Evaluation of the Effect of Peripheral Injection of Corticosterone on Acute Pain in Mice: the Likely Interaction with Nitric Oxide System

  Background and Objectives: Previous studies have suggested that glucocorticoids have modulatory effects on acute pain, and possibly one of the mechanisms that mediate these effects is nitric oxide. The aim of this study was to determine the interaction between Corticosterone and Nitric Oxide (NO) system on acute pain in Hot plate (HP) and Tail Flick (TF) models in mice. Materials and Methods: This experimental study was done in Semnan physiology research center in 2008. One handered forty male albino mice (25-30 g) were used. For evaluation of acute pain, HP and TF tests were used. All animals received two IP injection, L-NAME (10 mg/kg) as a NO synthesis inhibitor or L-Arginine (20 mg/kg), as a NO precursor or saline (6 ml/kg) for 60 min. Different doses of Corticosterone (1 and 3 mg/kg) or Vehicle (Propylene glycol + Saline in 6 ml) were injected for 30 min before the evaluation tests. One way and two way ANOVA and Tukey test were used for data analysis. Results: Findings indicated that Corticosterone at doses of 1 and 3 mg significantly reduced acute pain reaction in mice (p<0.001). Also pretreatment of LA inhibited the analgesic effects of Corticosterone in both tests (p<0.05), while injection of LN did not have any significant effects. Conclusion: It is concluded that Corticosterone induced analgesic effects possibly through modulation of NO system. The increase of NO production inhibits this effect. Key words: Pain, Corticosterone, Hot plate, Tail Flick, L-Arginine, L-Nitroarginine Methyl Ester   Funding: This research was funded by Semnan University of Medical Sciences. Conflict of Interest: None declared. Ethical approval: The Ethics Committee of Semnan University of Medical Sciences approved the study.