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Synthesis and Inducibility of the Uterine Estrogen-Induced Protein, IP, During the Rat Estrous Cycle: Clues to Uterine Estrogen Sensitivity^{1 ,2}

Department of Physiology and Biophysics, University of Illinois, and School of Basic Medical Sciences, University of Illinois College of Medicine Urbana, Illinois 61801

Abstract

Analysis of newly labeled soluble proteins in uteri of mature rats throughout the estrous cycle indicates that the relative rate of synthesis of the uterine estrogen-induced protein, IP, is high at proestrus, when endogenous estrogen secretion is maximal; it is not synthesized at detectable levels at estrus and metestrus; and some minimal synthesis is seen in diestrus uteri. Injection of exogenous estrogen results in some increase in the IP synthesis rate at proestrus; slight induction of IP synthesis at estrus; and maximal induction (as great as that induced in the mature, ovariectomized uterus by estrogen) at metestrus and diestrus.

Studies in the immature (day 21–24) rat, aimed at determining the possible causes of the uterine recalcitrance to exogenous estrogen seen at estrus, indicate that one can reproduce in the immature uterus a period of feeble responsiveness to a second injection of estrogen after exposure to a first, high dose of estrogen. After a single injection of estrogen, there is a lag between the gradual return of full IP inducibility (requiring over 40 hours to reach the control level) and the return of nucleartranslocatable receptor (at control level by 24 hr). This suggests that in addition to the presence of nuclear-translocatable receptor, the response to a second injection of estrogen is dependent upon other factors whose replenishment and/or reactivation is slower than that of the receptor. (Endocrinology 96: 289, 1975)

Footnotes

¹ Supported by National Institutes of Health Grant HD06726 and Ford Foundation Training Grant 700–0333.

² Presented at the IV International Congress on Hormonal Steroids, Mexico City, September, 1974 and is listed as reference 30.

Received July 1, 1974.