Inflammatory mediators, including LTs and PGs, increase the sensitivity of nociceptors and potentiate pain perception. Both PGE2, through the EP1 and EP4, and PGI2, via the IP, reduce the threshold to stimulation of nociceptors, causing “peripheral sensitization”. Centrally, both COX-1 and COX-2 are expressed in the spinal cord under basal conditions and release PGs in response to peripheral pain stimuli. PGE2, and perhaps also PGD2, PGI2, and PGF2α, can increase excitability in pain transmission neuronal pathways in the spinal cord, causing hyperalgesia and allodynia. Hyperalgesia also is produced by LTB4. The release of these eicosanoids during the inflammatory process thus serves as an amplification system for the pain mechanism.The role of PGE2 and PGI2 in inflammatory pain is discussed in more detail in Ch34
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