Systemic plasma levels of nitrite/nitrate (NO_X) reflect brachial flow-mediated dilation responses in young men and women

1. The aim of the present study was to determine the relationship between plasma levels of nitrite/nitrite (NO_x) and brachial flow-mediated dilation (FMD) in healthy young men and women. 2. Brachial artery FMD was assessed non-invasively using high-resolution ultrasound in 36 young men and women (21 ± 3 years; 18 men and 18 women). Blood samples for NO _x assays were collected from an indwelling venous catheter in the forearm following an overnight fast and a 36 h low-nitrate diet. 3. Plasma levels of NO_x were related to peak brachial FMD% (r = 0.53; P = 0.001). The relationship was maintained when the brachial dilation was expressed as absolute diameter change (Δmm; r = 0.51; P = 0.002) and when it was normalized (/s) to the mean shear rate (r = 0.50; P = 0.002). 4. The present study demonstrates a relationship between peak FMD in the brachial artery and plasma levels of NO_x in young men and women. This relationship suggests that brachial FMD and/or plasma NO_x may be used as markers of peripheral endothelial function.