“…Opioid peptides were detected in human subcutaneous and synovial cells, mast cells, granulocytes, lymphocytes, and macrophages. The prevailing peptides are END and Met-enkephalin, but dynorphin and endomorphins were also found Likar et al, 2004Likar et al, , 2007Heurich et al, 2007;Mousa et al, 2007b;Rittner et al, 2007a;Straub et al, 2008). In patients undergoing knee surgery, blockade of intra-articular opioid receptors by the local administration of naloxone resulted in significantly increased postoperative pain .…”