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, Therfore 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 thyroptropin level was 1.43 ± 0.11 μU/ml (range 0.18-3.52 μU/ml). Results: Comparing subjects in the upper, middle and lower tertile of TSH (2.38 ± 0.14 μU/ml, 1.23 ± 0.04 μU/ml and 0.65 ± 0.06 μU/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: THS has no predictive value towards endothelial dysfunction in subjects with thyrotropin levels within the normal range.