Plasma nitrate/nitrite levels are unchanged after long-term aerobic exercise training in older adults

Reduced nitric oxide (NO) production and bioactivity is a major contributor to endothelial dysfunction. Animal data suggest that improvements in endothelial function in response to aerobic exercise training may depend on the duration of the training program. However, no studies have examined changes in NO (as assessed by the major NO metabolites, nitrate and nitrite, NOx) after long-term training in humans. In addition, aging may impair the ability of the vasculature to increase NO with exercise. Thus, we determined whether 24 weeks of aerobic exercise training increases plasma NOx levels in sedentary older adults. We also examined changes in forearm blood flow (FBF) at rest and during reactive hyperemia as a measure of vasomotor function. Plasma NOx levels were measured in 82 men and women using a modified Griess assay. FBF was assessed in a subset of individuals (n = 15) using venous occlusion plethysmography. After 24 weeks of exercise training, there were significant improvements in maximum oxygen consumption, HDL cholesterol, triglycerides, and body fat. Changes in plasma NOx levels ranged from −14.83 to +16.69 μmol/L; however, the mean change overall was not significant (−0.33 ± 6.30 μmol/L, p = 0.64). Changes in plasma NOx levels were not associated with age, gender, race, HDL cholesterol, triglycerides, body weight, body fat, or maximal oxygen consumption. There were also no significant changes in basal FBF, peak FBF, hyperemic response, total hyperemic flow, or minimum forearm vascular resistance with exercise training. In conclusion, improvements in plasma NOx levels and FBF are not evident after long-term training in older adults.