Effects of exercise training on endothelium-dependent peripheral vascular responsiveness.

Endurance training results in peripheral vascular adaptations in skeletal muscle which enhance perfusion and vascular flow capacity. These adaptations could result from structural modifications of the vasculature and/or alterations in the control of vascular tone. One potential mechanism through which vascular control may be modified is through adaptive changes in the intrinsic responsiveness of vascular endothelium. Experiments have demonstrated that vascular responsiveness to endothelium-dependent vasodilators are enhanced in exercise-trained animals. The enhanced endothelium-dependent relaxation appears to be mediated through elevations in the formation of endothelium-derived nitric oxide. Training also results in a decreased sensitivity to the vasoconstrictor effects of norepinephrine. This alteration appears to be due to an endothelium-dependent mechanism involving alpha 2-adrenergic receptors. One stimulus that appears to be important in initiating the adaptation of the endothelium to training is the increase in muscle blood flow and shear stress which occurs during exercise. However, other factors associated with exercise may be necessary to induce endothelial adaptations produced by endurance training. Further research is needed to determine the significance of changes in endothelium-dependent vascular responsiveness and whether this is associated with training-induced increases in muscle perfusion and vascular flow capacity.