Pharmacological and contractile response of myocardium of Chagasic albino Swiss mice.

The isometric developed tension (IDT) and the pharmacological response of isolated myocardium from T. cruzi infected Albino Swiss mice in the acute and chronic Chagas' disease, were studied. The animals were infected with 7 X 10(4) trypomastigotes, form of T. cruzi, Tulahuen strain for the acute infection and with 45 parasites for the chronic stage. The isolated myocardium from acute and chronic chagasic mice reached IDT levels similar to normal hearts. The addition of norepinephrine (NE) to acute ventricles led to lower IDT values than in control group; this hyporeactivity to NE was absent in the chronic stage. On the other hand, epinephrine (EPI) effects on acute and chronic ventricles lead to significantly higher IDT values when compared with their controls. Propranolol blocked the higher effect of EPI in isolated myocardium from the acute stage, but the hyperreactivity described in the chronic stage could not be inhibited by the beta receptors antagonist. The agonist and antagonist tested act on cardiac plasma membrane beta receptors and their actions modify transmembrane calcium fluxes, so that the present study shows that Chagas' disease modifies the normal behavior of adrenergic beta cardiac receptors in different degree depending on the stage of the trypanosomiasis.