The Relationship Between Brachial Artery Flow-Mediated Dilation and Plasma Levels of Nitrite/Nitrate (NOx)

Abstract

Brachial artery flow-mediated dilation (FMD) is a bio assay that is predominantly dependent on endothelium-derived nitric oxide (NO). Because of the difficulty in the direct assessment of NO in humans, estimation of NO production from endothelial cells has been performed by quantifying the stable NO end products (nitrite and nitrate; NOx) in plasma as an alternative measure. However, plasma NOx can reflect NO production from sources other than the endothelium and may not reflect endothelial function. PURPOSE: To determine the relation between brachial FMD and plasma levels of NOx. METHODS: Brachial artery FMD was assessed non-invasively using high-resolution ultrasound in thirty six young men and women (23 ± 3 yr; 18M/18F). Brachial FMD was expressed as an absolute (?mm) and as a percent increase from baseline (FMD%). Since the amount of dilation depends on the hyperemic flow stimulus, all measurements of FMD were normalized (norm s-1) to the mean shear rate. Blood samples were collected from an indwelling venous catheter in the forearm following an overnight fast and a 36 hour low nitrate diet. Plasma blood samples were used to determine levels of NOx. Bivariate correlation analyses (Pearson) were performed to determine relations between NOx and brachial FMD (%, mm, and norm s-1). RESULTS: There was a significant relation between brachial FMD% and plasma NOx (r= 0.53, p≤ 0.001). The significant relationship was maintained when the brachial dilation was expressed as δmm (r= 0.51, p ≤ 0.002) and when it was normalized (s-1) to the mean shear rate (r= 0.50, p ≤ 0.002). CONCLUSION: This study demonstrates a close relation between FMD in the brachial artery and plasma levels of NOx in young healthy men and women. This relationship suggests that brachial FMD and plasma NOx may be used either together or alone as markers of peripheral endothelial function.