Evidence for an androgen-binding component in the cytosol of the human term placenta

The present communication describes a specific, high-affinity (Kd = 1.9 +/- 0.21 x 10(-9)M; n = 3) binding component for dihydrotestosterone present in the high-speed, hormone-stripped cytosol fraction of the human term placenta. In order to delineate the nature of this substance, the synthetic steroids R1881 (progesterone and androgen receptor specific) and R5020 (progesterone receptor specific) were employed. Minimal binding of H3-R5020 was observed; however, H3-R1881 was found to bind with a Kd = 0.6 +/- 0.18 x 10(-9)M (n = 3). The relative displacing ability of R5020 for H3-R1881 was only 1.3%, substantiating the presence of an androgen binder and negating the presence of a significant level of a progesterone-binding component. Evidence that the binder is of placental origin and does not result from blood contamination includes no significant binding of H3-R1881 to pregnancy serum, binder thermolability at 45 degrees C, and precipitation of the binder by ammonium sulfate at 30% saturation. Speculations as to the receptor or receptor-like nature of the binder are presented.