Estrogen binding in mammary tissue of C3H mice with or without the mouse mammary tumor virus

Substrains of C3H mice, with and without the milk-transmitted form of the mouse mammary tumor virus (MMTV)1, were compared to determine if the presence of MMTV altered estrogen action. Uterine weight response to oral diethylstilbestrol was the same for both substrains, (MMTV+ and MMTV-). The concentration of high-affinity estrogen binding sites ("receptors") in lactating mammary tissue did not differ significantly for MMTV+ versus MMTV- mice; the affinity of the estradiol-receptor interaction appeared higher, however, in cytosol from MMTV- mice. Sucrose density gradient analysis revealed no significant differences in sedimentation properties of cytosol receptor from the two substrains.