Interleukin-6 response to exercise and high-altitude exposure: influence of alpha-adrenergic blockade

Interleukin-6 (IL-6), an important cytokine involved in a number of biologi cal processes, is consistently elevated during periods of stress. The mecha nisms responsible for the induction of IL-6 under these conditions remain u ncertain. This study examined the effect of alpha -adrenergic blockade on t he IL-6 response to acute and chronic high-altitude exposure in women both at rest and during exercise. Sixteen healthy, eumenorrheic women (aged 23.2 +/- 1.4 yr) participated in the study. Subjects received either a-adrenerg ic blockade (prazosin, 3 mg/day) or a placebo in a double-blinded, randomiz ed fashion. Subjects participated in submaximal exercise tests at sea level and on days 1 and 12 at altitude (4,300 m). Resting plasma and 24-h urine samples were collected throughout the duration of the study. At sea level, no differences were found at rest for plasma IL-6 between groups (1.5 +/- 0 .2 and 1.2 +/- 0.3 pg/ml for placebo and blocked groups, respectively). On acute ascent to altitude, IL-6 levels increased significantly in both group s compared with sea-level values (57 and 84% for placebo and blocked groups , respectively). After 12 days of acclimatization, IL-6 levels remained ele vated for placebo subjects; however, they returned to sea-level values in t he blocked group. alpha -Adrenergic blockade significantly lowered the IL-6 response to exercise both at sea level (46%) and at altitude (42%) compare d with placebo. A significant correlation (P = 0.004) between resting IL-6 and urinary norepinephrine excretion rates was found over the course of tim e while at altitude. In conclusion, the results indicate a role for alpha - adrenergic regulation of the IL-6 response to the stress of both short-term moderate-intensity exercise and hypoxia.