EFFECTS OF THYROTROPIN AND THYROID HORMONES ON THE ENDOTHELIUM IN THYROID DYSFUNCTIONS

Abstract

Background: The relationship between thyroid hormones and cardiovascular system has been extensively analyzed in experimental and clinical studies in overt and subclinical thyroid dysfunctions. Endothelium and vascular smoot-muscle cells are biological target of thyroid hormones action and their role have been investigated in hypothyroidism and hyperthyroidism. On the contrary the potential pathophysiological role of thyrotropin (TSH) on the cardiovascular system has been poorly investigated. The studied conducted so far to assess the direct effects of TSH in the peripheral vascular endothelium in thyroidectomized patients produced conflicting results. Moreover the effect of TSH on coronary endothelial cells has never directly studied in humans before our study. Aim of the study: The present study was designed to investigate the endothelial response of coronary flow to recombinant human TSH (rhTSH) in patients with differentiated thyroid cancer (DTC) without cardiovascular risk factors to assess the direct effects of TSH on coronary endothelium. Methods: The study population consisted of 10 consecutive patients (mean age = 32.6±8 years) who were submitted to total thyroidectomy for DTC. All were receiving therapy with L-thyroxine to maintain TSH within the reference range. No patient enrolled presented obesity, hypertension or hyperglycemia. Patients underwent standard echocardiography-Doppler examination with evaluation of the coronary flow reserve (CFR) of the distal left anterior descending artery obtained by cold pressure test (CPT) before and 24 h after the second rhTSH injection. Results: Left ventricular morphology and systolic and diastolic function were normal in all patients. Thyroid hormones, thyroglobulin and antithyroglobulin antibodies levels did not differ before and after rhTSH. On the contrary TSH levels were higher after rhTSH administration. Blood pressure and heart rate were not affected by rhTSH. Coronary flow peak velocity at rest was similar at baseline and 24 hours post-rhTSH (22.3 ± 6 vs 23.2 ± 8.7; p = 0.66). On the contrary the post-CPT velocity (29.3 – 6.8 vs 34.4 – 10.9; p < 0.05) and the CFR were higher after rhTSH administration (1.32 – 0.2 vs. 1.53 – 0.2; p < 0.01) than at baseline in patients with DTC. Conclusion: In the present study, we demonstrated that CPT improves CFR after rhTSH administration in DTC patients receiving replacement doses of LT4. The increase of coronary blood flow after rhTSH suggests that TSH may exert a protective effect on the coronary endothelium.