Capillary density changes in rat femur from youth to aging

Background: The aging process, bone remodeling, and risks of fracture were associated with alteration of blood perfusion in the bone. However, capillary changes during aging in the bone have not been examined due to methodological difficulties.

Objective: Investigate changes of capillary density and length during aging in rat femur using intravital confocal laser microscopy.

Methods: Two-month male Wistar rats were divided into three groups: young (aged 4 to 6 months), adult (aged 12 to 14 months), and aged group (aged 20 to 22 months). The microvasculature of femur periosteum of each rat was visualized with FITC-labeled dextran, and observed via the window chamber under a confocal laser microscopic system. Capillary diameters, lengths, and densities were measured based on the obtained images. Capillary changes (density and length) during aging were analyzed.

Results: The mean capillary density increases up to 130% from young to adult, but decreases up to 15% from adult to aged. Capillary densities against diameter were in a near-normal distribution with a maximum of 130, 250, and 15/mm² at 3 to 5, 3 to 5, and 5 to 7 μm diameter in the young, adult and aged group, respectively. The capillary length in the adult group was much shorter than those in the young and aged groups

Conclusion: The capillary density in the rat femur changes from youth to aging. This can alter blood perfusion and result in bone changes.