Fasting and Postprandial Activity of Brown Adipose Tissue in Healthy Men
ABSTRACT The role of brown adipose tissue (BAT) in adult metabolism is poorly understood. This study aimed to examine the differential effects of an overnight fast and the postprandial state on BAT activity.
We included 10 healthy, lean male volunteers. BAT uptake of glucose was visualized using (18)F-FDG PET/CT during mild cold exposure. Each subject underwent PET/CT twice. The first scan was obtained after an overnight fast; the second after a standardized meal.
(18)F-FDG uptake in BAT was observed in 6 of 10 volunteers. These subjects were found to have a higher maximal standardized uptake value when fasting (median, 13.1 g/mL; range, 6.1-27.6 g/mL) than when in the postprandial state (median, 6.8 g/mL; range, 2.1-13.4 g/mL) (P = 0.03).
Cold-stimulated (18)F-FDG uptake by BAT in humans is more pronounced during fasting. The lower maximal standardized uptake value in the postprandial state may be explained by increased insulin-stimulated glucose uptake in muscle.
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ABSTRACT: This review focuses on the diagnostic value of hybrid F18-FDG Positron Emission Tomography/Computerized tomography (PET/CT) in fever of unknown origin (FUO) and inflammation of unknown origin (IUO). Due to the wide range of possible causes both FUO and IUO remain a clinical challenge for both patients and physicians. In addition, the aetiology of IUO shows the same variation in diseases as the FUO spectrum and probably requires the same diagnostic approach as FUO. There are numerous historically used diagnostic approaches incorporating invasive and non-invasive, and imaging techniques, all with relative high specificity but limited sensitivity. This hampers the generalization of these diagnostic approaches. However, recently published reports show that F18-FDG PET/CT in FUO and IUO has a high sensitivity and a relative non-specificity for malignancy, infection and inflammation. This makes F18-FDG PET/CT an ideal diagnostic tool to start the diagnostic process and to guide subsequent focused diagnostic approaches with higher specificity. In addition, F18-FDG PET/CT has a relative high negative predictive value. Therefore F18 FDG PET/CT should be incorporated in the routine diagnostic work-up of patients with FUO and IUO, preferably at an early stage in the diagnostic process.12/2012; 2012:165080. DOI:10.1155/2012/165080
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ABSTRACT: Brown adipose tissue (BAT) plays a key role in energy homeostasis and thermogenesis in animals, conferring protection against diet-induced obesity and hypothermia through the action of uncoupling protein 1 (UCP1). Recent metabolic imaging studies using positron emission tomography computerized tomography (PET-CT) scanning have serendipitously revealed significant depots of BAT in the cervical-supraclavicular regions, demonstrating persistence of BAT beyond infancy. Subsequent cold-stimulated PET-CT studies and direct histological examination of adipose tissues have demonstrated that BAT is highly prevalent in adult humans. BAT activity correlates positively with increment of energy expenditure during cold exposure and negatively with age, body mass index, and fasting glycemia, suggesting regulatory links between BAT, cold-induced thermogenesis, and energy metabolism. Human BAT tissue biopsies express UCP1 and harbor inducible precursors that differentiate into UCP1-expressing adipocytes in vitro. These recent discoveries represent a metabolic renaissance for human adipose biology, overturning previous belief that BAT had no relevance in adult humans. They also have implications for the understanding of the pathogenesis and treatment of obesity and its metabolic sequelae.Endocrine reviews 04/2013; 34(3). DOI:10.1210/er.2012-1081 · 19.36 Impact Factor
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ABSTRACT: BACKGROUND: Studies in rodents have shown that brown adipose tissue (BAT) is activated on food intake, thereby reducing metabolic efficiency. OBJECTIVE: The current study investigated whether a single high-calorie, carbohydrate-rich meal activates BAT in lean human adults. DESIGN: BAT activity was studied in 11 lean adult men [age: 23.6 ± 2.1 y; body mass index (BMI; in kg/m(2)): 22.4 ± 2.1] after consumption of a high-calorie, carbohydrate-rich meal (1622 ± 222 kcal; 78% carbohydrate, 12% P, 10% F). BAT activity during 2 h of mild cold exposure served as a positive control experiment. BAT activity was assessed by [(18)F]fluorodeoxyglucose (FDG)-positron emission tomography-computed tomography. Energy expenditure was measured by indirect calorimetry. RESULTS: Postprandial [(18)F]FDG uptake was significantly higher in BAT [1.65 ± 0.99 mean standard uptake value (SUVmean)] than in subcutaneous (0.35 ± 0.15 SUVmean; P < 0.05) and visceral (0.49 ± 0.24 SUVmean; P < 0.05) white adipose tissue and liver (0.95 ± 0.28 SUVmean; P < 0.05). Postprandial BAT activity was lower than cold-induced BAT activity (7.19 ± 2.09 SUVmean). However, postprandial BAT activity may have been underestimated because of high postprandial [(18)F]FDG uptake in skeletal muscle compared with cold (1.36 ± 0.31 compared with 0.59 ± 0.07 SUVmean, P < 0.05), which reduces [(18)F]FDG bioavailability for BAT and other tissues. No direct relation was found between BAT and diet-induced thermogenesis (DIT). CONCLUSIONS: Glucose uptake in BAT increases after a meal in humans, which indicates a role for BAT in reducing metabolic efficiency. However, the quantitative contribution of BAT to DIT relative to other tissues, such as skeletal muscle, remains to be investigated. This trial was registered at www.controlled-trials.com as ISRCTN21413505.American Journal of Clinical Nutrition 05/2013; 98(1). DOI:10.3945/ajcn.113.059022 · 6.92 Impact Factor