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) treatment on the leucocyte infiltration into the airways and pleural cavity was investigated in rats actively sensitized with ovalbumin. The animals were neonatally 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 actively sensitized with ovalbumin (200 microg, s.c.) and 14 days later they were intratracheally (or intrapleurally) challenged with ovalbumin. The substance P level in bronchoalveolar lavage fluid of the capsaicin group was reduced by >90% compared to control group (vehicle), confirming the efficacy of capsaicin treatment. In the capsaicin group, the number of neutrophils (but not of eosinophils and mononuclear cells) in bronchoalveolar lavage fluid of sensitized animals was significantly higher than the control group. Intrapleural injection of ovalbumin in sensitized rats caused a significant neutrophil influx at 6 h that was markedly increased in the capsaicin-pretreated animals compared to control group. The counts of eosinophils and mononuclear cells in the pleural exudates did not differ significantly between capsaicin and control groups. The increased levels of immunoglobulin (Ig)E, IgG1 and IgG2a anti-ovalbumin antibodies in serum of sensitized rats did not differ between capsaicin and control groups. In conclusion, the exacerbated pulmonary neutrophil recruitment caused by the capsaicin neonatal treatment is unrelated to increase in serum immunoglobulin antibodies, and suggests a protective role for C-fibers in attenuating the allergic neutrophil infiltration.