Expression of estrogen and androgen receptor in the bovine gastrointestinal tract
Sauerwein, H.; Pfaffl, M.; Hagen-Mann, K.; Malucelli, A.; Meyer, H.H.
Deutsche Tierärztliche Wochenschrift 102(4): 164-168
1995
ISSN/ISBN: 0341-6593 PMID: 7555698 Document Number: 439245
Reproductive and maturational nutritive needs are examples for situations in which alterations in circulating concentrations of sex steroids are associated with changes in gastrointestinal function. In order to investigate whether there is a causal relationship between sex steroids and gastrointestinal function, we aimed to investigate the responsiveness for androgens and for estrogens of the bovine gastrointestinal tract. Using Northern blot analysis, estrogen receptor (ER) mRNA was detected in rumen tissue. Comparing the ER expression in rumen from females of different reproductive stages, we found that no differences related to cycle stage, pregnancy or parturition could be detected. In contrast, the ER expression rates in the uterus of the respective animals showed the same dependency of reproductive stage as demonstrated earlier for the ER protein, indicating that there might be a tissue specific regulation of ER. By in-situ hybridization of rumen tissue sections the expression of ER was localized in the epithelium of the papillae. In the muscular layer no positive signals for ER mRNA were observed. Above rumen, the presence of ER and androgen receptor (AR) mRNA was determined in various intestinal tissues using reverse transkription (RT) and polymerase chain reaction (PCR). Primers were selected from the bovine androgen and estrogen receptor sequence to amplify parts of the sequence coding for the hormone binding part of the respective receptor. The PCR amplificates were subsequently electrophoresed on 1% agarose gels and visualized by ethidium bromide staining. ER mRNA expression was demonstrated in reticulum, omasum, abomasum, duodenum, jenunum, ileum, caecum and colon. AR mRNA expression was not determined in the forestomaches, but was present in all intestinal segments investigated. To assess AR and ER as functional proteins, ligand binding studies were performed in the cytosolic fraction of gastrointestinal tissues using 3H-methyltrienolone or 3H-estradiol as ligands in a charcoal assay system. Specific binding for estradiol was observed in rumen and abomasum as well as in duodenum, ileum and colon; the concentrations measured were between 0.4 and 2.2 fmol/mg cytosolic protein. AR was present in all intestinal segments investigated (0.2 to 0.7 fmol/mg cytosolic protein). These concentrations are comparable to those observed in skeletal muscle. The functional relevance of sex steroid hormone receptors in the gastrointestinal tract as well as their regulation remains to be elucidated.