IJCS | Volume 31, Nº6, November / December 2018

590 Figure 3 - Frequency distribution histogram of atrial granules in relation to their diameter (small [S], medium [M], and large [L]) in the studied groups. Ferraboli et al. Effect of mild aerobic exercise in Chagas’disease Int J Cardiovasc Sci. 2018;31(6)585-593 Original Article In acute Chagas disease, there is intense myocarditis associated with changes in the secretory complex in atrial myoendocrine cells and consequent heart failure. Additionally, it is known that ANP and BNP levels also increase in patients with Chagas with echocardiographic changes. 1 Our data showed that the UI group had a significant reduction in the density of granules when compared with the UC group. However, this difference was not observed in the density per area, indicating no substantial difference in the amount of granules between the UI and UC groups. Additionally, theTI grouppresenteddensityparameters similar to those observed in the TC group and different from those in the UI group, indicating that exercise training can approximate the physiology of infected cardiac cells to that found in uninfected cells. As for the interstitium, there was no significant difference between the untrained groups compared with the swimming groups. The myofibril density was higher among groups that performed exercise (TC and TI) comparedwith those that did not exercise (UC and UI). This indicates that physical activity contributes to increasing the number of myofibrils in the heart muscle. 39,40 When comparing the numerical density of atrial granules in all four groups of animals, we observed no statistically significant difference among the groups (p > 0.05). However, there were differences between large and small granules. Interestingly, physical training promoted a decrease in the diameter of small granules and an increase in the diameter of large granules in both controls and infected animals. Additionally, we also observed that the frequency distribution of granules in relation to the areas was significant in the UI group compared with the other groups, with 80% of small granules. The TI group showed the smallest percentage of large granules (0.9%) compared with the other groups. Activation of the renin-angiotensin-aldosterone system in congestive heart failure results in sodium and fluid retention, with increased blood volume and central venous pressure, and consequent stretching of the atrial wall, 41,42 as well as morphologic and morphometric changes in cytoplasmic organelles in atrial and ventricular cells. 43,44 The lowest concentration of large granules observed may represent a more effective elimination of the contents present in the granules, resulting in endocrine benefits to the cardiovascular and renal systems. Structural differences were identified in untrained animals with Chagas disease when compared with those in the UC group. The granules of UI animals had a heterogeneous size and dispersed electron density in the cytoplasm permeating the sarcolemma, cytoplasmic condensation, and characteristic changes in cell chromatin and nuclear envelope with several indentations in the cytoplasm. The chagasic swimming group (TI) presented reduced interstitium and plasma membrane of irregular contour with numerous invaginations containing electron-dense granules. Numerous mitochondria, some with signs of degeneration, were also observed. Nuclear chromatin appeared hazy and electron dense,