Pain inhibition by endomorphins.
Spinal analgesic effects of endomorphin-1 and endomorphin-2 were studied during acute, inflammatory, and neuropathic pain in rats chronically implanted with intrathecal cannulas. Endomorphin-1 and endomorphin-2 (2.5-10 micrograms i.t.), as well as their analogues, increased the tail-flick and the paw pressure latencies. In a model of inflammatory pain, the formalin-induced behavior was attenuated by endomorphins; however, the effect studied was not dose-dependent and was less pronounced in comparison with that evoked by morphine. On the other hand, in rats with a sciatic nerve injury (crush), endomorphins antagonized allodynia in a dose-dependent manner, whereas morphine was found to be ineffective in a similar dose range. Endomorphins also exhibited an antinociceptive potency in rats tolerant to morphine. In conclusion, our results show a powerful analgesic action of endomorphins at the spinal level. The most interesting finding is a strong effect of endomorphins in neuropathic pain, which opens up a possibility of using these compounds in pain therapy.
Przewłocki
R
R
Department of Molecular Neuropharmacology, Polish Academy of Sciences, Kraków, Poland. nfprzewl@cyf-kr.edu.pl
Labuz
D
D
Mika
J
J
Przewłocka
B
B
Tomboly
C
C
Toth
G
G
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D007249:Inflammation; D009437:Neuralgia / Q000503:physiopathology / Q000517:prevention & control; D009842:Oligopeptides / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology / Q000517:prevention & control*; D017288:Pain Threshold / Q000187:drug effects*; D051381:Rats; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology* / Q000503:physiopathology
D000701:Analgesics, Opioid; D009842:Oligopeptides; C105293:endomorphin 1; C105294:endomorphin 2