| Abstract: | The peripheral opioid activity of six homologous β-endorphins (β-EPs) were assayed on the guinea pig ileum and the vas deferens of the mouse, the rat and the rabbit. In the guinea pig ileum assay, human β-EP (βh-EP) was less potent than camel, turkey, and ostrich β-EPs, of the same potency as equine β-EP and more active than des-acetyl salmon β-EP. In the rat vas deferens, mammalian β-EPs showed higher activity than those from the bird and the fish, whereas in the mouse vas deferens assay, βh-EP is more active than those from other species. In the rabbit vas deferens, however, all homologous β-EPs show very weak activity. The relative potency of β-EP homologues obtained from rat vas deferens assay is in good correlation with the analgesic potency, while the receptor binding activity does not correlate with any of the four bioassays, but appears to be related to the charge properties of the peptides. |
