The occurrence of individual amino acids and dipeptide fragments in the sequences of 60 known atypical opioid peptides was analyzed. An expressed predominance of Tyr-Pro fragment suggested a high probability of analgesic activity for this dipeptide, and it was experimentally studied. It was shown on somatic and visceral pain sensitivity models that, on the i.p. administration of Tyr-Pro at doses of 1.0-10 mg/kg of body mass, it exhibits an analgesic activity eliminated by naloxone and naloxone methiodide. However, in tests on ileum preparations of guinea pig and mouse vas deferens in vitro, Tyr-Pro was devoid of opioid activity, which proved its indirect influence on opioid receptors.
Amino Acid Sequence Analgesics, Opioid