Effects of Muscular Stretch Training on Vasculature in the Proximal Tibial Metaphysis

Past studies have shown the blood flow to the proximal tibial metaphysis increases with muscular stretch training in aged Fischer 344 rats. Previous work also showed an increase in total bone volume of the proximal tibial metaphysis after muscular stretching; however, bone volume/total volume decreased in response to stretching, indicating a morphological change occurred within the bone that involved non-ossified tissue. We reasoned that this morphological change was due to vascular remodeling within trabecular bone through the process of angiogenesis. To the vascular volume within the trabecular bone of the proximal tibial metaphysis, longitudinal sections of the tibia were stained with lectin, an endothelium-specific stain. Fluorescent images of lectin and DAPI stains of the proximal metaphyses of stretched and non-stretched limbs were assessed. Quantitative analysis using a custom-made program in Python was used to assess vascular volume in the fluorescent images. Vascular volume increased by 65% in the proximal tibial metaphysis of the stretched limb, as compared to the non-stretched limb. These data suggest that daily muscular stretching produces signals, such as increased shear stress, that stimulate angiogenesis leading to increased vascular volume within the trabecular bone of the stretched limb.