Preliminary study of experimental acute Chagasic cardiomyopathy and its relation
to sex steroid administration

Background. According to our experimental model, along the acute phase of Chagas illness, adult rats infected with Trypanosome cruzi (T. cruzi) presents very low and almost undetectable parasitemias, whereas in prepubertal animals (PP) parasitemias reported were higher than in the adult ones. These differences could be associated with the immunological immaturity exhibited by younger animals, but also owing to the different sexual maturity of the host at the time of infection. As testosterone (T) is a hormone that can influence immune system cells and thus modify the course of parasitic infections, we have evaluated the effect of physiological doses of T on early acute stage of myocarditis in rats PP.
Methods and material. Two doses of T (1 mg/kg) were inoculated to weaning rats (prior infection) followed by the inoculation of 1 million of T. cruzi trypomastigotes. The proper controls were performed, including an experimental group which received a concomitant therapy of bicalutamide, an antagonist of T (5 mg/kg/day), plus T and T. cruzi inoculation. Parasitemia was assessed at 7, 10 and 14 days post infection (pi) and the anatomopathological studies of heart, thymus and spleen were also performed at 4, 7 and 14 days pi.
Results. At 14 day pi, those animals receiving physiological doses of T showed a significant increase in parasitemia and developed a higher splenomegaly compare to the rest of the infected groups. The histological examination of these groups presented a myocarditis of similar intensity -moderate to intense-, and amastigotes nests, while at days 4 and 7, amastigotes nests were observed without inflammatory reaction. Controls did not present histological alterations.
Conclusions. Administration of T in the PP animals prior to T. cruzi infection led to an early parasite replication, as evidenced by the increase in parasitemia, however, it was not able to modify the acute cardiac injury during the early or late stage.

Keywords: Acute chagasic myocarditis; Testosterone; Experimental model in rats