Relations between cytosolic and nuclear estrogen receptors in castrated rat uterus following low 17β-estradiol doses

Abstract

The effects of low 17β-estradiol (E 2) doses (500, 10 or 1 ng/kg b.wt) on the uterine cytosolic (Rc) and nuclear (Rn) estrogen receptor content have been studied in adult-ovariectomized rats. The uterine Rc content after 500 ng E 2/kg showed a depletion-replenishment-overshoot cycle. No significant Rc depletion could be observed with 1 or 10ng E 2/kg, but their corresponding overshoots were more intense than those observed for 500 ng E 2/kg. The uterine Rn levels after 500 ng E 2/kg increased during the Rc depletion and also during the replenishment and overshoot of Rc. With the lower doses Rn increased during the overshoot of Rc. In each dose Rn and Rc attained maximal values simultaneously. The return from Rc and Rn maxima to control levels was simultaneous in all cases. The high Rc overshoots obtained with 1 or 10 ng E 2/kg could be the expression of a process of receptor synthesis induced by E 2, more intense than the Rc breakdown produced by the complex formation with E 2. The similar Rc and Rn time courses obtained with the lower doses suggest that the unbound receptor could enter into the nucleus. The simultaneous Rc and Rn decrease suggests the induction of a receptor degradation process affecting both cytosolic and nuclear compartments.