Adenosine and A2A Receptors in Human Brown Adipose Tissue

Overview

This study investigates the significance of adenosine and A2A receptors in human brown adipose tissue (BAT) in vivo. Using positron emission tomography (PET), perfusion and the density of A2A receptors will be measured in supraclavicular BAT and other tissues in healthy men. The investigators hypothesize, that adenosine can activate BAT, and that adenosine A2A receptor density changes when BAT is activated by cold exposure. Understanding the mechanisms of BAT activation and the role of endocannabinoids in humans is important and beneficial in fighting against the epidemic of obesity and diabetes.

Adenosine is a purine nucleoside released locally in BAT when noradrenaline and ATP are released from sympathetic nerves. Recently it was found that adenosine activates murine and human brown adipocytes, and recruits beiging of white fat via adenosine A2A receptors (A2AR). Furthermore, studies with mice have shown improvements in glucose homeostasis after administration of A2AR agonists. In this study the investigators use the PET radiotracer \[15O\]-H2O to quantify perfusion of BAT, white adipose tissue (WAT) and muscle in three conditions: room temperature, cold exposure and intravenous infusion of adenosine. Another PET radiotracer \[11C\]TMSX is used to quantify adenosine A2A receptor density of BAT, WAT and muscle in room temperature and during cold exposure.

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