The characterization of trypan blue-induced tumors in Wistar rats.

Trypan blue is an azo dye widely used for testing cell viability. The dye has been identified as a mutagen and a carcinogen. In some strains of rats, particular Wistar rats, chronic exposure induces a reticuloendothelial neoplasm, predominantly in the liver. These tumors were studied with the use of immunologic cell membrane markers, electron microscopy, and histochemistry to characterize tumor cell type. The authors have studied this tumor in two inbred lines of Wistar rats to compare the efficacy of two previously described dye regimens on tumor incidence and to ascertain whether a short, intense exposure was as effective as chronic protracted exposure. No significant difference in tumor incidence was observed between the two regimens. These studies suggest that the tumor is composed of a macrophage-like cell that retains some characteristics of normal macrophages and that is a reproducible model for carcinogen-induced lymphoreticular human lymphomas.