Acupuncture significantly increases the concentration of nitric oxide (NO, a key biological signalling molecule involved in vasodilation and neurotransmission) in local body tissues.

In a randomised, double-blind, crossover study, 20 volunteers underwent one session each of real and non-invasive sham acupuncture in a single hand and forearm, with a one-week interval between treatments. NO concentration in plasma samples from the acupunctured arm was found to be significantly increased 60 minutes after acupuncture.

Blood flow to the palm of the acupunctured arm also increased, and this correlated with NO increase. These changes were not observed with non-invasive sham-acupuncture. The authors speculate that these effects might contribute to the pain relief provided by acupuncture.

(Acupuncture enhances generation of nitric oxide and increases local circulation. Anesth Analg. 2007 Feb;104(2):301-7).