| Male Sprague-Dawley rats flown for 10 days aboard the Space Shuttle Endeavor (STS-77) and compared to simultaneous vivarium ground controls exhibited decreases in splenic helper T-cell and neutrophil percentages. There was a simultaneous increase in the percentage of splenic cytotoxic/suppressor T-Cells. Several aspects of spaceflight may be involved with these population shifts. Launch & landing loads are the primary acute stressors experienced by animals flown on the space shuttle. Cephalic fluid distribution shifts, unloading of the limbs and exposure to a novel environment are the primary chronic stressors. Two experimental conditions can be used to model either the acute or chronic stressors: centrifugation a and anti-orthostatic tail suspension.; Experiments were designed to examine these stressors. Anti-orthostatic tail suspension was used to simulate the chronic stress of microgravity, unloading of the limbs, and cephalic fluid distribution shifts. A large centrifuge was used to simulate the launch and landing loads of a typical shuttle mission. Sprague-Dawley rats exposed to tail suspension, centrifugation, or a combination of the stressors. The rats were then sacrificed and dissected. Splenocytes were labeled with antibodies against CD4, CD8, CD11b, and αβTCR and analyzed by flow-cytometry. There were no consistent changes in these treatment groups in the cell populations observed. This finding supports the hypothesis that there are stressors unique to the spaceflight environment that can not be fully modeled on the ground. |
