It has been suggested in cross-sectional studies that provocation with
adenosine 5'-monophosphate (
AMP) more closely reflects the inflammatory process in
asthma than does provocation with
methacholine or
histamine. We investigated whether the
steroid-induced improvement in the provocative concentration of
AMP producing a 20% decline in FEV1 (PC20
AMP) is more closely associated with the concomitant reduction in airway
inflammation than is the improvement in PC20
methacholine. In 120 asthmatic patients, we measured PC20
methacholine and PC20
AMP as well as sputum induction and
nitric oxide (NO) in exhaled air before and after 2 weeks of treatment with
corticosteroids. Improvement in PC20
AMP was solely related to reduction in airway
inflammation (i.e., change in the number of sputum eosinophils, lymphocytes, epithelial cells, and concentration of NO in exhaled air). In contrast, improvement in PC20
methacholine was related to both reduction in airway
inflammation (i.e., change in the number of sputum eosinophils and lymphocytes) and increase in FEV1 %predicted. The total explained variance of the improvement in bronchial hyperresponsiveness was greater for
AMP than for
methacholine (36% versus 22%, respectively). We conclude that PC20
AMP is more sensitive to changes in acute airway
inflammation than is PC20
methacholine, further reinforcing the notion that PC20
AMP can be a useful tool for monitoring the effects of antiinflammatory
therapy.