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The Effects of Radiation on the Rat Bone.  L.G. Harris1, M.J. Pecaut2, G.A. Nelson2, D.S. Gridley2, T.A. Bateman3.  1Southern Illinois Univ School of Medicine, Springfield, IL, 2Loma Linda Univ & Medical Center, Loma Linda, CA, and 3Clemson Univ, Clemson, SC.       

   Prolonged space travel poses many health risks to astronauts.  One of the main concerns is the effects of radiation on the human body since astronauts will be exposed to larger and more prolonged doses once they leave the earth's magnetic field.   Radiation has the potential to cause detrimental effects on organs such as bone, kidney, liver, and heart.  Although small doses of radiation have been used for cancer treatment and have been observed to cause osteoradionecrosis, the effects of whole body radiation have not been well documented.  These effects need to be understood before astronauts can be sent on long duration space missions.            In this study, the effects of radiation on the body were simulated using a 5 GeV/n iron beam with a dose rate of approximately 1.5 Gy/min.  Twenty four rats were irradiated at varying levels, 1 (n=10), 2 (n=6), and 4 Gy (n=8).  The rats were sacrificed 9 months after exposure.  Ten rats were not exposed to radiation and served as controls.  Femur lengths were not changed between the groups.  MicroCT was used to determine if significant differences in the trabecular bone were present between the 0 Gy and 4 Gy groups.  The 0 Gy group was found to have a greater total volume of 14.9%, bone volume of 40.0%, trabecular density of 29.0%, connective density of 31.7%, trabecular number of 11.4%, and trabecular thickness of 8.7% than the 4 Gy group, while the difference in the trabecular spacing was -15.8%.  No significant differences were found in the serum calcium, phosphate, alkaline phosphatase, and tartrate resistant acid phosphatase, though there was a trend between the 1 and 4 Gy groups having an increase in bone marker for resorption.   This data suggests that while radiation does not effect the overall size of the bone, it does negatively effect its microarchitecture and mineral content.  This indicates that whole body radiation has similar effects on bone as that of microgravity and this synergistic effect may pose a serious health risk for long duration space travel.  (Supported by SIUSOM MPEE)