Influence of female gonadal hormones on the parasitemia of female Calomys callosus infected with the "Y" strain of Trypanosoma cruzi.

Calomys callosus is a wild rodent found infected with Trypanosoma cruzi in nature. Groups of female C. callosus were subjected to ovariectomy or sham operation or served as intact controls. At 1 month after surgery, animals were inoculated intraperitoneally with 4000 blood trypomastigotes of the "Y" strain of T. cruzi. Parasitemia during the course of infection was significantly higher in ovariectomized animals as compared with sham-operated rodents and controls. On steroid hormone replacement the parasitemia of ovariectomized animals dropped to levels close to those of controls. High or low doses of progesterone, estrogen, or a combination of both exerted similar effects. Splenocyte proliferation of ovariectomized animals was unresponsive to stimuli with concanavalin A and lipopolysaccharide as compared with that of control and sham-operated groups. The results show that gonadal hormones play a fundamental role in the defense against T. cruzi infection. The influence of these procedures on the immune defense in experimental Chagas' disease is being further investigated.