Evaluation the interaction of nitric oxide and corticosterone on Neurogenic and Inflammatory pains in mice

Many evidence indicated that glucocorticoids have modulatory effects on pain and probably one of the mechanism that mediate of these effects is nitric oxide system. The aim of this study was determine of interaction between corticosterone and Nitric oxide (NO) system on acute (Neurogenic) and chronic (Inflammatory) pains in Formalin Test (FT) model in mice. In this experimental study we used 70 male albino mice (25-30 g) in 7 groups. Also we used of FT for evaluation of acute and chronic pain. The criteria for evaluation of pain was measure of all time that animal reaction to pain responses (Licking Time) after injection of formalin 5%) in sub-plantar area of the right hind paw in each of 5 min, during 40 min. 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, 60 min and different doses of corticosterone (1and 3 mg/kg) or Vehicle (Propylene glycol 40% + Saline in 6 ml/kg) were injected 30 min before of FT. Analysis of data indicated that corticosterone at doses of 1 and 3 mg significantly reduced pain reaction in mice. Also pretreatment of L-Name enhanced the analgesic effects of corticosterone in chronic pain, while injection of Larginine, as a NO precursor had not significantly effects. The findings indicated that glucocorticoids induce analgesic effects probably through of modulation of NO system.