Intense (18)F-FDG uptake in brown fat
can be reduced pharmacologically.
Tatsumi M, Engles JM, Ishimori T, Nicely O, Cohade C, Wahl RL.
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. CONCLUSION: 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.
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