EXCRETION OF IL-6 BY ASTRONAUTS DURING SPACEFLIGHT

Ascent to and living under the microgravity conditions found during sp aceflight is an unfamiliar environment for humans. The adaptation to t he space environment may be perceived by the body as a stress. On the ground, stress results in increased cytokine activity. The objective o f this study was to determine whether spaceflight is associated with i ncreased 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 landin g for a total of 27 days. In addition, in-flight data were obtained fr om two orbiter crew members. The experiment was conducted before, duri ng, and after the 1991 9.5-day SLS-1 (Columbia) space shuttle mission. Dietary intake and urine output were monitored continuously for the 2 7-day period for the four payload crew. Results are as follows: 1) uri nary IL-6 excretion and cortisol excretion were increased on the Ist d ay of spaceflight, suggesting an acute-phase response; 2) elevated lev els of IL-6 were not found in the urine on any other days before or du ring flight; and 3) two of the subjects had markedly increased IL-6 ex cretion rates after landing.