Ornithine decarboxylase activity in the livers, spleens, and kidneys of
tumor-bearing mice changed markedly during
tumor growth. These changes in
enzyme activity were not due to infiltration or
metastasis of
tumor cells in these organs. After i.p. inoculation of Ehrlich
tumor cells,
enzyme activity in the liver and spleen increased remarkedly, reaching a peak in 4 to 6 days and then quickly decreasing. Conversely, activity in the kidney, which was very high in normal mice, decreased markedly during
tumor growth, nearly reaching zero on Day 6 and remaining very low until death. Upon injection of a cell-free homogenate of Ehrlich
tumor or cell-free
ascites fluid,
enzyme activity in the liver and spleen also increased markedly, but that in the kidney did not change. These increases in activity were not due to the effects of living
tumor cells. Similar increases in
enzyme activity were also observed in the livers of mice given
injections of homogenates of
Sarcoma 180 or Act. S
tumor, or plasma from
tumor-bearing mice, but not in the livers of mice given
injections of homogenates of various nontumorous tissues, such as liver, kidney, spleen, muscle, regenerating liver, and fetus, or plasma obtained from normal mice. A similar increase in
enzyme activity in the liver after injection of a cell-free preparation of
tumor cells was observed in hypophysectomized and adrenalectomized mice; thus, these endocrine systems are probably not involved in the increase in
enzyme activity in the livers of
tumor-bearing mice.