Changes in relations between two pathways of synthesis of RNA precursors in the tissues of animals with fast growing hepatomas

The ratio between the de novo and “reserve” pathways of synthesis of pyrimidine nucleotides of RNA changes in the de novo direction in the spleen, thymus, and liver of mice and rats with fast growing transplantable hepatomas. This phenomenon is due to a sharp decrease in uridine utilization by the tissues of the tumor-bearing animal, for the tumor utilizes mainly this precursor to synthesize RNA. This observation is regarded as the result of successful competition between the tumor and the host tissues for vitally important metabolites, one form of systemic action of the malignant tumor