Estrogen Regulation of Protein Synthesis in the Immature Rat Uterus: The Effects of Progesterone on Proteins Released into the Medium duringin VitroIncubations*

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Abstract
We have previously identified two major medium proteins secreted from the rat uterus during in vitro incubations that appear to be estrogen regulated. In this study, immature rats were treated with estradiol (E2) progestins, and actinomycin D. Medium proteins were analyzed after incubation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. E2 (1 .mu.g) increased the synthesis of proteins with mol wt of 115,000 and 65,000. Progesterone inhibited this increase when given in doses of 500 and 250 .mu.g and when given within 8 h of estradiol. Lower doses of progesterone were not completely inhibitory. When actinomycin D was given within 6 h of E2, it also inhibited the E2 stimulated increase. This system may provide a useful marker for monitoring hormonal action in the luminal epithelium and may help in understanding hormonal regulation of gene expression.