Intense (18)F-FDG uptake in brown fat can be reduced pharmacologically.
Physiologic (18)F-FDG uptake in areas of supraclavicular fat in humans ("USA-Fat") has recently been recognized as (18)F-FDG uptake in apparent brown adipose tissue (BAT) using fused PET/CT technology. In this study, we evaluated (18)F-FDG uptake in BAT of rats to determine whether pharmacologic or physiologic interventions affect the uptake, knowing that BAT has a high density of adrenergic innervation.


METHODS
Seven- to 8-wk-old female Lewis rats receiving intravenous (18)F-FDG injections were examined under various conditions to evaluate (18)F-FDG biodistribution into interscapular BAT and major organs. In series 1, rats were given ketamine-based anesthesia or were exposed to cold (4 degrees C for 4 h) to determine whether these interventions increased (18)F-FDG uptake in BAT. In series 2, anesthetized rats (ketamine-based anesthesia) were given propranolol, reserpine, or diazepam intraperitoneally before (18)F-FDG injection to determine whether the drug reduced (18)F-FDG uptake in BAT. The control and treated groups in series 2 were also evaluated with (18)F-FDG PET/CT imaging.


RESULTS
In series 1, anesthesia or exposure to cold increased (18)F-FDG uptake in BAT to levels 14-fold and 4.9-fold, respectively, greater than the control nonstimulated values. BAT uptake was high, comparable to that in the brain. In series 2, (18)F-FDG uptake in BAT was significantly decreased to less than 30% of the control level after propranolol or reserpine (P < 0.05). Diazepam did not significantly decrease (18)F-FDG uptake in BAT. (18)F-FDG PET/CT findings reflected these biodistribution data: The control and diazepam groups exhibited intense (18)F-FDG uptake in BAT, whereas the propranolol and reserpine groups showed only faint to mild (18)F-FDG uptake in BAT. Among several organs whose (18)F-FDG uptake was affected after predosing drugs, the heart exhibited considerable decreases in tracer uptake with propranolol or reserpine.


CONCLUSIONS
This rodent study demonstrated that BAT can exhibit high (18)F-FDG uptake under stimulated conditions including exposure to cold and that propranolol or reserpine treatment can remarkably reduce the high (18)F-FDG uptake in BAT. The effect of these drugs on (18)F-FDG uptake in human BAT, as well as on tracer accumulation in other organs, should carefully be evaluated clinically to minimize the USA-Fat artifact.
Tatsumi
Mitsuaki
M
Division of Nuclear Medicine, Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287, USA.
Engles
James M
JM
Ishimori
Takayoshi
T
Nicely
O'Bod
O
Cohade
Christian
C
Wahl
Richard L
RL
D000075:Acepromazine / Q000494:pharmacology; D002001:Adipose Tissue, Brown / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018663:Adrenergic Agents / Q000494:pharmacology*; D000758:Anesthesia / Q000379:methods; D000818:Animals; D003080:Cold Temperature; D003975:Diazepam / Q000494:pharmacology; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D007649:Ketamine / Q000494:pharmacology; D009928:Organ Specificity; D011433:Propranolol / Q000494:pharmacology; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D051381:Rats; D012110:Reserpine / Q000494:pharmacology; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed / Q000379:methods
D018663:Adrenergic Agents; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D000075:Acepromazine; D007649:Ketamine; D012110:Reserpine; D011433:Propranolol; D003975:Diazepam