Effect of donor age on the levels of activity of rat, hamster and human liver S9 preparations in the Salmonella mutagenicity assay

Liver S9 fractions were prepared from male and female Syrian Golden hamsters and Sprague‐Dawley rats, 1, 3, 6 and 12 months of age, which were either iuninduced (corn‐oil treated) or induced with Aroclor 1254 suspended in corn oil. These preparations were compared at varying protein levels for their ability to metabolize polycyclic aromatic hydrocarbons (benzo(a)pyrene, 3‐methylcholanthrene, 7,12‐dimethylbenzanthracene), aromatic amines (N‐2‐acetyl‐aminofluorene, β‐naphthylamine, benzidine), and nitroso compounds (N‐nitroso‐diethylamine, nitrosopyrrolidine, nitrosodiethylmethylurea) to products mutagenic to Salmonella typhimurium. With 3‐methylcholanthrene or benzo(a)pyrene in the presence of S9 preparations from Aroclor‐treated male rats, the numbers of revertant colonies decreased with increasing age of the animals. Mutagenicity of aromatic amines was not affected by the age of the donor animals from which the S9 was prepared. The use of liver S9 from 1‐month‐old hamsters produced the highest number of revertant colonies with nitrosodiethylamine. This number decreased with preparations from animals of increasing age. The greatest number of revertant colonies with nitrosopyrolidine occurred with preparations from male hamsters. A decrease in numbers of revertant colonies with increasing age was observed with the S9 preparation from Arcolor‐treated male rats. Nitroso‐diethylmethylurea was mutagenic only in the presence of S9 from male or female Aroclor‐treated hamsters and the metabolic activity of the S9 preparations did not change with age. S9 preparations from livers of 50–70‐year‐old humans were compared for their ability to produce mutagenic metabolites at a number of protein levels. Very low levels of mutagenicity with polycyclic aromatic hydrocarbons were seen with all human liver S9. Two preparations from human liver obtained shortly after death metabolized both benzidine and β‐naphthylamine (known human carcinogens) to mutagenic products. Very low or no increases in the number of revertant colonies were seen with the other human S9s. However, all of these liver S9 preparations gave a positive mutagenic response with N‐2‐acetylaminofluorene. The only nitrosamine mutagenic with human liver S9 was nitrosopyrrolidine. All of the human preparations metabolized this carcinogen at similar levels. To obtain a positive mutagenic response with a number of these compounds, it was important that the tissue samples be obtained with minimum delay after death. T