Opioid properties of several morphiceptin- (Tyr-Pro-Phe-Pro-NH2), Tyr- MIF-1 (Tyr-Pro-Leu-Gly-NH2) and dynorphin-derivatives were characterized in rat brain in vitro receptor binding assay and in electrically stimulated longitudinal muscle strip preparation of guinea pig ileum. In the case of morphiceptin-related peptides, an excellent correlation was found between the [3H]-naloxone binding displacement data and the agonist potencies determined in the bioassay. The 'turning point' was the C-terminal amidation in the tri- and tetrapeptide pairs in both series. Tyr-MIF-1 derivatives showed weak affinity in the opioid receptor binding assay and none of them had any remarkable effect in the bioassay either as agonist or antagonist. The dynorphin A((1-10))-peptides modified at positions 5 and 8 retained their affinity with Pro5-, Pro8-, and Ala8- substituents, whereas some loss of affinity was observed in the case of Gly8-Dyn A((1-10)).
ASJC Scopus subject areas
- Endocrine and Autonomic Systems
- Cellular and Molecular Neuroscience