Evaluation of the Effect of Chronic Administration of Silymarin on Thermal and Chemical Hyperalgesia in an Experimental Model of Diabetic Neuropathy in Male Rats

Hyperalgesia is recongnized as one of the marked signs of diabetic neuropathy. Considering the hypoglycemic and antioxidant effects of silymarin, this study was designed to investigate the analgesic effect of silymarin in an experimental model of diabetic neuropathy in male rats.

In warm tail immersion test, rats were divided into control, silymarin-treated control, diabetic, silymarin-treated diabetic groups. For the formalin test, sodium salicylate (SS)-treated control and diabetic groups were addded to the previous four groups. For induction of diabetes, streptozotocin (60 mg/Kg, i.p., STZ) was administered as a single dose. The treatment groups(in diabetic group, before induction of diabetes), first received a single dose (200mg/kg i.p) and then a daily dose(100mg/kgi.p) of silymarin for eight weeks.

Results showed that diabetic rats exhibited a higher score of pain during both phases of the formalin test(P=0.03-0.006) and significant decrease in tail flick latency (P<0.02) after eight weeks of diabetic induction in the warm tail immersion test. Treatment with silymarin for eight weeks caused significant decrease in pain scores at both phases of the formalin test(P=0.06-0.0006) and increase in tail flick latency (P=0.03). On the other hand, silymarin caused no significant decrease in pain scores of control rats.

It seems that eight weeks i.p. administration of silymarin could attenuate nociception in an experimental model of diabetic neuropathy, which may be considered as a treatment for painful diabetic neuropathy.