An alternative pathway for metabolism of leukotriene D4: effects on contractions to cysteinyl-leukotrienes in the guinea-pig trachea

摘要

class="enumerated" style="list-style-type:decimal">Contractions of guinea-pig tracheal preparations to cysteinyl-leukotrienes (LTC4, LTD4 and LTE4) were characterized in organ baths, and cysteinyl-leukotriene metabolism was studied using radiolabelled agonists and RP-HPLC separation.In the presence of S-hexyl GSH (100 μM) the metabolism of [³H]-LTC4 into [³H]-LTD4 was inhibited and the LTC4-induced contractions were resistant to CysLT1 receptor antagonism but inhibited by the dual CysLT1/CysLT2 receptor antagonist BAY u9773 (0.3–3 μM) with a pA2-value of 6.8±0.2.In the presence of L-cysteine (5 mM), the metabolism of [³H]-LTD4 into [³H]-LTE4 was inhibited and the LTD4-induced contractions were inhibited by the CysLT1 receptor antagonist ICI 198,615 (1–10 nM) with a pA2-value of 9.3±0.2. However, at higher concentrations of ICI 198,615 (30–300 nM) a residual contraction to LTD4 was unmasked, and this response was inhibited by BAY u9773 (1–3 μM).In the presence of the combination of S-hexyl GSH with L-cysteine, the LTD₄-induced contractions displayed the characteristics of the LTC₄ contractile responses, i.e. resistant to CysLT₁ receptor antagonism, increased maximal contractions and slower time-course. This qualitative change of the LTD₄-induced contraction was also observed in the presence of S-decyl GSH (100 μM), GSH (10 mM) and GSSG (10 mM).S-hexyl GSH, S-decyl GSH, GSH and GSSG all stimulated a formation of [³H]-LTC₄ from [³H]-LTD₄.In conclusion, GSH and GSH-related compounds changed the pharmacology of the LTD₄-induced contractions by stimulating the conversion of LTD₄ into LTC₄. Moreover, the results indicate that, in addition to the metabolism of LTC₄ into LTD₄ and LTE₄, also the formation of LTC₄ from LTD₄ may regulate cysteinyl-leukotriene function.