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The Distribution and Metabolism of 3'-Methyl-C¹⁴-4-dimethylaminoazobenzene in the Liver and Tissues of the Rat^*

David A. Salzberg

( Palo Alto Medical Research Foundation, Palo Alto, Calif.)

1. The azo dye, 3'-methyl-4-dimethylamino-azobenzene, labeled with carbon-14 in the 3'-methyl position, was fed as a single dose to normal rats and to rats previously fed for 3 weeks diets containing 0.06 per cent of nonradioactive dye. Rats were sacrificed 24 and 96 hours after administration of the labeled dye, and the livers were homogenized and differentially centrifuged into the particulate cell fractions (nuclei, mitochondria, microsomes) and supernatant fluid fraction.

2. All the cell fractions from normal rat liver contained more carbon-14 activity at 24 hours than did the corresponding fractions from dyeprefed rat liver. At 96 hours this pattern was reversed, and the radioactivity of each of the prefed rat liver fractions was greater than that for the corresponding normal liver fraction. The radioactive contents of all the cell fractions from prefed rat liver at 96 hours were increased above those of the prefed fractions at 24 hours, and the greatest increase occurred in the supernatant fluid.

3. Almost 40 per cent of the radioactive dose was eliminated in the urine of both groups of rats within 24 hours. From 55 to 76 per cent of the radioactivity eventually appeared in the urine, and 12–22 per cent was excreted in the feces. No radioactivity could be detected in the expired carbon dioxide from normal or prefed rats.

4. Pancreas, bone, skin, brain, adrenal gland, lung, testis, and muscle contained no radioactivity. Spleen, kidney, heart, and depot fat contained small amounts of radioactivity at 24 hours, but none at 96 hours.

5. Normal rats were also fed 3'methyl-C¹⁴-4-dimethylaminoazobenzene in the diet for 21 days. Of the above organs and tissues, only the adrenal glands contained carbon-14 activity after this prolonged period of administration of labeled dye.

6. Riboflavin prepared from the livers of rats fed labeled dye for 21 days contained radioactivity. This radioactive component accompanied the riboflavin in various chemical procedures for the isolation of flavin compounds. Paper chromatograms of this riboflavin preparation contained a zone of riboflavin, located by its fluorescence in ultraviolet light, and a zone of radioactivity which was close to but not identical with the riboflavin zone.

^* Presented in part at the 118th National Meeting of the American Chemical Society, Chicago, Illinois, September, 1950, and the meeting of the American Association for Cancer Research, Cleveland, Ohio, April, 1951.

Scholar in Cancer Research, American Cancer Society. A portion of this work was done at Stanford University, Stanford, California, during the tenure of an American Cancer Society postdoctoral fellowship. This work was supported in part by Public Health Service Grant C-2869.

Received 7/23/57.