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

We have examined the tissue-specific mRNA expression of ER alpha and ER bet a 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 (alpha -Zearalanol ), a derivative of the mycotoxin Zearalenon, shows strong estrogenic and an abolic effects, and exhibits all symptoms of hyperestrogenism, in particula r reproductive and developmental disorders. Eight heifers were treated over 8 weeks with multiple-dose implantations (0 x, 1 x, 3 x, 10 x) of Zeranol. Plasma Zeranol concentration, measured by enzyme immunoassay, of multiple treated heifers was elevated. To quantify ER alpha and ER beta transcripts also in low-abundant tissues, sensitive and reliable real-time RT-PCR quant ification methods were developed and validated on the LightCycler. Expressi on results indicate the existence of both ER subtypes in all 15 investigate d tissues. All tissues exhibited a specific ER alpha and ER beta expression pattern and regulation. With increasing Zeranol concentrations, a signific ant downregulation of ER alpha mRNA expression could be observed in jejunum (p<0.001) and kidney medulla (p<0.05). These data support the hypothesis t hat ER beta may have different biological functions than ER alpha, especial ly in kidney and jejunum.