Polyamine metabolism in tumor, spleen and liver of tumor‐bearing rats

A brain tumor, originally induced by weekly IV injections of N‐nitro‐somethylurea in CD Fisher rats and subsequently carried in serial subcultures, was inoculated SC in the flank of CD Fisher rats. The synthesis and concentrations of the polyamines were studied at various times after the beginning of tumor growth. Higher activities of ornithine decarboxylase, S‐adenosylmethionine decarboxylase and higher concentrations of putrescine, spermidine and spermine were observed in the periphery when compared to the center of the solid tumor, and correlated with a higher growth rate in the periphery of the tumor. In the serum of rats with advanced tumors the concentration of spermidine was higher than in the serum of normal rats. Furthermore, putrescine was detectable in the serum of tumor‐bearing rats but not in normal rats. The tumor, which grows in a well‐defined non‐invasive manner, caused increased concentrations of putrescine and spermidine in spleen, and of spermidine in liver, at the time of most rapid growth. The increased polyamine concentrations may denote increased proliferation in the spleen and liver and are presumably part of an immunological response of the host animal to the growing tumor.