RESUMO
Background: Chagas disease presents in different clinical forms, ranging from asymptomatic to acute, with destruction of heart cells and a possibility of death. In the chronic phase, the parasites can cause serious injuries to different tissues.Objectives: Our objective was to study the effects of physical exercise (swimming) in atrial granules and components of cardiomyocytes in mice with chronic Chagas disease. Methods: In total, 20 male mice were divided into four different groups: untrained control (UC), trained control (TC), untrained infected (UI), and trained infected (TI). In the UI and TI groups, 1,000 forms of Trypanosoma cruzi (Y strain) were inoculated intraperitoneally. After 40 days of infection and proof of chronic phase, the exercise protocol began. The UC and UI groups performed exercise for 10 min/day, and the TC and TI groups followed a training protocol five times a week for 30 minutes during 8 weeks. Ultrathin sections were subjected to morphometric and stereological analyses using electron photomicrographs (x15000) obtained by transmission electron microscopy.Results: The TI group showed the lowest percentage of small granules (58%), while the UI group presented 80% of these granules. The volume density of the Golgi complex and myofibrils in the TI group were reduced compared with those in the UI group, while the parameters of atrial granules and mitochondria increased. Conclusion: Our results suggest that mild physical exercise changes the morphological and morphometric parameters of granules and organelles in the cardiac atrium of mice infected with T. cruzi, and produces moderate beneficial effects on the cardiovascular system