ENDORPHINS AND ACUPUNCTURE ANALGESIA

Abstract

Evidence indicates that acupuncture analgesia is mediated primarily by the mobilization of endorphins in the central nervous system. Endorphins are naturally occurring peptides containing different numbers of amino acids (ranging from 5 to 31) which are found in various regions of the brain, the spinal cord, and a variety of non-nervous tissues such as the adrenal medulla and GI tract. They are sysnthesized from high molecular weight protein precursors by processing enzymes and are released at a steady rate within the nervous system and at other sites. When injected directly into the CNS they produce analgesia. Ordinarily, the endogenous levels of endorphins at varous sites of generation and release are quite low due to rapid enzymatic degradation. However, if the CNS is stimulated by acupuncture, TNS, or tetanic stimulation, there is rapid mobilization of endorphins. In recent years, animal models of acupuncture have been developed which have contributed greatly to the concept that acupuncture analgesia is mediated by the mobilized endorphins. This form of analgesia is reversed by the specific opiate and endorphin antagonist naloxone. Endorphin levels increase dramatically in a number of brain regions of animals, coinciding with the production of analgesia. Specific inhibitors of degradation of endorphons, e.g., D-phenylalanine (DPA) and bacitracin, increase such levels even further and intensify and prolong acupuncture analgesia. Studies by Hyodo and Han, among others, have confirmed a similar potentiation of acupuncture analgesia in humans by DPA. Han and coworkers have shown that antibodies to endorphins attenuate acupuncture analgesia.

In recent years, many other far-reaching consequences of the mobilization of endorphins have been uncovered. Some of these will be discussed in relation to important manifestations of acupuncture other than the production of analgesia.