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Hormonal Effects on Thymidine Kinase and Thymidylate Kinase Activity of Estrogen-dependent Tumors in the Rat¹

Cancer Research Centre [M. J. T., M. R. G., J. F. R.], and Department of Biochemistry, [J. F. R.], University of British Columbia, Vancouver, British Columbia, Canada

In estrogen-induced, estrogen-dependent, mammary and adrenocortical carcinomas, the specific activities of the thymidine kinase and thymidylate kinase decreased significantly within 2 to 4 days after removal of the source of estrogen of the host. After 7 days, these changes were even more marked in the adrenal tumors. Similar changes were not observed in the activity of these enzymes in autonomous tumors in response to alterations in the supply of estrogen to the host. The treatment with antiestrogenic compounds of estrogenized animals bearing dependent adrenal tumors also caused a decrease in the activity of the two enzymes. The replacement of estrogen by treatment with adrenocorticotropic hormone in animals with adrenal tumors caused a stimulation of kinase activity at 2 days but did not prevent the decrease observed at 7 days after the removal of estrone. Growth of the mammary and adrenocortical carcinomas, as indicated by activity of the kinases, was maintained after estrogen removal by treatment of the host with prolactin.

¹ This work was supported in part by the Medical Research Council of Canada.

Received 8/10/72. Accepted 10/18/72.