OBJECTIVE: To assess the latent and active TGFbeta1 localization in the heart, to evaluate whether or not radiation induces latent TGFbeta1 activation, and to study the distribution of collagen fibers in the irradiated heart. MATERIALS AND METHODS: Thirty-two C57BL mice were randomly assigned in two groups: GI (non irradiated animals) and GII (irradiated animals). The mice from GII received a single whole-body radiation dose of 7Gy, using a 60Co source at a dose rate of 0.97 Gy/min. The animals were sacrificed by cervical dislocation at 1, 14, 30 and 90 days after irradiation. RESULTS: The irradiated hearts showed: 1) nuclear changes and muscle cells with decreased striations; 2) significant increase in the collagen deposition 90 days after irradiation; 3) latent TGFbeta1 activation in the cardiomyocytes and connective tissue cells after irradiation. CONCLUSION: Our results show the importance of TGFbeta1 protein in the process of radiation-induced heart fibrosis and suggest that cardiomyocytes and connective cells may play a role in this mechanism acting as cellular sources of active TGFbeta1.

Keywords: Ionizing radiation, Heart fibrosis, Transforming growth factor beta (TGFbeta)