[Mediated participation of the opioid system in regulation of pain sensitivity by peptide fragments MP1 and MP2].

The naloxone-dependent modulating effect of synthetic analogs of myelopeptides, MP1 and MP2, on pain sensitivity in mice was determined at doses 10(-13) and 10(-8) g/animal. Binding of the peptides to opioid receptors of mouse brain membranes was studied by the radioligand assay. For MP1, the displacement of [3H]DAGO (selective mu-agonist) by IC50 = 7.3 x 10(-5) M and [3H]DSLET (selective delta-agonist) with IC50 = 7.0 x 10(-5) M. The data obtained suggest that the hypoalgesic effect of the peptides cannot be due to their direct interaction with opioid receptors. However, the naloxone dependence provides a possibility of mediated involvement of the opioidergic system in the realization of this effect.