VEGF receptor antagonism blocks arteriogenesis, but only partially inhibits angiogenesis, in skeletal muscle of exercise-trained rats

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 days after bilateral occlusion of the femoral arteries. Total daily treadmill run time increased appreciably from similar to 70 to similar to 100 min ( at 15 - 20 m/min, twice per day) and produced a large ( similar to 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- to 3.5-fold), VEGF-R1 (similar to 2-fold), and endothelial nitric oxide synthase ( 2- to 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 ( similar to 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.