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Comparison of Phosphohexose Isomerase and Lactic Dehydrogenase Activities in Plasma, Liver, and Tumor Tissue of Tumor-bearing Rats^*

( Divisions of Experimental Pathology and Experimental Chemotherapy, Sloan-Kettering Institute, and the Sloan-Kettering Division, Cornell Medical College, New York, N.Y.)

The phosphohexose isomerase and lactic dehydrogenase activities of liver, plasma, and tumor were determined at intervals after the implantation of Walker carcinosarcoma 256 in CFN-Wistar rats. These enzyme activities in the livers of the tumor-bearing animals did not differ significantly at any time from those of the control animals. The contents of the enzymes in the liver rose after about the 10th day of tumor implantation, but this rise was attributable to the relative increase in liver weight of the tumor-bearing animals. The plasma enzyme levels in the tumor-bearing animals remained within normal limits until the 7th day after implantation of the tumor. The plasma phosphohexose isomerase activity then rose until it attained a level at 20 days that was about 9 times the mean normal value, whereas the serum lactic dehydrogenase activity reached a maximum that was only twice its mean normal value. Consideration of individual values showed that at plasma isomerase activities up to about 8 times the upper limit of the normal range, there were no significant rises in plasma lactic dehydrogenase.

The relationship of these plasma enzyme levels to the enzyme content of the tumor and to other factors is considered.

^* Reported in abstract form at the American Association for Cancer Research, Atlantic City, 1956. This investigation was supported by the following grants: Maude K. Irving Memorial grant-in-aid, EDC (MKI)-12A, from the American Cancer Society upon the recommendation of the Committee on Growth of the National Research Council; a Damon Runyon memorial fund grant, No. DRG-332; a research grant (No. C-415) from the National Cancer Institute of the National Institutes of Health, Public Health Service.

Received 5/28/56.