Impaired estrogen stimulation of RNA polymerase II activity in uterine nuclei of senescent rats.

The effects of age on estrogen stimulated nuclear RNA polymerase II activity were studied in uteri of ovariectomized mature (6-8 months) and senescent (24 months) rats. Basal levels of RNA polymerase II activity were the same in both age groups. Following 17 beta-estradiol (E2) administration, RNA polymerase II activities increased at 6 h and reached a peak at 12 h in mature rats. In old rats, however, activities did not change until 12 h and reached a maximum at 18 h after injection. The effects of various E2 doses were examined at 6 h after injection. In mature rats, 1 microgram of E2 per 100 g body weight stimulated polymerase II activity, and maximum response was observed above 3 micrograms per 100 g. In senescent rats, this activity did not increase at doses below 3 micrograms per 100 g, but was stimulated by 10 micrograms of E2 per 100 g body weight to levels similar to those in mature rats. These results indicate that induction of uterine nuclear RNA polymerase II activity is delayed and less sensitive to E2 in old female rats than in their young counterparts.