The effect of immobilization and dietary phosphorus on bone density of mature female rats

The right femurs of adult female rats were bound to their chests over a 14 week period. During this time rats were fed diets providing adequate calcium (Ca) and adequate (0.4%) or high (1.2%) phosphorus (P). Rats fed the high P diet tended to lose more weight during the experimental period than rats fed the adequate P diet. Both immobilization and a high P diet significantly reduced bone density. Thin cortical widths of rats fed the high P diet were apparently due to an increased medullary width rather than to a decreased subperiosteal width, while the reverse was true for the immobilized femur as compared to that of the mobile limb. A high P diet greatly increased the concentration of Ca and P in the kidney.