A comparison of the ability of frog and rat S‐9 to activate promutagens in the Ames test

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Abstract
A mutagenesis assay employing the frog, Rana pipiens. is currently under development [McKinnell et al, 1979]. A question that must be answered is whether the frog is metaboiically capable of activating a large number of promutagens. The Ames assay offers a simple means of comparing the metabolism of mutagens by different animal species. The Ames response obtained with frog-liver S-9 was compared to the response with rat-liver S-9, using the following compounds: Benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene, 2-aminofluorene, azobenzene, Sudan II, dibutylnitrosamine, hydrazine sulfate, hydroxyethylhydrazine, cyclophosphamide, 1,2-dichloroethane, tris(2,3-dibromopropyl)phosphate, diallate, quinoline, quercetin, aflatoxin B 1, emodin, and safrole. Of these compounds, activation by rat S-9 was observed for all except hydrazine sulfate and safrole. All except Sudan II, 1,2-dichloroethane, quinoline, and safrole gave positive Ames responses with frog S-9. In general, the responses with frog S-9 were quantitatively lower than those obtained with Aroclor-induced rat S-9; however, the optimum procedure for frog-liver induction has not been determined. The response to dichloroethane is very sensitive to the amount of activating enzyme present; it might be positive with optimally induced frog S-9. Thus, only two of the 15 compounds positive with rat S-9 were definitely missed when tested with frog S-9. We feel that the frog assay appears to be promising from the standpoint of false-negatives.

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