Met-enkephalin, sometimes referred to as opioid growth factor (OGF) is an endogenous opioid peptide neurotransmitter found naturally in many parts of the animal and human's body. One of the primary locations is in segment II of the dorsal horn of the spinal cord. It is one of the two forms of enkephalin; the other is leu-enkephalin. The tyrosine residue at position 1 is thought to be analogous to the 3-hydroxyl group on morphine. Methionine-enkephalin (MET) and Dynorphin-A (DYN) are endogenous opioids with preference for delta- and kappa-opioid receptors, respectively. Both MET and DYN are produced and contained within immune cells. The goal of this study was to determine the release characteristics of MET and DYN in a rat model of localized hindpaw inflammation and to examine the antinociceptive role of MET and DYN in a Freund's adjuvant induced model of inflammatory pain.
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