[Regulation of triiodothyronine levels in fatty tissue in obese patients].

Specific activity of T4-5'-deiodinase, the enzyme which catalyze peripheral production of triiodothyronine (T3) from thyroxine (T4) has been evaluated in the subcutaneous adipose tissue of obese patients. In lean healthy women (BMI less than 21) mean activity of T4-5'-D was found to be 122 +/- 29.4 fmol T3/mg of protein/min and was higher then respective activity of the enzyme in adipocytes of patients with mild obesity (22 less than BMI less than 30) where the mean was 92.14 +/- 18.05 fmol T3/mg/min. The activity of T4-5'-D was significantly decreased in patients with severe obesity (BMI less than 30) when compared with respective activity of the enzyme found in controls (47.36 +/- 18.4 fmol T3/mg/min vs 122.4 +/- 29.4 fmol T3/mg/min; p less than 0.01). As T4-5'-D in human adipose tissue has been previously characterized as type II of the enzyme, diminished activity found in obese subjects means that thyroid metabolic activity of adipocyte is decreased. Such a state would lead to antilipolytic action of catecholamines in obesity.