A new class opioid peptide, [D-Arg2, beta-Ala4]-dermorphin tetrapeptide; physical dependence liability in mice.

Development of morphine-like physical dependence of the [D-Arg2, beta-Ala4]-dermorphin tetrapeptide (H-Tyr-D-Arg-Phe-beta-Ala-OH) has been evaluated and compared with the physical dependence liability of morphine or pentazocine. Degree of the physical dependence was assessed by the naloxone-precipitated jumping behaviour in mice after treatment of a single dose of each compound. The number of jumps and the time of latency to first jump were recorded in this experiment. Number of jumps in a group pretreated with the peptide showed less than that in morphine-treated group. In addition, latency to the appearance of the first jump in the peptide-treated mice was later than that in the morphine-treated group. The present results indicate that the physical dependence induced by [D-Arg2, beta-Ala4]-dermorphin tetrapeptide may be less marked than that produced by morphine. It is also interesting to note that the antinociceptive effect of this opioid peptide is more powerful and of longer duration than that induced by morphine or pentazocine.