Association between shear stress, angiogenesis, and VEGF in skeletal muscles in vivo

Objective: To investigate the hypothesis that capillary proliferation in sk eletal muscles, induced by a long-term increase in blood flow which elevate s capillary shear stress. is associated with capillary expression of vascul ar endothelial growth factor (VEGF). Methods: Adult rats received prazosin in drinking water (similar to2 mg per day) or had extensor digitorum longus (EDL) muscles stimulated by implante d electrode, for up to 14 days. At intervals, serial frozen sections of EDL were stained for alkaline phosphatase to identify capillaries. proliferati ng cell unclear antigen (PCNA). and VEGF-A protein. Shear stress was estima ted from capillary red blood cell velocities and diameters. measured by dir ect observation of epi-illuminated EDL. Results: Chronic stimulation and prazosin treatment both increased capillar y: fiber ratio by similar to 40% after 14 days. In stimulated muscles, the percentage of capillaries positively stained for VEGF increased within 3 to 4 days, while the density of PCNA-positive capillaries had increased 20-fo ld after 2 days. With prazosin. VEGF-positive capillaries increased after 2 and 4 days, accompanied by a threefold increase in PCNA. By 14 days, PCNA labeling and VEGF were still high in stimulated muscles but no longer diffe rent from controls with prazosin. After 3 to 4 days of treatment. capillary shear stress in resting muscle was 57% higher than in controls as a result of stimulation, but 4 times higher with prazosin. Conclusions: Higher capillary shear stress with prazosin than with stimulat ion may upregulate VEGF expression in the early stages of treatment. Greate r proliferation of capillaries preceding a higher proportion of VEGF-positi ve capillaries in stimulated muscles, in the presence of a modest increase in shear stress suggests, that angiogenesis was initiated by other factors, in addition to shear stress.