Paradoxical Normoxia-Dependent Selective Actions of Inorganic Nitrite in Human Muscular Conduit Arteries and Related Selective Actions on Central Blood Pressures

Abstract

Background— Inorganic nitrite dilates small resistance arterioles via hypoxia-facilitated reduction to vasodilating nitric oxide. The effects of nitrite in human conduit arteries have not been investigated. In contrast to nitrite, organic nitrates are established selective dilators of conduit arteries. Methods and Results— We examined the effects of local and systemic administration of sodium nitrite on the radial artery (a muscular conduit artery), forearm resistance vessels (forearm blood flow), and systemic hemodynamics in healthy male volunteers (n=43). Intrabrachial sodium nitrite (8.7 μmol/min) increased radial artery diameter by a median of 28.0% (25th and 75th percentiles, 25.7% and 40.1%; P <0.001). Nitrite (0.087–87 μmol/min) displayed conduit artery selectivity similar to that of glyceryl trinitrate (0.013–4.4 nmol/min) over resistance arterioles. Nitrite dose-dependently increased local cGMP production at the dose of 2.6 μmol/min by 1.1 pmol·min −1 ·100 mL −1 tissue (95% confidence interval, 0.5–1.8). Nitrite-induced radial artery dilation was enhanced by administration of acetazolamide (oral or intra-arterial) and oral raloxifene ( P =0.0248, P <0.0001, and P =0.0006, respectively) but was inhibited under hypoxia ( P <0.0001) and hyperoxia ( P =0.0006) compared with normoxia. Systemic intravenous administration of sodium nitrite (8.7 μmol/min) dilated the radial artery by 10.7% (95% confidence interval, 6.8–14.7) and reduced central systolic blood pressure by 11.6 mm Hg (95% confidence interval, 2.4–20.7), augmentation index, and pulse wave velocity without changing peripheral blood pressure. Conclusions— Nitrite selectively dilates conduit arteries at supraphysiological and near-physiological concentrations via a normoxia-dependent mechanism that is associated with cGMP production and is enhanced by acetazolamide and raloxifene. The selective central blood pressure–lowering effects of nitrite have therapeutic potential to reduce cardiovascular events.