Endocrine Abstracts

Human brown adipose tissue (hBAT) has recently been re-discovered and found to be functionally and metabolically highly active when exposed to cold. Advanced imaging technology, namely the development of hybrid positron-emission tomography (PET)/computed tomography (CT) scanners has been the premise for the progress. The main areas of activated BAT have been found in supraclavicular regions and in the neck, and paravertebral regions. When we quantified glucose uptake in these supraclavicular regions during cold activation, it was found to be more than 10 times higher than in the scan performed in normal room temperature. Surgical biopsies from this location demonstrate significant mRNA and protein levels of uncoupling protein 1 (UCP1) and histology multilocular intracellular lipid droplets. In our study population of 27 normal-weighed adults ¹⁸F-FDG uptake was activated in 60% of cases during experimental cold exposure. Obesity decreases this probability and female gender and younger age enhances it.

Animal studies have suggested, that BAT can be activated also by high fat diet. Our resent data shows that glucose metabolism of hBAT is activated by insulin. Activation by insulin but not activation by cold is perfusion-independent. Recent studies have shown that thyroid hormones play an important role in development and function of BAT. Our data suggests that glucose metabolism of hBAT is enhanced in hyperthyroid patients with Graves disease. An explanation for this could be increased activity of the sympathetic nervous system is in hyperthyroid diseases.

Further studies are needed for the evaluation of the importance of hBAT in human physiology and for the possibilities for its manipulation. Brown adipose tissue also serves new pharmaceutical targets for drug development against the obesity pandemic.