Effect of aerobic training on 99mTc-methoxy isobutyl isonitrile (99mTc-sestamibi) uptake by myocardium and skeletal muscle: implication for noninvasive assessment of muscle metabolic profile

Aim: The effect of long‐term endurance training on skeletal muscle and myocardial uptake of ^99mTc‐sestamibi, a radiopharmaceutical accumulating in the mitochondria, was investigated. Methods: Twenty‐six Wistar rats were divided into a trained (5 days week^?1 endurance running for 14 weeks) and an untrained group. On completion of training, ^99mTc‐sestamibi was administered and, 2 h post‐injection, the myocardium and the soleus, extensor digitorum longus (EDL) and medial gastrocnemius (MG) muscles were removed for the measurement of cytochrome c oxidase (CCO) activity and ^99mTc‐sestamibi uptake. Tissue ^99mTc‐sestamibi kinetics was preliminarily studied in 16 other rats for up to 2 h post‐injection. Results: Two hours post‐injection ^99mTc‐sestamibi uptake was either stable (myocardium) or still rising (skeletal muscles). Both CCO activity and ^99mTc‐sestamibi uptake decreased in the same order (myocardium, soleus, EDL, MG) in the tissues examined. The CCO activity of the EDL and MG muscles was higher (P < 0.05) in the trained compared to the untrained group. ^99mTc‐sestamibi uptake in the soleus and EDL muscles was higher (P < 0.05) in the trained compared to the untrained rats, whereas the difference in MG was marginally significant (P = 0.06) in favour of the trained group. Conclusions: Long‐term endurance training, resulting in elevated skeletal muscle CCO activity, is also associated with a similar increase in ^99mTc‐sestamibi uptake. This finding suggests that ^99mTc‐sestamibi could be used in imaging assessment of skeletal muscle metabolism with possible applications in both clinical and sports medicine settings.