Histamine in C3H/W mice carrying spontaneous tumors of the mammary gland

Adenocarcinoma mammae, a spontaneously growing mammary cancer in C3H/W mice, contrary to many transplanted tumors does not evoke any rise in histamine level either in the tumor or in distant tissues. On the other hand, the histamine level is reduced by 90% in the tumor in comparison with the healthy gland. This seems to be a consequence of the fall of histidine decarboxylase activity to below a detectable level. There is also a significant reduction in histamine N-methyltransferase activity to onefifth of the control level. The healthy mammary gland contains a high concentration of histamine and catabolizes it exclusively through the methylation pathway.