Alpha adrenergic receptor blockade increases capillarization and fractional O2 extraction and lowers blood flow in contracting human skeletal muscle

Aim: To assess the effect of elevated basal shear stress on angiogenesis in humans and the role of enhanced skeletal muscle capillarization on blood flow and O ₂ extraction. Methods: Limb haemodynamics and O ₂ extraction were measured at rest and during one-leg knee-extensor exercise (12 and 24 W) in 10 healthy untrained young men before and after 4-week treatment with an α ₁ receptor-antagonist (Terazosin, 1–2 mg day ⁻¹). Corresponding biopsies were taken from the m. vastus lateralis. Results: Resting leg blood flow was increased by 57% 6 h following Terazosin treatment (P < 0.05), while basal capillary-to-fibre ratio was 1.69 ± 0.08 and increased to 1.90 ± 0.08 after treatment (P < 0.05). Leg O ₂ extraction during knee-extensor exercise was higher (4–5%; P < 0.05), leg blood flow and venous lactate levels lower (6–7%; P < 0.05), while leg VO ₂ was not different after Terazosin treatment. Conclusions: These results demonstrate that daily treatment with an α-adrenergic receptor blocker induces capillary growth in human skeletal muscle, likely due to increased shear stress. The increase in capillarization resulted in an increased fractional O ₂ extraction, a lower blood flow and venous lactate levels in the exercising leg. The increase in capillarization, and concomitant functional readouts in the exercising leg, may provide a basis for novel angiotherapy.