Shear stress‐induced angiogenesis in mouse muscle is independent of the vasodilator mechanism and quickly reversible

Aim Is modulation of skeletal muscle capillary supply by altering blood flow due to a presumptive shear stress response per se , or dependent on the vasodilator mechanism? Methods The response to four different vasodilators, and cotreatment with blockers of NO and prostaglandin synthesis, was compared. Femoral artery blood flow was correlated with capillary‐to‐fibre ratio (C:F) and protein levels of putative angiogenic compounds. Results All vasodilators induced a similar increase in blood flow after 14 days, with a similar effect on C:F (1.62 ± 0.05, 1.60 ± 0.01, 1.57 ± 0.06, 1.57 ± 0.07, respectively, all P  <   0.05 vs. control 1.20 ± 0.01). Concomitant inhibitors revealed differential effects on blood flow and angiogenesis, demonstrating that a similar response may have different signalling origins. The time course of this response with the most commonly used vasodilator, prazosin, showed that blood flow increased from 0.40 mL min −1 to 0.61 mL min −1 by 28 days ( P  <   0.05), dropped within 1 week after the cessation of treatment (0.54 mL min −1 ; P  <   0.05) and returned to control levels by 6 weeks. In parallel with FBF , capillary rarefaction began within 1 week ( P  <   0.05), giving C:F values similar to control by 2 weeks. Of the dominant signalling pathways, prazosin decreased muscle VEGF , but increased its cognate receptor Flk‐1 (both P  <   0.01); levels of eNOS varied with blood flow ( P  <   0.05), and Ang‐1 initially increased, while its receptor Tie‐2 was unchanged, with only modest changes in the antiangiogenic factor TSP ‐1. Conclusion Hyperaemia‐induced angiogenesis, likely in response to elevated shear stress, is independent of the vasodilator involved, with a rapid induction and quick regression following the stimulus withdrawal.