Evidence that endogenous enkephalins and a delta opioid receptor agonist have a common site of action in spinal antinociception.

A selective agonist at the delta subtype of the opioid receptor (Tyr-D-Ser(Otbu)-Gly-Phe-Leu-Thr) (DSTBULET), and kelatorphan, a mixed peptidase inhibitor which can protect endogenous enkephalins were applied together onto to the lumbar spinal cord of the intact anaesthetized rat. The combined administration of these agents produced inhibitions of the responses of dorsal horn neurones activated by peripheral stimulation which were no greater than the inhibitions with either the agonist or peptidase inhibitor alone (50-60% inhibitions). The results indicate that endogenous opioids protected by kelatorphan and delta opioid receptor agonists act on a common receptor site to produce spinal antinociception.