IJCS | Volume 31, Nº6, November / December 2018

586 Ferraboli et al. Effect of mild aerobic exercise in Chagas’disease Int J Cardiovasc Sci. 2018;31(6)585-593 Original Article in the shape of granules of varying size, and play an important role in the pathophysiology of heart failure, including that of Chagas etiology. ANP and BNP are very similar to each other with respect to amino acid sequence and pharmacological spectrum. Patients with congestive heart failure have high levels of ANP and BNP in the atrial and ventricular cardiomyocytes and increased secretion of their contents. 1,7-11 The pathophysiological role of ANP and BNP in cardiovascular diseases is related to their endogenous diuretic and vasodilator action, with both peptides working as protectors of the cardiovascular system in situations of volume and pressure overload. 12-14 In addition, ANP or BNP administration produces clinical improvement in patients with heart failure. 15,16 According to Bianchi et al., 17 the action of exercise on the normal heart provides benefits. The increase in blood volume caused by physical exercise raises the ANP and BNP levels, facilitating the metabolism of all organs involved. 17 The effect of physical exercise onANP levels in healthy subjects and in individuals with nonspecific heart failure is evident. In these cases, depending on the type and intensity, physical exercise increases ANP production and secretion in cardiomyocytes, greatly increasing the serum levels of this peptide. 18,19 The aim of this study was to evaluate the effect of an exercise program on the cardiomyocytes of mice with chronic Chagas disease. The data showed an experimental basis for measuring the effects of regular exercise practice in patients with chronic Chagas disease. Methods Animals and procedures Experimental animals The experiment included 20 young, male, Swiss mice (20 - 25 g, 21 days old) from the Animal House of the Dante Pazzanese Institute of Cardiology, São Paulo, Brazil. The animals were housed in collective polycarbonate cages in a temperature-controlled room (21 - 24°C) with a 12 h dark-light cycle (light 7:00 am to 7:00 pm). Water and food were available ad libitum . All procedures were approved by the Research Ethics Committee of the Universidade São Judas Tadeu (060/2007). This investigation was conducted in accordance with the Principles of Laboratory Animal Care formulated by the National Institutes of Health (Publication No. 96–23, Revised 1996). The mice were randomly assigned to four groups: untrained control (UC, n = 5), trained control (TC, n = 5), untrained infected (UI, n = 5), and trained infected (TI, n = 5). The TC and TI groups were submitted to swimming exercise. The sample size was defined based on the parameters established by the Conselho Nacional de Controle de Experimentação Animal (CONCEA) concerning the use of animals in research. The number of animals used was sufficient to evaluate the hypothesis of this study. Parasitemia and exercise training Inoculum and strains of 20-day-old Trypanosoma cruzi were inoculated intraperitoneally in 10 Swiss mice (groups UI and TI) with 10³ trypomastigotes of the Y strain of T cruzi . 19 The parasitemia curve and parasitemia peak were determined by collecting 5 µL blood samples from the animals’ tails using the Brenner protocol. 19 Blood was collected daily from the second day of the infection until no parasites were observed (~40 days), characterizing the chronic phase of the infection. 20,21 After 60 days of life, all animals were adapted to the liquidmedium in collective tanks with a temperature of 30 ± 2ºC for a week during 15minutes in order to reduce their stress during physical exercise in the water. The training protocol (swimming) adapted from Lancha et al. 22 was performed by the TC and TI groups for 8 weeks, 5 days a week, lasting 30 minutes per day. The training load was equal to 5%of the bodyweight of eachanimal. This protocol was characterizedas low-intensity and long-termtraining. 22 Tissue sample preparation At the end of the experiment, when the animals were around 120 days old, theywere sacrificed by decapitation. Subsequently, thoracotomy was performed, and the hearts in diastole were removed and weighed. After that, the hearts were perfused via the aorta at a constant pressure of 80 mmHg using 0.1 M cacodylate buffer (3min), followed by 2.5%glutaraldehyde solution diluted in cacodylate buffer. Subsequently, in each animal, the atria were separated from the ventricles, and the right atrium (RA) was separated from the left atrium. Right atrium Fragments of the RA of approximately 3 mm wide and 5mm lengthwere fixed in 2%paraformaldehyde and 2.5% glutaraldehyde in0.1Mbuffer for 2hat 4°Candpostfixed in 1% osmium tetroxide in the same buffer for 2 h at 4°C. The