Histopathological analysis of rat mesentery as a method for evaluating neutrophil migration: differential effects of dexamethasone and pertussis toxin

• Published in: Brazilian journal of medical and biological research Vol. 31; no. 10; pp. 1319 - 1327
• Main Authors: Brito, G A, Falcão, J L, Saraiva, S N, Lima, A A, Flores, C A, Ribeiro, R A
• Format: Journal Article
• Language: English
• Published: Brazil Associação Brasileira de Divulgação Científica 01-10-1998
• Subjects: Animals; Anti-Inflammatory Agents - pharmacology; BIOLOGY; Cell Movement - drug effects; dexamethasone; Dexamethasone - pharmacology; Escherichia coli; histopathological approach; Inflammation - chemically induced; Leukocyte Count; Lipopolysaccharides - adverse effects; LPS; Male; MEDICINE, RESEARCH & EXPERIMENTAL; Mesenteric Veins; mesentery; Mesentery - pathology; N-Formylmethionine Leucyl-Phenylalanine - adverse effects; neutrophil migration; Neutrophils - drug effects; Pertussis Toxin; Rats; Rats, Wistar; Virulence Factors, Bordetella - pharmacology; dexamethasone; pertussis toxin; mesentery; neutrophil migration; histopathological approach; LPS
• DOI: 10.1590/S0100-879X1998001000013
• EISSN: 0100-879X; 1414-431X

In the present study, histopathological analysis of rat mesentery was used to quantify the effect of two anti-inflammatory agents, dexamethasone (Dex) and pertussis toxin (Ptx), on leukocyte migration. The intravenous injection of Dex (1 mg/kg) and Ptx (1,200 ng) 1 h prior to the intraperitoneal injection of the inflammatory stimuli lipopolysaccharide (LPS) or formyl-methionyl-leucyl-phenylalanine (fMLP) significantly 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/field) 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 agonists in the rat mesentery. The inhibitory effect of Dex and Ptx was clearly visible in the fields nearest the venule (up to 200 microns), demonstrating that these anti-inflammatory agents act preferentially in the transmigration of neutrophils from the vascular lumen into the interstitial space, but not in cell movement in response to a haptotactic gradient. The mesentery of rats pretreated with Dex showed a decreased number 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 neutrophils 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, the number of neutrophils found in mesenteric venules was significantly elevated in animals pretreated with Ptx (LPS: Ptx = 9.85 +/- 2.25 vs S = 4.20 +/- 1.01; fMLP: Ptx = 4.66 +/- 1.24 vs S = 2.20 +/- 0.34 neutrophils in the lumen/field). This discrepancy shows that Ptx and Dex act via different mechanisms and suggests that Ptx prevents locomotion of neutrophils from the vascular lumen to the interstitial space. In conclusion, the method described here is useful for quantifying the inflammatory and anti-inflammatory effect of different substances. The advantage of this histopathological approach is that it provides additional information about the steps involved in leucocyte migration.