The aim of this study was to investigate the anti-inflammatory effects of low frequency electroacupuncture (EA) with different intensities in carrageenan-injected rat paw. Bilateral 2 Hz EA stimulation with 0.5, 1 and 3 mA were delivered at those acupoints corresponding to Zusanli and Sanyinjiao in man via needles for 30 min. We first examined the degrees of edema and hyperalgesia using measurements of paw swelling and hot plate latency over 180 min, at 30 min intervals, after the carrageenan injection. The edema and thermal sensitivities of the hind paw induced by a carrageenan-injection were strongly inhibited by EA stimulation, especially at low intensity. At 3 h after carrageenan-injection, we investigated whether the effects of a 2 Hz EA on a carrageenan-induced edema and hyperalgesia are associated with peripheral cyclooxygenase (COX) mRNA induction and prostaglandin E2 (PGE2) synthesis. Although the induction of COX-2 mRNA was inhibited by 2 Hz EA at various intensities, there was no significant change. However, the synthesis of PGE2 induced by a carrageenan injection was significantly attenuated in rat paw with low intensity EA treatment. The data indicate that low frequency EA treatment with relatively low intensity might be a useful therapy for mitigation of inflammatory edema and hyperalgesia through the regulation of COX-2 expression and PGE2 production in a model of peripheral inflammation in rats.

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