Reduction in blood pressure following acute dietary nitrate ingestion is correlated with increased red blood cell S-nitrosothiol concentrations

Dietary nitrate (NO3- ) supplementation can enhance nitric oxide (NO) bioavailability and lower blood pressure (BP) in humans. The nitrite concentration ([NO2- ]) in the plasma is the most commonly used biomarker of increased NO availability. However, it is unknown to what extent changes in other NO congeners, such as Snitrosothiols (RSNOs), and in other blood components, such as red blood cells (RBC), also contribute to the BP lowering effects of dietary NO3- . We investigated the correlations between changes in NO biomarkers in different blood compartments and changes in BP variables following acute NO3- ingestion. Resting BP was measured and blood samples were collected at baseline, and at 1, 2, 3, 4 and 24 h following acute beetroot juice (-12.8 mmol NO3-, -11 mg NO3-/kg) ingestion in 20 healthy volunteers. Spearman rank correlation coefficients were determined between the peak individual increases in NO biomarkers (NO3-, NO2-, RSNOs) in plasma, RBC and whole blood, and corresponding decreases in resting BP variables. No significant correlation was observed between increased plasma [NO2- ] and reduced BP, but increased RBC [NO2- ] was correlated with decreased systolic BP (rs = -0.50, P = 0.03). Notably, increased RBC [RSNOs] was significantly correlated with decreases in systolic (rs = -0.68, P = 0.001), diastolic (rs = -0.59, P = 0.008) and mean arterial pressure (rs = -0.64, P = 0.003). Fisher's z transformation indicated no difference in the strength of the correlations between increases in RBC [NO2- ] or [RSNOs] and decreased systolic blood pressure. In conclusion, increased RBC [RSNOs] may be an important mediator of the reduction in resting BP observed following dietary NO3- supplementation.