[Involvement of purines in analgesia produced by weak electro-acupuncture].

In the present investigation the intensity of stimulated electro-acupuncture (EA) was measured by electrophysiological collision technique. In the behavioral experiments, by applying the weak electro-acupuncture pulses (50 Hz, 1-1.5mA), not enough to activated A delta afferent fibers, to Yanglingquan and Xuanzhong points, the latency of nociceptive hind limb withdrawal reflex, but not tail-flick latency was prolonged. Administered intraperitoneally, both theophylline and caffeine, P1-purinergic (adenosine) receptor antagonists, could block the electroacupuncture-induced elevation of the nociceptive thresholds in a dose-effect related manner, whereas dipyridamole, an inhibitor of adenosine release, could shorten the after of electro-acupuncture in a dose dependent way. These results suggest that weak electro-acupuncture may induce analgesia and purines appear to be involved in this process.