Effect of maturation on allergen-induced airflow obstruction and airway plasma exudation in sensitized guinea pigs.

Airway reactivity to bronchoconstrictor mediators changes with age. We studied the effects of maturation on airway responses provoked by allergen challenge [ovalbumin (OA) 0.05, 0.15 and 0.5 mg/kg i.v] in passively sensitized immature (190 +/- 2 g: 2 weeks old) and adult guinea pigs (566 +/- 16 g: 13 weeks old). In both groups of animals, we measured both lung resistance (RL) to monitor airflow obstruction and extravasation of Evans blue dye, to quantify airway plasma exudation. Immature guinea pigs required a larger dose of OA at the challenge to induce a significant increase in RL and extravasation of Evans blue dye compared with adult guinea pigs. In addition, immature animals responded less to the lower doses of OA than adults. Pretreatment with pyrilamine, an antihistamine, suppressed the increase in RL in immature animals, whereas the remaining component of the increase in RL was seen in adult animals. Intravenous allergen challenge causes less airflow obstruction and airway plasma exudation in immature than in adult guinea pigs. Allergen-induced airflow obstruction is mediated mainly via histamine in immature animals, whereas this may not be the case in adult animals.