Identification of estrogen receptors in granulosa cells of immature rats

Abstract

Nuclear and cytoplasmic binding sites for estradiol (E 2-17 β) in granulosa cells of immature rats were characterized. These binding sites for estrogen were high affinity, low capacity with an affinity constant (Kd) of 1.9 × 10 −10 M (binding capacity, Ro = 80 pM) for nuclear sites and a Kd = 3.5 × 10 −10 M (Ro = 45 pM) for cytosol sites. Binding was specific for biologically active estrogens. The estrogen receptor in granulosa cells is a protein and heat-labile as treatment with protease or pre-incubation at 37° C for 1 h significantly diminished binding. RNase and DNase had no effect on estrogen binding. Sedimentation coefficients for nuclear and cytosol binding components were 5S and 8S respectively, similar to values obtained with uteri. Finally, translocation was demonstrated after a s.c. injection of E 2-17 β. Forty-five minutes post-injection, cytosol binding sites for estradiol were depleted concomitant with accumulation of nuclear binding sites. We concluded that granulosa cells of immature rats have binding sites specific for estradiol which have characteristics similar to the classical estrogen receptor in uteri.