Microvascular Function Is Impaired after Short-Term Immobilization in Healthy Men

Purpose We examined whether 2 wk of one-leg immobilization would impair leg microvascular function and to what extent a subsequent period of intense aerobic cycle training could restore function. Methods Study participants were healthy young men (n= 12; 20-24 yr of age). Leg microvascular function was determined before the intervention, after the immobilization period, and after a 4-wk exercise training period. Microvascular function was assessed as the vasodilator response to intra-arterial infusion of acetylcholine and sodium nitroprusside and as the vasoconstrictor response to endogenous noradrenaline release induced by tyramine infusion. Vasodilator enzymes as well as prooxidant and antioxidant enzymes were assessed by protein analysis in skeletal muscle samples: endothelial nitric oxide synthase, NADPH oxidase (NOX p67(phox)and NOX gp91(phox)), and superoxide dismutase 2 (SOD2). Results The acetylcholine-induced change in vascular conductance was reduced after the 2 wk of immobilization (P= 0.003), tended to increase (P= 0.061), and was back to baseline levels after the subsequent 4 wk of exercise training. Plasma prostacyclin levels in response to acetylcholine infusion were lower after immobilization than before (P= 0.041). The changes in vascular conductance with sodium nitroprusside and tyramine were similar during all conditions. Skeletal muscle protein levels of endothelial nitric oxide synthase in the experimental leg were unchanged with immobilization and subsequent training but increased 47% in the control leg with training (P= 0.002). NOX p67(phox), NOX gp91(phox), and SOD2 in the experimental leg remained unaltered with immobilization, and SOD2 was higher than preimmobilization after 4 wk of training (P< 0.001). Conclusions The study shows that 2 wk of immobilization impairs leg microvascular endothelial function and prostacyclin formation but that 4 wk of intense aerobic exercise training restores the function. The underlying mechanism may reside in the prostacyclin system.