A PCR analysis of ERα and ERβ mRNA abundance in rats and the effect of ovariectomy

To study the relative abundance and the changes of both estrogen receptor alpha (ER alpha) and ER beta mRNA before and after ovariectomy in major organs important to the regulation of calcium homeostasis, we compared the degree of mRNA expression of ER beta to that of ER beta in rat tissues by performing competitive reverse transcription polymerase chain reaction (RT-PCR) with internal standards. Both ER alpha and ER beta were highly expressed in the ovary {ER alpha[(2.2 +/- 0.33) x 10(7) copies/mu g of total RNA] > ER beta[(1.2 +/- 0.33) x 10(5) copies/mu g of total RNA]} as we expected. The bone marrow and renal cortex were very important target organs of estrogen because ER alpha was highly expressed similar to 2 x 10(5) copies/mu g of total RNA, but marrow cells revealed only a very weak expression of ER beta [(0.7 +/- 0.21) x 10(2) copies/mu g of total RNA]. Both ER alpha and ER beta were expressed in the trabecular bone [(3.2 +/- 0.56) x 10(3) copy/mu g of RNA] and [(2.8 +/- 0.21) x 10(2) copy/mu g of RNA], respectively. However, they mere not detected in the cortical bone. In the jejunum, the expression of ER alpha was not detectable, while ER beta was expressed very weakly [(1.1 +/- 0.24) x 10(2) copies/mu g of total RNA]. The thyroid gland expressed low copy numbers of ER beta [(6.0 +/- 0.23) x 10(2) copies/mu g of total RNA], but the parathyroid gland was negative for both ER alpha and ER beta mRNA. In cultured stromal cells, ER alpha and ERP mRNAs were not detected after a 24-h culture; however, the rates of mRNA expression of ER alpha and ERP reached similar to 10(5) copies/mu g of total RNA and similar to 10(2) copies/mu g of total RNA, respectively, after 9-, 11-, and 13-day cultures. After ovariectomy, the expression of ER alpha mRNA decreased abruptly in the bone marrow and renal cortex, and both ER alpha and ER beta mere barely detected in the trabecular bone. In conclusion, ER alpha might be the main ER in organs important for calcium homeostasis, except in the jejunum, The mRNA expression of ER alpha in the bone marrow and renal cortex decreased abruptly after ovariectomy, which mag partially explain why the effect of estrogen deficiency can be amplified and why trabecular bone loss is more predominant than cortical bone loss shortly after surgical or natural menopause.