Abstract
IntroductionBrown adipose tissue (BAT) is a thermogenic organ with substantial metabolic capacity and has important roles in the maintenance of body weight and metabolism. Regulation of BAT is primarily mediated through the β-adrenoceptor (β-AR) pathway. The in vivo endocrine regulation of this pathway in humans is unknown. The objective of our study was to assess the in vivo BAT temperature responses to acute glucocorticoid administration. MethodsWe studied 8 healthy male volunteers, not pre-selected for BAT presence or activity and without prior BAT cold-activation, on two occasions, following an infusion with hydrocortisone (0.2mg.kg−1.min−1 for 14h) and saline, respectively. Infusions were given in a randomized double-blind order. They underwent assessment of supraclavicular BAT temperature using infrared thermography following a mixed meal, and during β-AR stimulation with isoprenaline (25ng.kg fat-free mass−1.min−1 for 60min) in the fasting state. ResultsDuring hydrocortisone infusion, BAT temperature increased both under fasting basal conditions and during β-AR stimulation. We observed a BAT temperature threshold, which was not exceeded despite maximal β-AR activation. We conclude that BAT thermogenesis is present in humans under near-normal conditions. Glucocorticoids modulate BAT function, representing important physiological endocrine regulation of body temperature at times of acute stress.
Highlights
Brown adipose tissue (BAT) is a thermogenic organ with substantial metabolic capacity and has important roles in the maintenance of body weight and metabolism
The pre-partum elevation of cortisol is pivotal in the initiation of nonshivering BAT thermogenesis at birth [7], and glucocorticoids have recently been proposed as regulators of BAT activity in healthy adult females [8] and in individuals pre-selected for the presence of active BAT [9]
Meal Ingestion Leads to Increased BAT Thermogenic Activity
Summary
Brown adipose tissue (BAT) is a thermogenic organ with substantial metabolic capacity and has important roles in the maintenance of body weight and metabolism. The in vivo endocrine regulation of this pathway in humans is unknown. The objective of our study was to assess the in vivo BAT temperature responses to acute glucocorticoid administration. There is increasing evidence that brown adipose tissue (BAT) has important physiological roles beyond thermoregulation in newborn infants and rodents [1]. Adult humans have significant amounts of BAT [2] and, as a highly metabolic tissue with the capacity to oxidize both glucose and lipid, attention has turned to its involvement in the pathogenesis of obesity and the metabolic syndrome [3]. Systemic β-adrenoceptor (β-AR) activation promotes BAT activity in humans [6], but the role of other endocrine factors remains largerly unknown. We studied whether BAT is activated by feeding, or by an acute increase in cortisol under basal and β-AR stimulated conditions
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