Evaluation of Organic Solvent-Induced Inflammation Modulated by Neuropeptides in the Abdominal Skin of Hairless Rats

In this study, the severity and time course of inflammation induced by 4 organic solvents (acetone, cyclohexane, toluene and m-xylene), and the effect of neuropeptides during the inflammation were investigated in the hairless rat abdominal skin. Plasma extravasation used as a parameter of inflammation was measured by Evans blue and 125I-bovine serum albumin (BSA). Total volume of plasma extravasation induced by 4 organic solvents in 240-min exposure was as follows: toluene>m-xylene>cyclohexane>acetone=0. While hydrophobic solvents (toluene, m-xylene, cyclohexane) induced plasma extravasation, the hydrophilic solvent, acetone, did not induce plasma extravasation. It was suggested that the severity and time course of plasma extravasation depend on chemical characteristics of the organic solvents. In immunohistochemical study, substance P (SP)-immunoreactive nerve fibers (IRNF) and calcitonin gene-related peptide (CGRP) -IRNF were intact during 240-min exposure to acetone. In contrast, cyclohexane, toluene, and m-xylene reduced the number of SP-IRNF and CGRP-IRNF in 10min exposure and further reduced immunoreactivity. In hairless rats treated with systemic capsaicin, the above plasma extravasation was significantly reduced, along with SP-IRNF and CGRP-IRNF; however, protein gene product 9.5 (PGP 9.5)-IRNF was nearly intact. These results indicated that certain organic solvents induce instance of inflammation that vary widely in terms of their severity and time course, and that these differences are correlated with neuropeptides.