Inhibitory Influence of a Normally Occurring Pyrimidine Precursor upon Methylcholanthrene Carcinogenesis.

Abstract

The carcinogenic influence of methylcholanthrene on the lungs of mice may be considerably reduced by increasing the intake of a normal dietary constituent, orotic acid, a substance well known to be of great importance to the synthesis of nucleic acid pyrimidines. The absence of influence of this substance upon the condition of the mice or the size of the tumors indicates that it is acting at the level of initiation of the pulmonary tumors rather than upon their subsequently growth. This fact suggests that the metabolic mechanisms through which methylcholanthrene initiates neoplastic change is, like urethane, closely related to the synthesis of nucleic acid.