Absence of spinal response to extracorporeal shock waves on the endogenousopioid systems in the rat

Extracorporeal shock wave therapy (ESWT) seems to be a new therapeutic stra tegy for chronic pain due to tendopathies, Neurophysiological mechanisms of action for pain relief following ESWT are still unknown, The aim of this s tudy was to investigate if the analgesic effect of ESWT is caused by modula tion of the endogenous spinal opioid system, Rats were treated with two dif ferent energy flux densities (0.04 and 0.11mJ/mm(2)) and immunohistochemica l analysis of met-enkephalin (MRGL) and dynorphin (Dyn) was performed at 4 or 72 h after ESWT, ESWT had no modulatory influence on the expression of t he spinal opioid systems, Different energy doses or repetitive treatment di d not alter MRGL or Dyn immunoreactivity in the spinal cord. Furthermore, a delayed effect of ESWT at 72 h after treatment was not detectable, We conc lude from these findings that the analgesic effects of ESWT treatment are n ot supported by endogenous opioids. (C) 2001 World Federation for Ultrasoun d in Medicine & Biology.