Intraperitoneal administration of ascorbic acid attenuates hyperalgesia in a rat model of neuropathic pain

Background: Ascorbic acid is a well-known antioxidant but its antinociceptive effect on chronic pain is not known. The aim of this study is to evaluate the analgesic effect of intraperitoneal administration of different doses of ascorbic acid in a peripheral neuropathic pain model. Methods: To investigate the efficacy of ascorbic acid on neuropathic pain, male rats were allocated to 5 acute administration and 2 chronic administration groups. Pain induced by chronic constriction injury of sciatic nerve (CCI). Different amount of ascorbic acid (1, 3, 5 and 10 mg/kg) and normal saline were injected in acute protocol (single injection two weeks after CCI). In addition, ascorbic acid was administrated with dose of 3 mg/kg (daily injection for three weeks; chronic administration). Hyperalgesia and allodynia were assessed. Results: Chronic intraperitoneal injection of 3 mg/kg ascorbic acid for 3 weeks increase pain threshold from the second week after CCI. Acute administration of 1 mg/kg ascorbic acid did not produce any changes in pain threshold of neuropathic rats but acute injection of 5 and 10 mg/kg, significantly alleviate pain 30 minutes after injection in the second week following CCI. Similar result observed in chronic administration of ascorbic acid. Conclusion: These data suggest that ascorbic acid produces analgesia in neuropathic rats