Increase in histidine decarboxylase activity in tissues of mice bearing Colon-26 tumor cells

The changes in histidine decarboxylase (HDC) activity, histamine and tele-m ethylhistamine contents were examined in tissues of mice after the inoculat ion of Colon-26 tumor cells subcutaneously into the lower back. The HDC act ivity in the spleen of mice increased significantly 14 days after the inocu lation of Colon-26 and the increase in HDC activity continued for up to 28 days. However, the histamine content in the spleen of tumor-bearing mice wa s not changed significantly during the observation period. In the following experiments, two subclones of the Colon-26 cell line, cachexia-inducing cl one-20 and non cachexia-inducing clone-5, were used and the induction of HD C activity in mice was examined in four tissues, spleen, lung, liver and ki dney. Both clone-20 and clone-5 induced the increase in HDC activity to the same extent in the spleen and lung, but not in the liver and kidney. As ob served using the Colon-26 original cell line, the histamine contents in the four tissues of tumor-bearing mice were: not different from those in the c ontrol mice. In contrast, the levels of tele-methylhistamine, one of the ma jor catabolites of histamine, in the tumor-bearing mice increased significa ntly compared with the control mice in all four tissues examined. There was a correlation between the increase in tele-methylhistamine level and the i ncrease in HDC activity in the tissues. A histological study indicated that the tissue mast cells were not increased in spleen and lung of tumor-beari ng mice. These findings indicated that the increase in HDC activity in the spleen and lung occurred in parallel with the growth of inoculated tumor ce lls in mice and suggested that the cells other than mast cells may be invol ved in the increase in HDC activity. The tumor-bearing state produced hista mine with a high turnover rate in the mouse tissues, especially in the sple en and lung.