Regulation of the expression and bioactivation of the epidermal growth factor receptor system by estradiol in pig oviduct and endometrium.

Growth factors, such as epidermal growth factor (EGF), have been suggested to mediate local effects of steroid hormones within female reproductive tissue. In the present study, the influence of estrogen on the expression and bioactivity of the EGF receptor (EGF-R) system was investigated in pigs. Oviducal and endometrial tissue from gilts was analysed either at two different time points after ovulation (Day 12 and Day 20), or from ovariectomized animals, with or without steroid-replacement treatment. Estrogen receptor protein concentrations were significantly down-regulated both in oviducal and endometrial tissue under estrogen-influence, in contrast to increased progesterone receptor concentrations. Transcript levels of EGF and transforming growth factor alpha remained unchanged in both the oviduct and endometrium during treatment. Oviducal EGF-R mRNA was found to be increased after estradiol treatment with concurrent increases in EGF-R protein. However, in endometrial tissue of estradiol-substituted ovariectomized pigs, the receptor transcript was significantly reduced, indicating a different regulation of EGF-R transcription within the endometrium. The bioactivity of the EGF-R, analysed by tyrosine kinase assays, was preserved throughout experiments in the porcine oviduct and endometrium without obvious changes caused by the steroids. In conclusion, estradiol may play a key role during the proliferation and differentiation of porcine oviducal tissue by activating the important paracrine or autocrine EGF system through its receptor. The cell-specific influence of progesterone during regulation of the EGF-R expression in the endometrium requires further investigation.