[Thymidine kinase activity in mammary tumors of animals exposed to estradiol as an index of tumor hormone dependence].

The effects of ovariectomy and estrogen treatment on the activity of thymidine kinase in estrogen-dependent and estrogen-independent mammary gland tumors (MGT) of experimental animals were studied. Thymidine kinase activity decreased 3-18 fold after ovariectomy in estrogen-dependent MGT only. It increased 3-7 fold again after estradiol treatment. These changes were significantly greater than those in hexokinase and glucose-6-phosphate dehydrogenase activity. High doses of estrogens (200 micrograms/day) resulted in an 1.8-3.5-fold decrease in thymidine kinase in estrogen-dependent MGT. The enzyme activity in estrogen-independent MGT did not change. It is suggested to use thymidine kinase activity as a marker of proliferative processes in evaluation of hormone-dependency of tumors and the effects of other factors on tumor growth.