Endorphin levels in cerebrospinal fluid of patients with postoperative and chronic pain

Abstract

The authors measured endorphin levels in the cerebrospinal fluid (CSF) of 12 patients with chronic pain due to lumbar disc syndrome and eight patients with acute postoperative pain. These were compared with CSF endorphin levels in 20 control patients with no history of pain. Endorphins were extracted by adsorption to a synthetic resin (Amberlite XAD-2®), eluted with methanol, and assayed using the electrically stimulated mouse vas deferens. Results were expressed as methionine-enkephalin (Met-E) equivalents, which was standard in the bioassay. The CSF endorphin level was 0.42 ± 0.07 pmol/ml (mean ± SE) in the postoperative group, 1.44 ± 0.2 pmol/ml in the chronic pain group, and 4.36 ± 0.89 pmol/ml in the control group. CSF endorphin levels in the two pain groups differed significantly from both the control group and each other. These results suggest a correlation between pain levels and endorphin concentration in the CSF; however, in the acute postoperative pain group the influence of other factors such as anesthesia or surgical stress cannot be evaluated.