Observations, With the Aid of the Electron Microscope, on the Mitochondrial Structure of Experimental Liver Tumors in the Rat

Abstract

The size and structure of mitochondria in electron micrographs of liver cells and cells of experimentally induced liver tumors were studied in albino rats. In addition to structural differences from normal mitochondria, the mitochondria in tumor cells also were smaller in diameter. About the same small average mitochondrial diameter was found in liver cells of rats that were kept on a rice diet. Therefore it seemed possible that the small diameter of tumor mitochondria was exclusively an effect of a protein-deficient rice diet, since animals in which tumor growth was induced were kept on a rice diet plus N,N-dimethyl-p-phenylazoaniline. However, measurements of mitochondria in serial biopsies of liver tissue of an animal under different nutritional conditions indicate that the effect of the rice diet is reversible. This reversibility was not seen in tumor tissue, nor, in general, in liver tissue surrounding the tumor. In one of the animals that had received a carcinogenic diet no liver tumor developed during the 6-month period after this diet was discontinued. In the liver of this animal the mitochondria were nearly normal in diameter. These experiments indicated that tumor cells differed from normal liver cells with respect to their mitochondria, the size of which did not show the normal dependence on nutrition.