Effect of nicotine and ephedrine on the accumulation of ¹⁸F-FDG in brown adipose tissue

This study evaluated the effect of various β-adrenergic agonists on ¹⁸F-FDG uptake in brown adipose tissue (BAT) in rats using ex vivo biodistribution studies. Methods: Caffeine (10 mg/kg of body weight, n = 4), ephedrine (5 mg/kg of body weight, n = 4), nicotine (0.8 mg/kg of body weight, n = 9), or a mixture of nicotine and ephedrine (0.8 mg/kg of body weight and 5 mg/kg of body weight, respectively, n = 9) was injected into the peritoneal cavity of female Lewis rats 30 min before intravenous ¹⁸F-FDG injection. One hour after injection of ¹⁸F-FDG, the animals were sacrificed, and BAT, other major organs, and blood were extracted. The biodistribution results were compared with body temperature data. Results: In the rats injected with nicotine or ephedrine, the mean uptake of ¹⁸F-FDG, in percentage injected dose (%ID)/(g of interscapular BAT) x (kg of body weight), was significantly increased (7.9-fold for nicotine and 3.7-fold for ephedrine), compared to the control rats. Nicotine had the strongest effect on ¹⁸F-FDG uptake in BAT. Caffeine increased BAT uptake slightly, but this increase did not reach statistical significance. The combination of nicotine and ephedrine increased the uptake 12.0-fold, compared with control rats; more than either nicotine or ephedrine alone. Uptake of ¹⁸F-FDG in most other major organs did not change significantly. The effect of nicotine was blocked by prior injection of β-adrenergic antagonists. A transient decrease in body temperature was observed in the nicotine-injected group, and this effect was canceled by prior injection of β-adrenergic antagonists. No significant change in baseline temperature was seen before or after β-adrenergic agonist injection. Conclusion: Nicotine caused a greater increase in ¹⁸F-FDG uptake in BAT than did other interventions, and the effect was increased when nicotine was combined with ephedrine. The effect of nicotine was completely blocked by prior injection of β-adrenergic antagonists, indicating that β-adrenergic agonists increase the metabolism of BAT. These preclinical data suggest that patients should avoid nicotine and ephedrine before undergoing ¹⁸F-FDG PET to minimize ¹⁸F-FDG uptake in BAT.