Evaluation of a methodology for the use of preparations from rat small intestine in the Salmonella/microsome assay.

A methodology is evaluated for the use in the Ames assay of a microsomal metabolising system derived from villous tip cells of rat small intestine. The procedure involved high frequency vibration of everted gut segments followed by gentle lysis and homogenisation. This technique, which has previously been shown to result routinely in high levels of cytochrome P450 and linked enzymes, has now been investigated for its ability to yield preparations capable of activating several promutagens in the Salmonella/plate incorporation test. The data obtained have been compared with results observed with standard rat liver metabolising fractions. In the presence of intestinal microsomes, 2-aminoanthracene, 2-aminofluorene, 2-acetylaminofluorene, aflatoxin B1, benzo[a]pyrene and cyclophosphamide all caused dose-related increases in revertants, the maximum yields of which were lower than those detected with liver microsomes or S9 mix. These and other differences in dose-responses have been discussed in relation to the levels of microsomal protein and cytochrome P450 plated and with respect to the activities of relevant enzymes in the tissue extracts.