Capillarization and vascular endothelial growth factor expression in hypertrophying anterior latissimus dorsi muscle of the Japanese quail.

Hypertrophy may increase the diffusion distances from capillaries to the interior of the muscle fibers. We hypothesized that capillary proliferation occurs during hypertrophy, which is accompanied by an up-regulation of vascular endothelial growth factor (VEGF). Hypertrophy of the left anterior latissimus dorsi muscle of Japanese quail (2-3 months old) was induced by 1-4 week stretch-overload. Capillarization was analyzed in cross-sections stained for ATPase. VEGF expression was determined with RT-PCR. Initially, hypertrophy was not accompanied by increases in fiber cross-sectional area (FCSA), but after 1 week the average FCSA did increase. The capillary to fiber ratio was decreased after 1 week, but returned to control values in subsequent weeks. This indicates that capillary proliferation occurred, because this model is characterized by extensive fiber proliferation. The absence of any significant change in VEGF mRNA levels indicates that increased levels of VEGF mRNA are not crucial for capillary proliferation during muscle hypertrophy.