Cysteinyl leukotrienes mediate enhanced vasoconstriction to angiotensin IIbut not endothelin-1 in SHR

We assessed whether cysteinyl leukotrienes mediate the vasoconstrictor resp onses to angiotensin II and endothelin-1 in the mesenteric vascular bed of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) perfused ex vi vo at a constant flow rate of 5 ml/min with Krebs buffer. Maximal perfusion pressure response (E-max) but not EC50 values to angiotensin II (P<0.001) and endothelin-1 (P<0.01) were significantly higher in the SHR, whereas the responses to potassium chloride remained unchanged. Inclusion of the selec tive 5-lipoxygenase inhibitor AA-861 or the cysteinyl leukotriene receptor antagonist MK-571 significantly reduced the vasoconstrictor responses to an giotensin II but not to endothelin-1 and potassium chloride. The reduction in Emax to angiotensin II was more pronounced in SHR (P<0.001) than in WKY (P<0.05) rats. Cysteinyl leukotrienes LTC4-, LTD4-, and LTE4 (1 muM)-evoked vasoconstrictor responses were significantly higher in SHR (P<0.05), where as LTB4 failed to evoke any response in either strain. These data suggest t hat 5-lipoxygenase metabolites, particularly cysteinyl leukotrienes, contri bute to the exaggerated vasoconstrictor responses to angiotensin II but not to endothelin-1.