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Disuse-induced Bone Loss is Impacted by Age

Abstract

Bone is a dynamic tissue that responds and adapts to stresses and strains. When bones are more frequently subjected to mechanical loads (i.e. weight-bearing exercise), bones adapt by increasing in bone mass. The opposite occurs when the bones are not regularly exposed to mechanical loads leading to a loss of bone mass and increased risk of fracture. Patients on extended bed rest or astronauts in long duration spaceflight space experience disuse-induced bone loss. PURPOSE: The purpose of this experiment was to see if young (growing) and old (skeletally mature) rats respond differently to short term disuse. We hypothesized young rats would experience greater decrements in bone due to disuse than old rats. METHODS: Male Sprague Dawley rats either 3 months old (Y) or 9 months old (O) were divided into hindlimb unloaded (HU) or ambulatory control (CON) for 14 days. Peripheral quantitative computed tomography and static histomorphometry was completed on the excised bones to measure volumetric bone mineral density (vBMD) and cancellous microarchitecture of the proximal tibia metaphysis. T-tests between CON and HU were completed in Y and separately in O. RESULTS: Total vBMD (cortical shell+cancellous core) and cancellous vBMD were lower in Y-HU compared to Y-CON. Trabecular number was lower in Y-HU compared to Y-CON and trabecular separation trended to be higher (p=0.08). In O-HU vs. O-CON, there were no difference in vBMD or any measures of trabeculae between the groups. CONCLUSION: In this study we demonstrated that the older rats were less impacted by short-term disuse than the younger rats. Therefore, younger individuals who experience bone loss due to disuse may potentially be affected more than skeletally mature adults.

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