Representative histology showing the effects of topical treatment with 2,5-diacetoxyphenyl sulfonate (DAPS; 2.5%
; eq. to 0.08 mmol/ml) on benzalkonium chloride-induced dermatitis in the rat ear. The first row shows the macroscopic appearance of both ears of a rat treated with vehicle alone (glycerol: A) and those of a rat treated with DAPS (B), which evidently reduces the erythema caused by dermatitis. In the second row, the tissue edema on the ear of a rat with dermatitis treated only with glycerol (C) was not observed in DAPS-treated rats (D). The third row shows the intense leukocyte infiltration in a glycerol-treated rat ear (E), an effect that was clearly reduced by DAPS treatment (F). Magnification of the boxed area in E and F reveals that in the capillaries of vehicle-treated rats, there are leukocytes adhered to the endothelial cells, which rolled and extravasated to infiltrate the surrounding tissue (G), a feature not observed in the vessels of DAPS-treated rats (H). The infiltration of leukocytes into the erector muscle of the ear in glycerol-treated rats (I) was also attenuated by DAPS treatment (J). Magnifications: C-F, x100; G-H x400; I-J x200. Panel K shows the effects of topic treatment with 2,5-dihydroxyphenyl sulfonate (DHPS; 5%; eq. to 0.22 mmol/ml), DAPS (2.5%; eq. to 0.08 mmol/ml) or the vehicle alone (glycerol) on the myeloperoxidase (MPO) activity associated with benzalkonium chloride-induced dermatitis on the rat ear. Dermatitis was not induced in the control group. MPO activity is expressed as the mean ± SEM of the absorbance at 460 nm normalized to the weight (mg) of the tissue of the corresponding ear. The numbers of animals used is shown in parentheses: **p < 0.01 vs. control; † p < 0.05, †† p < 0.01 vs. vehicle by one-factor ANOVA followed by Student-Newmann-Keuls test.