Goldman et al. have found a greater than 20-fold increase in adenosine, a nerve modulator with anti-nociceptive (i.e. anti-pain) properties, in tissue around the point where acupuncture needles are rotated in a mouse's paw. This reduces pain in the paw caused by an injected inflamatory chemical, and the effect is not observed in mice genetically altered to delete the pain nerve adenosine receptors. An adenosine receptor agonist (enhancer) boosts the effectiveness of the acupuncture treatment.
Now, what one needs to see next is experiments with humans in which adenosine release caused by rotating a needle at the classical acupuncture needle points is measured and compared with the release at randomly placed needles. Also, it would be interesting to see whether other placebo interventions shown to cause endorphin release also caused adenosine release.