endomorphin-1 and morphiceptin

The partial mu-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-Met2)-endomorphin-2) using morphine, normorphine, morphiceptin, (D-Ala2,MePhe4,Gly5-ol)-enkephalin (DAMGO) and its amide (DAMGA) as reference opioid agonists. Agonist affinities (KA) and efficacies were assessed both by the "null" and the "operational" method. The KA values determined by the two methods correlated significantly with each other and also with the displacing potencies against 3H-naloxone in the receptor binding assay in the presence of Na+. DAMGO and DAMGA were full agonist prototypes, morphine, endomorphin-1, endomorphin-1-ol, Dmt-endomorphin-1, endomorphin-2-ol and (D-Met2)-endomorphin-2 were found by both methods to be partial agonists whereas the parameters for normorphine, morphiceptin and endomorphin-2 were intermediate.

Topics: Animals; Brain; Dose-Response Relationship, Drug; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Male; Mice; Morphine Derivatives; Naloxone; Oligopeptides; Rats; Receptors, Opioid, mu; Vas Deferens

A functional assay, based on aequorin-derived luminescence triggered by receptor-mediated changes in intracellular calcium levels, was used to examine relative potency and efficacy of the mu-opioid agonists endomorphin-1, endomorphin-2, morphiceptin, and their position 3-substituted analogs, as well as the delta-agonist deltorphin-II. The results of the aequorin assay, performed on recombinant cell lines, were compared with those obtained in the functional assay on isolated tissue preparations (guinea pig ileum and mouse vas deferens). A range of nine opioid peptide ligands produced a similar rank order of potency for the mu- and delta-opioid receptor agonists in both functional assays. The highest potency at the mu-receptor was observed for endomorphin-1, endomorphin-2, and [D-1-Nal3]morphiceptin, whereas deltorphin-II was the most potent delta-receptor agonist. In the aequorin assay, the mu- and delta-agonist-triggered luminescence was inhibited by the opioid antagonists naloxone and naltrindole, respectively. We can conclude that the use of the aequorin assay for new mu- and delta-receptor-selective opioid analogs gives pharmacologically relevant data and allows high-throughput compound screening, which does not involve radioactivity or animal tissues. This is the first study that validates the application of this assay in the screening of opioid analogs.

Topics: Aequorin; Analgesics, Opioid; Animals; Biological Assay; Calcium; CHO Cells; Cricetinae; Cricetulus; Endorphins; Ligands; Luminescent Agents; Oligopeptides; Receptors, Opioid

In the present study, we reported on the synthesis of two new mu-opioid peptide analogs, [D-1-Nal3]morphiceptin and [D-1-Nal4]-morphiceptin [1-Nal=3-(1-naphthyl)-alanine] which expressed receptor binding affinities at least at the level of the primary opioid ligands. The new analogs also labeled mu-opioid receptors on the cells of human breast cancer MCF-7 cell line with affinity much higher than that of endomorphins and morphiceptin, the well-known mu-selective opioid peptides. However, none of the tested peptides significantly decreased cell proliferation of MCF-7 cells.

Topics: Animals; Breast Neoplasms; Cell Proliferation; Convulsants; Endorphins; Humans; Ligands; Male; Oligopeptides; Protein Binding; Rats; Rats, Wistar; Receptors, Opioid, mu; Tumor Cells, Cultured

The dipeptidyl aminopeptidase IV (DP IV) inhibitor Diprotin A produces a full, dose-dependent, short-lasting and naloxone-reversible analgesia in the rat tail-flick test when given intracerebroventricularly, with an ED50 of 295 nmol/rat but it has no direct opioid agonist activity in the longitudinal muscle strip of guinea-pig ileum bioassay. Two of the potential DP IV substrates, morphiceptin and endomorphin 1, identified recently in bovine brain were also analgesic given by similar route. The action of endomorphin 1 was more potent (ED50 = 7.9 nmol/rat) and slightly but significantly more sustained than that of Diprotin A. Diprotin A neither potentiated nor prolonged the effect of a marginally analgesic dose of endomorphin 1. The distinct time course and the lack of potentiation indicate that in the analgesic effect of Diprotin A in rats the protection of a brain Tyr-Pro-peptide other than endomorphin 1 is involved.

Topics: Analgesia; Analgesics, Opioid; Animals; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; Dose-Response Relationship, Drug; Drug Synergism; Endorphins; Guinea Pigs; In Vitro Techniques; Male; Mice; Muscle, Smooth; Naloxone; Narcotic Antagonists; Oligopeptides; Pain Measurement; Rats; Rats, Wistar