Circulating opioids: possible physiological roles in central nervous function

Evidence is reviewed regarding the release of endorphins by such diverse conditions as stress, long distance running, acupuncture, sexual activity, suggestion and ritualistic dancing ceremonies. Additional evidence is cited regarding possible physiological roles of endorphins in antinociception, socialization, euphoria, some mental disorders, drive states and vegetative functions. The concentration of this latter type of evidence is on conditions during which endorphins seem to be exerting effects on a number of different systems together (for example, euphoria is almost always accompanied by analgesia), and the possibility is suggested that the activation of a number of functions together may be due to a global activation of opiate receptors throughout the CNS. A possible basis for this global activation arises from results from this laboratory indicating the presence of a blood-borne opioid hormone, secreted by the pituitary or by an endocrine gland under pituitary control, which is capable of passing from the blood into the CNS. This diffuse endorphinergic system, which is complementary to the well-established endorphinergic neuronal systems in the CNS, thus derives its property of global action on opiate receptors by the diffuse means by which the hormone reaches its target sites, i.e., by passing through the blood brain barrier. Thus, while each specific endorphin-mediated function can be activated by the activation of its respective neural pathway, it is proposed that the hormonal endorphinergic mechanism is activated to produce a global response provoked by conditions to which a more generalized response, including physiological and behavioural changes, is most appropriate.