Changes in composition and metabolic activity of the skeletal parts of the extremity of the adult rat following immobilisation in a plaster cast.

Immobilisation of the one hind leg in adult male rats was followed by characteristic changes of the bone mass and the percentage composition of the tibia and the femur of the immobilised leg. These changes were studied during an immobilisation period of 1 to 24 weeks. The tibia of the immobilised leg showed significant loss of bone mass expressed as a decrease of its organic and ash weights as compared with the tibia of the non-immobilised leg. There was a significant increase of its percentage water content and significant decrease of its organic and its ash contents. The specific activity of the tibia was increased throughout but the increase was independent of time. The observed changes in bone mass and in percentage composition of the femur of the immobilised leg were almost identical with those of the immobilised tibia. The specific activity of the femur showed a positive almost linear regression. There were observations indicating that the skeletal changes recorded for the tibia were progressive during the period of observation. The changes noted in the femur seemed to be stabilised or even somewhat declining towards the end of the experiment.