Regulation of estrogen receptor alpha and beta expression by testosterone in the rat prostate gland.

Although ER beta is known to be expressed at high levels in the rat prostate gland, its regulation is not well understood. Here we examined ER mRNA expression and the effects of testosterone administration in male rats at 1, 4 and 9 weeks of age who were castrated and/or treated with testosterone for a week, and then sacrificed. ER alpha was the major type of ER expressed in 2 week-old animals while dominant expression of ER beta mRNA was apparent in older age groups. Interestingly while ER beta expression was diminished and ER alpha mRNA increased in the castrated group, testosterone administration reversed this effect. A time-course study indicated that induction of ER beta mRNA increased within 9 hr and ER alpha decreased in 2 days after an injection (i.p.) of testosterone. Our results suggested that 1) testosterone up-regulates ER beta mRNA expression while ER alpha is down-regulated; and that 2) great changes in ER alpha and beta expression in the prostate gland during development from the newborn to adult may be due to the influence of testosterone.