Assessment of Hyoscyamus niger seeds alcoholic extract effects on acute and chronic pain in male NMRI rats

Background and Objective: Recent studies have shown that anticholinergic alkaloids compounds have strong analgesic effects. Due to presence of anticholinergic alkaloids in Hyoscyamus niger and its mentioned effects in Iranian traditional medicine, its analgesic effects were assessed. At first, acute and chronic pain thresholds in male NMRI rats with formalin test was evaluated, then oral and injection forms of alcoholic extract of Hyoscyamus niger seeds were assessed. Materials and Methods: Male NMRI rats weighted 300-350 g were randomly selected. Alcoholic extracts of Hyoscyamus niger seeds with 500, 1000 and 2000 mg/kg of body weight were injected intraperitoneally (10 rats per group). Also, Hyoscyamus niger seeds was prescribed orally with a proportion of 1 to 14 in their standard food to another group of rats (n=8) within 2 weeks. After all, acute and chronic pain were evaluated in control group rats (n=8) and aforementioned rats with formalin test. Moreover its analgesic effects were compared with sodium salicylate. Results: Statistical analyses show that injection of Hyoscyamus niger seeds alcoholic extract with the mentioned dosage reduces the acute and chronic pain induced by formalin test significantly (P<0.001). Also, orally prescribed Hyoscyamus niger seeds significantly increased chronic pain threshold. Conclusion: The results of this investigation revealed that injection of Hyoscyamus niger seeds extract with the above dosages have a significant analgesic effect on acute and chronic pain thresholds. Additionally, orally prescribed only affects chronic pain in formalin test, which indicates different mechanisms of parenteral and oral on acute pain.