Characterization of estrogen binding in uterine cytosol from the fetal rhesus monkey

Cytosol receptor binding of 17 beta-estradiol was demonstrated in the uterus of the late-gestation, fetal rhesus monkey. Sucrose density gradient analysis performed in low-ionic strength buffer indicated a binding component with a sedimentation coefficient of 6-7 S. Under high-ionic strength conditions, the component shifted to a sedimentation coefficient of approximately 4 S. The specificity of the receptor for estrogens was indicated by inhibition of [3H]estradiol binding by both natural and synthetic estrogen competitors, but not by progesterone. Saturation analysis indicated a high degree of nonspecific binding with saturation of specific binding occurring at 2-3 nM. Computer-assisted Scatchard analysis of the data resolved a one-receptor model having a limited number of binding sites and an apparent dissociation constant of 10(-10) M. The interaction of estrogens with the fetal uterus and the cellular mechanisms which permit this interaction are discussed in relation to the development of models for extrapolation to the human.