The 'estrogen-induced protein': Quantitation by autoradiography of polyacrylamide gels

The increased rate of synthesis of the "estrogen-induced protein" (IP) first detected by Notides and Gorski is one of the earliest macromolecular responses to estrogen by the rat uterus. The IP detected by autoradiography of sodium dodecyl sulfate polyacrylamide gel electropherograms was shown to correspond to a stainable protein band in electropherograms of cytosol from uteri of both untreated and estrogen-treated rats. The uteri of 9-10-day-old rats showed a maximum rate of IP synthesis 1 h after estrogen-treatment, followed by a decrease to constitutive levels by 24 h. The rate of synthesis of IP was doubled by estrogen administration to 10-30-day-old rats. The improved sensitivity of the autoradiographic method permitted the detection of some stimulation of IP synthesis in uteri of 5-day-old rats, in contrast to our previous findings in Wistar rats using a double isotope labelling technique.