Time sequence of action of estrogen on nucleic acid and protein synthesis in the uterus and blastocyst during delayed implantation in the rat

The time sequence of action of estrogen on the incorporation of 3H-cytidine, 3H-thymidine and 3H-phenylalanine in the uterus and blastocyst during delayed implantation in the rat was studied autoradiographically. 1. Estrogen enhances within 1 hr the synthesis of RNA in the blastocyst and this is maintained up to 18 hr; the uptake is seen in the nucleus as well as in the cytoplasm. RNA synthesis increases in the uterus within 3 hr of estrogen treatment, reaches a peak by 6 hr, is maintained up to 12 hr and declines by 18 hr; the uptake is predominantly located in the nuclei. 2. Estrogen also increases uterine protein synthesis by 6 hr, which reaches a peak by 12 hr and is maintained up to 18 hr. 3. Estrogen causes enhanced DNA synthesis in the blastocyst by 42 hr, while the uterus is yet unresponsive at this time. DNA synthesis in the uterus is initiated at about 50 hr after estrogen treatment. 4). It has been shown that estrogen has a differential time sequence of action on the uterus and blastocyst