Lung epithelial permeability: relation to nonspecific airway responsiveness.

Lung epithelial permeability was measured in five normal, five asthmatic, and five smoking subjects by quantifying removal from the lung and accumulation in the blood of an inhaled radiolabeled low-molecular-weight substance, technetium-99m-labeled diethyleneaminepentaacetate (99mTc-DTPA). Measurements on 2 control days were highly reproducible. Nonspecific bronchial responsiveness to histamine was determined in all subjects on a 3rd day, and the results were expressed as the provocation concentration producing a fall in forced expiratory volume in 1 s of 20% (PC20 histamine). Lung epithelial permeability was similar for the normal and asthmatic subjects. However, smokers had greatly increased permeability when compared with the other two groups. The responsiveness to histamine was increased in the asthmatics but within the normal range for normal subjects and smokers. No relationship was established between increased epithelial permeability and increased responsiveness to histamine. Results indicate that increased permeability of the epithelial lining of the bronchi is not a dominant factor in the increased nonspecific responsiveness to histamine observed in asthma.