Activation of Brown Adipose Tissue Metabolism Using Mirabegron

In brief, participants will take part in 2 metabolic studies (A and B) performed in random order and at an interval of 7 to 14 days. Each metabolic study will last 8.5 hours with a baseline period of 2.5 hours. Participants will ingest either 200 mg of the ADRB3 agonist mirabegron (Myrbetriq, Astellas Pharma Canada) alone (study A) or in combination with 10 mg of bisoprolol, an ADRB1-antagonist (study B), at time 0. The radioactive PET tracers (PET: positron emission tomography) used in this study are the \[11C\]-acetate and \[18F\]-FDG to estimate BAT oxidative metabolism and glucose metabolism, respectively. The perfusion of \[6,6 D2\]-glucose, \[1,1,2,3,3-2H\]-glycerol and \[U-13C\]-palmitate stable isotopes will also be performed in this study from time -150 min. to +300 min to examine the systemic appearance rate of glucose, glycerol and fatty acids, respectively. These studies will be almost identical (same perfusion of stable and radioactive tracers, same number of PET acquisitions) except for the drug which will be administered orally at time 0.