Propylthiouracil, independent of its antithyroid effect, produces endothelium-dependent vasodilatation through induction of nitric oxide bioactivity

ObjectivePropylthiouracil (PTU), independent of its antithyroid effect, is recently found to have a potent antiatherosclerotic effect. The aim of this study is to investigate whether PTU has a beneficial effect on endothelial function.Methods and resultsNinety patients with a history of hyperthyroidism receiving either PTU (n = 45) or methimazole (MMI) (n = 45) during the euthyroid status were enrolled in this study. Brachial artery endothelium-dependent (flow-mediated dilatation [FMD]) and endothelium-independent (nitroglycerin-mediated dilatation) responses were assessed by high-resolution ultrasound image. Data for these two groups were compared with those of 41 healthy control subjects. The FMD values were significantly increased in patients maintained on PTU versus those in the MMI and control groups (9.3 ± 4.4%, 3.4 ± 2.5%, and 3.6 ± 3.4%, respectively; P < 0.01). Nitroglycerin-mediated dilatation had no significant difference between the PTU, MMI, and control groups (17.4 ± 7.5%, 15.9 ± 6.1%, and 17.5 ± 6.8%, respectively; P = 0.455). On multivariate analysis, no significant relationship was found between the FMD and thyroid hormone index levels. To further elucidate whether PTU has a direct effect on endothelial function, the effect of PTU on isolated segments of Sprague–Dawley rat aorta was studied. Vasodilatation induced by PTU was endothelium-dependent and could be blocked by pretreatment with nitric oxide (NO) inhibitors. PTU also increased NO formation in aortic segments.ConclusionsThis study demonstrated that PTU produced endothelium-dependent vasodilatation through thyroid-independent and NO-mediated mechanisms that may contribute to its beneficial effect on atherosclerosis.