Increased energy expenditure in gastric bypass rats is not caused by activated brown adipose tissue.

OBJECTIVE To investigate whether gastric bypass induces a higher activity of brown adipose tissue and greater levels of the brown adipose tissue-specific protein uncoupling protein-1 (UCP-1) in rats. METHODS Gastric bypass rats and sham-operated controls (each n = 8) underwent whole body (1)H-MR spectroscopy for analysis of body composition and (18)F-fluorodeoxyglucose positron emission tomography combined with computed tomography ((18)F-FDG PET/CT) imaging for measurement of the metabolic activity of brown adipose tissue. Brown adipose tissue was harvested and weighed, and UCP-1 mRNA content was measured by Northern Blot technique. RESULTS Gastric bypass rats had a significantly lower percentage of whole body adipose tissue mass compared to sham-operated rats (p = 0.001). There was no difference in brown adipose tissue activity between the two groups (standardised uptake value sham 2.81 ± 0.58 vs. bypass 2.56 ± 0.46 ; p = 0.73). Furthermore, there was no difference in the UCP-1 mRNA content of brown adipose tissue between the two groups (sham 49.5 ± 13.2 vs. bypass 43.7 ± 13.1; p = 0.77). CONCLUSION Gastric bypass does not increase the activity of brown adipose tissue in rats suggesting that other mechanisms are involved to explain the increased energy expenditure after bypass surgery. Our results cannot justify the radiation dose of (18)F-FDG PET/CT studies in humans to determine potential changes in brown adipose tissue after gastric bypass surgery.