Urinary leukotriene E₄ levels increase upon exposure to hypobaric hypoxia

Study objective: To determine whether urinary leukotriene E₄ (uLTE₄) levels increase upon exposure to high altitude, and also to ascertain the relationship between uLTE₄ levels and symptoms of acute mountain sickness (AMS). Design: Prospective, unblinded, single-factor (altitude) experimental study. Settings: US Army research laboratory facilities at sea level ([SL] 50 m), 1,830 m, and 4,360 m. Participants: Eight healthy male subjects ranging in age from 19 to 24 years. Measurements: uLTE₄ levels and symptoms of AMS were measured at just above SL (50 m), 3 1/4 days after being transported from SL to moderate altitude (MA) (1,830 m), and 1 1/4 days after ascent from 1,830 to 4,300 m (high altitude [HA]). Symptoms of AMS were assessed using standard indexes derived from the Environmental Symptoms Questionnaire weighted toward cerebral (AMS-C) and respiratory (AMS-R) manifestations. Oxygen saturation was measured noninvasively by pulse oximetry at SL and HA. Results: The mean (± SEM) uLTE₄ levels (pg/mg creatinine) were 67.9 (± 13.2) at SL; 82.3 (± 5.5) at MA; and 134.8 (± 19.4) at HA (p<0.05 comparing HA with SL and MA). Conclusions: We conclude that uLTE₄ levels increase shortly after exposure to HA even after staging for 4 days at MA. Although this study does not clearly demonstrate a relationship between uLTE₄ levels and symptoms of AMS, it supports the hypothesis that leukotrienes may be involved in the pathophysiologic state of AMS.