Recombinant human thyrotropin enhances endothelial-mediated vasodilation of conduit arteries.

Context: Endothelial cells possess receptors to TSH. Their role is largely unknown.
Objectives: The objective of the study was to determine whether elevated serum TSH levels, as occur in hypothyroidism, affect endothelial function of large arteries and vascular risk biomarkers.
Subjects and Methods: Thirty-four consecutively recruited patients, who had undergone thyroidectomy for thyroid carcinoma, were studied in connection with one of the monitoring procedures based on recombinant human (rh) TSH administration. Flow-mediated dilation (FMD) of the brachial artery and serum vascular risk markers were measured at baseline and for 5 d after the administration of rhTSH (0.9 mg im on d 1 and 2). Holter electrocardiogram and echocardiography were performed on d 2.
Results: rhTSH caused a rapid increase in flow-mediated dilation from the basal value of 10.2 to 15.6% at 6 h (P < 0.0000001), to 16.1% on d 2 (P < 0.0000001), and to 14.9% on d 6 (P = 0.0015). The results were identical when the analysis was made in a subgroup of 19 patients free of vascular risk conditions. Vascular cell adhesion molecule-1, TNFalpha, IL-6, and high sensitive C-reactive protein were unaffected by rhTSH, whereas homocysteine was decreased. Arterial blood pressure, mean 24-h heart rate, and left ventricular function were unaffected by rhTSH.
Conclusions: rhTSH causes marked and persistent activation of the endothelial mediated vasodilation, independent of systemic hemodynamic changes.