The lipophilic cationic radiotracer 99m Tc-sestamibi, known to be concentrated within mitochondria, is widely used for myocardial perfusion and to a lesser extent for muscle metabolism imaging. However, the exact distribution pattern in skeletal muscle has not been yet studied in detail. The present study aims to investigate the 99m Tc-sestamibi uptake in rat skeletal muscle and myocardium in relation to their metabolic characteristics. 99m Tc-sestamibi was i.v. administered in twenty adult male Wistar rats and uptake, as percent of injected dose per tissue gram (%ID/g), in the myocardium, soleus, extensor digitorum longus and gastrocnemius muscles was assessed 2 h after the injection. Muscle uptake was also correlated with myocardial uptake, muscle weight and body weight. Skeletal muscle 99m Tc-sestamibi uptake was a small (9-16 %) fraction of that found in myocardium (1.71 ± 0.63 %ID/g). Among the three hindlimb muscles considered, the slow-oxidative soleus muscle showed the highest uptake (0.28 ± 0.16 %ID/g). Metabolically diverse parts of the gastrocnemius muscle showed different uptake. Skeletal muscle uptake was positively correlated with myocardial uptake and both were negatively correlated with tissue and body weight. Skeletal muscle and myocardium 99m Tc-sestamibi uptake is related to their metabolic profile. Myocardium, with an exceptional rich mitochondrial concentration, shows much higher 99m Tc-sestamibi uptake compared to skeletal muscles. Among muscles, uptake is dependent on their mitochondrial content. Evidence of matching exists between myocardial and muscle uptake, and both are size-dependent., G. Arsos ... [et al.]., and Obsahuje seznam literatury
Brown adipose tissue (BAT) physiology and imaging have recently attracted considerable attention. BAT is characterized both by enhanced perfusio
n and increased mitochondrial activity. 99mTc-sestamibi is a lipophilic cationic
tracer that concentrates in mitochondria. Data on the accumulation of 99mTc-sestamibi in BAT are currently lacking. This study investigates the
in vivo99mTc-sestamibi uptake in rat BAT. 99mTc-sestamibi was administered in male Wistar rats of various age and body size. 99mTc-sestamibi uptake was measured in vitro in BAT and white fat (WF) together with cytochrome c oxidase activity. Both 99mTc-sestamibi uptake and cytochrome c oxidase activity were higher in BAT than in WF (P<0.05). 99m
Tc-Sestamibi uptake in both BAT and WF was negatively related to body weight (r= -0.96 and -0.89, respectively) as was the BAT/WF uptake ratio (r = -0.85). These data show a higher 99mTc-sestamibi uptake in
BAT compared to WF, in agreement with the high mitochondrial content and respiratory activity of the former. The strong negative correlation between 99mTc-sestamibi uptake in BAT and body weight (negative allometry), is in accordance to increased needs of thermogenesis in smaller animals. Implications of increased 99mTc-sestamibi uptake in BAT in radionuclide imaging are also discussed.