Beta-endorphin. Biological activity of analogs containing dermorphin and dynorphin sequences: ileum and vas deferens assays.

Biological activity of synthetic beta-endorphin (beta-EP) analogs containing dermorphin or dynorphin-A-(1-13) structure has been investigated using the guinea pig ileum and the vas deferens of the mouse, rat and rabbit. Replacement of NH2-terminal 1-7 segment of camel beta-EP [beta c-EP-(1-7)] with dermorphin caused a great increase in opiate potency of the analog. [Dermorphin (1-7)]-beta c-EP was 120 times more potent than beta c-EP in the guinea pig ileum assay, 49 times more potent in the mouse vas deferens assay; and only 4 times more potent in the rat vas deferens assay. Replacement of NH2-terminal 1-13 segment of human beta-EP [beta h-EP-(1-13)] with dynorphin-A-(1-13) caused an increase in opiate potency in both the guinea pig ileum and rabbit vas deferens assays, a complete loss of potency in the rat vas deferens assay, and no change in the mouse vas deferens assay. In comparison with dynorphin-A-(1-13), the hybrid peptide was less potent in the guinea pig ileum assay as well as in mouse and rabbit vas deferens assay. It is suggested that beta c-EP-(8-31) facilitates the dermorphin moiety to act on opiate mu and delta receptors but not on the epsilon receptor, while beta h-(14-31) reduces the action of dynorphin on mu, delta and kappa receptors.