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A Sex Difference in the Development of Liver Tumors in Rats Fed 3'-Methyl-4-dimethylaminoazobenzene or 4'-Fluoro-4-dimethylaminoazobenzene^*

( Department of Biochemistry, College of Agriculture, University of Wisconsin, Madison 6, Wis.)

1. Male rats fed 3'-methyl-4-dimethylaminoazobenzene developed liver tumors more readily than females. This has been noted periodically over a 5-year period and has now also been demonstrated in controlled experiments. The incidence of induced liver tumors in castrates was intermediate between that in males and females.

2. 4'-Fluoro-4-dimethylaminoazobenzene also appeared to be more carcinogenic in male rats than in females. The sex differences in tumor incidence did not depend upon differences in the intake of food or of carcinogen.

3. The ability of liver slices or homogenates to destroy DAB, 3'-Me-DAB, or 4'-F-DAB in vitro did not vary with sex unless a carcinogen had been fed for a long period of time.

^* Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. Supported in part by the Jonathan Bowman Cancer Fund and by a grant from the Committee on Growth, American Cancer Society.

Received 7/ 2/51.