Besides the liver, other organs such as lung, kidney, and placenta possess microsomal enzymes. Since several antitumoral drugs are metabolized by this enzyme system, it was of interest to investigate whether the microsomal fraction of the tumor tissue was able to metabolize foreign compounds. The present paper shows that within the sensitivity of the method, 9000 × g and 105,000 × g fractions of various experimental tumors of the rat and the mouse do not metabolize known substrates of the microsomal enzymes such as p-nitro-anisol and aniline. Lack of metabolism was also observed by increasing the amount of tumor tissue employed, the amount of cofactors and the incubation time. Neither pretreatment of the tumor-bearing animals with phenobarbital or 3-methylcholanthrene induces metabolization.
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