A COMPARISON OF THE EFFECTS OF L-NAME, 7-NI AND L-NIL ON CARRAGEENAN-INDUCED HINDPAW EDEMA AND NOS ACTIVITY

1 Intraplantar injection of carrageenan (150 mu l, 1-3% w/v) in the ra t resulted in a dose-related increase in hindpaw weight (oedema) chara cterized by a rapid 'early' phase (up to 2.5 h) response followed by a more sustained 'late' phase (2-6 h) response. No change in weight of either the contralateral (i.e. noninjected) hindpaw or hindpaws inject ed with saline was observed. 2 Six hours after intraplantar injection of carrageenan (1-3% w/v) hindpaw constitutive (i.e, calcium-dependent ) nitric oxide synthase (cNOS) activity (determined ex vivo as the con version of radiolabelled L-arginine to radiolabelled citrulline) was i ncreased (e.g. 2% w/v; 0.64 +/- 0.08 pmol citrulline mg(-1) protein 15 min(-1) c.f. 0.08 +/- 0.04 pmol citrulline mg(-1) protein 15 min(-1) in saline-injected, control animals, n=4, P < 0.05). Carrageenan injec tion also resulted in the appearance in hindpaw homogenates of inducib le (i.e. calcium-independent) nitric oxide synthase (iNOS, e.g. 2% w/v ; 0.67+/-0.14 pmol citrulline mg(-1) protein 15 min(-1), n = 4). Hindp aw cyclic GMP concentration was also significantly increased 6 h after intraplantar injection of carrageenan (e.g. 2% w/v; 379.6 +/ -26.8 fm ol mg(-1) protein c.f. 261.8 +/- 42.2 fmol mg(-1) protein, in saline-i njected, control animals, n = 4, P < 0.05). 3 Pretreatment (5-25 mg kg (-1), i.p., 30 min before carrageenan, 2% w/v) of animals with L-N-G n itro arginine methyl ester (L-NAME; isoform nonselective inhibitor of NOS) or 7-nitro indazole (7-NI; inhibitor of neuronal NOS, nNOS) cause d dose-related inhibition of both the early (2 h) and late (6 h) phase hindpaw oedema, associated with reduced hindpaw iNOS and cNOS activit y and cyclic GMP concentration in animals killed at 6 h. Administratio n of 7-NI (5-25 mg kg(-1), i.p.) to animals 2.5 h after intraplantar c arrageenan (2% w/v) injection (i.e. at the end of the early phase oede ma response) produced dose-related inhibition of the late phase respon se. 4 Pretreatment (5-25 mg kg(-1), i.p., 30 min before carrageenan, 2 % w/v) of animals with L-N6-iminoethyllysine (L-NIL, selective inhibit or of iNOS) (5-25 mg kg(-1)) failed to affect the early phase hindpaw oedema response but did produce a dose-related inhibition of the late phase oedema. L-NIL pretreatment also inhibited the carrageenan-induce d increase in both hindpaw iNOS and cNOS activity as well as the rise in hindpaw cyclic GMP concentration. 5 The present experiments demonst rate an anti-inflammatory effect of 7-NI as evidenced by inhibition of carrageenan-induced hindpaw oedema in the rat. Inhibition of nNOS (ea rly phase) and iNOS Gate phase) at the site of inflammation most proba bly accounts for the anti-inflammatory activity observed. These data s uggest a role for nitric oxide synthesized by the nNOS isoform (most p robably within sensory nerves) in this model of inflammation.