Involvement of nitric oxide in a rat model of carrageenin-induced pleurisy

Abstract

Some evidence indicates that nitric oxide (NO) contributes to inflammation, while other evidence supports the opposite conclusion. To clarify the role of NO in inflammation, we studied carrageenin-induced pleurisy in rats treated with an NO donor (NOC-18), a substrate for NO formation (L-arginine), and/or an NO synthase inhibitor (S-(2-aminoethyl) isothiourea or N(G)-nitro-L-arginine). We assessed inflammatory cell migration, nitrite/nitrate values, lipid peroxidation and pro-inflammatory mediators. NOC-18 and L-arginine reduced the migration of inflammatory cells and edema, lowered oxidative stress, and normalized antioxidant enzyme activities. NO synthase inhibitors increased the exudate formation and inflammatory cell number, contributed to oxidative stress, induced an oxidant/antioxidant imbalance by maintaining high O(2) (-), and enhanced the production of pro-inflammatory mediators. L-arginine and NOC-18 reversed the proinflammatory effects of NO synthase inhibitors, perhaps by reducing the expression of adhesion molecules on endothelial cells. Thus, our results indicate that NO is involved in blunting-not enhancing-the inflammatory response.

Figure 1

Time course of rat Cg pleurisy. Exudate volume (a) and leukocyte infiltration (b) were evaluated at different time points after Cg injection. The values are expressed as mean ± S.E.M. of 6 to 8 rats.

Figure 2

Time course of nitrite/nitrate levels. The nitrite/nitrate assay was performed in rat pleural exudates collected from control rats (C) or Cg-treated rats at 2, 6, 12, 24, 36, 54, and 72 hours after pleural injection. The values are expressed as mean ± S.E.M. of 6 to 8 rats.

Figure 3

Effects of AE-ITU and L-NNA on rat Cg pleurisy and nitrite/nitrate levels. AE-ITU or L-NNA was injected into the pleural cavity immediately before Cg injection. The exudate volume (a), cell number (b), and nitrite/nitrate levels (c) in the pleural exudates were determined 6 hours after Cg injection. Data are expressed as mean ± S.E.M. of 6 to 8 rats. *P < .05, **P < .01 as compared to the Cg group.

Figure 4

Effects of NOC-18 and L-arginine on rat Cg pleurisy and nitrite/nitrate levels. NOC18 or L-arginine was injected into the pleural cavity immediately before Cg injection. The exudate volume (a), cell number (b), and nitrite/nitrate levels (c) in the pleural exudates were determined 6 hours after Cg injection. Data are expressed as mean ± S.E.M. of 6 to 8 rats. *P < .05, **P < .01 as compared to the Cg group.

Figure 5

Effects of NOC-18 on the influence of AE-ITU and L-NNA on exudate volume (empty columns) and cell infiltration (filled columns) 6 hours after Cg challenge. Each column represents the mean ± S.E.M. of 6 rats. *P < .05, **P < .01 as compared to the vehicle plus vehicle; ^## P < .01 as compared to the vehicle plus AE-ITU; ^†† P < .01 as compared to the vehicle plus L-NNA.

Figure 6

Effect of AE-ITU, L-NNA, NOC-18, and L-arginine on malondialdehyde (MDA) content in the pleural exudates 6 hours after Cg challenge. Data are expressed as mean ± S.E.M. of 6 to 8 rats. **P < .01 as compared to control group; ^## P < .01 as compared to Cg group.

Figure 7

Effects of AE-ITU, L-NNA, NOC-18 and L-arginine on the release of cytokines. Tumor necrosis factor-α (TNF-α) (a), interleukin-1β (IL-1β) (b) and monocyte chemoattractant protein-1 (MCP-1) (c) levels in the pleural exudates 6 hours after Cg challenge. Data are expressed as mean ± S.E.M. from 6 to 8 rats. *P < .05, **P < .01 as compared to control group; ^# P < .05, ^## P < .01 as compared to Cg group.

Figure 8

Effect of AE-ITU, L-NNA, NOC-18, and L-arginine on total antioxidant status (TAOS) activity in pleural exudates 6 hours after Cg challenge. Data are expressed as mean ± S.E.M. from 6 to 8 rats. **P < .01 as compared to the control group; ^## P < .01 as compared to the Cg group.