IJCS | Volume 31, Nº6, November / December 2018

588 Figure 1 - Electron micrographs of atrial cardiomyocytes in the control groups. The image in (A) shows the untrained group (UC) with plenty of interstitium with regular architecture and presence of collagen fibers. Preserved mitochondria, Golgi complex, myofibrils, and Z line are observed in the cytoplasm. The nucleus shows nuclear chromatin with heterogeneous density, clear nuclear envelope, and irregular contour at the intersection with the cytoplasm. The atrial granules have different size and density and agglomerate closer to mitochondria, Golgi complex, and polar region of the nucleus. In (B), the trained control group (TC) shows numerous lined mitochondria, thickened myofibrils, and Z lines, reduced interstitium and, consequently, reduced collagen fibers. The nuclear envelope presents extremely irregular and electron-dense contour. Compared with the untrained control group (UC), in the TC, most atrial granules display variable size and electron density, are dispersed in the cytoplasm in less quantity around the nuclear envelope and closer to the mitochondria, Golgi complex, and the periphery of myocytes. Ferraboli et al. Effect of mild aerobic exercise in Chagas’disease Int J Cardiovasc Sci. 2018;31(6)585-593 Original Article Together, the trained groups (TC and TI) showed a decrease in volume density of myofibrils and increase in volume density of mitochondria when compared with the untrained groups (UC and UI). The distribution of organelles of cardiomyocytes and interstitium in the RA (Figure 4) showed a greater presence of granules in the trained groups, especially in the TI. Discussion Our results show an influence of a nonpharmacologic treatment (physical exercise) on cardiovascular control in an experimental model of chronic Chagas disease. We showed an improvement promoted by moderate aerobic exercise in both endocrine activity andmechanical action of the heart in animals with chronic Chagas disease. Thehistopathological analysis followedtheDallas criteria advocated by Aretz 24 and confirmed the occurrence of chagasicmyocarditis in the studied animals.Moreover, the positive influence of light exercise on heart morphological andmorphometric parameters in an experimentalmodel of micewithChagasdiseasehas been reportedwithevaluation of the left and right ventricles of these animals. 25 Corroborating previous data, our results indicated an increased density of atrial granules by area and number of mitochondria in cardiomyocytes promoted by exercise training, giving evidence of increased ANP plasma in animals submitted to physical exercise. Other studies have shown that physical activitymodulates the increase in ANP gene expression in atrial receptors. 26,27 This effect is explained by increased pressure in atrial walls caused by blood volume during physical exercise, inducing an increase in ANP levels in the swimming animals, and regulating the cardiovascular response. 28 During physical exercise, there is an increase in plasma levels of catecholamines and ANP, as well as physiological lipolysis with an increase in fatty acids, providing important nutrition to the heart. 29,30 Hu et al. 31 investigated the effects of physical exercise and ANP circulation in patients with and without ischemic