Spinal antinociceptive effect of epidural nonsteroidal antiinflammatory drugs on nitric oxide-induced hyperalgesia in rats

Abstract

Background: Nonsteroidal antiinflammatory drugs (NSAIDs) suppress various hyperalgesia perhaps via inhibition of cyclooxygenase activity at the spinal cord. The present study aimed to examine whether epidural application of NSAIDs affects hyperalgesia induced by nitric oxide. Methods: The authors studied the antinociceptive effects of epidurally administered NSAIDs in rats with a chronically indwelling epidural catheter by three hyperalgesic models, including nitric oxide-induced hyperalgesia by nitroglycerin (10 μg) or 1- arginine (100 μg), and the biphasic response in the formalin test. Results: Epidural, but not systemic, nitroglycerin induced hyperalgesia that was completely blocked by methylene blue but not by Nω-nitro-L-arginine methyl ester (L-NAME). Epidural 1-arginine, but not d-arginine, also induced hyperalgesia that was completely blocked by L-NAME. Epidural S(+)ibuprofen (100-1,000 μg) suppressed the nitroglycerin- and 1-arginine-induced thermal hyperalgesia and also the second phase response in the formalin test. Neither systemic S(+)ibuprofen nor epidural R(-)ibuprofen suppressed the hyperalgesia. Epidural indomethacin (10-100 μg) or diclofenac (101,000 μg) dose-dependently suppressed nitroglycerin-induced thermal hyperalgesia. The order of potency for this suppression (ID50 in μg) was indomethacin = diclofenac > S(+)ibuprofen >> R(-)ibuprofen. Conclusions: The antinociceptive action of epidurally administered NSAIDs could be the result of suppression of spinal sensitization, perhaps induced with nitric oxide in the spinal cord. The ID50 values for epidural indomethacin, diclofenac, and S(+)ibuprofen were about 10 times higher than those reported in other studies for intrathecal NSAIDs in hyperalgesia models.