Nitric oxide biomarkers increase during exercise-induced vasodilation in the forearm

The purpose of the study was to determine if exercise-induced vasodilation was associated with an increase in forearm plasma levels of nitric oxide (N O) biomarkers (NO2- + NO3- and L-citrulline). Twelve healthy subjects (27 /- 6 yrs) performed incremental rhythmic forearm exercise with the nondomin ant hand for 6 min each at 15, 30 and 45 % of maximal voluntary contraction (MVC), Forearm blood flow (FBF) was determined in the exercise arm using v enous occlusion plethysmography. Blood samples were obtained from the antec ubital vein of the exercise and nonexercise arms for the measurement of NO biomarkers. In the exercise arm, FBF increased by a mean of 150 %, 335 % an d 585 % above baseline at 15, 30 and 45 % of MVC, respectively. (ANOVA, P = 0.0001). Venous plasma NO2- + NO3- levels increased from 24 +/- 4 mu mol/L at baseline, to 29 +/- 5, 32 +/- 4 and 35 +/- 4 mu mol/L (ANOVA. P = 0.000 1). Venous plasma L-citrulline levels increased from 31 +/- 5 mu mol/L at b aseline to 58 +/- 10, 87 +/- 7 and 141 +/- 15 mu mol/L (ANOVA, P = 0.0001). There was a linear relationship between FBF and venous plasma NO2- + NO3- (slope = 0.38 +/- 0.10, P = 0.0007) and between L-citrulline, (slope = 5.1 +/- 1.3, P = 0.0004). Venous plasma levels of NO2- + NO3- and L-citrulline in the nonexercise arm were unchanged. These results demonstrate that exerc ise-induced vasodilation in the forearm is associated with forearm plasma l evels of NO2- + NO3- and L-citrulline, in vivo markers of NO production.