Endocrine Abstracts

Levels of TSH respond to fluctuations in serum free T(4) (fT(4)) and remain in a very narrow individual range. There exists current controversy regarding the upper limit of normal serum TSH values above which treatment should be indicated. In a cohort of healthy men from the general population, both serum TSH and fT(4).TSH product were positively associated with fasting and postload insulin concentration and negatively with insulin sensitivity.It was concluded that thyroid function tests were intrinsically linked to variables of insulin resistance and endothelial function. It is possible that underlying factors lead simultaneously to increased serum TSH, insulin resistance, ensuing dyslipidemia, and altered endothelial function even within current normal TSH levels.

In fact, type I iodothyronine 5′-deiodinase (D1) gene expression and activity were found in adipose tissue of obese subjects, hinting at a role of 3,5,3′-triiodo-L-thyronine formed by D1 in response to leptin in the modulation of adipose tissue metabolism. On the other hand, recent observations disclosed that visceral adipose tissue μ-Crystallin was an adipose tissue factor linked to parameters of thyroid hormone action and might mediate the interaction of thyroid function and insulin sensitivity.

Additionally, total (t)- and a splice variant (v)-TSHβ were consistently detected in adipose tissue from euthyroid subjects, and positively associated with serum total- and LDL-cholesterol, the lipidomics and metabolomics profile of adipose tissue, and with adipose tissue, liver and circulating markers known to change with cholesterol levels TSHβ could be an adipose tissue marker of hypothyroidism, possibly produced to maintain energy storage during fasting.