Comparison of a chemical assay with a tissue-mediated bio-assay for chemical mutagens

Abstract

Summary A tissue-mediated bioassay has been developed and coupled with a chemical test for the purpose of assessing the effect of mammalian physiology on chemical mutagens. In the bio-assay, the hamster, Mesocricetus auratus , was injected with the alkylating agent, ethyl methanesulfonate (EMS), and Drosophila melanogaster served as the genetic indicator. The hamster's plasma was obtained by heart punctures at 2, 4, and 8 h after injection and was chemically analyzed for the presence of alkyl groups. Parallel plasma samples were fed to Drosophila males (10 per vial) on a saturated paper tissue for 24 h. The flies were subsequently mated for 2 days to virgin females, and their progeny were analyzed for sex-linked recessive lethals. A correlation of 0.9 was found between lethal mutations in the bio-assay and the amount of EMS in the blood plasma as measured by the chemical test. Since the dosage of EMS in the plasma was determined chemically, it was possible to reconstruct the genetic experiment, feeding similar doses of EMS in a 1% sucrose solution. A radiotracer experiment using [ 14 C]EMS revealed that the flies would consume only 0.56 as much of the plasma as a 1% sucrose in a 24-h feeding period. After correcting for the lower consumption of plasma, it was possible to determine whether EMS itself was responsible for the observed sex-linked recessive lethals or whether they were the result of some intermediate metabolite produced by the hamster. That the sex-linked recessive lethals rates of the two genetic experiments were the same within 0.95 confidence limits indicates that no intermediate metabolite was in the plasma. Thus the chemical assay is positively correlated with the mutation rate measured by the bioassay of the blood plasma. It was also found (by radiotracer methods) that Drosophila would feed upon other hamster tissues (kidney, lung, liver, and testes). Consequently it will be possible to extend these assays to evaluate the action of possible mutagens (carcinogens) in specific tissues of a given mammal.