Estrogen Receptor Binding in the Oviduct Magnum of Guineafowl Hens

Estrogen receptor bindings in cytosol and nuclear fractions of the magnum tissue of laying guineafowl and White Leghorn hens were examined by binding assays using [3H]-estradiol-17β. The value of equilibrium dissociation constant (Kd) in both the cytosol and the nuclear fractions was not different between the two different times, 1.5h and 23h after oviposition, and also between the guineafowl and the chicken. The maximum binding capacity (Bmax) was greater at 1.5h after oviposition than at 23h after oviposition in both cytosol and nuclear fractions of White Leghorn hens and in the nuclear fraction of the guineafowl hens, although the Bmax value was smaller in the guineafowl hens than in White Leghorn hens. The results suggest that the smaller binding capacity of the estrogen receptor in the oviduct magnum may be related to the less amount of albumen secreted from the oviduct magnum in the guineafowl hens than in White Leghorn hens.