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Quantitative Morphological Studies on the Livers and Liver Homogenates of Rats Fed 2-Methyl- or 3'-Methyl-4-dimethylaminoazobenzene

( National Cancer Institute, National Institutes of Health, Bethesda 14, Md.)

1. Four groups of male rats of the Holtzman strain were fed Purina chow, a basal semi-synthetic diet, the basal diet supplemented with 0.064 per cent 2-Me-DAB, and the basal diet plus 0.064 per cent 3'-Me-DAB, respectively. The animals were allowed to eat ad libitum and were killed after 28 days of feeding. The nuclei and mitochondria present in homogenates of the livers of these animals were counted. Stained tissue sections of the same livers were analyzed by the method of Chalkley (2) for the percentage of the liver volume occupied by parenchymal cytoplasm and nucleus, and bile duct tissue.

2. Feeding 2-Me-DAB resulted in a striking increase in the number of mitochondria in the liver, 302 x 10⁹ per gram, as compared to 118 x 10⁹ and 120 x 10⁹ per gram liver for rats fed the chow or the basal diet. The rats fed 3'-Me-DAB, with an average of 71 x 10⁹ per gram, showed a marked decrease in the number of mitochondria.

3. The average number of nuclei per gram (599 x 10⁶) in the livers of rats fed 3#x2032;-Me-DAB was much greater than that found in the livers of the rats fed the chow or basal diets (236 x 10⁶ and 229 x 10⁶ per gram, respectively). There were fewer nuclei per gram (192 x 10⁶) in the livers of rats fed 2-Me-DAB than were found in the livers of the control animals.

4. Quantitative analysis of the tissue sections showed that, on an average, the livers of the rats fed 3'-Me-DAB contained only 55 per cent of parenchymal tissue, while the livers of rats fed chow, basal, or basal plus 2-Me-DAB contained an average of 85, 90, and 91 per cent of parenchymal tissue, respectively. Further analysis of the data showed that the decrease in the volume of parenchymal tissue in the livers of rats fed 3'-Me-DAB was the result of a decrease in volume of parenchymal cytoplasm, while the volume occupied by the nuclei remained comparable to that of the livers of rats fed the basal diet. It was concluded that the number of mitochondria in the average parenchymal cell of the livers of rats fed 3'-Me-DAB must be considerably reduced in comparison with the parenchymal cells of rats fed the basal diet.

Received 11/10/52.