OPIOID-PEPTIDES IN PAIN CONTROL

This study presents a brief description of the role of opioid peptides in pain control. an inhibitory effect of beta-endorphin and Met-enkep halin has been described in the peripheral inflamed tissues; this evid ence suggests a local action of these peptides during inflammation. In hibitory pain systems have also been documented either within the spin al cord and in relation with the descending inhibition from midbrain n uclei to dorsal horn of the spinal cord, by the efferent conexions loc alized throughout dorsolateral fascicules to the dorsal horn of the sp inal cord. Whit this idea in mind, beta-endorphine and related substan ces participation in analgesia has been analyzed. The involvement of m u, delta and kappa receptors in pain control is discussed. The evidenc e suggests that opioid analgesia is due to mu receptor activation, but delta and kappa receptors may be also activated by their endogeneous ligands and potentiate analgesia. Enkephalines show high-affinity by d elta opioid receptors and an indirect involvement in analgesia has bee n suggested. The role of kappa receptors and dynorphin in analgesia re mains unclear, even controversial results have been published. On the other hand, naloxone (an opioid antagonist) exhibits paradoxical effec ts on pain: high doses induce hyperalgesia and low doses produce analg esia.