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

Abstract

This study evaluated the effect of various beta-adrenergic agonists on (18)F-FDG uptake in brown adipose tissue (BAT) in rats using ex vivo biodistribution studies. 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 (18)F-FDG injection. One hour after injection of (18)F-FDG, the animals were sacrificed, and BAT, other major organs, and blood were extracted. The biodistribution results were compared with body temperature data. In the rats injected with nicotine or ephedrine, the mean uptake of (18)F-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 (18)F-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 (18)F-FDG in most other major organs did not change significantly. The effect of nicotine was blocked by prior injection of beta-adrenergic antagonists. A transient decrease in body temperature was observed in the nicotine-injected group, and this effect was canceled by prior injection of beta-adrenergic antagonists. No significant change in baseline temperature was seen before or after beta-adrenergic agonist injection. Nicotine caused a greater increase in (18)F-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 beta-adrenergic antagonists, indicating that beta-adrenergic agonists increase the metabolism of BAT. These preclinical data suggest that patients should avoid nicotine and ephedrine before undergoing (18)F-FDG PET to minimize (18)F-FDG uptake in BAT.