Analgesic, receptor binding, and peripheral opioid activities of synthetic dermorphin‐dynorphin hybrid peptides

The effects of substituting the enkephalin moiety of dynorphin with the dermorphin sequence were studied on the receptor preference, analgesic, and peripheral opioid potencies by using synthetic dermorphin‐dynorphin hybrid peptides as the probe. Replacement of the enkephalin moiety of dynorphin with the dermorphin or dermorphin^1–5 sequence caused a remarkable increase in analgesic potency, and a 3‐6 fold increase in potency of binding against [³H]‐dihydromorphine. The potency of receptor binding against [³H]‐EKC was also increased by incorporation of the whole dermorphin sequence into the dynorphin molecule. In the presence of NaCl (100mM), the effect of enhancing binding against [³H]‐EKC due to dermorphin substitution disappeared, suggesting the contribution of opioid μreceptor. Peripheral opioid activities assayed by various smooth muscle preparations showed that dermorphin incorporation caused a decrease in the potency of inhibition of the contractions of the guinea pig ileum and the rabbit vas deferens, no change in potency on the mouse vas deferens, and a marked increase in the inhibition of the rat vas deferens. Among the peripheral opioid activities only that assayed with the rat vas deferens appears to correlate approximately with the analgesic and the receptor binding activities. Judging from the relative potencies obtained from all assays, it is evident that the N‐terminal dermorphin moiety, but not the C‐terminal dynorphin fragment, dominates the opioid activity and receptor preference of the hybrid peptide.