Comparison of the antinociceptive effects of intracerebroventricular injection of kyotorphin, cyclo (N-methyl-Tyr-Arg) and Met-enkephalin in mice.
Intracerebroventricular (i.c.v.) administration of kyotorphin (L-Tyrosine-L-Arginine) or Metenkephalin (Met-ENK) to conscious mice resulted in a dose-dependent antinociceptive effect as measured by three pain tests. Cyclo(N-methyl-L-Tyrosine-L-Arginine) (cyclo NMTA), an analogue of kyotorphin, increased the reaction time in the tail-pressure and tail-flick tests. Both dipeptides also decreased writhing induced by acetic acid. However, the antinociceptive activity of cyclo NMTA was substantially greater than that of kyotorphin or Met-enkephalin. At the maximum effective dose of 62.7 nmol/mouse, this cyclic dipeptide produced a more long-lasting antinociceptive effect than did kyotorphin or Met-enkephalin. Antinociception induced by cyclo NMTA or kyotorphin was significantly reversed by pretreatment with naloxone (2 or 8 mg/kg, i.p.), though naloxone was not as effective an antagonist of the antinociceptive action of these peptides as it was against Met-enkephalin. The results indicate that the antinociceptive effect induced by cyclo NMTA may in part involve the endogenous opioid system in mice.
D000698:Analgesia; D000700:Analgesics; D000818:Animals; D004723:Endorphins / Q000008:administration & dosage / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000008:administration & dosage / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects; D010456:Peptides, Cyclic / Q000008:administration & dosage / Q000494:pharmacology*
D000700:Analgesics; D004723:Endorphins; D010456:Peptides, Cyclic; C019448:kyotorphin; D009270:Naloxone; D004744:Enkephalin, Methionine; C039517:cyclo(N-methyltyrosylarginyl)