Enhancement of endothelium-dependent flow-mediated vasodilation in hyperthyroidism

Objective: Vascular responsiveness changes in hyperthyroid patients remains controversial. This study attempts to determine whether the vasomotor activity can be influenced by hyperthyroid conditions, and, if so, whether changes induced by hyperthyroidism may be restored to normal during the euthyroid state after treatment. Design: A case-control clinical study. Patients and measurements: Forty-five pretreated hyperthyroid patients (mean age 36.62 ± 10.12 years, 36 female) were compared with 45 gender- and age-matched control subjects (mean age 38.98 ± 11.17 years, 40 female). Brachial artery endothelium-dependent flow-mediated vasodilation (FMD) and endothelium-independent nitroglycerin-mediated vasodilation (NMD) responses were assessed noninvasively by high-resolution ultrasound imaging. Among the 45 hyperthyroid patients, 27 patients underwent the same procedures prospectively in the post-treatment euthyroid state. Results: The FMD values were significantly increased in hyperthyroid patients vs. those of controls (8.94 ± 5.65% vs. 3.77 ± 3.42%, P < 0.001), whereas NMD levels were not significantly different (18.17 ± 7.76% vs. 17.28 ± 6.63%, P = 0.560). Multiple regression analysis revealed that the presence of hyperthyroidism was the only significant factor associated with FMD. In the follow-up study of 27 hyperthyroid patients, the FMD values were significantly decreased in the post-treatment euthyroid state compared with those in the pretreated hyperthyroid state (6.40 ± 4.27% vs. 8.83 ± 4.61%, P = 0.021), although these values were still higher than those of controls. Conclusions: This study demonstrated that endothelium-dependent FMD was increased in the hyperthyroid patients, and could be partially restored by treatment with antithyroid agents.