Regional differences in dermal inflammatory reactions

Regional differences in dermal inflammatory reactions in the dorsum of rat trunk were studied in three commonly used inflammatory models, i.e., reverse passive Arthus reaction (RPAR), passive cutaneous anaphylaxis (PCA), and histamine-induced inflammatory (HI) reaction. The RPAR showed an increasing severity from cranial to caudal regions, as measured by water content in the skin lesions. The PCA reaction, as measured by Evans blue leakage was not influenced by regional differences. The HI reaction, as measured by water content and leakage of radioactively labeled human serum albumin ( [125I]HSA), was significantly smaller in the central regions of the dorsum than in the most cranial and sacral regions. However, no regional differences were observed when the reaction was evaluated by protein-bound Evans blue leakage. A comparison of the three different methods to determine the HI reaction showed a correlation (r = 0.70) between measurements of water content and [125I]HSA leakage. There was less correlation of these two methods with measurements of Evans blue skin lesion diameter (r = 0.31 and 0.56, respectively). In conclusion, regional differences in inflammatory responses, and methodological differences to measure them, may influence the results of commonly used tests like RPAR, PCA and HI reactions. Such differences should be considered when quantitating dermal inflammatory reactions.