Endorphins and the modulation of acute pain

The endorphins constitute a large family of structurally but not generically related peptides. They act pharmacologically like narcotic analgesics. An intimate connection between endorphin fibers and pain pathways is present, for instance, at the spinal level and at the first synapse of primary afferent pain fibers. These fibers may contain the neuropeptide substance P. In acute pain, naloxone injection causes a significant increase in pain suffering. A patient with high preoperative endorphin levels in the cerebrospinal fluid will require less pethidine for adequate pain relief after major abdominal surgery. Pethidine administration reduces substance P levels in the cerebrospinal fluid. The data suggest that endorphins do not have a protective role in acute pain conditions.