NITRIC-OXIDE - A KEY MEDIATOR IN THE EARLY AND LATE-PHASE OF CARRAGEENAN-INDUCED RAT PAW INFLAMMATION

1 The role of nitric oxide (NO) derived from constitutive and inducibl e nitric oxide synthase (cNOS and iNOS) and its relationship to oxygen -derived free radicals and prostaglandins (PG) was investigated in a c arrageenan-induced model of acute hindpaw inflammation. 2 The intrapla ntar injection of carrageenan elicited an inflammatory response that w as characterized by a time-dependent increase in paw oedema, neutrophi l infiltration, and increased levels of nitrite/nitrate (NO2-/NO3-) an d prostaglandin E(2)(PGE(2)) in the paw exudate. 3 Paw oedema was maxi mal by 6 h and remained elevated for 10 h following carrageenan admini stration. The non-selective cNOS/iNOS inhibitors, N-G-monomethyl-L-arg inine (L-NMMA) and N-G-nitro-L-arginine methyl ester (L-NAME) given in travenously (30-300 mg kg(-1)) 1 h before or after carrageenan adminis tration, inhibited paw oedema at all time points. 4 The selective iNOS inhibitors, N-iminoethyl-L-lysine (L-NIL) or aminoguanidine (AG), fai led to inhibit carrageenan-induced paw oedema during the first 4 h fol lowing carrageenan administration, but inhibited paw oedema at subsequ ent time points (from 5-10 h). iNOS mRNA was detected between 3 to 10 h following carrageenan administration using ribonuclease protection a ssays. iNOS protein was first detected 6 h and was maximal 10 h follow ing carrageenan administration as shown by Western blot analysis. Admi nistration of the iNOS inhibitors 5 h after carrageenan (a time point where iNOS was expressed) inhibited paw oedema at all subsequent time points. Infiltrating neutrophils were not the source of iNOS since pre treatment with colchicine (2 mg kg(-1)) suppressed neutrophil infiltra tion, but did not inhibit the iNOS mRNA expression or the elevated NO2 -/NO3- levels in the paw exudate. 5 Inhibition of paw oedema by the NO S inhibitors was associated with attenuation of both the NO2-/NO3- and PGE(2) levels in the paw exudate. These inhibitors also reduced the n eutrophil infiltration at the site of inflammation. 6 Recombinant huma n Cu/Zn superoxide dismutase coupled to polyethyleneglycol (PEGrhSOD;1 2 x 10(3) u kg(-1)), administered intravenously either 30 min prior to or 1 h after carrageenan injection, inhibited paw oedema and neutroph il infiltration, but had no effect on NO2-/NO3- or PGE(2) production i n the paw exudate. The administration of catalase (40 x 10(3) u kg(-1) ), given intraperitoneally 30 min before carrageenan administration, h ad no effect on paw oedema. Treatment with desferrioxamine (300 mg kg( -1)), given subcutaneously 1 h before carrageenan, inhibited paw oedem a during the first 2 h after carrageenan administration, but not at la ter times. 7 These results suggest that the NO produced by cNOS is inv olved in the development of inflammation at early time points followin g carrageenan administration and that NO produced by iNOS is involved in the maintenance of the inflammatory response at later time points. The potential interactions of NO with superoxide anion and PG is discu ssed.