Ribonucleic acid synthesis in the rat uterus and its early response to estrogen

The synthesis of rapidly labeled RNA in the rat uterus, measured by in vivo cytidine-H 3 incorporation into RNA for a 20-minute period, was increased by approximately 88% within 1 hour after estrogen administration. Fractionation by sucrose density gradient centrifugation of RNA from the uterus synthesized in 20- and 60-minute time periods in vivo indicated that estrogen increased the synthesis of all RNA fractions. The percentage of RNA which would form hybrids with DNA was less than 5% and did not indicate that estrogen was having an effect on any specific DNA loci. It is concluded that methods having greater resolving power are necessary to determine whether the synthesis of specific RNA molecules in the rat uterus is involved in early estrogen action.