Changes in myocardial norepinephrine levels in response to stress, exercise and aging in control and T. cruzi-infected rats.

The effect of mild acute exercise (swimming for 1 h), restraint for 1 h and fasting for 48 h on myocardial norepinephrine concentration was compared with rats "at rest" using 320 control and chronically T. cruzi-infected rats at 50, 110, 200 and 380 days of age. Ventricular norepinephrine concentrations of control and similarly aged T. cruzi-infected rats were different for 2 of 4 "at rest" groups. Significant and opposite differences in ventricular norepinephrine were observed for restrained T. cruzi-infected rats when compared to controls (-35% in 50-day old rats and +40% in 110-day old rats). Exercised, "at rest" and fasted control rats presented a significant age-dependent decrease of ventricular norepinephrine concentration, which was not observed for restrained control rats. Norepinephrine levels of pooled atria from 120-day old "at rest" T. cruzi-infected rats were significantly lower than those from non-infected controls, whereas no difference was found in serotonin levels. The lability of myocardial norepinephrine levels in T. cruzi-infected rats suggests, but does not demonstrate, that there is a disturbance of the cardiac sympathetic control.