Androgen binding in human fetal amnion.

Human fetal amnion cytosol obtained at term is able to bind specifically [3H]testosterone. The cytosol (105,000 g supernatant) from human amnion was used after a 30 min treatment with dextran-coated charcoal and incubated with increasing concentrations of [3H]testosterone, [3H]dihydrotestosterone, [3H]methyltrienolone for 2 h at 4 degrees C and for 16 h at 15 degrees C. To avoid any possible contamination of sex hormone binding globulin we used a Sepharose 4B column. Scatchard plot analysis of the data after incubation at 4 degrees C for 2 h showed that the amnion possesses high affinity (Kd = 0.62 +/- 0.20 nM) and low capacity (95.0 +/- 21.1 fmol/mg protein) binding sites for [3H]testosterone. After incubation at 15 degrees C for 16 h, we obtained a high affinity (Kd = 0.29 +/- 0.14 nM), low capacity (49.5 +/- 12.8 fmol/mg protein) and a low affinity (Kd = 5.55 +/- 2.55 nM), high capacity (181.7 +/- 20.8 fmol/mg protein) binding sites for [3H]testosterone. The values of Kd, calculated from Scatchard plot analysis were 1.03 +/- 0.7 nM with 20.2 +/- 10.4 fmol/mg protein and 1.97 +/- 1.06 nM with 55.6 +/- 15.9 fmol/mg protein for [3H]methyltrienolone and [3H]dihydrotestosterone respectively. These findings suggest that human fetal amnion cytosol at term contains a specific binding protein for androgens.