Background: Aerobic exercise enhances endothelium-dependent vasodilation in hypertensive patients, patients with chronic heart failure, and healthy individuals. However, it is unclear how the intensity of exercise affects endothelial function in humans. The purpose of the present study was to determine the effects of different intensities of exercise on endothelium-dependent vasodilation in humans.
Methods and results: We evaluated the forearm blood flow responses to acetylcholine, an endothelium-dependent vasodilator, and isosorbide dinitrate, an endothelium-independent vasodilator, before and after different intensities of exercise (mild, 25% VO2max; moderate, 50% VO2max; and high, 75% VO2max; bicycle ergometers, 30 minutes, 5 to 7 times per week for 12 weeks) in 26 healthy young men. Forearm blood flow was measured using a mercury-filled Silastic strain-gauge plethysmograph. Twelve weeks of moderate-intensity exercise, but not mild- or high-intensity exercise, significantly augmented acetylcholine-induced vasodilation (7.5+/-2.4 to 11.4+/-5.8 mL/min per 100 mL tissue; P<0.05). No intensity of aerobic exercise altered isosorbide dinitrate-induced vasodilation. The administration of NG-monomethyl-L-arginine, a nitric oxide synthase inhibitor, abolished the moderate-intensity exercise-induced augmentation of the forearm blood flow response to acetylcholine. High-intensity exercise increases plasma concentrations of 8-hydroxy-2'-deoxyguanosine (from 6.7+/-1.1 to 9.2+/-2.3 ng/mL; P<0.05) and serum concentrations of malondialdehyde-modified low-density lipoprotein (from 69.0+/-19.5 to 82.4+/-21.5 U/L; P<0.05), whereas moderate exercise tended to decrease both indices of oxidative stress.
Conclusions: These findings suggest that moderate-intensity aerobic exercise augments endothelium-dependent vasodilation in humans through the increased production of nitric oxide and that high-intensity exercise possibly increases oxidative stress.