Nitric oxide and superoxide radical are involved in both initiation and development of adjuvant arthritis in rats.

Nitric oxide synthase(NOS) inhibitor,N omega-nitro-L-arginine methyl ester (L-NAME, 10-300 mg/kg) and L-NG-monomethyl-arginine (L-NMMA, 30-300 mg/kg) suppressed the swellings of adjuvant-injected paw of rats (25-54%) at day 2 and 8 when dosed intraperitoneally and orally for 4 days from day -1 to day 2 after adjuvant. L-NAME (30-300 mg/kg) also suppressed the edema of the non adjuvant-injected paws (15-42%) at day 28. Local injection of this inhibitor (2 and 10 mg/kg) was without effect. L-arginine (1 g/kg, i.p.), impaired the suppression by L-NAME. Bovine blood Cu, Zn-superoxide dismutase (SOD, 3 mg/kg, i.p.: 28% suppression) and L-NAME (30 mg/kg i.p.: 36% suppression) showed additive effect (52%) in adjuvant-injected paws at day 8 when co-injected. As the effect of 30 mg/kg L-NAME corresponded nearly to that of 10 mg/kg VoltarenR, this NOS inhibitor would be worth considering as an anti-inflammatory agent. Sodium nitroprusside (NO-donor) and methylene blue (guanylate cyclase inhibitor) had no effect. L-NAME was also suppressive when dosed after adjuvant inoculation and NO is involved in the development and maintenance of swelling.