STIMULATION BY ESTRADIOL-17-BETA OF THYMIDINE KINASE-ACTIVITY IN THE RAT UTERUS

The action of estradiol-17.beta.(E2) on thymidine kinase (TK) activity was studied in uteri from immature female rats. It was demonstrated that a single injection of E2 highly stimulated the enzyme activity which reached its maximum level 24 h after hormone administration. Physiological amounts of E2 were efficient and changes in TK activity were observed exclusively in uterus and liver. A single injection of Tamoxifen produced the same effect as E2 but repeated administration resulted in the complete inhibition of enzyme activity. Using antibiotics it was demonstrated that E2 induced the synthesis of new enzyme molecules rather than an increase in TK activity was preceded by an increase in RNA-polymerase activity and followed by that in DNA-polymerase .alpha. activity. The separation of TK isoenzymes on DEAE-Sephadex and the use of d-CTP as inhibitor of the adult isozyme suggested that E2 induced the fetal form of the enzyme. TK activity in uteri from ovariectomized adult female rats was enhanced by E2 administration, and that the increase was due to the stimulation of the fetal isoenzyme. TK apparently could be used as a marker of the action of estrogens and antiestrogens in target organs.