Time course of morphometric changes after acute allergic bronchoconstriction in the guinea pig

Experimental allergic bronchoconstriction was induced in guinea pigs by passive sensitization with a standard dose of homologous antiserum followed by challenge with aerosolized antigen. Lungs were removed from animals at intervals of up to 6 days thereafter, and several parameters of the reaction were assessed morphometrically by comparison with lungs from unsensitized guinea pigs. We determined all changes in volume of the lung tissue resulting from fixation through to the preparation of histologic sections, but no significant differences were observed between the time course subgroups. The size of both large and small airways was assessed by a point-counting technique, as well as by measurement of the percentage of the diameter of the airways contributed by the mean thickness of the muscular layer. Maximal bronchoconstriction was observed morphometrically to correspond with the peak of a response as determined clinically by the use of a strain gauge around the chest. This was followed by a return to normal of the airway size. The number of mast cells and eosinophils around large and small airways, around branches of the pulmonary artery and in random fields of the lung parenchyma was tabulated. The maximal decrease in mast cells was seen in animals which died immediately following challenge, but the numbers were not restored to the control level even in animals which had survived for 6 days. The greatest increase in eosinophil response occurred in lungs obtained 10 min following challenge. This model will be of value in determining the effects at the tissue level of pharmacological inhibitors of this reaction.