Some biochemical changes preceding regression of 7,12-dimethylbenz(a)anthracene-induced mammary tumors following oophorectomy.

Abstract

Mammary tumors in rats induced by 7,12-dimethylbenz(a)anthracene were assayed for nine different enzymes and for synthesis of macromolecules at 1, 2, 3, 4, or 5 days after oophorectomy. Lactate dehydrogenase activity was significantly decreased in neoplasms obtained at 4 days, whereas decreased activities of pyruvate kinase and glucose 6-phosphate dehydrogenase were first noted at 5 days after oophorectomy. In contrast, hexokinase and aspartate aminotransferase activities demonstrated slight increases in carcinomas examined at 1, 2, 3, or 4 days following removal of the ovaries of the tumor-bearing host. The rate of synthesis of RNA and protein, measured by incorporation of labeled uridine and leucine, respectively, showed a decrease with time, becoming significant within 4 days after oophorectomy. Since all of the above alterations occurred prior to any significant decrease in tumor mass, the importance of certain components in maintenence of hormone-dependent neoplastic growth is suggested.