Introduction . Vitamin K2 is a deriv ative of vitamin K. Effect o f vitamin K2 on the release and function of n eurotransmitters remain ed unknown; b ut du e to the effects of this substance in many neural processes, neu rod egen erative diseases (e.g. Alzheimer, Parkinso n, etc.) and inflammation , its influence on the mechanisms of neurotransmitter release and pain also can be involv ed. Therefore, this stud y examines th e effect of intrathecal admin istration ( i.t.) of vitamin K2 on the chemical pain. Materials and methods. The adult male Wistar rats (250-300 g) initially were subjected to i.t. surgery as 8cm of PE-10 cannula was inserted into the spinal subarachnoid space. Groups were included: control, sham (salin+DMSO، i.t) and treatments consists of vitamin K2 (2, 10 and 20 µg/10µl, i.t). Five min after intrathecal administration, 0.05 ml of formalin %2/5 injected in the sub plantar region of the right hind paw and immediately rat’s behavioral responses to pain were recorded for 60 min. Results. Intrathecal adminis tration of vitamin K2 (20-10-2µg/10µl) in the first and second phases of the formalin test showed a significant decrease in pain (P <0.001, P <0.01), the analgesic effect of dose (2µg/10µl) were higher than the others. The intermediate stage was also affected by vitamin and became longer but was not significant compared with the control. Conclusion. Probably Vitamin K2 with indirect influence on the activity of NMDA receptors and inhibiting the release of mediators such as Brady kinin and SP, the enzyme inhibition of iNOS and reduction in the production of NO and its antioxidant property, reduces pain and inflammation. Also the effect of vitamin K2 in the blockage of sodium channels, poss ibly responsible for part of its analgesic function is in the spinal cord.

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