Contribution of C-fibers to leucocyte recruitment in bronchoalveolar lavage fluid and pleural cavity in the rat

The effect of neonatal capsaicin (8 methyl-N-vanillyl-6-nonenamide) treatme nt on the leucocyte infiltration into the airways and pleural cavity was in vestigated in rats actively sensitized with ovalbumin. The animals were neo natally injected with either capsaicin (50 mg/kg, s.c., 2nd day of life) or vehicle (10% ethanol and 10% Tween 80). At adult ages, the animals were ac tively sensitized with ovalbumin (200 mug, s.c.) and 14 days later they wer e intratracheally (or intrapleurally) challenged with ovalbumin. The substa nce P level in bronchoalveolar lavage fluid of the capsaicin group was redu ced by > 90% compared to control group (vehicle), confirming the efficacy o f capsaicin treatment. In the capsaicin group, the number of neutrophils (b ut not of eosinophils and mononuclear cells) in bronchoalveolar lavage flui d of sensitized animals was significantly higher than the control group. In trapleural injection of ovalbumin in sensitized rats caused a significant n eutrophil influx at 6 h that was markedly increased in the capsaicin-pretre ated animals compared to control group. The counts of eosinophils and monon uclear cells in the pleural exudates did not differ significantly between c apsaicin and control groups. The increased levels of immunoglobulin (Ig)E, IgG(1) and IgG(2a) anti-ovalbumin antibodies in serum of sensitized rats di d not differ between capsaicin and control groups. In conclusion, the exace rbated pulmonary neutrophil recruitment caused by the capsaicin neonatal tr eatment is unrelated to increase in serum immunoglobulin antibodies, and su ggests a protective role for C-fibers in attenuating the allergic neutrophi l infiltration. (C) 2001 Elsevier Science B.V. All rights reserved.