Characterization of the airway response to inhaled leukotriene D4 in normal subjects.

To better understand the role of leukotriene D4 (LTD4) in the pathogenesis of airway hyperreactivity, we administered aerosolized LTD4 on multiple occasions to 6 normal subjects and measured specific airway conductance (SGaw) by body plethysmography and the flow rate at 30% of vital capacity from partial forced expiratory maneuvers (V30P). Dose-response curves generated from standard bronchoprovocation tests revealed that LTD4 was 280 to 590 times more potent as a bronchoconstrictor than was methacholine. The airway response to single bronchoconstricting doses of LTD4 administered on separate days was reproducible for SGaw (r = 0.86, p less than 0.05) and V30P (r = 0.95, p less than 0.005). The response to 3 consecutive single-dose LTD4 challenges performed on the same day, allowing SGaw and V30P to return to greater than 90% of the control value between challenges, demonstrated tachyphylaxis: the response to the third dose was significantly less than the response to the first dose for SGaw (p less than 0.001) and for V30P (p less than 0.01). A single bronchoconstricting dose of LTD4, given before a standard methacholine dose-response challenge, lowered the concentration of methacholine needed to decrease V30P 30% (p less than 0.05) and SGaw 35% (p = 0.09). A single bronchoconstricting dose of methacholine preceding a standard methacholine challenge did not have this effect. LTD4 and methacholine demonstrated a cumulative dose-effect when progressively higher concentrations were inhaled. In summary, the airway response to LTD4 is reproducible, exhibits tachyphylaxis, and a cumulative dose-effect occurs. As well, LTD4 increases the responsiveness of normal airways to methacholine.