[Peripheral opioid receptors and their role in postoperative pain management.]

Animal experiments have unequivocally demonstrated peripheral antinociceptive effects of opioids in inflamed tissue. Exogenous mu-, delta- und kappa-agonists can produce such effects. Opioid receptors are present on peripheral terminals of primary afferent neurons and their endogenous ligands are produced and contained in resident immune cells within the inflamed tissue. These endogenous opioid peptides can apparently be released during stress and produce intrinsic antinociception. A small number of clinical studies has examined the peripheral analgesic effects of opioids. Their results are equivocal so far. In view of the predominant role of the inflammatory process in the manifestation of peripheral opioid effects, the postoperative situation seems to be particularly worthwhile to study.