The gastrointestinal tract as target of steroid hormone action:: Quantification of steroid receptor mRNA expression (AR, ERα, ERβ and PR) in 10 bovine gastrointestinal tract compartments by kinetic RT-PCR

We have examined the tissue-specific mRNA expression pattern of androgen receptor (AR), both estrogen receptor (ER) subtypes ERalpha and ERbeta and progestin receptor (PR) in 10 bovine gastrointestinal compartments. Goal of this study was to evaluate the deviating tissue sensitivities and the influence of the estrogenic active preparation Ralgro(R) on the compartment-specific expression regulation. Ralgro(R) contains Zeranol which shows strong estrogenic and anabolic effects. Eight heifers were treated for 8 weeks with Ralgro(R) at different dosages (0, 1, 3, and 10 times). To quantify the very low abundant steroid receptor mRNA transcripts sensitive and reliable real-time (kinetic) reverse transcription (RT)-PCR quantification methods were validated on the LightCycler. Expression results indicate the existence of AR and both ER subtypes in all 10 gastrointestinal compartments. PR receptor was expressed at very low abundancy. Gastrointestinal tissues exhibit a specific ERalpha and ERbeta expression pattern with high expression levels for both subtypes in rectum, colon and ileum. With increasing Zeranol concentrations a significant down-regulation for ERalpha and ERbeta was observed in jejunum (P < 0.001 and <0.05, respectively). Significant up-regulations under estrogen treatment could be shown in abomasum for ERalpha (P < 0.05) and in rectum for ERbeta (P < 0.001). The authors conclude, that especially estrogens and the expression of their corresponding receptor subtypes may play an important role in the modulation and regulation in gastric as well as gut functions, cell proliferation and possibly in the pathophysiology of cell cancer. The different expression patterns of ERalpha and ERbeta can be regarded as support of the hypothesis that the subtype proteins may have different biological functions in the gastrointestinal tract. AR and PR seem to be not estrogen dependent. (C) 2003 Elsevier Science Ltd. All rights reserved.