ANTI-OESTROGEN ACTION: UTERINE NUCLEAR RETENTION OF THE CI-628 ANTI-OESTROGEN RECEPTOR COMPLEX IN VITRO

Abstract

Experiments which compared the nuclear retention of the anti-estrogen receptor complex formed by CI-628 [.alpha.-[4-pyrrolidinoethoxy) phenyl-4-methoxy-.alpha.-nitrostilbene] and the nuclear retention of the estrogen receptor complex formed by estradiol-17.beta. were performed in vitro in rats. Uterine nuclei retained the CI-628 receptor complex regardless of whether uterine incubations were carried out in the continued presence of CI-628 or whether, after 1 h, uterine incubations were continued in fresh medium. However, for estradiol-17.beta. there was a rapid decrease in the amount of receptor complex retained in the nucleus with time. When extraction using KCl were performed on nuclei after maximal accumulation of receptor complex by estradiol-17.beta. or CI-628, the estrogen receptor complex was found to have a higher relative nuclear affinity than did the CI-628 receptor complex. Different nuclear binding sites for these complexes are suggested.