Electroacupuncture potentiates the antinociceptive effect of intrathecal endomorphin-1 in the rat formalin test.
Endomorphin-1 is a novel endogenous mu-opioid peptide. In this study, we examined the effects of 2 Hz electroacupuncture in the rat tail flick test and the formalin test (a persistent noxious model). Moreover, we investigated if the electroacupuncture potentiated the effect of intrathecal endomorphin-1. The results demonstrated that electroacupuncture alone produced a significant antinociception in the tail flick test, but not in the formalin test, and that intrathecal endomorphin-1 dose-dependently suppressed the biphasic nociceptive behavior in the formalin test. Electroacupuncture enhanced the antinociceptive effect of intrathecal endomorphin-1 in the formalin test, resulting in a significant leftward shift in the dose-response curves for intrathecal endomorphin-1 antinociception. The enhanced effect was antagonized by intraperitoneal naltrexone. The study suggests that electroacupuncture may potentiate the intrathecal endomorphin-1 antinociception partially mediated by opioid receptors.
Hao
S
S
Department of Anesthesiology & Critical Care Medicine, Asahikawa Medical College, Midorigaoka-Higashi, 2-1-1-1, 078-8510, Asahikawa, Japan. hao@asahikawa-med.ac.jp
Takahata
O
O
Iwasaki
H
H
D000701:Analgesics, Opioid / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D015671:Electroacupuncture; D005557:Formaldehyde / Q000009:adverse effects; D007278:Injections, Spinal; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects* / Q000378:metabolism; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology*; D010147:Pain Measurement; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology
D000701:Analgesics, Opioid; D009842:Oligopeptides; D011957:Receptors, Opioid; C105293:endomorphin 1; D005557:Formaldehyde; D009271:Naltrexone