Endogenous Opioid Analgesia

Anesth Analg. 2008 Sep;107(3):1058-63.

Pre-Irradiation of the blood by gallium aluminum arsenide (830 nm) low-level laser enhances peripheral endogenous opioid analgesia in rats.

Hagiwara S, Iwasaka H, Hasegawa A, Noguchi T.

Department of Brain and Nerve Science, Anesthesiology, Oita University Faculty of Medicine, 1-1 Idaigaoka-Hasamamachi-Yufu City-Oita 879-5593, Japan. saku@med.oita-u.ac.jp

BACKGROUND: Low-level laser therapy (LLLT) has been reported to relieve pain, free of side effects. However, the mechanisms underlying LLLT are not well understood. Recent studies have also demonstrated that opioid-containing immune cells migrate to inflamed sites and release beta-endorphins to inhibit pain as a mode of peripheral endogenous opioid analgesia. We investigated whether pre-irradiation of blood by LLLT enhances peripheral endogenous opioid analgesia.

METHODS: The effect of LLLT pretreatment of blood on peripheral endogenous opioid analgesia was evaluated in a rat model of inflammation. Additionally, the effect of LLLT on opioid production was also investigated in vitro in rat blood cells. The expression of the beta-endorphin precursors, proopiomelanocortin and corticotrophin releasing factor, were investigated by reverse transcription polymerase chain reaction.

RESULTS: LLLT pretreatment produced an analgesic effect in inflamed peripheral tissue, which was transiently antagonized by naloxone. Correspondingly, beta-endorphin precursor mRNA expression increased with LLLT, both in vivo and in vitro.

CONCLUSION: These findings suggest that that LLLT pretreatment of blood induces analgesia in rats by enhancing peripheral endogenous opioid production, in addition to previously reported mechanisms.