The genotoxicity of a variety of hydrazine derivatives was examined in the DNA‐repair test on rat or mouse hepatocytes. Out of 32 hydrazine derivatives, 6 chemicals, i.e., N‐acetyl‐4‐(hydroxymethyl)phenylhydrazine, 1,2‐dimethylhydrazine ‐ 2HCl, 1‐hydrazinophthalazine ‐ HCl, methylhydrazine‐sulfate, p, p′‐oxybisbenzene disulfonylhydrazide and phenylhydrazine‐HCl, elicited positive DNA repair responses in the test on rat hepatocytes. In the test on mouse hepatocytes, 4 more hydrazine derivatives, i.e., 1,1‐dimethylhydrazine, hydrazine hydrate, hydrazine sulfate and 2‐methyl‐4‐chlorophenoxyacetic acid hydrazide‐HCl also generated positive responses, in addition to the 6 positive compounds in the rat assay. These results suggest that mouse hepatocytes are more susceptible to the genotoxicity of hydrazine derivatives, and that the species differences in genotoxicity appear to he in agreement with the in vivo carcinogenicity of these agents.

No mutagenic activity was observed in the 41 chemicals including 4 volatile and gaseous compounds.

We conducted a collaborative validation study, under the auspices of the Japanese Ministry of Labour, on the in vitro micronucleus test to see if it could be used as an alternative to the in vitro chromosome aberration test for evaluation of chemical safety. We used the Chinese hamster lung cell line (CHL/IU), which is the most widely used system for the latter test in Japan, and evaluated 66 chemicals, including clastogens and polyploidy inducers. The cytochalasin B cytokinesis blocking method, which is commonly used in human lymphocyte culture, was applied to the established cell line, but did not improve the detection of chemically-induced micronuclei in continuously growing cells. The highest micronucleus frequencies were obtained at 48 or 72 h continuous treatments. In short treatments (6 h), a 42 h recovery time yielded the best responses. Concordance between the results of the micronucleus test and the chromosomal aberration test was satisfactorily high (88.7%), and we concluded that the in vitro micronucleus test could be used in place of the chromosomal aberration test as a simple and rapid method for detecting clastogens and aneugens in vitro. We also propose a protocol for the test.

No abstract

It is considered that a decrease of the ratio of polychromatic erythrocytes (PCE) to normochromatic erythrocytes (NCE) (P/N) in the micronucleus test is an indicator of bone marrow toxicity induced by mutagens. However, the exact meaning of fluctuation in the P/N ratio is not yet known. We have studied this point by counting the total number of erythrocytes and nucleated cells in the bone marrow following various treatments. The P/N ratio decreased gradually with time after administration of mitomycin C. Our data suggest that the decrease of P/N ratio was attributable to an increase in the numbers of the denominator, i.e. NCE, caused by rapid differentiation and multiplication or denucleation of erythroblasts which remained in the bone marrow instead of entering the peripheral blood stream. A decrease of P/N ratio was also observed in the early phase after administration of erythropoietin, an agent which induces differentiation and multiplication of erythroblasts. This phenomenon might result from an increase of PCE delivery into the blood circulation. However, following the initial decrease, the P/N ratio increased gradually 48 h after administration of erythropoietin. It is supposed that this increase probably resulted from an increase in PCE in the bone marrow due to the direct effects of erythropoietin on erythropoiesis. The drastic change in erythropoiesis in the bone marrow induced by either mutagen or erythropoietin treatment will affect the fluctuations of the P/N ratio or the number of micronucleated erythrocytes per non-micronucleated erythocytes in the micronucleus test. This contrasts with the original explanation for such fluctuations which attributed them to replenishment of the marrow by peripheral blood.