The Effects of Estradiol on Uterine Estrogen Receptor and Thymidine Kinase in Immature and Spayed-adult Rats

Abstract

Uterine estrogen receptor (ER) and thymidine kinase (TK) activity were investigated in response to an injection of estradiol (E₂) (1.43μg/ 100g body weight) in SD-strain immature female rats aged 21 days and spayed-adult rats aged 104 days (14 days after castration).
In immature rats, uterine cytosol ER decreased abruptly after the injection of E₂ and increased gradually from 4 hours later. On the other hand, nuclear ER increased rapidly and shaped a peak 1 hour after the injection of E₂ and decreased gradually afterward. Uterine TK activity began to increase rapidly from 18 hours and shaped a peak 24 hours after the injection of E₂ and was reduced to the same level as the controls 48 hours later.
No differences in behavior of uterine cytosol and nuclear ER after the injection of E₂ between immature and spayed-adult rats were noticed.
Although uterine TK activity in immature rats was stimulated 30 times 24 hours after the injection of E₂, that of spayed-adult rats increased only twice. Uterine TK was separated into 3 fractions (A, B and C) by means of a DEAE-cellulose column chromatography. In immature rats, 95% of the great TK activity induced by E₂ was involved in fraction A, which was not inhibited by dCTP. In contrast, uterine TK isozymes in spayed-adult rats were at fraction B and C, whose activities were inhibited by dCTP, without relation to the administration of E₂. The molecular weight of fraction A was estimated to be approximately 125,000 and that of B was 100,000 by the method of gel filtration on a Sepharose CL-6B column.
No differences in uterine ER levels between immature and spayed-adult rats were found, but E₂ -induced different TK isozymes seem to depend on the stage of uterine growth.