The Impact of Lower Limb Immobilization and Rehabilitation on Angiogenic Proteins and Capillarization in Skeletal Muscle.

PURPOSE Skeletal muscle vascularization is important for tissue regeneration after injury and immobilization. We examined whether complete immobilization influences capillarization and oxygen delivery to the muscle and assessed the efficacy of rehabilitation by aerobic exercise training. METHODS Young healthy males had one leg immobilized for 14 days and subsequently completed four weeks of intense aerobic exercise training. Biopsies were obtained from m.vastus lateralis and a-v blood sampling for assessment of oxygen extraction and leg blood flow during exercise was done before and after immobilization and training. Muscle capillarization, muscle and platelet content of vascular endothelial growth factor (VEGF) and muscle thrombospondin-1 were determined. RESULTS Immobilization did not have a significant impact on capillary per fiber ratio or capillary density. The content of VEGF protein in muscle samples was reduced by 36% (P=0.024) and VEGF to thrombospondin-1 ratio was 94 % lower (P=0.046). The subsequent four-week training period increased the muscle VEGF content and normalized the muscle VEGF to thrombospondin-1 ratio but did not influence capillarization. Platelet VEGF content followed the trend of muscle VEGF. At the functional level, oxygen extraction, blood flow and oxygen delivery at rest and during submaximal exercise were not affected by immobilization or training. CONCLUSION The results demonstrate that just two weeks of leg immobilization leads to a strongly reduced angiogenic potential as evidenced by reduced muscle and platelet VEGF content and a reduced muscle VEGF to thrombospondin-1 ratio. Moreover, a subsequent period of intensive aerobic exercise training fails to increase capillarization in the previously immobilized leg, possibly due to the angiostatic condition caused by immobilization.