Retinol (vitamin A) inhibits the mutagenicity of o-aminoazotoluene activated by liver microsomes from several species in the Ames test.

Retinol (vitamin A) has earlier been shown to inhibit the mutagenicity of o-aminoazotoluene (OAAT) in the Salmonella/microsome assay when OAAT is activated with S9 from Sprague-Dawley rats. The results presented in this paper confirm this and also show that S9 from mice, hamsters and gerbils activates OAAT to mutagenic metabolites detected by Salmonella typhimurium TA100. However, S9 from rabbits is inactive. The S9 fraction from rabbits also shows a low aryl hydrocarbon hydroxylase (AHH) activity. The AHH activity or protein content of the microsomal fraction cannot be used to predict the activating capacity of S9 from the other species. Retinol, added in vitro, inhibits the mutagenic effect of OAAT activated by mouse, gerbil or hamster S9. The strongest inhibition is observed with hamster S9 while the inhibition of mouse and gerbil S9 is lower but still higher than in the rat.