Enhancement of the Bronchial Reactivity in Immunized Rats by Neonatal Treatment with Capsaicin

Rats were injected with capsaicin at 1–2 days of age to abolish the content of substance P (SP) in nerve terminals. At 6 weeks of age the capsaicin-treated and control rats were sensitized daily for 1 or 2 subsequent weeks Monday through Friday with ovalbumin (OA). The OA was given without adjuvant as 300 ng subcutaneous (s.c.) injections in the neck region or as 1% aerosol for 30 min. The capsaicin-treated animals which were sensitized s.c. for 2 weeks reacted moderately with increased transpulmonary pressure (TPP) to airway challenge with OA, and strongly to intravenous (i.v.) challenge with OA or serotonin. The capsaicin-untreated animals, which were sensitized with OA, reacted weakly to the challenge. In the animals sensitized with aerosolized OA, slightly lower reactivity was seen compared with those sensitized s.c. Untreated and unsensitized control rats reacted only to serotonin challenge. No animal had any detectable serum or bronchial IgE antibodies. Aerosol-sensitized animals had IgG antibodies in both serum and bronchial lavage. Histologically, the animals treated with capsaicin in contrast to the untreated controls demonstrated a pronounced increase of lymphoid tissue around their bronchi. Their mast cell numbers were increased around vessels and in the pleura and their mucous cell numbers were increased in the epithelium of the bronchi and bronchioli. The sensitization did not add much to this histological picture.