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: Objective Hypoglycemia is associated with increased heat production and, despite of this, hypothermia. Heat production is likely to be mediated by sympathetic innervation. Brown adipose tissue is activated by cold exposure and stimulated by the sympathetic nervous system. We therefore examined the effect of hypoglycemia on uptake of the labeled glucose analogue 18 F-fluorodeoxyglucose in brown adipose tissue using positron emission tomography and computer tomography. Methods In nine healthy adults 18 F-fluorodeoxyglucose uptake as measure of brown adipose tissue activity was assessed in a cold environment (17 °C) during euglycemia (blood glucose 4.5 mmol/L) and hypoglycemia (2.5 mmol/L) using a hyperinsulinemic glucose clamp. Results Brown adipose tissue activity was observed in all participants. No difference was observed in the median (range) maximal standardized uptake values of 18 F-fluorodeoxyglucose in brown adipose tissue between euglycemia and hypoglycemia: 4.2 (1.0-7.7) versus 3.1 (2.2-12.5) g/mL (p = 0.7). Similarly there were no differences in mean standardized 18 F-fluorodeoxyglucose uptake values or total brown adipose tissue volume between euglycemia and hypoglycemia. Body temperature dropped by 0.6 °C from baseline during the hypoglycemic condition and remained unchanged during the euglycemic condition. There was no correlation between the maximal standardized uptake values of 18 F-fluorodeoxyglucose in brown adipose tissue and levels of counterregulatory hormones. Conclusions This study shows that there is a similar amount of 18 F-fluorodeoxyglucose uptake in brown adipose tissue during hypoglycemia when compared to euglycemia, which makes a role for systemic catecholamines in brown adipose tissue activation and a role for brown adipose tissue thermogenesis in hypoglycemia associated hypothermia unlikely. Future studies in humans should determine whether hypoglycemia indeed increases energy expenditure, and if so which alternative source can explain this increase.Metabolism 10/2014; 63(10). DOI:10.1016/j.metabol.2014.06.017 · 3.61 Impact Factor
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ABSTRACT: The relevance of functional brown adipose tissue (BAT) depots in human adults was undisputedly proven approximately seven years ago. Here we give an overview of all dedicated studies that were published on cold-induced BAT activity in adult humans that appeared since then. Different cooling protocols and imaging techniques to determine BAT activity are reviewed. BAT activation can be achieved by means of air- or water-cooling protocols. The most promising approach is individualized cooling, during which subjects are studied at the lowest temperature for nonshivering condition, probably revealing maximal nonshivering thermogenesis. The highest BAT prevalence (i.e. close to 100%) is observed using the individualized cooling protocol. Currently, the most widely used technique to study the metabolic activity of BAT is [(18)F]FDG-PET/CT-imaging. Dynamic imaging provides quantitative information about glucose uptake rates, while static imaging reflects overall BAT glucose uptake, localization and distribution. In general, standardized uptake values (SUV) are used to quantify BAT activity. An accurate determination of total BAT volume is hampered by the limited spatial resolution of the PET-image, leading to spill over. Different research groups use different SUV threshold values, which make it difficult to directly compare BAT activity levels between studies. Another issue is the comparison of [(18)F]FDG uptake in BAT with respect to other tissues or upon with baseline values. This comparison can be performed by using the 'fixed volume' methodology. Finally, the potential use of other relatively noninvasive methods to quantify BAT, like MRI or thermography, is discussed.