Analgesic effects of endomorphin-1 and endomorphin-2 in the formalin test in mice.
Two recently isolated peptides, endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2), are highly selective micro-opioid receptor agonists with analgesic actions in the tail-flick test. To further assess the analgesic properties of these peptides, the effects of endomorphin-1, endomorphin-2, and morphine were examined in the formalin test. Male Swiss Webster mice were injected i.c.v. with endomorphin-1, endomorphin-2, or morphine (0, 1, 3, 10 microg) 5 min before injection of 20 microl of 5% formalin s.c. into the plantar surface of one hind-paw. The mice were observed for 60 min after formalin injection. Endomorphin-1 and endomorphin-2 produced dose-dependent analgesia that was shorter in duration than for morphine. Increased locomotion was observed after morphine, but not after endomorphin-1 or endomorphin-2. These findings extend previous results and suggest that endomorphins may have therapeutic potential for the treatment of acute pain.
Soignier
R D
RD
Department of Psychology, University of New Orleans, LA 70148, USA.
Vaccarino
A L
AL
Brennan
A M
AM
Kastin
A J
AJ
Zadina
J E
JE
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005557:Formaldehyde; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D009842:Oligopeptides / Q000494:pharmacology*
D000701:Analgesics, Opioid; D009842:Oligopeptides; C105293:endomorphin 1; D005557:Formaldehyde; C105294:endomorphin 2