Prevention of 2-acetylaminofluorene-induced extrahepatic short-term effects by 3-methylcholanthrene.

It is well known that simultaneous application of polycyclic carcinogenic hydrocarbons, especially 3-methylcholanthrene (MC) inhibits or prevents tumorigenesis induced by carcinogenic aromatic amines or azo dyes. Short-term tests showed a mitogenic effect upon adrenal cortex 48 hours following a single dose of 2-acetylaminofluorene (AAF) among other carcinogenic substances. 6 mg/kg body weight given simultaneously prevent the proliferative response of the adrenals by AAF (60 mg/kg b.w.) in male Sprague-Dawley rats. These different effects can be assumed to depend on the production of carcinogenic derivatives or their non-production. Therefore, the positive adrenal reaction by other substances tested is probably also provoked by carcinogenic compounds. The lack of responsiveness by MC may reflect a fundamental change of AAF metabolism. The mode of action is unknown. Possible explanations are discussed.