['Previous studies showed that endothelium-dependent arterial dilation is impaired in first-degree relatives of type 2 diabetes in the fasting state. In the present study, we examined whether endothelial dysfunction occurs when acute hyperglycemia is induced by oral glucose loading in this cohort.', 'This study included 32 normal glucose tolerant subjects. Of them, 17 with a family history (FH) of type 2 diabetic parents (FH+) and 15 with no first-degree relative with diabetes or coronary artery disease (FH-). The examination of vascular function was performed in fasting state and repeated 1 and 2 hours after a 75-g oral glucose loading by high resolution ultrasound.', 'Endothelium- dependent arterial dilation in FH+ group were significantly lower than those in FH- before and after oral glucose loading (5.12+/-0.61% vs 6.03+/-0.56%, fasting; 4.0+/-0.65% vs 5.70+/-0.42%, 1 h; 4.43+/-0.61% vs 5.82+/-0.67% 2 h, p<0.05 each). In FH+ group, endothelium-dependent arterial dilation decreased significantly at 60 min (4.0+/-0.65% vs 5.12+/-0.61%, p<0.01) and increased markedly from 60 min at 120 min (4.43+/-0.61% vs 4.0+/-0.65%, p<0.05), which was still significantly lower than baseline (4.43+/-0.61% vs 5.12+/-0.61%, p<0.01) . In FH- group, however, the arterial dilation did not differ significantly among the three time points (p 0.05). In multiple regression analysis, endothelium-dependent arterial dilation was significantly correlated to FH+(r=-0.302, p<0.01). In addition, endothelium-dependent arterial dilation showed a correlation with plasma glucose (r=-0.460, p<0.01) and TBARS (r=-0.382, p<0.01) during OGTT in FH+ subjects.'] Does acute hyperglycemia rapidly suppress endothelium-dependent arterial dilation in first-degree relatives of type 2 diabetic patients?