HISTOPATHOLOGICAL ANALYSIS OF RAT MESENTERY AS A METHOD FOR EVALUATING NEUTROPHIL MIGRATION - DIFFERENTIAL-EFFECTS OF DEXAMETHASONE AND PERTUSSIS TOXIN

In the present study, histopathological analysis of rat mesentery was used to quantify the effect of two anti-inflammatory agents, dexametha sone (Dex) and pertussis toxin (Ptx), on leukocyte migration. The intr avenous injection of Dex (1 mg/kg) and Ptx (1,200 ng) 1 h prior to the intraperitoneal injection of the inflammatory stimuli lipopolysacchar ide (LPS) or formyl-methionyl-leucyl-phenylalanine (fMLP) significantl y reduced the neutrophil diapedesis (LPS: Ptx = 0.86 +/- 0.19 and Dex = 0.35 +/- 0.13 vs saline (S) = 2.85 +/- 0.59; fMLP: Ptx = 0.43 +/- 0. 09 and Dex 0.01 +/- 0.01 vs S = 1.08 +/- 0.15 neutrophil diapedesis/fi eld) and infiltration (LPS: Ptx = 6.29 +/- 1.4 and Dex = 3.06 +/- 0.76 vs S = 15.94 +/- 3.97; fMLP: Ptx = 3.85 +/- 0.56 and Dex = 0.40 +/- 0 .16 vs S = 7.15 +/- 1.17 neutrophils/field) induced by the two agonist s in the rat mesentery. The inhibitory effect of Dex and Ptx was clear ly visible in the fields nearest the venule (up to 200 mu m), demonstr ating that these anti-inflammatory agents act preferentially in the tr ansmigration of neutrophils from the vascular lumen into the interstit ial space, but not in cell movement in response to a haptotactic gradi ent. The mesentery of rats pretreated with Dex showed a decreased numb er of neutrophils within the venules (LPS: Dex:= 1.50 +/- 0.38 vs S = 4.20 +/- 1.01; fMLP: Dex = 0.25 +/- 0.11 vs S = 2.20 +/- 0.34 neutroph ils in the lumen/field), suggesting that this inhibitor may be acting at a step that precedes neutrophil arrival in the inflamed tissue. In contrast to that observed with Dex treatment, 1:he number of neutrophi ls found in mesenteric venules was significantly elevated in animals p retreated with Ptx (LPS: Ptx = 9.85 +/- 2.25 vs S = 4.20 +/- 1.01; fML P: Ptx = 4.66 +/- 1.24 vs S = 2.20 +/- 0.34 neutrophils in the lumen/f ield). This discrepancy shows that Ptx and Dex act via different mecha nisms and suggests that Ptx prevents locomotion of neutrophils from th e vascular lumen to the interstitial space. In conclusion, the method described here is useful for quantifying the inflammatory and anti-inf lammatory effect of different substances. The advantage of this histop athological approach is that it provides additional information about the steps involved in leucocyte migration.