Peripheral Opioid Analgesia

Abstract

Opioids have long been thought to act exclusively within the central nervous system. An increasing number of studies recently reported the existence of opioid receptors outside the central nervous system and therefore suggested that opioids are also able to produce analgesic effects in the periphery. Such effects are particularly prominent under painful inflammatory conditions, both in animals and in humans. During inflammatory processes, opioid receptors are transported from dorsal root ganglia towards the peripheral sensory nerve endings. At the same time, immune cells containing endogenous opioid peptides accumulate within the inflamed tissue. Environmental stimuli (e.g. stress) as well as releasing agents (e.g. corticotropin releasing factor, cytokines) can liberate these opioid peptides to interact with the neuronal opioid receptors and elicit local analgesia. The inflammation-induced activation of opioid production and the release of endogenous opioids from immune cells may lead to novel approaches for the development of peripherally acting analgesics. Clinical investigation now focuses on the development of new peripheral opioid agonists as well as on ways to stimulate the endogenous analgesic system in order to induce effective peripheral analgesia with reduced central side effects typically associated with opioids.

Effects of Intraarticular Tramadol Administration on Biochemical and Cytological Properties of Equine Synovial Fluid: Comparison with Lidocaine

“…In equine medicine, there is a reluctance to use systemically administered opioids, based on concern that there may be adverse side effects. Therefore, clinical investigations now focus on the development of new peripheral opioid agonists as well as on ways to stimulate the endogenous analgesic system in order to induce effective peripheral analgesia with reduced central side effects (Janson and Stein, 2003).…”

Involvement of Peripheral Beta-Endorphin and MU, Delta, Kappa Opioid Receptors in Electro Acupuncture Analgesia for Prolonged Inflammatory Pain of Rats

“…The rat model of unilateral inflammatory pain induced by CFA has been extensively used in the study of peripheral opioid system (19,25). Most of these studies employed CFA model with a duration of no more than 4 days.…”

The role of beta-endorphin in horses: a review

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