Does acute swimming exercise alter the bioavailability of the radiopharmaceutical technetium-99m methylenediphosphonate (99mTc-MDP) in Wistar rats?

Experimental models have aided to understand the mechanism and the exercise effects on biological systems. To evaluate the effects of acute swimming exercise on the bioavailability of the radiopharmaceutical technetium-99m methylenediphosphonate (99mTc-MDP) used for bone scintigraphy, the rats were divided into control, sedentary, and exercised groups. Sedentary and exercised groups were adapted to water for 2 weeks (5 min/day, 5 days/week). After that, the exercised groups (EG) were submitted to acute swimming exercise for 5, 10 or 20 min (loads of 5% of body weight), and then all animals were anaesthetized, 99mTc-MDP was administered and after 180 min the animals were sacrificed. Blood and organs were removed, the radioactivity was determined in a well counter and the percentage per gram of tissue of injected dose (%ID/g) was calculated. The findings showed a significant decrease of %ID/g in the hearts of the sedentary group, EG-5min, EG-10min and EG-20min when compared to the control group, in the bones of EG-20min when compared to the control group, and in the lungs of EG-5min and EG-10min when compared to the control group. These findings could be associated with specific modifications of the metabolism in certain organs, which are highly relevant when evaluations of the bone using 99mTc-MDP are being carried out.