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.