Oral nitrate therapy does not affect glucose metabolism in healthy men

Previously, we demonstrated that nitric oxide (NO) may be an important mediator of peripheral glucose disposal. The aim of the present study was to determine whether acute oral nitrate therapy improves glucose metabolism in healthy individuals. Healthy men (n = 10), aged between 19 and 46 years, participated in a randomized cross-over placebo-controlled study. During Visit 1, participants received a dose-graded intravenous infusion of sodium nitroprusside (SNP; titrated from a dose of 0.5 μg/kg per min to a maximum of 2 μg/kg per min and delivered at a rate of 2 mL/min over 30 min). On Visits 2, 3 and 4, participants received oral extended-release isosorbide mononitrate (120 mg), pentaerythritol tetranitrate (160 mg) and placebo in a randomized Latin square design (one treatment per visit). The main outcome measures were plasma glucose and insulin levels and glucose tolerance determined by an oral glucose tolerance test following the SNP infusion and 3 h after nitrate/placebo administration. Exhaled NO, cGMP and pulmonary blood flow were also measured for 3 h after administration of nitrate/placebo and after SNP infusion. None of the nitrate interventions influenced measures of glucose metabolism. Following SNP infusion, there was no change in plasma glucose (P = 0.42) or insulin (P = 0.25) levels, and the response to a glucose load did not different from baseline (P = 0.46). Similarly, neither of the oral nitrates altered plasma glucose (P = 0.24) or insulin levels (P = 0.90) or glucose tolerance (P = 0.56) compared with placebo. In conclusion, these results indicate that acute oral nitrate therapy does not influence glucose metabolism. Studies using NO donors in a chronic setting are required to clarify the role of NO in mediating peripheral glucose uptake.