Antigen-induced hyperresponsiveness to methacholine in ventilated, anesthetized guinea pigs.

Guinea pigs were actively sensitized to ovalbumin and exposed 2-3 weeks later to an aerosol of ovalbumin or saline. Changes in lung function were assessed 0.5, 1, 6, 24 and 72 h later by measuring the peak increase in pulmonary inflation pressure induced by i.v. methacholine during constant-volume ventilation. Responses to methacholine were significantly potentiated at 0.5, 1, 6 and 24 h but not at 72 h following exposure to antigen. Hyperresponsiveness to methacholine was maximal at 0.5-1 h and, in terms of magnitude, comparable to the early increase in airway reactivity found in mild asthmatics after allergen challenge. Whether the hyperresponsiveness to methacholine induced by antigen in the guinea pig can be attributed solely to an increase in airway reactivity or is due, at least in part, to decreased lung compliance requires further study.