ABSTRACT
Chronic motor nerve stimulation or exercise conditioning (Hudlickaetal., 1992; Annexe? al., 1998), simulating physiological demand in animal models, have been shown to result in proliferation of endothelial cells, and in an increase in capillaries between exercised muscle fibers. Vascular endothelial growth factor (VEGF), the prototypic angiogenic growth factor that causes endothelial cell proliferation in vitro and is associated with angiogenesis in vivo (Folkman, 1995; Ferrara and Alitalo, 1999), has been shown to play a pivotal role in this adaptive response (Annex et al., 1998) in which other angiogenic growth factors are also involved (Morrow et al., 1990; Breen et al., 1996). Similar adaptive mechanisms in human skeletal muscle were recently identified by Vogt et al. on muscle biopsies taken before and after high and low intensity-training periods (Vogt et al., 2001). RT-PCR revealed elevated mRNA concentrations of hypoxia-inducible factor-la (HIF-la) after high and low intensity training, and of VEGF after high-intensity training under hypoxic conditions. The VEGF mRNA data were supported by structural analyses, which revealed an increase in capillary length density.
