Further study of the neurohumoral factor, endorphin, in the mechanism of acupuncture analgesia.

Cross circulation was performed between the femoral arteries and veins of paired rabbits that were entirely conscious. Jaw opening reflex by dental pulp stimulation was used as pain index. When acupuncture was applied to the donor rabbit the pain thresholds of both the donor and recipient were elevated from 30 minutes to one hour after acupuncture stimulation and lasted for another 30 minutes after withdrawal of acupuncture. The analgesic effect in both the donor and recipient was abolished by the pretreatment of naloxone. The increase in the pain threshold of the non-acupunctured recipient was due to an opiate-like, humoral substance generated from the acupuncture donor. The possible role of endorphins in the mechanism of acupuncture analgesia is discussed.