DIFFERENTIAL EFFECT OF L-NAME AND S-METHYL-ISOTHIOUREA ON LEUKOCYTE EMIGRATION IN CARRAGEENAN-SOAKED SPONGE IMPLANTS IN RAT

1 The role of nitric oxide (NO) in leukocyte (polymorphonuclear cells, monocytes and lymphocytes) emigration was studied in a model of carra geenin-sponge implants in rats. 2 The subcutaneous implantation of 1% (w/v) of lambda-carrageenin-soaked sponges elicited an inflammatory re sponse that was characterized by a time-related increase in leukocyte infiltration in the sponges and increased levels of nitrite in the exu date. Total leukocyte infiltration and nitrite production were maximal at 24 h and decreased after 48 and 96 h. The mononuclear cell influx was maximal at 48 h (21% of the total leukocytes). Therefore, this tim e point was used in the successive experiments. 3 Polymorphonuclear ce ll (PMN) and lymphocyte infiltration in the sponges significantly incr eased when rats were treated with the non-specific NO-synthase (NOS) i nhibitor, N-G-nitro-L-arginine methylester (L-NAME) (1 mg ml(-1) in dr inking water ad libitum). Monocyte emigration was not affected by L-NA ME treatment. The nitrite levels in the exudate of L-NAME-treated rats were significantly reduced. The concomitant ingestion of L-arginine ( 30 mg ml(-1)) resulted in a reversion of the L-NAME effect, while D-ar ginine (30 mg ml(-1)) had no effect, indicating the involvement of the L-arginine: NO pathway. 4 Administration of L-NAME resulted also in a n increased release of tumour necrosis factor-a (TNF-a) and prostacycl in (measured as the stable metabolite, 6-keto-PGF(1 alpha)), L-NAME ha d no effect on monocyte chemoattractant protein-1 (MCP-1) release in t he exudate. 5 Since L-NAME may have effects on the local blood flow, p henylephrine (0.034 mg ml(-2) in drinking water) was used as it has an effect on the local blood flow similar to L-NAME. Phenylephrine had n o effect on either leukocyte emigration, or on nitrite, TNF-alpha, pro stacyclin or MCP-1 accumulation in the exudate. 6 In contrast, the mor e selective iNOS inhibitor S-methyl-isothiourea (SMT) (10 mu g ml(-1) in drinking water) significantly reduced PMNs and lymphocyte influx in the sponge, having no effect on monocyte influx. Moreover, SMT decrea sed nitrite production in the exudate to a comparable extent as L-NAME . 7 Administration of SMT significantly reduced MCP-1 release in the e xudate, without an effect on TNF-alpha or prostacyclin production. Mor eover SMT did not produce any changes in local blood flow. 8 Our resul ts show that a different outcome of the inflammatory process can be ob tained depending on the types of NOS inhibitor used.