Abstract: AIM: To compare the expression of three cyclooxygenase (COX) isoforms in the process of inflam-matory pain and evaluate the analgesic effects of different protocols about usage of COX inhibitors on inflammatory pain. METHODS: Formalinwas injected subplantarly to mice to induce inflammatory pain.The expression of COX-1, COX-2 and COX-3was evaluated by radioimmu-noassay and RT-PCR, respectively. For the analgesic ef-fect assay, animals were divided into 5 groups including control, SC, NS, IN and NS +SC group.The former 4 groups received saline, SC-560 (300μg°kg^-1), NS-398 (150 μg°kg^-1), and indomethacin (300μg°kg^-1), re-spectively. In the NS +SC group, animals received NS-398 during the first 1 month and SC-560 during the sec-ond month in the NS +SC group.RESULTS: The ex-pression of COX-1was higher at the late phase while that of COX-2 was higher at the early phase of inflammatory pain.The expression of COX-3 did not significantly change in the process of inflammatory pain.Additionally, behavioral assessment showed that using COX-2 inhibitors at the early phase followed by COX-1inhibitors at the late phase could get better analgesic effect on inflammatory pain compared with single using COX-1 selective or COX-2 selective inhibitors. CONCLUSION: In brain, the ex-pression of COX-2 increases rapidly in the inflammatory pain processwhile COX-1 expression does not increase till the late phase. Brain COX-3 is poorly involved in the in-flammatory process.Combined use of COX-1 and COX-2 selective inhibitors may be a better protocol in inflamma-tory pain treatment.

Key words: inflammatory pain, cyclooxygenase COX inhibitor, radioimmunoassay, RT-PCR, hot plate CLC Number :R966