NITRIC OXIDE PRODUCTION AND CYCLOPHOSPHAMIDE’S ADMINISTRATION IN CALOMYS CALLOSUS DURING THE EXPERIMENTAL CHRONIC CHAGA’S DISEASE. Leony Cristina Caetano; Marina Del Vecchio Filipin; Vânia Brazão; Miriam Paula Alonso Toldo; José Clóvis do Prado Júnior. Departamento de Análises Clínicas, Toxicológicas e Bromatológicas- Biociências Aplicadas a Farmácia- Faculdade de Ciências Farmacêuticas de Ribeirão Preto-USP. e-mail: firstname.lastname@example.org Introduction: Trypanosoma cruzi, the agent of Chagas disease, is known to cause enhanced nitric oxide (NO) production, which might be involved in host resistance. We studied the potential role of NO in Calomys callosus, a natural reservoir of this protozoan parasite. Objectives: to evaluate nitric oxide production in male and female Calomys callosus infected with T. cruzi during 450 days post-infection during the chronic phase of experiental Chaga’s disease and the role of cyclophosphamide (CY) in immune supression. Methods and Results: male and female C.callosus weighing 22-25gr were i.p infected with 1x105 blood trypomastigotes of the MORC-1 strain of T.cruzi. 0,2 mL of CY were i.p injected at concentration of 0,04mg/m for 3 days prior to animal death. It were realized lavado peritonial in animals to verifiction of the production of nitric oxide and stimulate with 1µg/ml of lipopolysaccharide (LPS) for 24hs. The production of the NO were detectable for the Griess reaction. Absorbance measured at 540 nm was compared to a sodium nitrite standard curve and data were expressed in μM. Results showed that exposure to 0,04mg/ml CY significantly decreased the viability and proliferation of cells stimulated with LPS. NO production in males and female infected was non- significant when compared to infected-CY (p›0,05). Furthermore, only the infection with the T. cruzi MORC- 1 strain resulted in a significant increase in NO production in C. callosus, whereas a non-significant increase in NO production levels. Conclusions: Presumably, nitric oxide is involved during T.cruzi infections in the proved Chagas tolerance of the protection of the sylvatic host C. callosus.