Cordycepin and early effects of estradiol on the immature rat uterus.

Estradiol induces the synthesis of a specific protein fraction (IP) in the uterus of the immature rat. The injection of cordycepin (3' deoxyadenosine), an inhibitor of poly A synthesis, inhibits the synthesis of IP. This fact suggests that one of the earliest effects of estrogen is the production of Hn-RNA poly-A relative to IP. Moreover, using electron microscopy, the stimulation by estradiol of the nucleolus of the immature rat uterine epithelium has been shown. Cordycepin does not affect this stimulation to any appreciable extent. Biochemical studies (incorporation of radioactive stracers into NRA, affinity chromatography on poly U-Sepharose) carried out in parallel with and under conditions comparable to those used in electron microscopy show that cordycepin does not greatly affect the increase in ribosomal RNA observed under the effect of estradiol. The blocking of IP by cordycepin and the lack of inhibition at the nucleolus level under the same conditions, show that the two early effects of the action of estrogen on the immature rat uterus are not directly correlated.