A prolonged treatment with 17β-estradiol reduces the frequency of spontaneous oscillations and the Na + /K + ATPase activity in rat uteri. Acute inhibition of Na + /K + ATPase activity by a Na + /K + ATPase inhibitor, ouabain, decreases the frequency of oxytocin-induced oscillations in uteri. Therefore, the purpose of this study was to examine whether the prolonged inhibition of Na + /K + ATPase activity by 17β-estradiol was estrogen receptor (ER)-dependent. The uterine explants from ovariectomized rats were cultured in vitro as our experimental model to compare the effect of two antiestrogenic compounds (ICI 182,780 and tamoxifen) on the Na + /K + ATPase activity and the frequency of spontaneous oscillations. ATPase assay and a standard muscle bath apparatus were to measure the activity and the contraction. When compared with the control, a 2-day treatment with 17β-estradiol in vivo or in vitro decreased the activity and the frequency. ICI 182,780 lowered the activity but tamoxifen did not. ICI 182,780 did not decrease the frequency but tamoxifen did. Even the reversal effects of these antiestrogenic compounds on the reduced activity and the frequency by 17β-estradiol were different. Tamoxifen elicited a greater reversal effect on the reduced activity but ICI 182,780 did not. In contrast, ICI 182, 780 elicited a greater reversal effect on the reduced frequency but tamoxifen did not. Prolonged inhibition of Na + /K + ATPase activity by K + -free solution suppressed the frequency with the elevation of basal tension. Addition of KCl at lower concentrations (0.3-1.2 mM) induced oscillatory contraction after reducing the basal tension. As our data suggest, the prolonged effect of 17β-estradiol may decrease uterine the activity through ER dependent and independent pathways. The reduction of uterine Na + /K + ATPase activity by estrogens may increase the basal tension after each oscillatory cycle, which, in part, contributes to the reduced frequency of spontaneous oscillations.
|Number of pages||8|
|Journal||Chinese Journal of Physiology|
|Publication status||Published - 2003 Jun 30|
All Science Journal Classification (ASJC) codes
- Physiology (medical)