Excretion of IL-6 by astronauts during spaceflight.

Ascent to and living under the microgravity conditions found during spaceflight is an unfamiliar environment for humans. The adaptation to the space environment may be perceived by the body as a stress. On the ground, stress results in increased cytokine activity. The objective of this study was to determine whether spaceflight is associated with increased cytokine activity. The mean daily urinary interleukin-6 (IL-6) excretion rate was measured on 24-h urine pools collected from four payload crew members from 11 days before launch to 7 days after landing for a total of 27 days. In addition, in-flight data were obtained from two orbiter crew members. The experiment was conducted before, during, and after the 1991 9.5-day SLS-1 (Columbia) space shuttle mission. Dietary intake and urine output were monitored continuously for the 27-day period for the four payload crew. Results are as follows: 1) urinary IL-6 excretion and cortisol excretion were increased on the 1st day of spaceflight, suggesting an acute-phase response; 2) elevated levels of IL-6 were not found in the urine on any other days before or during flight; and 3) two of the subjects had markedly increased IL-6 excretion rates after landing.