Specific binding of oestradiol to guinea-pig prostate cytosol and nuclear fractions

A high affinity (Kd approximately 0.15 nM), saturable oestradiol binding site, which is specific for natural and synthetic oestrogens has been identified in guinea-pig prostate cytosol fractions. The binding site is protein in nature (heat- and protease-sensitive) and has a sedimentation coefficient of approx. 8S on glycerol gradients. A high affinity (Kd approximately 0.16 nM), saturable oestradiol binding site was also identified in salt-extracted (0.5 M KC1) nuclear fractions. The optimum incubation conditions for measuring the cytosolic and nuclear oestradiol binding sites were determined to be 20 h at 4 degrees C. Saturation analysis studies revealed that following oestrogen treatment of intact animals, approx. 80% of the specific oestradiol binding sites in prostatic cytosol fractions were transferred into the nucleus. The presence of a specific oestradiol binding protein with characteristics of an oestrogen receptor in the guinea-pig prostate, is consistent with oestrogen having biological activity in this tissue. In view of the abundance of stroma in the prostate of this species, and the consistent finding that the stroma of male accessory sex tissues is oestrogen sensitive, the guinea-pig may be an appropriate experimental animal for further investigating the role of oestrogen in the growth and development of the prostate.