Augmented antinociception following 7-nitro indazole and flurbiprofen in the conscious mouse

Co-administration of the nitric oxide synthase inhibitor, 7-nitro indazole (1 mg/kg i.p.), with the cyclooxygenase inhibitor, flurbiprofen (5-75 mg/kg i.p.), resulted in significantly enhanced antinociceptive activity in mice (formalin-induced hindpaw licking assay) without affecting hindpaw inflammation. No antinociception was observed in animals pretreated with 7-nitro indazole (1 mg/kg i.p.) and flurbiprofen (100 micrograms subplantar). Flurbiprofen (50 mg/kg i.p.) pretreatment did not influence the inhibition of cerebellar or spinal cord nitric oxide synthase activity observed after 7-nitro indazole (1 or 25 mg/kg i.p.) administration and did not alter blood pressure in anaesthetised animals. Thus, flurbiprofen acts by a mechanism unrelated to a local anti-inflammatory effect in the hindpaw. Since nitric oxide synthase inhibitors are antinociceptive by an effect in the spinal cord (dorsal horn) this would appear to be a likely location for the nitric oxide synthase and cyclooxygenase enzymes targetted by 7-nitro indazole and flurbiprofen respectively.