Evaluation of nitric oxide or opioid receptors involvement in antinociceptive properties of silymarin

It has been shown that Silybum marianum or its extracts have hepatoprotective, antioxidant, anticancer, anti-inflammatory and anti-diabetic effects. Nitric oxide (NO) plays an important role in neurotransmission, neuroprotection, neurotoxicity and pathological pain, as a neurotransmitter or neuromodulator in the central nervous system. Therefore, this experiment was performed in order to assess the analgesic effects of single and multiple-dosed ip administration of silymarin and the probable role of nitric oxide or opioid receptors using tail flick assay. Based on our results, only silymarin 100 mg/kg showed analgesic properties. Since naloxone did not change silymarin’s analgesic effects, it is concluded that opioid receptors are not involved. Although in the presence of L-arginine, analgesic effect of silymarin remained intact, but it is not possible to strongly determine the involvement of nitric oxide pathway here. Based on our results, the difference between anti nociceptive properties of single and multiple-dosed treatment of silymarin 100 mg/kg is not significant. It is concluded that silymarin exert its analgesic effects via other mechanisms. Inhibiting 5-lipooxygenase and neutrophil chemotaxis to inflammation location could be the probable ways of silymarin’s action.