The age dependency of estrogen-induced uterine thymidine kinase isoenzymes in the rat; an analysis by radioautography (author's transl)

Abstract

We reported previously that estradiol (E2) administration did not cause any difference in uterine estrogen receptor (ER) levels between immature and castrated-adult rats, whereas it induced a specific thymidine kinase (TK) isozyme in immature rats only. This specific isozyme diminished as the rat grew.In the present paper, uterine TK activity was studied in rats administered with E2 at various ages. It was noted that TK activity was significantly increased by E2 administration at age 10 to 20 days, but TK activity was very low when E2 was administered at age about 50 days. The estrous cycle began to appear when the rats were around 50 days old.Despite E2 administration at age 20 days, TK activity did not increase in the rats pretreated with E2 dipropionate at age 2 days or with PMS at age 17 days. This result indicated the possibility that the disappearance of E2-induced TK isozyme was hormone-dependent. On the other hand, TK activity in the rats which were castrated at age 21 days did not increase despite E2 administration at age 50 days and was similar to that of E2-administered rats at age 50 days. This result indicated that the disappearance of TK isozyme might be age-dependent, too.3H-thymidine (5 uCi/g B.Wt.) was injected into the tail vein of immature and castratedadult rats 22 hours after E2 administration. Each uterus was removed 2 hours after theinjection to prepare for radioautography. No silver grain was observed in any uterine cells in both immature and castrated-adult control rats. Silver grains were clearly found in both endometrial and myometrial cells of immature rat administered with E2. In castrated-adult rats administered with E2, silver grains were observed in the endometrial cells only.It is believed that the specific TK isozyme in E2 administered immature rats was related to DNA synthesis induced by E2 administration in the myometrial cells. This TK isozyme disappears as the rat grows. It is likely that the disappearance of this specific TK isozyme is age- and hormone-dependent.