The mode of action of oestradiol. I. The transport of RNA precursors into the uterus.

Abstract 1. 1. The uptake of labelled RNA precursors into immature rat uterus under the influence of oestradiol-17β has been measured. 2. 2. There is a close correlation over the first 5 h of hormone action between the uptake of precursors and the amount incorporated into acid-insoluble material (RNA). 3. 3. When 80% of RNA synthesis is inhibited by actinomycin D the uptake of labelled RNA precursors 2 h after oestradiol administration is still increased by 212%. 4. 4. The size of the uterine nucleotide pool studied with ion-exchange chromatography does not show any significant changes up to 8 h of hormone action. 5. 5. The wet weight of the uterus under oestrogen stimulation shows a rapid rise up to 6 h, but thereafter remains at the same level for the next 10 h. 6. 6. We conclude that one of the primary effects of oestrogens is to cause an increased transport of RNA precursors into the uterus. This reaches a maximum between 2 and 3 h after administration of hormone which corresponds to a maximum in the uptake of water into the uterus. 7. 7. The increase in incorporation of radioactive precursors into RNA over the first 5 h of hormone stimulation is mainly due to an increased specific activity of the precursor pool due to an increased transport of radioactive precursors into the uterus.