EXERCISE TRAINING AND THE RESPONSE OF NITRIC OXIDE TO AN ORAL GLUCOSE TOLERANCE TEST (OGTT)

Abstract

Insulin-mediated glucose disposal has been postulated to partly depend on insulin-mediated nitric oxide (NO) production. Aerobic exercise training favorably alters glucose metabolism; however, the effect of training on postprandial NO is not known. PURPOSE To determine the response of plasma nitrate/nitrite (NOx), as an index of systemic NO production, to an OGTT before and after 6 months of aerobic exercise training in 50 to 75 year old men and women. METHODS NOx, insulin, and glucose responses to a 3-hr OGTT were assessed in 64 non-diabetic sedentary adults following dietary stabilization. Additionally, 40 of these individuals underwent a second 3-hr OGTT following six months of supervised aerobic exercise training. An insulin sensitivity index (ISI) was calculated by the method of Matsuda and Defronzo using fasted and OGTT glucose and insulin levels. OGTT NOx concentrations were analyzed using repeated measures ANOVA (and post-hoc means comparisons). Repeated measures ANOVA was used to examine the effects of aerobic exercise training on the NOx response area (NOxAREA). NOxAREA was calculated as the total area below the baseline minus the area below the curve. Pearson product-moment correlation analyses were used to identify variable associations. RESULTS NOx concentration decreased during the OGTT (p = 0.068 at 30 minutes, p ≤ 0.001 at 60 minutes, and p ≤ 0.05 for 90, 120, and 180 minutes vs. baseline levels). Before training, NOxAREA was not associated with OGTT insulin or glucose total areas or the ISI. Following aerobic exercise training, NOxAREA did not change; however, NOxAREA training responses were associated with training-induced changes in glucose total area (r = 0.42, p ≤ 0.01) and in the ISI (r = −0.32, p ≤ 0.05). CONCLUSION NO, as measured via systemic NOx concentrations, does not appear to be associated with glucose regulation during an OGTT. Additionally, aerobic exercise training does not appear to affect the response of NOx to an OGTT.