Nitrite and S-Nitrosohemoglobin Exchange Across the Human Cerebral and Femoral CirculationClinical Perspective
2017
Background: The mechanisms underlying red blood cell (RBC)–mediated hypoxic vasodilation remain controversial, with separate roles for nitrite (![Graphic][1] ) and S -nitrosohemoglobin (SNO-Hb) widely contested given their ability to transduce nitric oxide bioactivity within the microcirculation. To establish their relative contribution in vivo, we quantified arterial-venous concentration gradients across the human cerebral and femoral circulation at rest and during exercise, an ideal model system characterized by physiological extremes of O2 tension and blood flow.
Methods: Ten healthy participants (5 men, 5 women) aged 24±4 (mean±SD) years old were randomly assigned to a normoxic (21% O2) and hypoxic (10% O2) trial with measurements performed at rest and after 30 minutes of cycling at 70% of maximal power output in hypoxia and equivalent relative and absolute intensities in normoxia. Blood was sampled simultaneously from the brachial artery and internal jugular and femoral veins with plasma and RBC nitric oxide metabolites measured by tri-iodide reductive chemiluminescence. Blood flow was determined by transcranial Doppler ultrasound (cerebral blood flow) and constant infusion thermodilution (femoral blood flow) with net exchange calculated via the Fick principle.
Results: Hypoxia was associated with a mild increase in both cerebral blood flow and femoral blood flow ( P gradients reflecting consumption (arterial>venous; P arterial; P 0.05).
Conclusions: These findings suggest that hypoxia and, to a far greater extent, exercise independently promote arterial-venous delivery gradients of intravascular nitric oxide, with deoxyhemoglobin-mediated ![Graphic][3] reduction identified as the dominant mechanism underlying hypoxic vasodilation.
# Clinical Perspective {#article-title-44}
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[2]: /embed/inline-graphic-2.gif
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