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 tis sue. in the present study, the influence of estrogen on the expression and bioactivity of the EGF receptor (EGF-R) system was investigated in pigs. Ov iducal and endometrial tissue from gilts was analysed either at two differe nt time points after ovulation (Day 12 and Day 20), or from ovariectomized animals, with or without steroid-replacement treatment. Estrogen receptor p rotein concentrations were significantly down-regulated both in oviducal an d endometrial tissue under estrogen-in fluence, in contrast to increased pr ogesterone receptor concentrations. Transcript levels of EGF and transformi ng growth factor a remained unchanged in both the oviduct and endometrium d uring treatment. Oviducal EGF-R mRNA was found to be increased after estrad iol treatment with concurrent increases in EGF-R protein. However, in endom etrial tissue of estradiol-substituted ovariectomized pigs, the receptor tr anscript was significantly reduced, indicating a different regulation of EG F-R transcription within the endometrium. The bioactivity of the EGF-R, ana lysed by tyrosine kinase assays, was preserved throughout experiments in th e porcine oviduct and endometrium without obvious changes caused by the ste roids. In conclusion, estradiol may play a key role during the proliferatio n and differentiation of porcine oviducal tissue by activating the importan t 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.