Role of nitric oxide in exercise-induced vasodilation in man

Nitric oxide (NO) is a potent endothelium-derived vasodilator, which is known to play an important role in the regulation of resting vascular tone in animals and humans. However, the degree to which NO is involved in exercise-induced vasodilation in the skeletal muscle remains unclear. We studied the effect of N-monomethyl-L-arginine (L-NMMA) in a randomized, double-blind, placebo controlled cross over study in 16 young, healthy volunteers ( 8 male, 8 female) at rest and during bicycle exercise stress test. L-NMMA was given as a bolus of 3 mg/kg over 5 minutes followed by a continuous i.v. infusion of 50 microg/kg/min over 75 minutes. Subjects underwent a symptom-limited graded bicycle stress test with a 25 Watt increase in workload every 5 minutes. Skin and muscle blood flow were measured by laser Doppler flowmetry. L-NMMA slightly increased mean arterial blood pressure and decreased NO exhalation, but had no effect on pulse rate, oxygen consumption (VO2), skin or muscle blood flow at rest. Moreover, L-NMMA exerted no effect on exercise-induced changes in hemodynamics. Our results suggest that submaximal inhibition of NO-synthase with L-NMMA at doses that induce moderate hemodynamic changes does not affect exercise induced vasodilation.