Abstract
Purpose: This study investigated the basal activity, and cold-induced thermogenic response, of supraclavicular brown adipose tissue (BAT) under warm (23˚C) and cool (18˚C) ambient conditions using supraclavicular skin temperature as a measure of BAT activity. As a highly metabolic, heat-producing tissue, it has been hypothesised that under-active/dysfunctional BAT may underlie a pathological energy imbalance leading to obesity. Methods: Five lean, healthy participants underwent infrared thermography (IRT) of supraclavicular BAT before, and during, mild cold exposure (single-hand immersion in cool water at 20˚C), once at 18˚C and once at 23˚C. Energy expenditure (EE) was measured simultaneously using indirect calorimetry, and mean skin temperature (TMSK) was calculated at 1-minute intervals in parallel to IRT using wireless data loggers. Results: Following 30 minutes of hand cooling, supraclavicular skin temperature (TSCR) rose significantly from baseline at an ambient temperature of 23˚C (∆TSCR: 0.17 ± 0.03˚C, P < 0.01), and EE rose by 0.22 ± 0.02 kJ/min, P < 0.001. At an ambient room temperature of 18˚C, TSCR after hand cooling was similar to baseline, and EE remained unchanged. The TMSK response was indicative of a systemic vasoconstrictive response of similar magnitude in both warm and cool ambient temperatures. Conclusions: At 18˚C in light clothing, BAT may already be maximally stimulated at baseline, and respond minimally to additional cold exposure. Ambient temperature is recognised as a determinant of glucose uptake in BAT. In this study, we show, that it also modulates the TSCR response to further localised cold-stimulation, indicating an effect on BAT thermogenesis.
Highlights
Following the recent discovery of functional, metabolically active brown adipose tissue (BAT) in humans, interest lies in elucidating the mechanisms underlying the BAT mediated non-shivering thermogenic (NST) component of the physiological response to acute cold [9, 10, 28, 29, 30]
The most superficial thermogenic BAT depot in humans is found in the neck and upper thorax [9], and supraclavicular skin temperature has been used in conjunction with varying cold stimuli (e.g.: localised chest cooling, personalised whole body cooling protocols designed to achieve maximal NST) as a proxy measure of thermogenesis [15, 14,5, 16]
Ambient temperature is a determinant of FDG-detected BAT prevalence, and acute cold exposure has been shown to increase BAT activity on PET-CT [23, 25, 31]
Summary
Following the recent discovery of functional, metabolically active brown adipose tissue (BAT) in humans, interest lies in elucidating the mechanisms underlying the BAT mediated non-shivering thermogenic (NST) component of the physiological response to acute cold [9, 10, 28, 29, 30]. It is well established that cold-induced activation of uncoupling protein (UCP) on the inner mitochondrial membrane of thermogenic brown adipocytes uncouples oxidative phosphorylation from the generation of ATP, and that the excess chemical energy is dissipated as heat [6]. A crude measure of BAT activity, and when quantified as standard uptake values (SUV) on static FDG-PET-CT (e.g. SUVmean, SUVmax) may be considered semi-quantitative at best [20]. These measures do not quantify thermogenic output. We used direct measurements of supraclavicular skin temperature to investigate the basal activity and cold-induced thermogenic response of supraclavicular brown adipose tissue (BAT) under warm (23 ̊C) and cool (18 ̊C) ambient conditions. We hypothesised that the basal activity of BAT would be lowest under warm conditions and that the response to mild cold exposure would, be greater
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
