OBJECTIVE: To study the role of nitric oxide (NO) in the cell influx (CI) and the articular incapacitation (AI) in the zymosan induced-arthritis (ZyA). METHODS: Wistar rats received 1 mg of zymosan (Zy) into the right knee joint, and controls received saline. The AI was evaluated by the Test for AI in rats. After sacrifice, the CI and the release of prostaglandin E2 (PGE2) were assessed in the joint exudate. The joint edema was measured by the wet/dry weight ratio of the articular tissue. Groups were treated i.p. with L-NAME - NO synthase (NOS) inhibitor (LN = 30-300 mg/kg) or aminoguanidine (AG = 30-300 mg/kg) - selective iNOS inhibitor - 30 minutes before or 2 hours after the Zy. RESULTS: Pretreatment with L-NAME or AG dose-dependently inhibited the AI and the CI, but not altering edema or PGE2 release, being maximal for the 100 mg/kg doses of L-N and AG. Coinjection of L-arginine (1g/kg) and LN (100 mg/kg) reversed the inhibition of the AI and of the CI. D-NAME (100 mg/kg) had no effect. Coinjection of naloxone (opioid antagonist) reversed LN or AG effect on the AI. Mean arterial pressure increased (p<0,01) with LN (100 mg/kg), but not with AG (100 mg/ kg). LN and AG (100 mg/kg) given 2 hours after the Zy had no effect. Methylene blue (GMPc inhibitor), but not hemoglobin (NO scavenger) reversed AI and CI (p<0,01). Sodium nitroprusside (NO donor) given 2 hours after Zy reduced significantly AI, but not CI (p<0,01). CONCLUSIONS: The antinociceptive effect of iNOS inhibition in ZyA happens only with a prophylactic administration, due to an anti-inflammatory effect via GMPc, independently of exogenous NO or PGE2 release, but is associated to endogenous opioid release. The administration of an NO donor produces analgesia in ZyA.
Nitric oxide; arthritis; pain; hyperalgesia; neutrophils; zymosan
