Decreases in histamine forming enzyme activity of non-metastasizing fibrosarcomas in hamsters with progressive tumor growth.

A marked and progressive decrease in the activity of the histamine forming enzyme, histidine decarboxylase (HDC), of tumors was found to be associated with the progressive growth of SV-40 virus induced and transplanted syngeneic non-metastasizing fibrosarcomas in inbred LSH Syrian hamsters. Histamine forming enzyme activity was highest in the smallest tumors (p < .005) and in the tumors with the slowest growth rate (p < .005, r - 0.84). Tumor histamine forming enzyme activity was highest for each interval of animal exposure to inoculated tumor cells in those animals which had limited their tumor growth to the smallest tumor size. These findings suggested a local anti-inflammatory effect of progressive tumor growth. Induced local inflammation by repeated intratumor injections of bradykinin markedly elevated tumor histamine forming enzyme activity above expected levels for tumors of the same size in a small group of individual animals which were sampled at random from a larger group of animals which were being studied for the tumor growth kinetics effects of repeated intralesional injections of bradykinin. Tumor histamine forming enzyme activity was highest in those animals which were managed by the frequency of injection and dose schedules which were found in the tumor growth kinetics study to be most effective in limiting tumor growth. These findings suggested that the observed anti-inflammatory effects of progressive tumor growth may be reversed by locally induced inflammation at the tumor site with beneficial effects on tumor growth.