| Summary: | <p>Abstract</p> <p>We have shown previously that downregulation of intercaruncular stromal integrin α<sub>v</sub>β<sub>3 </sub>in bovine endometrium on day 16 of the estrous cycle coincided with the antibody recognition of estrogen receptors (ER) in the luminal epithelium. In pregnancy, these changes were not observed. Our hypothesis was that on day 16 of the estrous cycle, estrogen from the dominant follicle causes a reduction in integrin α<sub>v</sub>β<sub>3 </sub>and affects ERα in the luminal epithelium. The pregnancy recognition protein, interferon-τ (IFN-τ), may prevent downregulation of integrin α<sub>v</sub>β<sub>3 </sub>and suppress ERα expression in the luminal epithelium. On days 14 to 16, heifers received uterine infusions of the anti-estrogen ICI 182, 780, estradiol 17β, IFN-τ or the saline control. On day 16, reproductive tracts were collected for analysis of integrin α<sub>v</sub>β<sub>3 </sub>and ERα. Estrogen receptor α immunoreactivity was largely restricted to the luminal epithelium in control animals. Using anti-ERα recognizing the amino terminus, estrogen-treated animals showed reactivity in the stroma, shallow and deep glands and myometrium as is typical of estrus, whereas ICI 182, 870 treated heifers showed little or no reactivity. In contrast, carboxyl terminus-directed antibodies showed a widespread distribution of ERα with reactivity detected in the uterine epithelium, stroma and myometrium of both estrogen and ICI 182, 780 treated animals. Heifers treated with IFN-τ had low ERα reactivity overall. Control and IFN-τ treated heifers had lower intercaruncular stromal expression of integrin α<sub>v</sub>β<sub>3 </sub>in comparison to estrogen and ICI 182, 780 treatments. Overall, the results suggest that on day 16 of the estrous cycle, estrogen effects on integrin α<sub>v</sub>β<sub>3 </sub>are indirect and do not directly involve ERα in the luminal epithelium. During pregnancy, interferon-tau may block ERα in the luminal epithelium but likely does not rescue integrin α<sub>v</sub>β<sub>3 </sub>expression.</p>
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