Differing effects of two-week suspension on male and female mouse bone metabolism.

The effects of suspension on bone histomorphometry during the first and second week of tail suspension are compared for male and female mice of the common inbred strain, the C57BL/6J. In male mice, significant changes in bone formation rate (BFR) were largely confined to the endocortical perimeter. BFR along the endocortical mid-diaphysis in the femora of suspended male mice was reduced 54.1% and 55.6% for the first and second week, respectively. In female mice, however, measured metabolic changes due to suspension occurred along the periosteal perimeter, where there was a decrease in BFR of 58.3% for the first week and 60.9% for the second. The notable difference in the bone perimeter affected by suspension observed in male and female mice indicates a difference in the metabolic control of bone development in male and female C57BL/6J mice. More importantly, this may indicate a sex-based difference in preserving structural properties in the response of the skeleton to unloading.