Expression of estrogen receptor subtypes in rat pituitary gland during pregnancy and lactation

Abstract

The aim of this study was to examine whether the expression levels of mRNA of the three estrogen receptor (ER) subtypes, ERα, ERβ, and truncated ER product-1 (TERP-1) found in the rat pituitary gland were modified during gestation, lactation, and postlactation periods. By using relative quantitative RTPCR, we found that ERα mRNA significantly peaked in midpregnancy. However, the ERα protein level remained constant. ERβ gene expression did not change throughout pregnancy, suggesting that it was not related to estradiol levels during this reproductive period. In contrast, both TERP-1 mRNA and protein levels dramatically increased throughout the second half of gestation, being faintly detectable in early pregnancy. TERP-1 expression was rapidly reversed by lactation, whereas neither pituitary ERα nor ERβ relative levels were significantly altered. In addition, pup removal for 24-96 h on d 9 postpartum significantly reduced the expression of both ERα and ERβ mRNA compared with that in lactating animals, but the expression of TERP-1 mRNA was no longer detected. Collectively, our data indicate that 1) TERP-1, ERα, and ERβ expression levels are differentially regulated in the pituitary; 2) TERP-1 is variably expressed depending on the hormonal environment related to the estrous cycle, pregnancy, and lactation; and 3) TERP-1/ERα ratios dramatically change depending on reproductive periods, suggesting a critical role for TERP-1 in reproductive events.