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Characterization of the epidermal growth factor receptor in pig oviduct and endometrium

The aim of this study was to determine whether the stage of the oestrous cycle (day 1, n = 5; day 6, n = 5; day 12, n = 3 gilts) has an influence on the expression and activity of epidermal growth factor receptor (EGF-R) in the pig oviduct and uterus. Histochemistry, cross-linking of¹²⁵I-labelled EGF to isolated oviductal and endometrial membranes or on cryostat sections, and EGF-R binding assay were used to demonstrate the presence of the EGF-R in a qualitative and quantitative manner. The bioactivity of the EGF-R in the oviduct was estimated by means of a protein tyrosine kinase activity assay. This study suggests that EGF-R is widely distributed both in glandular and stromal cells of the endometrium and in epithelial cells of the oviduct in pigs. The concentrations of EGF-R were higher in oviductal membranes on day 1 (22.4 ± 8.7 fmol mg^–1 protein) in comparison with day 6 (11.0 ±0.42 fmol mg^–1 protein; P < 0.05), but not on day 12 (16.0 ± 2.9 fmol mg^–1 protein). The concentrations dropped similarly in the endometrium (day 1: 66.8 ± 16.4 fmol mg^–1 protein; day 6: 39.1 ± 3.4 fmol mg^–1 protein (P < 0.05); day 12: 38.0 ± 14.6 fmol mg^–1 protein). The dissociation constant (K_d) showed the same pattern. These data were supported by cross-linking of¹²⁵I-labelled EGF to a 170 kDa membrane protein representing the EGF-R. In contrast to day 6 and 12 of the cycle, a significantly (P < 0.05) higher endogenous protein tyrosine kinase activity was observed on day 1. In summary, changes in concentrations and functional status of the EGF-R may play a significant role in the cascade of cellular events in oviductal and endometrial tissues.