Increased leukotriene E₄ excretion during antigen-induced bronchoconstriction in allergic sheep

The metabolism of leukotrienes (LT) in the sheep was investigated to define markers of 5-lipoxygenase involvement in allergic responses, obtainable by noninvasive techniques. Intravenous administration of 14,15-[³H]LTC₄ (0.5 μCi/kg) revealed a rapid clearance from the circulation (half time = 90 s). Circulatory metabolism was apparent, with early formation (within 1 min) of LTD₄ and LTE₄ shown by reverse-phase high-pressure liquid chromatography (RP-HPLC). Urinary ³H excretion comprised 10% of the original dose. [³H]LTE₄ (characterized by coelution with authentic standards during RP-HPLC analysis) was observed in early urine samples. By use of a sensitive and specific RP-HPLC radioimmunoassay analysis, immunoreactive material coeluting with LTE₄ was detected in urine from allergic sheep. Excretion of this material was significantly increased during antigen-induced acute bronchoconstriction in eight conscious allergic sheep [preantigen, 65.70 ± 24.27 (SE) pg; 0-1 h postantigen, 208.00 ± 71.10 pg, P < 0.05], but not during late responses. However, total postantigen LTE₄ excretion (37.8-956.1 pg/8 h) was highly correlated (r = 0.976, P < 0.001) with the severity of bronchoconstriction (445.3-2,409.1% specific pulmonary resistance per hour) assessed by measurement of the area under the curve of pulmonary function plotted against time. These findings represent an important demonstration of in vivo allergen-induced peptide LT generation in a physiologically characterized animal model of prolonged allergic bronchoconstriction and further substantiate an important role for LT in this model of allergic asthma.