Characterization of cardiopulmonary function and cardiac muscarinic and adrenergic receptor density adaptation in C57BL/6 mice with chronic Trypanosoma cruzi infection.

Circulating antibodies in chagasic patients interact with myocardial beta adrenergic and muscarinic cholinergic receptors, triggering intracellular signals that alter cardiac function along the course of the disease. However, until now, experimental data in models of chronically infected chagasic mice linking the effects on myocardial beta adrenergic and muscarinic receptors to cardiopulmonary dysfunction is lacking. Thus, we studied C57BL/6 mice 8 months after intraperitoneal injection of 100 trypomastigote forms of the Colombian strain of T. cruzi. Uninfected mice, matched in age, were used as controls. Histopathological analyses (inflammation and fibrosis) and radio-ligand binding assays for estimation of muscarinic and adrenergic receptor density were performed in myocardium tissue samples. When compared to controls, infected mice had electrical conduction disturbances, diastolic dysfunction, lower O2 consumption and anaerobic threshold. In addition, hearts of chronic chagasic mice had intense inflammation and fibrosis, and decreased beta adrenergic and increased muscarinic receptor densities than normal controls. Our data suggest that chronic T. cruzi infection causes alterations in cardiac receptor density and fibrosis deposition which can be associated with cardiac conduction abnormalities, diastolic dysfunction and lower exercise capacity, associating for the first time all these functional and histopathological alterations in chagasic mice.