Journal of Rafsanjan University of Medical Sciences

  Comparison of Analgesic Response to Morphine After Ovariohysterectomy in Morphine Dependent Rats

  M. Shamsi Maimandi Pharm D^1*, GH. Sepehri PhD², L. Sabzevari³, A. Esmaieli³

 1- Pharmacologist, Neuroscience, Research Center, Kerman, Iran

  2- Associated Professor, Dept. of Physiology & Pharmacology, University of Medical Sciences, Kerman, Iran

  3- Medical Students, University of Medical Sciences, Kerman, Iran

  Background : The most effective groups of drugs for the treatment of surgical pain are opioid analgesics. But due to the development of tolerance, chronic use of opioids limits their effectiveness. However, the real need and analgesic response to opioids in postoperative pain has not been determined in addicted patients. Therefore this study was performed, to evaluate the analgesic response to morphine in postoperative pain of ovariohysterectomy in morphine dependent rats, compared with the non dependents.

  Materials and Methods: The present study was carried out on 36 adult female rats. Animals were divided into four groups (6 in each group): Control– ovariohysterectomy, control – sham, dependent– sham and dependent – ovariohysterectomy groups. Rats became dependent to morphine by taking morphine in their drinking water for 21 days. Rats were anaesthetized with ether, and after incision of the abdomen, uterus and ovaries were removed above the cervix. Latency time was assessed by Tail flick test before and after the operation and after inducing morphine 4 mg/kg (sub cutaneously). Data were expressed as latency time and percent of maximal possible effect [%MPE].

  Results: The results of present study showed that the mean latency time to noxious stimulus in tail flick test was not significantly different before and after the surgery in the four groups of animals Which indicated. that latency time in morphine dependent rats (9.1 ± 0.4s), was not significantly different from control rats (10.1 ± 1.25s) in tail flick test. Morphine injection increased the latency time in all of the groups significantly. The percent of MPE showed that the maximum analgesic effect of morphine in morphine dependent rats [48.7 ± 11.8s] after ovariohysterectomy was significantly higher than sham – dependent rats (19.6 ± 5s).

  Conclusion: The present study showed that there was not a significant difference in analgesic response to morphine after ovariohysterectomy in normal and morphine dependent rats.

  But ovariohysterectomy only increased the analgesic effect of morphine in dependent animals.

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  Key words: Postoperative-pain, Morphine Dependency, latency time

  *Corresponding author, Tel: (0341) 2111010

  Journal of Rafsanjan University of Medical Sciences and Health Services, 2004, 3(2: 104-112