Electron microscopic study of capillary network remodeling in the extensor digitorum longus muscle of normal adult...

Capillary networks demonstrate structural changes during maturation, aging, vascular disease, and cancer. Their morphological structure and function have an important influence on each other. Understanding the process of morphological vascular changes in the capillary network with advancing age may help overcome fatal vascular diseases. Aging-related structural changes of the capillary segments may accompany degeneration and regeneration of muscle fibers and serve to remodel the capillary network as a means of adapting to the changing environment. However, difficulty in obtaining human samples has hampered clarification of these microstructural changes. Herein, we examined serial ultrathin sections of capillary segments in the extensor digitorum longus muscle of normal mature (12 months old) rats in an attempt to analyze their structural changes. After bifurcation, a minimum of one capillary segment was filled with erythrocytes and was found to have fenestrations and plural endothelial disruptions, or pores, at the fenestrated portions. Some of the stagnated erythrocytes demonstrated extended protrusions, and their processes appeared to penetrate the basal lamina through the pores. These findings can also show that capillary segments are involved in partial remodeling of the capillary network. A better understanding of age-related structural changes of the capillary networks will help in fine-tuning novel vascular therapy for not only several fatal vascular diseases but also malignant tumors.