INFLUENCE OF PROLONGED EXERCISE ON MYOCARDIAL DISTRIBUTION OF I-123 MIBG IN LONG-DISTANCE RUNNERS

Background. A study was conducted to determine if prolonged exercise c ould provoke sympathetic neuronal alteration in an athlete's heart thr ough assessment of myocardial distribution of I-123-metaiodobenzylguan idine (MIBG) in nine ultramarathon runners at baseline and after a 4-h our race. Methods and results, After injection of 370 MBq of I-123-MIB G, the athletes ran for 4 hours, covering 45 +/- 8 km, Planar and sing le-photon emission computed tomography (SPECT) images of the thorax we re acquired at the end of the race, Two weeks later, studies at baseli ne were performed, A heart:mediastinum ratio (HMR) was calculated to q uantify MIBG uptake, Basal MIBG studies showed normal myocardial trace r uptake, on both planar and SPECT images, and the HMR was 1.84+/-0.16 . After the 4-hour race, MIBG studies showed decreased myocardial upta ke in all athletes, and the HMR was 1.70+/-0.18 (p < 0.005), A positiv e correlation between the percentage of decrease of HMR after the race and the distance covered was observed (r=.910, p < 0.001). Conclusion s. Myocardial MIBG activity is decreased by prolonged exercise in long -distance runners, The degree of reduction of myocardial MIBG activity is related to the distance covered, Prolonged exercise, as sustained sympathetic stimulus, may alter myocardial distribution of MIBG.