Mechanical loading is important for the maintenance of the skeleton. In this study we addressed the following question. What is the influence of long-term exposure to 2.5 g on bone architecture in male rats? We expect that bone density will increase.

For the experiments we used a total of 14 Long Evans rats. Two experiments were performed in which the rats were exposed to 2.5 g for a period between 33 and 44 weeks. In the first experiment we analyzed the 3D trabecular structure in the femoral head, and in the second one the structure in the proximal tibia (metaphysis) was analyzed using micro-computer-tomography.

Rats exposed to 2.5 g had between 6% and 29% less total body weight than controls. Changes in anisotropy, which is a measure for trabecular alignment, were negligible. In the femoral head, the bone volume fraction (BV/TV) was similar for rats exposed to 2.5 g and controls. The diameters of the femoral head and neck in rats exposed to hypergravity were smaller than in controls, but not significantly. In the tibia, the BV/TV was lower for rats exposed to 2.5 g than for control rats (p< 0.05), whereas the size of the tibial plateau was larger in the exposed rats (p< 0.05).

These preliminary results were in contrast to our expectation. When exposed to 2.5 g, the trabecular architecture in the femoral head hardly changed, and in the tibia the BV/TV decreased. The tibial plateau was however larger. Adaptation to hypergravity conditions might be more at the global, cortical level than at the trabecular level. Alternatively, it is possible that the activity of rats exposed to hypergravity was less compared to controls. This would result in decreased dynamic stimulation of the bone so that the BV/TV still may satisfy the mechanical demands of rats exposed to hyper-gravity.