Flow associated (endothelium dependent) vasodilation and TSH-levels in young normotensive and normoglycemic subjects.

Background: Endothelial dysfunction (ED) is regarded as an early step in the development of atherosclerosis. Recent experimental data showed a crosstalk between endothelial NO-synthase activity and thyrotropin production. Therefore we studied whether basal TSH can predict flow associated vasodilation (FAD) in a cohort of healthy young subjects with normal TSH levels.
Patients and Methods: FAD was evaluated in 60 normotensive and normoglycemic subjects (mean age 34 years; range 18-50). The mean thyrotropin level was 1.43 +/- 0.11 microU/ml (range 0.18-3.52 microU/ml).
Results: Comparing subjects in the upper, middle and lower tertile of TSH (2.38 +/- 0.14 microU/ml, 1.23 +/- 0.04 microU/ml and 0.65 +/- 0.06 microU/ml respectively) there was no difference in terms of the classical cardiovascular risk factor profiles (24 h blood pressure, HDL- and LDL-cholesterol, triglycerides, oral glucose load and body fat content). Regarding the vascular parameters, we could neither find an independent association with FAD (7.0 +/- 1.1%, 6.4 +/- 1.0% and 5.8 +/- 1.1% respectively) nor with endothelial independent vasodilation (after application of glycerol trinitrate GTN, 17.3 +/- 1.9%, 18.4 +/- 1.7% bzw. 17.5 +/- 1.6% respectively) between the groups. Furthermore, we could not find a significant association between free thyroid hormones (fT3/fT4) and FAD or GTN-induced vasodilation.
Conclusion: TSH has no predictive value towards endothelial dysfunction in subjects with thyrotropin levels within the normal range.