Abstract
1. The measurement of nitrite and nitrate levels in plasma and urine is an approach to assess the activity of the endogenous nitric oxide (NO) system. The aim of the present study was to evaluate whether metabolic control may affect plasma levels and urinary excretion of nitrates and nitrites in type 2 diabetic patients. 2. Twenty consecutive type 2 diabetic patients were studied twice: first (study 1), under poor metabolic control; and, second, after improved metabolic conditions. Determinations of the main metabolic parameters and of plasma nitrates and nitrites (NOX) were performed in the fasting state. A 24 h urinary specimen was obtained for glycosuria, NOX and creatinine. Diet compliance and home blood glucose monitoring was evaluated on a weekly basis until study 2 was performed after 32 +/- 7 days: then, an identical protocol was repeated (study 2). 3. Fasting plasma glucose was lower in study 2 (8.27 +/- 2.11 vs 10.77 +/- 3.88 mmol/L, respectively; P < 0.05); similarly glycosylated haemoglobin (HbA1c) improved significantly. Plasma NOX levels were similar between the first and second studies (14.3 +/- 7.8 vs 13.5 +/- 8.1 micromol/L, respectively); nor were any differences observed in urinary NOX excretion rates (726 +/- 607 vs 689 +/- 444 micromol/day, respectively). The urinary excretion fraction of NOX was higher during study 1 than during study 2 (3.22 +/- 2.38 vs 1.88 +/- 1.98%, respectively; P = 0.031). A relationship was observed between fasting plasma glucose levels and the urinary excretion fraction of NOX (r2 = 0.12; P = 0.026). 4. In type 2 diabetic patients, plasma and urinary levels of NOX do not change after improvement of metabolic control. A worse metabolic control is associated with an increased urinary fraction excretion of NOX: thus, changes in plasma NOX concentration may reflect the effect of hyperglycaemia in the renal handling of these compounds rather than the effects on the L-arginine-NO pathway.
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