Does L-NMMA alter exercise hemodynamics and femoral artery diameter in healthy volunteers?
Nitric oxide plays a role in resting vascular tone and pre-exercise vasodilation, but does not appear to significantly modulate muscular artery function during or immediately after exercise.
Background Basal release of nitric oxide ( NO ) from the vascular endothelium regulates the tone of muscular arteries and resistance vasculature. Effects of NO on muscular arteries could be particularly important during exercise when shear stress may stimulate increased NO synthesis. Methods and Results We investigated acute effects of NO synthase inhibition on exercise hemodynamics using N G ‐monomethyl‐ l ‐arginine ( l ‐ NMMA ), a nonselective NO synthase ‐inhibitor. Healthy volunteers (n=10, 5 female, 19–33 years) participated in a 2‐phase randomized crossover study, receiving l ‐ NMMA (6 mg/kg, iv over 5 minutes) or placebo before bicycle exercise (25–150 W for 12 minutes). Blood pressure, cardiac output (measured by dilution of soluble and inert tracers) and femoral artery diameter were measured before, during, and after exercise. At rest, l ‐ NMMA reduced heart rate (by 16.2±4.3 bpm relative to placebo, P <0.01), increased peripheral vascular resistance (by 7.0±1.4 mmHg per L/min, P <0.001), mean arterial blood pressure (by 8.9±3.5 mmHg, P <0.05), and blunted an increase in femoral artery diameter that occurred immediately before exercise (change in diameter: 0.14±0.04 versus 0.32±0.06 mm after l ‐ NMMA and placebo, P <0.01). During/after exercise l ‐ NMMA had no significant effect on peripheral resistance, cardiac output, or on femoral artery diameter. Conclusions These results suggest that NO plays little role in modulating muscular artery function during exercise but that it may mediate changes in muscular artery tone immediately before exercise.
O’Gallagher et al. (Wed,) studied this question.