radiolabeled endomorphin-2 (EM-2) analogs for elucidation of the topological requirements of peptide binding to μ-opioid receptors, we report here on the synthesis, radiolabeling, binding kinetics and binding site distribution of an EM-2 analog in which Pro 2 is replaced by 2-aminocyclohexanecarboxylic...
Morphiceptin (Tyr-Pro-Phe-Pro-NH 2 ), a tetrapeptide present in the enzymatic digest of bovine β-casein, is a selective ligand of the μ-opioid receptor. In the present study, we describe the synthesis of a series of novel morphiceptin analogs modified in positions 1–3. Two of the obtained analogs, [Dmt 1 , d-Ala 2 , d-1-Nal 3 ]morphiceptin and [Dmt 1 , d-NMeAla...
In our previous paper we reported synthesis and biological activity of two cyclic analogs of endomorphin-2 (EM-2): Tyr-c(Lys-Phe-Phe-Asp)-NH 2 and Tyr-c(Asp-Phe-Phe-Lys)-NH 2 , achieved by making an amid bond between Lys and Asp side-chains. The first analog did not bind to the μ-opioid receptor, the affinity of the second one was very low. In the present study, we describe the synthesis...
We have recently identified a specific binding site for the tachykinin peptide substance P (SP) fragment SP 1–7 in the rat spinal cord. This site appeared very specific for SP 1–7 as the binding affinity of this compound highly exceeded those of other SP fragments. We also observed that endomorphin-2 (EM-2) exhibited high potency in displacing SP 1–7 from this site. In the...
Met-enkephalin-Gly-Tyr (MEGY) is an endogenous peptide that binds to opioid sites in zebrafish and in rat brain homogenates. The aim of this work is to characterize the binding profile of this opioid ligand on two duplicate delta receptors from zebrafish, ZFOR1 and ZFOR4. Our results show that, while ZFOR1 presents one single binding site for [ 3 H]-MEGY (K D =4.0±0.4nM), the experimental...
Previously, we have shown that substitution of Pro 2 for cis-2-aminocyclopentanecarboxylic acid, ACPC in endomorphin-2 results in an analogue with greatly augmented proteolytic stability, high μ-opioid receptor affinity and selectivity. We now report the synthesis and biochemical characterization of [ 3 H][(1S,2R)ACPC 2 ]endomorphin-2 with a specific activity of 1.41TBq/mmol...
The partial μ-opioid receptor pool inactivation strategy in isolated mouse vas deferens was used to determine partial agonism of endomorphins and their analogs (endomorphin-1-ol, 2′,6′-dimethyltyrosine (Dmt)-endomorphin-1, endomorphin-2-ol and (d-Met 2 )-endomorphin-2) using morphine, normorphine, morphiceptin, (d-Ala 2 ,MePhe 4 ,Gly 5 -ol)-enkephalin (DAMGO) and its...
Endomorphin-1 (EM-1) and endomorphin-2 (EM-2) represent two opioid active tetrapeptides with high affinity and selectivity for the μ-opioid (MOP) receptor. Both EM-1 and EM-2 exhibit strong inhibition of pain signals in the central nervous system (CNS). In contrast to these compounds, the undecapeptide substance P (SP) facilitates pain influx in the CNS. SP has been implicated in a number of functions...
Nociceptin is an endogenous anti-opiate heptadecapeptide primarily interacting with the nociceptin (NOP) receptor. This neuropeptide–receptor system is involved in pain regulation, tolerance to and dependence on opiates as well as many other physiological and pathophysiological events. The role and mechanisms of nociceptin in pathological conditions is not clearly known yet. In an attempt to have...
Naturally occurring isoforms of the decapeptide gonadotropin-releasing hormone (GnRH) share residues 1–4 and 9–10. lGnRH-III, the third isoform isolated in the sea lamprey has no endocrine effect in mammals but shows a direct antiproliferative effect on human breast, prostate and endometrial cancer cell lines. To investigate these features, residues 5–8 of lGnRH-III were systematically replaced with...
Previously, the opioid peptide Tyr-d-Ala-Gly-(NMe)Phe-CH 2 Cl (DAMCK) has been shown to bind irreversibly to mu opioid receptors in vitro. In the present work, the antinociceptive effect of DAMCK has been evaluated. Rats treated systemically with DAMCK (1-100 pg/kg) displayed a dose-dependent increase in tail-flick analgesia that peaked by 15 min, then stayed about the same until 60 min, followed...
Substitution of the Phe 3 aromatic ring in H-Tyr-Ticψ[CH 2 -NH]Phe-Phe-OH with cyclohexylalanine (Cha) has been reported to result in a compound, H-Tyr-Ticψ[CH 2 -NH]Cha-Phe-OH (TICP[ψ]), showing substantially increased δ-opioid antagonist potency and high δ selectivity. TICP[ψ] was radiolabeled by catalytic tritiation of its precursor Tyr(3',5'-I 2 ) 1 TICP[ψ]...
Opioid receptor binding properties of [ 3 H]Tyr-d-Ala-Phe-Phe-NH 2 (TAPP) were characterized in rat brain and Chinese hamster ovary (CHO) cells expressing the rat μ-receptor. In rat brain, [ 3 H]TAPP labeled a single class of opioid sites with a dissociation constant (K d ) of 0.31 nM and maximal number of binding sites (B max ) of 119 fmol/mg protein...
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