Studies have been made of the effect of single or multiple injections of ethionine, alone or in combination with vitamin B12 and/or choline, on carcass weight, tumor growth, and/or the concentration of apparent free amino acids in the liver of tumorous and nontumorous rats of the Wistar strain.

There was a progressive decrease in carcass weight with increase in ethionine dosage in tumorous male rats.

The growth of Sarcoma R-1 was inhibited by 22 per cent and that of Walker carcinoma 256 by 20 per cent, in male rats receiving multiple injections of high levels of ethionine, while comparable treatment inhibited the growth of these tumors by 73 per cent and 84 per cent, respectively, in female rats. It was concluded that these tumors were similar in their response to ethionine treatment but that there was a marked difference in the response observed in male or female animals.

The concentration of apparent free arginine, lysine, and methionine in the liver increased with increased ethionine dosage following a single injection into either tumorous or nontumorous male rats. Consecutive daily injections of ethionine into tumorous male rats induced higher concentrations of apparent free methionine in the liver with increase in ethionine dosage.

The addition of vitamin B12 and/or choline to the ethionine injected had no significant effect on the carcass or tumor weight in male rats, although the presence of B12 improved the physical appearance of the rats. While vitamin B12 had no apparent effect on the liver amino acid levels, the addition of B12 plus choline to the injected ethionine markedly increased the liver serine concentration.

It was concluded that tumorous Wistar rats have a higher tolerance to ethionine than tumorous Long-Evans strain rats.

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Paper No. 117. This work was aided by grants from the American Cancer Society, U.S. Public Health Service, Swift and Company, and the University of California. The authors are indebted to Mrs. Grace Davis and Mrs. Aiko Schick for technical assistance and to Dr. T. A. McCoy, Samuel Roberts Noble Foundation for Biomedical Research, Ardmore, Oklahoma, for rats bearing Walker carcinoma 256 transplants.

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