Long-term Morphine-treated Rats are more Sensitive to Antinociceptive Effect of Diclofenac than the Morphine-naive rats

Authors

  • Ebrahim Mirzaei School of pharmacy, Mazandaran University of Medical Sciences, Sari, Iran.
  • Esmaeil Akbari Department of Physiology and Pharmacology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran.
  • Naghi Shahabi Majd Department of Physiology and pharmacology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran.
Abstract:

This study investigates the effectiveness of the antinociceptive effects of diclofenac, an NSAID, on the nociceptive behavior of morphine-treated rats on formalin test.Rats were treated with morphine-containing drinking water for twenty one days, which induced morphine dependence. The antinociceptive effects of 8, 16, and 32 mg/kg doses of diclofenac were then evaluated and compared with distilled water in a formalin-based model of pain.Diclofenac potentiated pain suppression in morphine-dependent rats during the interphase of the formalin test and reduced the pain score during phase II. The post-test analysis revealed that both 16 mg/kg (p < 0.0001) and 32 mg/kg (p < 0.0001) doses of diclofenac had a significant effect on the interphase, while 8 mg/kg (p < 0.05), 16 mg/kg (p < 0.05), and 32 mg/kg                      (p < 0.01) doses of diclofenac significantly affected phase II. In contrast, the antinociceptive effects of diclofenac on morphine-naïve rats were observed during phase II only with the a 32 mg/kg dose (p < 0.05).In general, these results suggest that the long-term use of morphine in rats increases their sensitivity to the antinociceptive effects of diclofenac. Furthermore, the results support the existence of a non-opioid-dependent mechanism of pain suppression during the interphase of formalin test.

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Journal title

volume 12  issue 1

pages  175- 184

publication date 2013-03-03

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