Effects of topical antiinflammatory agents on Freund's adjuvant-induced skin lesions in rats

Freund's adjuvant, when administered intradermally to rats, causes polyarthritis as well as inflammation of the skin, eye, gastrointestinal and genitourinary tracts. We assessed the effects of antiinflammatory drugs on ear skin lesions to determine if this might be a useful skin inflammation model. The hind paw of male Lewis rats was injected with Mycobacterium butyricum in paraffin oil. Lesions appeared between days 13 and 15 after adjuvant injection. Each ear exhibited on average 1 to 3 highly erythematous, elevated lesions, 2 to 3 mm in diameter. By histology, the lesions consisted of epidermal hyperplasia, with a prominent accumulation of inflammatory cells in the dermis. Ears were treated topically with glucocorticoids, cyclosporine and indomethacin on days 15 through 21 after adjuvant injection. By day 22, dexamethasone, fluocinolone acetonide, and cyclosporine caused near-complete clearing of lesions whereas indomethacin exacerbated the inflammation by causing increased numbers of skin lesions. These results show the potential usefulness of adjuvant-induced skin lesions in rats as a novel subchronic inflammation model.