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1 Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, MO, USA
* To whom correspondence should be addressed. E-mail: TerjungR{at}missouri.edu.
Both collateral vessel enlargement (arteriogenesis) and capillary growth (angiogenesis) in skeletal muscle occur in response to exercise training. Vascular endothelial growth factor (VEGF) is implicated in both processes. Thus, we examined the effect of a VEGF receptor (VEGF-R) inhibitor (ZD4190, AstraZeneca) on collateral-dependent blood flow in vivo and collateral artery size ex vivo (indicators of arteriogenesis) and capillary contacts per fiber (CCF; an index of angiogenesis) in skeletal muscle of both sedentary and exercise-trained rats 14 d following bilateral occlusion of the femoral arteries. Total daily treadmill run-time increased appreciably from ~70 to ~100 min (@ 15-20 m/min, twice/day) and produced a large (~75%, p<0.01) increase in calf muscle blood flow and a greater size of the collateral artery (wall cross-sectional area). ZD4190, which previously has been shown to inhibit the activity of VEGF-R2 and -R1 tyrosine kinase in vitro (IC50 = 30 and 700 nM, respectively), completely blocked the increase in collateral-dependent blood flow and inhibited collateral vessel enlargement. Thus, exercise-stimulated collateral arteriogenesis appears to be completely dependent on VEGF-R signaling. Interestingly, enhanced mRNA expression of the VEGF-family ligand, placental growth factor (2-3.5 fold), VEGF-R1 (~2 fold), and eNOS (2-3.5 fold) in an isolated collateral artery implicates these factors as important in arteriogenesis. Training of ischemic muscle also induced angiogenesis, as shown by an increase (~25%, p<0.01) in CCF in white gastrocnemius muscle. VEGF-R inhibition only partially blocked (p<0.01), but did not eliminate the increase (p<0.01) in capillarity. Our findings indicate that VEGF-R tyrosine kinase activity is essential for collateral arteriogenesis and important for the angiogenesis induced in ischemic muscle by exercise training; however, other angiogenic stimuli are also important for angiogenesis in flow-limited active muscle.
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