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