Estrogen receptor-beta messenger ribonucleic acid expression in the pituitary gland

Estrogen plays a key role in the regulation of many pituitary hormones. The presence of estrogen receptor-beta (ER beta) messenger RNA (mRNA) has been demonstrated in the adult anterior pituitary by RT-PCR to be at a level much greater than that of ER beta mRNA. Because the number of ERs has been shown to change during development, in this study we examined the distribution of pituitary ER beta mRNA in adult and prepubertal rats. Using RT-PCR, we confirmed that ER beta mRNA expression is less than that of ER alpha mRNA in adult females. In contrast, in prepubertal female pituitaries, ER beta mRNA levels are much greater than those of ER alpha mRNA. Film densitometric analysis of whole pituitaries, similarly showed that ER beta mRNA is greater in prepubertal pituitaries than in adult pituitaries. However, after emulsion autoradiography, cell counts confirmed that prepubertal and adult pituitaries differ, not in the level of ER beta mRNA expression, but in the number of cells expressing ER beta mRNA. In postnatal day 15 pituitaries, there were twice as many cells per mm2 as in adults. A comparison between prepubertal males and females showed that females exhibited a 2-fold greater level of ER beta mRNA expression. To determine which cell types express ER beta mRNA, we performed in situ hybridization for ER beta mRNA coupled with immunohistochemistry for FSH or PRL. In prepubertal pituitaries, 84.5 +/- 2.3% of FSH-immunoreactive cells also express ER beta. Nearly all of the PRL-immunoreactive cells lacked ER beta mRNA. These data demonstrate sex- and age-related differences in ER beta mRNA expression in the anterior pituitary. Furthermore, these data suggest that ER beta is not the specific mediator of estrogen action in lactotrophs, whereas ER beta may be the prime mediator of estrogen action in FSH-containing gonadotrophs.