Tissue-specific expression pattern of estrogen receptors (ER): Quantification of ERa and ERb mRNA with real-time RT-PCR

We have examined the tissue-specific mRNA expression of ERa and ERb in various bovine tissues using real-time RT-PCR. The goal of this study was to evaluate the deviating tissue sensitivities and the influence of the estrogenic active preparation RALGRO on the tissue-specific expression and regulation of both ER subtypes. RALGRO contains Zeranol (a-Zearalanol), a derivative of the mycotoxin Zearalenon, shows strong estrogenic and anabolic effects, and exhibits all symptoms of hyperestrogenism, in particular reproductive and developmental disorders. Eight heifers were treated over 8 weeks with multiple-dose implantations (0¿, 1¿, 3¿, 10¿) of Zeranol. Plasma Zeranol concentration, measured by enzyme immunoassay, of multiple treated heifers was elevated. To quantify ERa and ERb transcripts also in low-abundant tissues, sensitive and reliable real-time RT-PCR quantification methods were developed and validated on the LightCycler. Expression results indicate the existence of both ER subtypes in all 15 investigated tissues. All tissues exhibited a specific ERa and ERb expression pattern and regulation. With increasing Zeranol concentrations, a significant downregulation of ERa mRNA expression could be observed in jejunum (p,0.001) and kidney medulla (p,0.05). These data support the hypothesis that ERb may have different biological functions than ERa, especially in kidney and jejunum.