Endorphins and Pain
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It is well known for many centuries already that opium, derived from the poppy plant, causes pain relief and euphoria. This latter is thought to be an important factor in the addictive properties of opium (Van Ree, 1979). After the discovery of morphine as the most effective analgesic and addictive component of opium, attempts were made to prepare morphine related drugs in order to separate the desired analgesic and the undesirable addictive properties. Although these attempts were not very succesful, the structure activity relationship studies have revealed the concept that specific opiate receptors are present in the body. In 1973 binding studies with brain tissue indeed have suggested the existence of such receptors (Terenius, 1973). Subsequently the presence of endogenous substances that can activate these receptor systems was postulated. This suggestion accords well with findings showing that animals and humans have to a certain extent control over pain sensation. It was demonstrated in 1975 that brain tissue contains two pentapeptides, called enkephalins, that have morphine-like properties as assessed using isolated tissue preparations in vitro (Hughes et al., 1975). Since then several peptides with morphine-like action have been isolated from brain and other tissue. These substances are called endorphins (endogenous morphine). Soon after their discovery these peptides have been implicated in pain related mechanisms, in chronic pain and various psychopathological disorders such as psychosis, depression, mania and addiction.
KeywordsOpioid Receptor Opioid Peptide Addictive Behavior Opiate Antagonist Structure Activity Relationship Study
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