X‐irradiation and Simulated Microgravity affects Rat Weight, Food Intake, Insulin and Paw Pressure Pain Threshold

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The aim of this study is to examine various physiological measurements in response to range of space‐like radiation doses in a NASA‐validated rodent model of simulated microgravity.MethodsFour groups of rats (6 rats per group), control (CON), irradiated (IR), irradiated plus hindlimb suspended (IR+HLS) and suspended (HLS), were used in the study and maintained for two consecutive weeks. IR and IR+HLS groups were exposed to five sessions of X‐ray irradiation (0.5 Gy each, at 3–4 days intervals; cumulative dose 1.2 Gy). Body weights, food and water intakes, pressure pain thresholds and random blood plasma insulin levels were measured.ResultsCompared to CON, weight gain was slowed by about 25% in IR animals and by 50% in HLS and IR+HLS groups. IR acutely decreased food consumption by 20%‐50% when compared to pre‐exposure levels. Effect of HLS on food consumption (15% decrease) was evident during first day of post‐suspension. HLS but not IR resulted in deep tissue hyperalgesia (45% decreases in PPT) and a 40%–60% decrease in plasma insulin levels.Summary and ConclusionsThese observations suggest that exposure to IR may contribute to space flight‐associated anorexia and weight loss. However exposure to microgravity and lower limb disuse appear to be associated with complications. These include insulinopenia, deep tissue hyperalgesia and the muscle atrophy in addition to weight loss and, from our previous studies, bone degenerative effects.Support or Funding InformationSupported by a grant from Arkansas Space Grant Consortium