The uterus is a well-known target of endocrine, paracrine and autocrine acting molecules among which steroid hormones are of special importance. The objective of our work was to localize oestrogen receptors (ERα and ERβ) mRNA and protein in the pig uterus throughout pregnancy (10, 18, 32, 50, 71, 90 days post coitum) using RT-PCR, Western-blot and immunohistochemistry. The present study is the first one to demonstrate the presence of ERs protein in the porcine uterus not only at the beginning but also at mid- and late pregnancy. In the pregnant swine, ERα was immunolocalized in the luminal epithelium (LE) and glandular epithelium (GE) and the myometrium of the uterus with differences in the intensity of staining at different stages of pregnancy studied. The LE and GE of pregnant swine stained for ERβ regardless of the day of pregnancy examined, whereas only a few cells within the myometrium showed a weak immunoreactivity. Western blot analysis confirmed the presence of ERα and ERβ proteins on all investigated days of gestation. The expression of ERα and ERβ mRNA was detected by RT-PCR in all examined samples corresponding to each of the consecutive stages of pregnancy. The obtained results show that ERα is more abundant in comparison to ERβ within the porcine pregnant uterus. The presence of ERα and ERβ in all compartments of the pig uterus during pregnancy may indicate direct action of oestrogens on proliferation and differentiation of these cells.
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