[Highly active analogs of opiate-like peptides historphin and kapporphin].

Analgetic activity of analogues of new opioid peptides historphine Tyr-Gly-Phe-Gly-Gly and capporphine Tyr-Ser-Phe-Gly-Gly was studied. Analogues of historphine Tyr-D-Ala-Phe-Gly-Gly and of capporphine Tyr-D-Ser-Phe-Gly-Gly exceeded 10(3)-fold the Leu-encephaline efficiency using a tail-jerk test and their derivatives containing amide group in the C-end position--10(4)-fold. All the four analogues increased the resistance period in the heat plate test. Naloxone removed or decreased the effect of these peptides studied. After repeated administration peptides Tyr-D-Ala-Phe-Gly-Gly-NH2 and Tyr-D-Ser-Phe-Gly-NH2 were similar in the activity to the most strong native opioid peptide desmorphine. Considering that analogues of historphine and capporphine exhibited high analgetic activity, they may be used as promising structures in more complicated modifications in order to produce highly effective analogues of opioid peptides.