Effect of long-term ovariectomy and estrogen replacement on the expressionof 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 17 beta-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 st udy: sham operated (SO), OVX and OVXE2. Methods: SO and OVX were performed 2 weeks before starting the 17 beta-estradiol treatment. All groups were ma intained on liquid diet for 12 weeks from the time of estradiol treatment. Total RNA was prepared from the tissues of the rats and relative quantitati ve reverse transcription PCR was utilized to compare the ER alpha-subtype ( ER alpha) mRNA level in the three groups for each target tissue. Results: Following long-term OVX, the levels of ER alpha expression showed a significant increase in the uterus, kidney and cerebral cortex and no sig nificant change in the liver, cerebellum, brainstem, heart and thoracic and abdominal aorta compared with their SO levels. On the other hand, a 12-wee k treatment of OVX rats with 17 beta-estradiol restored the previously upre gulated ER alpha mRNA to near SO levels except for the liner where the 17 b eta-estradiol treatment resulted in a significant increase in the ER alpha mRNA level compared with that in SO rats. Conclusions: We conclude that the regulation of ERs by its ligand is tissue specific.