Impaired Glucose Tolerance: its Relevance to Early Endothelial Dysfunction

Abstract

We studied the effects of acute glycemia on plasma nitric oxide (NO; nitrite plus nitrate) levels, Cu-Zn Superoxide dismutase (Cu-Zn SOD) activity and thiobarbituric acid-reactive substances (TBARS) levels in age-matched female subjects before and tow hours after glucose loading. According to the results of glucose loading, subjects were divided in the three groups as normal (n = 13, NGT), impaired (n = 11, IGT) and diabetic glucose tolerance (n = 10, DGT). Plasma NO levels were significantly higher in subjects with DGT than in subjects with NGT (p < 0.001) and IGT (p < 0.05) at baseline. Two hours after glucose loading, plasma NO levels were significantly decreased in subjects with IGT and DGT (p < 0.001 and p < 0.001). Although plasma TBARS levels in subject with NGT did not change from the baseline levels after glucose loading, TBARS levels were significantly elevated in subjects with DGT and IGT (p < 0.001 and p < 0.001). Plasma Cu-Zn SOD activities were within a similar range in all subjects at baseline. Cu-Zn SOD activities were significantly increased in subjects with NGT, and were significantly decreased in subjects with IGT and DGT (p < 0.001 and p < 0.001) after glucose loading. There was a positive correlation between NO and glucose in subjects with NGT (r = 0.34, p < 0.01) and a negative correlation between NO and TBARS in IGT sum DGT during glucose tolerance (r = - 0.38, p < 0.01). We suggest that NO availability was decreased when the blood glucose levels were only moderately elevated above normal levels. This might be related with the enhanced oxidative stress.

Key words

Oral glucose tolerance test - Oxidative stress - Atherosclerosis - Nitric oxide - Glucose loading

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