Effect of long-term ovariectomy and estrogen replacement on the expression of estrogen receptor gene in female rats

Objective. Estrogen exerts a wide variety of actions involving many target tissues. We studied the effects of long-term ovariectomy (OVX) and OVX with 17β-estradiol treatment (OVXE2) on the level of estrogen receptor (ER) gene expression in target tissues of female rats. Design: Three groups of Sprague-Dawley female rats were utilized in this study: sham operated (SO), OVX and OVXE2. Methods: SO and OVX were performed 2 weeks before starting the 17β-estradiol treatment. All groups were maintained on liquid diet for 12 weeks from the time of estradiol treatment. Total RNA was prepared from the tissues of the rats and relative quantitative reverse transcription PCR was utilized to compare the ER α-subtype (ERα) mRNA level in the three groups for each target tissue. Results: Following long-term OVX, the levels of ERα expression showed a significant increase in the uterus, kidney and cerebral cortex and no significant change in the liver, cerebellum, brainsterm, heart and thoracic and abdominal aorta compared with their SO levels. On the other hand, a 12-week treatment of OVX rats with 17β-estradiol restored the previously upregulated ERα mRNA to near SO levels except for the liver where the 17β-estradiol treatment resulted in a significant increase in the ERα mRNA level compared with that in SO rats. Conclusions: We conclude that the regulation of ERs by its ligand is tissue specific.