Differential effects of leukotrienes C4, D4, and E4 in the pulmonary and systemic vasculature of sheep.

We investigated the comparative direct and cyclooxygenase-mediated effects of the constituents of slow-reacting substance of anaphylaxis (SRS-A), i.e., leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4) on pulmonary and systemic haemodynamics of sheep. In 20 conscious sheep, measurements of pulmonary vascular resistance (Rpv) and systemic vascular resistance (Rsv) were obtained before and after a rapid intravenous injection of LTC4 (0.1 micrograms X kg-1), LTD4 (0.1 micrograms X kg-1) and LTE4 (1 microgram X kg-1). The same protocol was carried out after pretreatment with the leukotriene antagonist FPL-57231 or the cyclooxygenase inhibitor indomethacin. LTD4 increased mean Rpv to 421% of baseline (p less than 0.001) and had a biphasic effect on mean Rsv, which, following an initial decrease of 18% (p less than 0.05), increased to 143% of baseline (p less than 0.05). LTC4 and LTE4 had no significant effects on Rpv, while they increased mean Rsv to 144% and 143% of baseline, respectively (p less than 0.05). This effect was not preceded by a decrease in Rsv. FPL-57231 completely blocked the effects of LTC4, LTD4 and LTE4 on Rsv, and of LTD4 on Rpv. Indomethacin had no effect on LTC4, LTD4 and LTE4-induced increases in mean Rsv, while it prevented the LTD4-induced initial decrease in mean Rsv. Indomethacin also prevented the LTD4-induced increase in Rpv. A dose-response curve (0.05, 0.1, 0.5 and 1 microgram X kg-1) demonstrated that in raising Rsv, LTE4 was approximately 10 times less potent than LTC4 and LTD4.(ABSTRACT TRUNCATED AT 250 WORDS)