The effect of melatonin treatment on oxidative and nitrosative stress in rats with thioacetamide-induced hepatic damage.

BACKGROUND:: The following study aimed to clarify the importance of arginase and NOS activities in thioacetamide-induced hepatic damage and to evaluate the underlying mechanism of proposed protection provided by melatonin, using commonly applied therapeutic dose. METHODS:: Rats were randomly assigned to four groups (n=5): control, melatonin (10mg/kg i.p.), thioacetamide (200mg/kg i.p., two doses with a 24h interval) and thioacetamide+three doses of melatonin (10mg/kg i.p., prior- and post-treatment with a 24h interval before thioacetamide administrations) treated groups. RESULTS:: Thioacetamide administration caused hepatic damage creating oxidative and nitrosative stress accompanying perivenous necrosis and eosinophil infiltration. The significant elevation of total nitrite level in livers of thioacetamide treated groups reflected the activation of inducible nitric oxide synthase activity. The decrease in arginase activity indicated hepatic damage. Non-altered specific activity of arginase in the livers of thioacetamide treated groups did not overcome the elevation of NO production. Melatonin treatment did not modulate the levels/activities significantly. CONCLUSIONS:: Our results have indicated that nitrosative stress seems to be essentially critical in thioacetamide-induced hepatic failure in rats. Possible regulatory effect of arginase on NO production and applied dose of melatonin could not prevent hepatic damage.