Objective: To assess the involvement of spinal inducible nitric oxide synthase (iNOS) in inflammation and nociception.
Materials and methods: The time course of iNOS mRNA expression in rat spinal cord and inflamed paw was assessed by means of quantitative real time RT-PCR. In addition, the effects of the iNOS inhibitor L-NIL on inflammatory paw edema and thermal hyperalgesia were studied in comparison to those of the NO-donor RE-2047. L-NIL (3, 9, 27 and 81 mg/kg) and RE-2047 (3, 9 and 27 mg/kg) or vehicle were administered orally 15 min prior to the intraplantar injection of 0.625 mg zymosan.
Results: Following zymosan injection, mRNA expression of iNOS increased in the inflamed paw and spinal cord with a maximum at 2.5 and 4 h, respectively. In the spinal cord iNOS mRNA started to decline at 10 h whereas it remained at maximum in the inflamed paw up to the end of the observation period of 24 h. As expected, RE-2047 had significant pronociceptive and proinflammatory effects. L-NIL significantly reduced paw inflammation at 27 and 81 mg/kg but failed to reduce hyperalgesia at the doses tested.
Conclusions: The results show that iNOS is upregulated in the inflamed tissue and spinal cord with a similar time course. The effects obtained with L-NIL suggest that iNOS differently contributes to the inflammatory and nociceptive response induced by zymosan.