Micronucleus incidence and hematological effects in bullfrog tadpoles (Rana catesbeiana) exposed to 2-acetylaminofluorene and 2-aminofluorene

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Abstract
The micronucleus technique used withRana catesbeiana tadpoles is useful for the evaluation of aromatic amine toxicity. When exposed to increasing concentrations of the aromatic amine 2-acetylaminofluorene (2-AAF 1 × 10−8 M to 5 × 10−5 M),R. catesbeiana tadpoles responded with an increasing frequency of micronuclei (MN) in the peripheral blood. Micronuclei increased fourfold with the 5 × 10−5 M 2-AAF exposure. Micronuclei frequency significantly increased with concentrations as low as 5 × 10−8 M. The time from initial mutagen exposure to the time of maximum number of MN present in the peripheral blood occurred at two separate times: 2 d and 14 d after exposure. The occurrence of two MN frequency peaks may be due to the presence of two erythrocyte populations from two hemopoietic sources (liver and kidneys) in young tadpoles. The occurrence of immature erythrocytes, as well as general degenerative changes [such as fragmentation (schistocytosis)] in the erythocytes and vacuolated cytoplasms suggested 2-AAF may contribute to hemolytic anemia effects. 2-AAF also increased the frequency of rubricytes found in the peripheral blood, but had no significant effect on the hematocrit values of animals exposed to concentrations up to 1 × 10−5 M. The tadpoles may have been producing rubricytes to replace the damaged red blood cells (RBCs). The direct-acting mutagen 2-aminofluorene (2-AF) was considerably more toxic to peripheral RBCs than the indirect-acting 2-AAF. Hematocrit values of the 2-AF (1 × 10−5 M)-exposed tadpoles declined severely (from 22 to 10%) because of a significant increase in osmotic fragility of erythrocytes, resulting in cell lysis. The general nature of these stress responses indicates that measurement of tadpole blood characteristics, including erythrocyte morphology, may provide a sensitive means of early warning for some water quality changes adverse to aquatic life.