The effect of simulated 1/6th and 1/3rd gravity on gastrocnemius muscle mass and fractional protein synthesis rates in mice
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During periods of disuse or unloading (0G), there is a substantial decline in mass and function of skeletal muscle. However the effects of partial weight bearing, similar to Lunar (G/6) or Martian (G/3) gravitational fields, have yet to be determined. We used a partial G mouse model to assess graded reductions in weight bearing on skeletal muscle. We hypothesized that mice exposed to 21 days of G/6 and G/3 would experience significant reductions of gastrocnemius (gastroc) mass compared ambulatory control animals (1G), but that the magnitude of these changes would be less than in 0G mice. Further, decrements of fractional protein synthesis rates (FSR) would be consistent with reductions of muscle mass. Female BALB/cByJ (4 month old; n=43) mice were randomly assigned to fill four groups (1G, 0G, G/6 or G/3). After a 21day suspension period gastroc muscles were excised and weighed, and cumulative FSR was assessed using deuterium oxide. Total body mass was similar among groups (p>0.05). However, wet weight of gastroc was lower in G/6 and G/3 compared to 1G (p<0.05), and even lower in HU (p<0.05 vs 1G, G/6 and G/3). FSR was not different among 1G, G/6 and G/3, but was lower in 0G animals (p <0.05). This study shows that muscle mass is related to applied load but partial loading is able to maintain FSR.Funded by National Space Biomedical Research Institute via NASA Cooperative Agreement NCC 958
