Enkephalin, drug addiction and acupuncture.

From the results of clinical and basic research, there is clear evidence that acupuncture analgesia is closely associated with the nervous system, especially the central nervous system. Stimulation of certain acupuncture loci which have been used for analgesia during operations also can calm the withdrawal symptoms of morphine and heroin addicts. Acupuncture analgesia can be antagonized by the specific narcotic antagonist, naloxone. These findings suggest the factor or factors produced by acupuncture stimulation would also have agonist activity on opiate receptors. Moreover, the morphine receptors are most concentrated in those parts of the brain concerned with perception of pain and the pathway of acupuncture stimulation. Since the opiate receptors are associated with the synaptic fraction of brain cell membrane preparations, the natural ligand of these receptors may be a neurotransmitter. Enkephalin has stronger binding affinity to opiate receptors than morphine, which suggests that it is the natural ligand for these receptors. In other words, enkephalin might be the natural "pain killer" produced in the brain to suppress pain. If we summate all the information available now, it is possible to suggest that enkephalin may be the product of the nervous system released by acupuncture stimulation to create an analgesic effect as well as suppress opiate withdrawal symptoms.