Background and purpose: Vitamin K2 is one of the derivatives of vitamin K belonging to fat-soluble vitamins’ family. Other derivatives of vitamin K in the brain must be converted to K2 and this can reflect its importance in the nervous system. There are some evidences on analgesic effects of vitamin K. This study investigated the effects of intrathecal administration of vitamin K2 on pain in the tail-flick and formalin-test. Material and methods: In this experimental study, male Wistar rats (200-250g) after cannulation surgery for intrathecal administration (i.t), were divided into four groups (n=7 per group) including (DMSO) and vitamin K2 (2, 10, 20µg/10µl). Pain threshold was measured in each group by tail-flick test and chemical pain was evaluated using the formalin-test. Results: Vitamin K2 (20µg/10µl,i.t) significantly reduced pain threshold and led to hyperalgesia in the tail-flick test (P<0.01). But intrathecal administration of all concentrations of vitamin K2 decreased formalin-induced pain during the two phases of formalin-test (P<0.05). Conclusion: This study showed that intrathecal administration of vitamin K2 in high concentrations induced hyperalgesia in the Tail flick test, but it produced analgesia during the formalin test. According to the essential roles of Aδ fibers in pain transmission during the tail-flick test and the role of NMDA receptor in the formalin test, determination of the mechanisms involved in these effects requires further research.

Keywords: Vitamin K2, Pain, Intrathecal administration, Tail-flick test, Formalin test

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