Abstract

Hyperresponsiveness of the airways to nonspecific stimuli is a characteristic feature of asthma. Airway responsiveness is usually characterized in terms of the position and shape of the dose–response curve to methacholine (MDR). In the study we have investigated the influence of fluticasone propionate (FP), a topically active glucocorticoid, on arachidonic acid (AA) metabolites in broncho-alveolar lavage (BAL) fluid (i.e. TxB₂, PGE₂, PGD₂, 6kPGF_1α and LTC₄) on the one hand and MDR curves on the other hand. The effect of FP was studied in a randomized, double-blind, placebo-controlled design in 33 stable nonsmoking asthmatics; 16 patients received FP (500 μg b.i.d.) whereas 17 patients were treated with placebo. We found that the forced expiratory volume in 1s (FEV₁ % predicted) increased, the log₂PC₂₀ methacholine increased and the plateau value (% fall in FEV₁) decreased after a 12 week treatment period. No changes in AA-metabolites could be determined after treatment except for PGD₂ which decreased nearly significantly (p = 0.058) within the FP treated group, whereas the change of PGD₂ differed significantly (p = 0.05) in the FP treated group from placebo. The levels of the other AA metabolites (i.e. TxB₂, PGE₂, 6kPGF_1α and LTC₄) remained unchanged after treatment and were not significantly different from the placebo group. Our results support the hypothesis that although FP strongly influences the position, the shape and also the maximum response plateau of the MDR curve, this effect is not mainly achieved by influence on the level of AA metabolites. Other pro-inflammatory factors may be of more importance for the shape of the MDR curve. It is suggested that these pro-inflammatory factors are downregulated by FP.