Contribution of nitric oxide to the blood pressure and arterial responses to exercise in humans

An exaggerated blood pressure (BP) response to exercise predicts future cardiovascular risk. The mechanisms underlying exercise-induced hypertension remain unclear, although endothelial dysfunction and elevated arterial stiffness may contribute. Given the association between reductions in nitric oxide (NO) and vascular dysfunction, we sought to determine whether acute inhibition of NO synthase with N^G-monomethyl-Larginine (L-NMMA) would lead to exaggerated BP responses to maximal exercise and attenuate exerciseinduced reductions in arterial stiffness. In 10 healthy subjects (31±5 years), BP and heart rate (HR) were measured before, during and after an incremental cycling exercise test to determine maximal oxygen consumption (VO₂max). Trials were performed with placebo (saline) or intravenous infusion of L-NMMA on separate days in a randomized, double-blind, crossover design. Central (aortic) and peripheral (femoral) arterial stiffness were assessed using pulse wave velocity (PWV). BP was increased with L-NMMA at rest and during sub-maximal exercise, but not at maximal exercise (mean BP 117±5 vs 118±8mmHg, saline vs L-NMMA, P40.05). Furthermore, L-NMMA had no influence on exercising HR or VO₂max (P>0.05). Notably, aortic PWV was similarly increased after exercise with either saline or L-NMMA (P<0.05), whereas postexercise decreases in femoral PWV were attenuated with L-NMMA (P<0.05). Our findings suggest that NO is an important contributor to reductions in femoral artery stiffness after maximal exercise in healthy individuals. Furthermore, acute pharmacological inhibition of NO synthase causes augmented BP responses to sub-maximal exercise, but does not lead to exaggerated BP responses to maximal exercise or reduce maximal oxygen consumption.