Using positron-emission tomography (PET), we found that cold-induced glucose uptake was increased by a factor of 15 in paracervical and supraclavicular adipose tissue in five healthy subjects. We obtained biopsy specimens of this tissue from the first three consecutive subjects and documented messenger RNA (mRNA) and protein levels of the brown-adipocyte marker, uncoupling protein 1 (UCP1). Together with morphologic assessment, which showed numerous multilocular, intracellular lipid droplets, and with the results of biochemical analysis, these findings document the presence of substantial amounts of metabolically active brown adipose tissue in healthy adult humans.

We investigated the metabolism of human brown adipose tissue (BAT) in healthy subjects by determining its cold-induced and insulin-stimulated glucose uptake and blood flow (perfusion) using positron emission tomography (PET) combined with computed tomography (CT). Second, we assessed gene expression in human BAT and white adipose tissue (WAT). Glucose uptake was induced 12-fold in BAT by cold, accompanied by doubling of perfusion. We found a positive association between whole-body energy expenditure and BAT perfusion. Insulin enhanced glucose uptake 5-fold in BAT independently of its perfusion, while the effect on WAT was weaker. The gene expression level of insulin-sensitive glucose transporter GLUT4 was also higher in BAT as compared to WAT. In conclusion, BAT appears to be differently activated by insulin and cold; in response to insulin, BAT displays high glucose uptake without increased perfusion, but when activated by cold, it dissipates energy in a perfusion-dependent manner.

Highlights d In-depth analysis of pure brown, brite, and white adipocyte transcriptomes d Identification of a signature that can classify brown and white adipose depots d BATLAS is a web tool that can be used to characterize complex fat tissues d BATLAS can predict the brown adipocyte content in mixed populations of adipocytes

Premedication has been shown to affect both oxygen consumption and metabolic rate. We have compared the perioperative metabolic and haemodynamic effects of two alpha 2-agonists, clonidine and the more selective dexmedetomidine, in 30 ASA I patients undergoing plastic surgical procedures under general anaesthesia. Patients were premedicated with clonidine 4 micrograms kg-1 (n = 10), dexmedetomidine 2.5 micrograms kg-1 (n = 10) or saline (n = 10) i.m. The doses of clonidine and dexmedetomidine were intended to be equipotent. The maximum decrease in preoperative oxygen consumption was 8% and decreases in systolic and diastolic arterial pressures were 11% from baseline after clonidine and dexmedetomidine. During operation, the maximum reduction in heart rate was 18% in the clonidine and dexmedetomidine groups compared with the placebo group. After operation, the maximum decrease in systolic arterial pressure was 11%, diastolic arterial pressure 15% and oxygen consumption 17% in the clonidine and dexmedetomidine groups compared with placebo. In summary, both clonidine 4 micrograms kg-1 and dexmedetomidine 2.5 micrograms kg-1 decreased perioperative oxygen consumption effectively, with a similar haemodynamic profile.

Highlights d A2B receptor regulates two major energy dissipating tissues: muscle and brown fat d Activation of A2B counteracts sarcopenia as well as obesity in mice d A2B forms heteromers that are crucial for physiological adenosine signaling d A2B expression correlates with energy expenditure in human muscle and brown fat