Changes in endothelium-dependent arterial dilation before and after subtotal thyroidectomy in subjects with hyperthyroidism.

OBJECTIVE: This case-control study was carried out to assess the alteration of endothelium-dependent arterial dilation before and after subtotal thyroidectomy in subjects with hyperthyroidism. PATIENTS AND METHODS: The study subjects included 12 patients with hyperthyroidism and 39 apparently healthy individuals. We performed a subtotal thyroidectomy on the hyperthyroid patients. The endothelium-dependent arterial dilation was determined with a high-resolution ultrasound method in each patient at the hyperthyroid stage before treatment (stage H), the euthyroid stage induced immediately before surgery (stage E), and the transient hypothyroid stage 1 or 2 months after surgery (stage L).
RESULTS: The flow-mediated arterial dilation decreased significantly from H to E and from E to L (P < 0.001). As compared with H, baseline blood flow decreased markedly at stages E and L (P < 0.001). The flow-mediated arterial dilation and baseline blood flow in the control subjects were very close to those at stage E of the hyperthyroid patients. The absolute change in the flow-mediated arterial dilation showed significant negative correlation with the changes in TSH (r =-0.86, P < 0.001), lipoprotein (a) [Lp(a)] (r =-0.77, P < 0.001) and low density lipoprotein (LDL) (r =-0.79, P < 0.001), and significant positive correlation with changes in fT3 (r =+0.88, P < 0.001). The absolute change in the baseline blood flow showed significant positive correlation with the change in fT3 (r =+0.85, P < 0.001) and significant negative correlation with the change in TSH (r =-0.63, P < 0.01).
CONCLUSION: The endothelium-dependent arterial dilation increases significantly in untreated hyperthyroid patients, and decreases markedly after a subtotal thyroidectomy. Therefore, we conclude that the endothelium is more responsive to reactive hyperaemia in the hyperthyroid than the euthyroid state.