Early and late phase bronchoconstrictions in conscious sensitized guinea-pigs after macro- and microshock inhalation of allergen and associated airway accumulation of leukocytes

Abstract

Guinea-pigs were sensitized by i.p. injection of 10 μg OA and 100 mg aluminium hydroxide in 1 ml normal saline. Fourteen to twenty-one days after sensitization, animals were exposed to macroshock (1% OA for 2 min) or microshock (0.01% for 60 min) inhalation challenges with OA. Animals were protected against fatal anaphylaxis in the case of macroshocks with mepyramine (30mg/kg i.p.) 30 min before exposure. Specific airway conductance (sG aw) was measured in conscious animals by whole body plethysmography at intervals up to 72h after challenge. An early phase bronchoconstriction peaked significantly ( P < 0.05) at 15 min after both macroshock and microshock OA exposures, with maximum falls in sG aw of 70.8 ± 3.8 and −40.0 ± 5.9%, respectively. These had resolved after 5 h. A late phase bronchoconstriction peaked variably between 17 and 24 h: the mean peak falls in sG aw after the macro- and microshock challenges were significantly different from baseline ( P < 0.05), at −21.6 ± 3.7 and −38.0 ± 3.9%, respectively. Control exposures of OA-sensitized guinea-pigs to saline for either 2 or 60 min, in place of OA, produced no significant variation in sG aw values over the predicted early and late phases. Bronchoalveolar lavage (BAL) performed at 5 or 24h after OA challenge revealed significant increases in total cell numbers ( P < 0.05) at 5 and 24 h after the OA macroshock challenge and at 24 h after the microshock, compared with saline challenges. Differential cell counts showed a significant ( P < 0.05) increase in the proportion of neutrophils at 5 h and of neutrophils and eosinophils at 24 h after the macroshock exposure to OA, compared with saline controls. A significant ( P < 0.05) increase in the proportion of eosinophils also occurred in BAL fluid at 24 h after microshock OA challenge. Neutrophils, however, did not alter at 24 h, yet a late phase bronchoconstriction was recorded. Thus, macroshock (with mepyramine cover) and microshock (without mepyramine cover) OA challenges result in both early and late phase bronchoconstrictions. The late phase is associated with influx of eosinophils in both models but neutrophils only appear after the macroshock, indicating that late phase responses may not involve neutrophil infiltration to the airways.