The purpose of this study was to evaluate the effects of administration of overnight 1 mg dexamethasone on vascular function in patients with nonfunctioning adrenal adenomas (NFA). Flow-mediated vasodilation (FMD) and nitroglycerine-induced vasodilation (NID) were measured to assess vascular function in 22 patients with NFA who had hypertension and/or diabetes mellitus (DM) and 272 patients without adrenal incidentalomas who had hypertension and/or DM (control patients with hypertension and/or DM). FMD and NID were measured in the morning before and after administration of 1 mg of dexamethasone at 2300 h in 18 patients with NFA. There were no significant differences in FMD and NID between control patients with hypertension and/or DM and patients with NFA who had hypertension and/or DM (3.4 ± 2.8% vs. 2.9 ± 1.9% and 11.5 ± 5.7% vs. 11.4 ± 4.3%, P = 0.46, and P = 0.99, respectively). There were no significant differences in vascular function between control patients with hypertension and/or DM and patients with NFA who had hypertension and/or DM even after adjustment for cardiovascular risk factors. Overnight 1 mg dexamethasone increased FMD from 2.4 ± 1.9% to 5.3 ± 3.2% (P < 0.01) and increased NID from 12.1 ± 4.2% to 14.0 ± 2.8% (P < 0.01) in patients with NFA. The overnight 1 mg dexamethasone suppression test does not impair FMD and NID in patients with NFA. Decreases in circulating levels of cortisol may improve vascular function.Clinical Trial Registration: This study was approved by principal authorities and ethical issues in Japan (URL for Clinical Trial: http://www.umin.ac.jp/ctr/index.htm Registration Number for Clinical Trial: UMIN000039512).
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