Brown adipose tissue (BAT) is present in small quantities in human adults (~100 g) and can have a significant influence on metabolism. This effect is mediated by rapid activation of the BAT specific uncoupling protein 1 (UCP1), following stimulation of β-adrenergic receptor (AR) by the sympathetic nervous system. AR agonists stimulate rodent BAT, but have so far provided inconsistent findings in humans when administered orally (Vosselman et al. 2012). Rapid activation of UCP1 at birth is mediated in part by the prepartum surge in cortisol (Mostyn et al. 2003), but whether this has any influence on BAT function in adults remains to be fully established. Our study therefore aimed to determine whether the non-selective AR agonist isoprenaline (ISO) increased the temperature of supraclavicular BAT in adult humans, and whether this could be modulated by infusion of hydrocortisone.
Eight healthy young males (1830 years) of normal body weight (BMI: 1824.9 kg×m2) were recruited. Participants underwent the study twice, after a hydrocortisone infusion (0.2 mg/kg per min for 16 h) or saline (control). Infusions were given in a randomised double-blind order with at least 2 weeks between treatment regimes. BAT activity was continuously measured by thermal imaging (Symonds et al. 2012), together with heart rate, at baseline and during a 1 h systemic infusion of ISO (25 ng×kg fat-free per mass per min). Environmental temperature remained constant at 2223 °C.
ISO resulted in a significant increase in temperature of the supraclavicular region (35.61±0.15 °C to 36.01±0.15 °C, P<0.001) and heart rate (62±4 bpm to 108±5 bpm, P<0.001). Peak responses occurred between 20 and 40 min, while responses were unaffected by hydrocortisone (P=0.56).
Infusion of a β-agonist stimulates the temperature of the main site of BAT in humans. This response appears to be unaffected by short-term infusion of hydrocortisone, suggesting raised cortisol has limited influence on BAT activity in young adult males in this model.