Epidermal Growth Factor and Its Receptor in Bovine Corpus Luteum during the Estrous Cycle.

The epidermal growth factor (EGF) concentration and its binding characteristics in bo-vine corpus luteum (CL) during the estrous cycle (early: Days 3-5, mid-: 8-12, late stage: 15-18) were determined. The EGF concentrations in corpus luteum tissue, evaluated by a radioreceptor assay using human placenta, were 3.0 ± 0.7 ng/g in early luteal phase, 43.9 ± 2.2 ng/g in mid-luteal phase and 18.6 ± 2.7 ng/g in late luteal phase. Specific EGF receptors were present in bovine corpus luteum of all luteal phases. TGFα, but not IGF-I, FGF and NGF competitively displaced EGF binding. The binding affinity of luteal EGF receptors differed between the luteal stages and decreased significantly from early (Kd=0.8 ± 0.04 nM) to mid-luteal stage (Kd=1.6 ± 0.34 nM, P<0.05). The binding capacity of luteal EGF receptor at different luteal stages were similar (early stage; Bmax=35.1 ± 5.7 fmol/mg protein, mid-luteal stage; Bmax=46.3 ± 4.0 fmol/mg protein, late stage; Bmax=35.1 ± 5.7 fmol/mg protein, all values mean ± SEM). These results suggest that EGF plays a physiological role for the regulation of luteal function during the estrous cycle.